what is the meaning for photosynthesis

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Photosynthesis

Reviewed by: BD Editors

Photosynthesis Definition

Photosynthesis is the biochemical pathway which converts the energy of light into the bonds of glucose molecules. The process of photosynthesis occurs in two steps. In the first step, energy from light is stored in the bonds of adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). These two energy-storing cofactors are then used in the second step of photosynthesis to produce organic molecules by combining carbon molecules derived from carbon dioxide (CO 2 ). The second step of photosynthesis is known as the Calvin Cycle. These organic molecules can then be used by mitochondria to produce ATP, or they can be combined to form glucose, sucrose, and other carbohydrates. The chemical equation for the entire process can be seen below.

Photosynthesis Equation

Above is the overall reaction for photosynthesis. Using the energy from light and the hydrogens and electrons from water, the plant combines the carbons found in carbon dioxide into more complex molecules. While a 3-carbon molecule is the direct result of photosynthesis, glucose is simply two of these molecules combined and is often represented as the direct result of photosynthesis due to glucose being a foundational molecule in many cellular systems. You will also notice that 6 gaseous oxygen molecules are produced, as a by-produce. The plant can use this oxygen in its mitochondria during oxidative phosphorylation . While some of the oxygen is used for this purpose, a large portion is expelled into the atmosphere and allows us to breathe and undergo our own oxidative phosphorylation, on sugar molecules derived from plants. You will also notice that this equation shows water on both sides. That is because 12 water molecules are split during the light reactions, while 6 new molecules are produced during and after the Calvin cycle. While this is the general equation for the entire process, there are many individual reactions which contribute to this pathway.

Stages of Photosynthesis

The light reactions.

The light reactions happen in the thylakoid membranes of the chloroplasts of plant cells. The thylakoids have densely packed protein and enzyme clusters known as photosystems . There are two of these systems, which work in conjunction with each other to remove electrons and hydrogens from water and transfer them to the cofactors ADP and NADP + . These photosystems were named in the order of which they were discovered, which is opposite of how electrons flow through them. As seen in the image below, electrons excited by light energy flow first through photosystem II (PSII), and then through photosystem I (PSI) as they create NADPH. ATP is created by the protein ATP synthase , which uses the build-up of hydrogen atoms to drive the addition of phosphate groups to ADP.

The entire system works as follows. A photosystem is comprised of various proteins that surround and connect a series of pigment molecules . Pigments are molecules that absorb various photons, allowing their electrons to become excited. Chlorophyll a is the main pigment used in these systems, and collects the final energy transfer before releasing an electron. Photosystem II starts this process of electrons by using the light energy to split a water molecule, which releases the hydrogen while siphoning off the electrons. The electrons are then passed through plastoquinone, an enzyme complex that releases more hydrogens into the thylakoid space . The electrons then flow through a cytochrome complex and plastocyanin to reach photosystem I. These three complexes form an electron transport chain , much like the one seen in mitochondria. Photosystem I then uses these electrons to drive the reduction of NADP + to NADPH. The additional ATP made during the light reactions comes from ATP synthase, which uses the large gradient of hydrogen molecules to drive the formation of ATP.

The Calvin Cycle

With its electron carriers NADPH and ATP all loaded up with electrons, the plant is now ready to create storable energy. This happens during the Calvin Cycle , which is very similar to the citric acid cycle seen in mitochondria. However, the citric acid cycle creates ATP other electron carriers from 3-carbon molecules, while the Calvin cycle produces these products with the use of NADPH and ATP. The cycle has 3 phases, as seen in the graphic below.

During the first phase, a carbon is added to a 5-carbon sugar, creating an unstable 6-carbon sugar. In phase two, this sugar is reduced into two stable 3-carbon sugar molecules. Some of these molecules can be used in other metabolic pathways, and are exported. The rest remain to continue cycling through the Calvin cycle. During the third phase, the five-carbon sugar is regenerated to start the process over again. The Calvin cycle occurs in the stroma of a chloroplast. While not considered part of the Calvin cycle, these products can be used to create a variety of sugars and structural molecules.

Products of Photosynthesis

The direct products of the light reactions and the Calvin cycle are 3-phosphoglycerate and G3P, two different forms of a 3-carbon sugar molecule. Two of these molecules combined equals one glucose molecule, the product seen in the photosynthesis equation. While this is the main food source for plants and animals, these 3-carbon skeletons can be combined into many different forms. A structural form worth note is cellulose , and extremely strong fibrous material made essentially of strings of glucose. Besides sugars and sugar-based molecules, oxygen is the other main product of photosynthesis. Oxygen created from photosynthesis fuels every respiring organism on the planet.

Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology 6th. ed . New York: W.H. Freeman and Company. Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry . New York: W.H. Freeman and Company.

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photosynthesis

Definition of photosynthesis

Did you know.

Photosynthesis Has Greek Roots

The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light". Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules (made of hydrogen and oxygen) held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.

Examples of photosynthesis in a Sentence

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'photosynthesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

1898, in the meaning defined above

Dictionary Entries Near photosynthesis

photosynthate

photosynthetic ratio

Cite this Entry

“Photosynthesis.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/photosynthesis. Accessed 25 Jul. 2024.

Kids Definition

Kids definition of photosynthesis, medical definition, medical definition of photosynthesis, more from merriam-webster on photosynthesis.

Nglish: Translation of photosynthesis for Spanish Speakers

Britannica.com: Encyclopedia article about photosynthesis

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Photosynthesis

Photosynthesis n., plural: photosyntheses [ˌfŏʊ.ɾoʊ.ˈsɪn̪.θə.sɪs] Definition: the conversion of light energy into chemical energy by photolithorophs

Table of Contents

Photosynthesis is a physio-chemical process carried out by photo-auto-lithotrophs by converting light energy into chemical energy . Among the endless diversity of living organisms in the world, producers are a unique breed.

Unlike consumers ( herbivores , carnivores , omnivores , or decomposers ) that rely upon other living organisms for their nutritional requirements and nourishment, producers have been distinguished by their ability to synthesize their own food. This is the reason that we call producers “autotrophic or self-reliable” in nature while consumers of all the different categories are called “heterotrophic or dependent” in nature.

Now among producers, there are different categories of producers, i.e. different mechanisms via which they produce their own food.

• Photo-auto-litho-trophs: Since these organisms tend to derive their nutrition by channeling the sun’s light energy, they are termed phototrophic in nature. Also, since they utilize inorganic carbon and translate it into organic carbon atoms, i.e. their means of deriving food becomes autotrophic. Additionally, since the source of electrons (electron donors) here are inorganic compounds, they are specified as lithotrophic . In totality, they can be called photo-auto-litho-trophic in nature. Example : Green plants are nature’s brilliant entities that come under this category. They carry out a photosynthesis cycle by taking in carbon dioxide and fixing it into carbohydrates (energy storage molecule). Some of them also give out oxygen gas that’s vital for the other life forms to survive in the earth’s atmosphere.
• Chemo-auto-lithotrophs: Many of us might be unaware of the fact that there are some autotrophs that don’t utilize sunlight. Rather they derive their energy stored from a different energy source like oxidation of inorganic compounds.

The scope of today’s discussion is limited to photosynthesis and photoautotrophs. So, let’s get started and get to know the answers to these common questions: what is the photosynthesis process, what are the 3 stages of photosynthesis, what does photosynthesis produce, what is a byproduct of photosynthesis, what is the purpose of photosynthesis, is photosynthesis a chemical change, the various inputs and outputs of photosynthesis, which organisms perform photosynthesis , and many other more questions!!!

What is Photosynthesis?

Photosynthesis definition: Photosynthesis is a physio-chemical process carried out by photo-auto-lithotrophs . In simpler language, photosynthesis is the process by which green plants convert light energy into ‘chemical energy’.

This energy transformation is only possible due to the presence of the miraculous pigment molecule chlorophyll in photosynthesis. The chemical energy as referred to before is the fixed carbon molecules generated during photosynthesis.

Green plants and algae have the ability to utilize carbon dioxide molecules and water and produce food (carbohydrates) for all life forms on Earth. There’s no doubt in the fact that life is impossible and unimaginable without green plants that photosynthesize and sustain the cycles of life.

Let’s give you a brief outline of the topic before we head forward.

• Etymology: The photosynthesis process finds its origin in 2 Greek words, firsts one being “phōs (φῶς)” meaning ‘light’ and the second one being “sunthesis (σύνθεσις)” meaning ‘putting together’ . The process of photosynthesis aids the conversion of light energy to chemical energy in varied forms of carbohydrate molecules like sugar molecules and starches.
• Organisms that perform photosynthesis: The organisms are called photo-auto-litho-trophs or simply photoautotrophs.
• Atmospheric gas consumed: Photosynthesizing organisms utilize carbon dioxide in photosynthesis (CO 2 ).
• Atmospheric gas released by “some” photosynthetic organisms (MIND IT-Not all): Some photosynthesizing organisms convert carbon dioxide and aid the process of producing oxygen gas (O2).
• Examples of photosynthesizing organisms: Green plants, cyanobacteria (earlier termed as blue-green algae), and different types of algae that essentially carry out phytoplankton photosynthesis.
• Why is photosynthesis important? The important function of photosynthesis: Food supply for the organisms on Earth, Oxygen supply for the survival of all organisms.
• Site of photosynthesis: Leaves and green tissues. (So when asked where photosynthesis takes place, we can tell that it is this site.)
• What are the reactants of photosynthesis: Carbon dioxide molecules + Water molecules + Light energy
• Products of photosynthesis: Fixed carbon (carbohydrates) + Oxygen (some cases) + Water

Watch this vid about photosynthesis:

Biology Definition: Photosynthesis is the synthesis of complex organic material using carbon dioxide , water , inorganic salts , and light energy (from sunlight) captured by light-absorbing pigments , such as chlorophyll and other accessory pigments . Photosynthesis may basically be simplified via this equation: 6CO 2 +12H 2 O+energy=C 6 H 12 O 6 +6O 2 +6H 2 O, wherein carbon dioxide (CO 2 ), water (H 2 O), and light energy are utilized to synthesize an energy-rich carbohydrate like glucose (C 6 H 12 O 6 ). Other products are water and oxygen .

• Photosynthesis occurs in plastids (e.g. chloroplasts ), which are membrane-bounded organelles containing photosynthetic pigments (e.g. chlorophyll ), within the cells of plants and algae .
• In photosynthetic bacteria ( cyanobacteria ) that do not have membrane-bounded organelles, photosynthesis occurs in the thylakoid membranes in the cytoplasm .

Etymology: from the Greek photo-, “light”, and synthesis, “putting together” Related forms: photosynthetic (adjective) Compare: chemosynthesis See also: photoautotroph

Types of Photosynthesis

Plant photosynthesis and photosynthetic organisms can be classified under different categories on the basis of some characteristic features. They are:

• Types of organisms that carry out photosynthesis on the basis of “cellular structure” Both prokaryotic and eukaryotic organisms carry out photosynthesis.
• Photosynthetic prokaryotes: for example, cyanobacteria
• Eukaryotic: for example, protists ( diatoms , dinoflagellates , Euglena) and green plants. In particular, algae photosynthesis can be observed in green algae , red algae , brown algae , & land plants, like bryophytes , pteridophytes, gymnosperms , and angiosperms .
• Prokaryotic ONLY (anoxygenic photosynthetic bacteria, green sulfur bacteria and purple bacteria)

Photosynthesis: a two-stage process

Photosynthesis is an example of a metabolic process with 2 stages. Both the stages need light (direct or indirect sunlight). Hence, the long-claimed notion of the 2 processes being ‘absolute LIGHT and DARK reactions’ isn’t apt.

Scientific studies have pointed out that even the 2nd stage of photosynthesis requires indirect sunlight. Therefore, rather than classifying the stages as light and dark photosynthesis reactions, we’ll like to classify the 2 stages as follows:

• Photochemical Reaction Process: Light energy is converted to ATP ; photophosphorylation process (light-dependent reactions)
• Through Calvin cycle: In oxygenic photosynthesis as well as anoxygenic photosynthesis
• Through Non-Calvin cycle: Only is some anoxygenic photosynthesis

Evolution of Photosynthesis Process

It is postulated that the very first photosynthetic beings and photosynthesis evolved quite early down the evolutionary timescale of life.

It is also believed that the first photosynthetic beings would have initially resorted to other available reducing agents like hydrogen ions or hydrogen sulfide in contrast to the modern-day photosynthetic organisms that utilize water as the “prime and only sources of electrons”.

It is believed that cyanobacteria would have appeared on the surface of Earth much later than the first photosynthetic beings. Once appeared they must have saturated the Earth’s atmosphere with oxygen gas and led to its oxygenation. Only after the Earth was oxygenated, the more complex forms of life would have later evolved.

When we compare photosynthesis to other metabolic processes like respiration, we can clearly notice that these two processes are almost opposite to each other. But another point to note is that both the processes in synchrony sustain life on Earth.

You cannot separate respiration from photosynthesis or photosynthesis from respiration and expect life to run normally. It is not possible that way. Let’s try to compare and list some characteristic features of photosynthesis and cellular respiration processes.

Photosynthesis vs. Respiration

• Photosynthesis: Anabolic process
• Cellular respiration: Catabolic process By anabolic, we mean the photosynthesis process “utilizes energy to build biomolecules” like carbohydrates, starch, and sugars. These biomolecules are further utilized by both the plants and the organisms dependent on plants for their nutritional needs. On the other hand, respiration is a catabolic process. This energy is utilized to break down complex molecules to derive nutrition out of them.
• Photosynthesis: In the chloroplasts of the eukaryotic phototrophic cells.
• Respiration: Primarily in the mitochondria of the cell.
• Photosynthesis: Carbon dioxide molecules + Water molecules + Light energy
• Respiration: Glucose + Oxygen
• Photosynthesis: Fixed carbon (carbohydrates) + Oxygen (some cases) + Water
• Respiration: Carbon dioxide + Water +energy (ATP)
• Photosynthesis: Endergonic and endothermic
• Respiration: Exergonic and exothermic Just note that these terms endergonic and endothermic both convey the same meaning of “absorbing heat”. And the terms exergonic and exothermic also convey the same meaning of “releasing heat”. The only difference is that –gonics relates to “the relative change in the free energy of the system” while –thermic relates to “the relative change in enthalpy of the system”.
• Photosynthesis: 6CO 2 + 6H 2 O → C6H 12 O 6 + 6O 2
• Respiration: C 6 H 12 O 6 6 + 6O 2 → 6CO 2 + 6H 2 O

Photosynthetic Membranes and Organelles

When we begin the discussion on this topic, it’s important that we know that no photosynthesis is possible without the pigment molecules that absorb light. The absorption of sunlight is the most vital step of photosynthesis.

We should also note that the energy of photons is different for every light of different wavelengths. And the energy needed for the photosynthesis to be conducted is of “a very specific wavelength range”.

For the absorption of lights of desired wavelengths, phototrophs organize their pigment molecules in the form of reaction center proteins . These proteins are located in the membranes of the organisms. Let’s learn how these pigment molecules reside inside the organism and how they make the membranes photosynthetic in nature.

• Prokaryotic photosynthetic organisms: These organisms have their pigment systems or photosystems located in the cell membranes or the thylakoid membranes in the cytosol itself. There are no special organelles called chloroplasts in the prokaryotes.

• Eukaryotic photosynthetic organisms (like green plants): These organisms have their pigment systems or photosystems located in the thylakoids of the chloroplast membranes. Eukaryotes have specialized organelles called chloroplasts (chlorophyll-containing plastids) in their cells.

Photosynthetic Pigments

There are 2 types of photosynthetic pigments in the oxygenic photosynthesizing organisms . They are as follows:

• Porphyrin-derivatives (Chlorophyll in plants and Phycobilin)

Carotenoids

Chlorophyll.

Chlorophyll is the green-colored pigment essential for photosynthesis. Let’s try to list its major characteristic features and roles of it.

• Nature: Lipid
• Location: Embedded in the thylakoid membrane
• Types: 9 types as identified by Arnoff and Allen in 1966 (chlorophyll-a, b, c, d, e, bacteriochlorophyll a, b, chlorobium chlorophyll-650,666). Bacteriochlorophylls are present in the anoxygenic photosynthetic organisms.
• Primary photosynthetic pigment: Chlorophyll-a
• Presence: In all oxygenic photosynthetic organisms
• Absorption range: Visible (blue and red) and IR (Infra-red)
• Ion important for its biological functioning: Magnesium ion (Mg 2+ )
• Structure: Chlorophyll-a, b, and d are “ chlorin ” derivatives; c is a “ porphyrin ” derivative.
• Chlorophyll Tail: Oxygenic photosynthetic organisms have a “ phytol ” tail in their chlorophyll; anoxygenic photosynthetic organisms have a “ geranyl ” tail in their bacteriochlorophylls.
• Main pigment for capturing and storing solar energy
• Photochemical reaction (chlorophyll-a is present in the photochemical reaction center i.e. PCRC. Chlorophyll a, b, c, and d play a role in resonance energy transfer.)

Carotenoid is the photosynthetic pigment essential for working in conjunction with chlorophyll. Let’s try to list its major characteristic features and roles of it.

• Nature: Lipid-soluble
• Types: More than 150
• Absorption range: 400-500nm
• Forms: Carotene (simple hydrocarbon, for example, beta carotene) and xanthophyll (oxygenated hydrocarbon, for example, lutein)
• In excitation and resonance energy transfer
• Photo-protection (work as a free-radical scavenger as well as a quencher)

Phycobilins

Phycobilins aren’t present in all the oxygenic photosynthetic organisms. They have a tetrapyrrole structure (no need for magnesium ion).

• Types: Phycoerythrobilin, Phycocyanobilins, Allophycocyanobilins When these pigment molecules combine with a water-soluble protein, they form the pigment-protein complex (phycobiliproteins, like phycoerythrin and phycocyanin).
• Location: Since these phycobiliproteins are water-soluble, they can’t exist in the membranes like chlorophyll and carotenoids. Therefore, phycobilin pigments as their pigment-protein complex aggregate into clusters and adhere to the membrane. These clusters are called phycobilisomes .
• Exceptional Note: These are the only pigments that are associated with protein molecules.
• Role: Resonance energy transfer

Organelle for Photosynthesis

What is chloroplast? In eukaryotes, photosynthesis occurs in chloroplasts as they are the designated organelles for the photosynthesis process. There are nearly 10-100 chloroplasts in a typical plant cell .

Inside chloroplasts are the thylakoids; the very specific site for the light capturing. The structure of this very unique part of the chloroplasts is briefly discussed here.

Thylakoid is a membrane-bound compartment in the chloroplasts of eukaryotic organisms. They are also present as such in the cytosol of cyanobacteria (cyanobacteria don’t have chloroplasts but they have simply thylakoids).

These thylakoids are the “primary site of the 1st stage of photosynthesis. i.e. “photochemical reaction” or popularly called “light-dependent reactions of photosynthesis”. The main components of the thylakoid are membrane, lumen, and lamellae. The chlorophyll molecules are present inside these thylakoid membranes.

Light-dependent Reactions

The first stage of photosynthesis is popularly called “light-dependent reactions” . We choose to call this stage the “1st stage: PHOTOCHEMICAL REACTION STAGE”. It is also called the “thylakoid reaction stage” or “hill’s reaction” .

This stage is marked by 3 essential steps of photosynthesis: Oxidation of water , reduction of NADP + , and ATP formation . The site where these reactions occur is the lamellar part of the chloroplast. The units of light-dependent reactions are quantosomes .

Let’s discuss this stage under some subheadings:

Wavelengths of light involved and their absorption

The white light that reaches Earth has subparts of different wavelengths together constituting the visible spectrum (390-760nm). But the photosynthetic organisms specifically use a subpart called PAR ( P hotosynthetically A ctive R adiation).

PAR ranges from 400-760nm. Blue light is 470-500nm while red light is 660-760nm). The green light (500-580nm) is reflected back by the plants and this is the reason that plants appear green in color. Blue-green light is not used, only blue light is used.

Absorption spectrum and action spectrum

• Absorption Spectrum: This is a pigment-specific entity or terminology. To find the absorption spectrum of a pigment, you need to plot “the amount of absorption of different wavelengths of light by that particular pigment” . The graph has the “wavelengths of light (in nanometers/nm)” on the X-axis and the “percentage of light absorption” on the Y-axis.

• Action Spectrum: To find the action spectrum of a pigment, you need to plot the “effectiveness of the different wavelengths of light in stimulating photosynthesis process” . The graph has the “wavelengths of light (in nanometers/nm)” on the X-axis and the “rate of photosynthesis (measured as oxygen released)” on the Y-axis. When you superimpose the action spectrum of photosynthesis with the absorption spectrum of the specific pigment, you can find the contribution of each different wavelength in the photosynthesis rate, photosynthetic efficiency, and photosynthetic productivity.

IMPORTANT NOTE: The absorption spectrum is calculated for any of the many pigments involved in photosynthesis. Contrastingly, the action spectrum is calculated only for the photochemical reaction performing pigment i.e. chlorophyll-a present at the reaction center. We identify the progress of photochemical reactions as the “evolution of oxygen gas” that primarily happens at the reaction center where only chlorophyll-a is present. Since the action is directly correlated to the specific excitation of chlorophyll-a molecule, the action spectrum is scientifically calculated only for this chlorophyll-a.

• Absorption spectrum of chlorophyll- a : 430 nm (blue), 660nm (red) {more absorbance at 660 nm)
• Absorption spectrum of chlorophyll-b: 430 nm (blue), 660nm (red) {more absorbance at 430 nm)

What actually happens in the Light-dependent reaction

Let’s briefly describe what actually happens here.

• 1 photon is absorbed by 1 molecule of the chlorophyll (P680) and simultaneously 1 electron is lost here.
• The electron flow of the photochemical reaction begins here.
• The electron is transferred to D1/D2 protein, then to a modified form of chlorophyll and “pheophytin”.
• After that, it’s transferred to plastoquinone A and then B.
• Initiates an electron flow down an electron transport chain.
• Ultimately aids the NADP reduction to NADPH.
• Creation of a proton gradient across the chloroplast membrane.
• Further on this proton gradient is exploited by the ATP synthase for the generation of ATP molecules.

Water photolysis

Now, if you are wondering how the first electron lost by the 1st chlorophyll is replenished to keep this cycle going, read on. The answer to this query is “photolysis of water molecules” . The chlorophyll molecule regains the lost electron when the “oxygen-evolving complex” in the thylakoid membrane carries out the photolysis of water. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases oxygen.

Many scientists had a doubt about the source of oxygen in photosynthesis. Some speculated the oxygen atom of the CO 2 gas is the source of oxygen post-photosynthesis. But it was the collective contribution of some 4 scientists that gave clarity on this topic.

C.B. Van Niel worked on purple photosynthetic bacteria ( Chromatium vinosum ) and found out that the source of oxygen is the oxidation of water molecules (‘indirect evidence’). While Ruben, Hassid, and Kamen carried out an isotopic study that gave ‘direct evidence’ of oxygen-evolving from H 2 O molecules and not CO 2 molecules.

Hydrolysis of 2 molecules of water leads to the evolution of 1 molecule of oxygen gas. The photosynthesis equation for light-dependent reactions (non-cyclic electron flow) or the chemical formula for photosynthesis:

2 H 2 O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O 2

The photochemical reaction (or the light-dependent reactions) can be classified as:

• Cyclic reaction: Only 1 photosystem ( PS1 ) is involved. (Photon excites P700 in PS1, electron reaches Fe-S, then Ferredoxin, then Plastoquinone and then Cyt b6f complex and then Plastocyanin). Since in the solo involvement of PS1 here, the electron flow becomes cyclic. And this phosphorylation process is called cyclic phosphorylation. It happens in the stroma lamellae when light beyond 680nm is available.
• Non-cyclic reaction: Both photosystems (PS1 and PS2 ) are involved. (Photon excites P680 in PS2, the electron is lost and transferred to pheophytin, then sent on a roller coaster (Z-scheme). Within the z-scheme, the final redox reaction enables the reduction of NADP+ to NADPH. And the chemiosmotic potential generation via proton pumping proton across the membrane and into the thylakoid lumen ensures ATP synthesis.

Data Source: Akanksha Saxena of Biology Online

Light-Independent Reactions (Carbon-fixation Reaction)

Also called the carbon fixation process, the “light-independent reactions” is a misnomer as Science has now already proved that the second stage of photosynthesis isn’t really light-independent reactions. Though it doesn’t need direct light, indirect light is involved even in this process. We choose to label this stage of photosynthesis as the “2nd stage: CARBON-FIXATION REACTION STAGE ”, which is also called:

• Calvin Cycle or “stromal reaction” as it manifests in the stroma part of the chloroplast
• “C3 Cycle” or the “reductive pentose phosphate cycle”

Calvin cycle

The inputs for the Calvin cycle  in most plants come from the previously occurred photochemical reaction. In this cycle, the carbon dioxide produced is fixed to a glucose molecule. To be very specific, the Calvin cycle directly doesn’t produce glucose, rather it produces glyceraldehydes-5-phosphate (G-3-P). Glucose is formed after these G-3-P molecules move into the cytosol from the chloroplast .

It consists of primarily 3 steps as follows:

• Carboxylation: Acceptance of CO 2 by RuBP which is a 5-carbon compound and the CO2-acceptor). 2 molecules of 3-phosphoglycerate are generated as the result of the carboxylation process.
• Reduction: Generation of 3C/4C/5C/6C/7C molecules.
• Regeneration of RUBP: 3 molecules of RuBP are regenerated.

In totality, 3 molecules of CO 2 produce 1 molecule of G-3-P. This uses 9 ATPs and 6 NADPHs. And, 6 molecules of CO 2 produce 2 molecules of G-3-P which further produce 1 molecule of glucose. This uses 18ATPs and 12 NADPHs.

The main enzyme is RuBisCo . It’s a multi-enzyme complex with 8 large and 8 small subunits. The substrates for this enzyme are CO 2 , O 2 , and RuBP. An essential ion for the biological functioning of this enzyme: Mg 2+ . The role of RuBisCo is that it captures carbon dioxide gas from the atmosphere and utilizes the NADPH from the 1st stage (photochemical reaction/light-dependent reaction stage) to fix the CO 2 .

The equation of dark reaction of photosynthesis/light-independent reaction stage/2nd stage is: 3 CO 2 + 9 ATP + 6 NADPH + 6 H + → C 3 H 6 O 3 -phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H 2 O

The simple carbon sugars formed via the C3 cycle are utilized by the biological systems to form complex organic compounds like cellulose, precursors for amino acids synthesis and thereby proteins, precursors for lipids, and the source of fuel for respiration.

Important Point To Note: It happens in all the photosynthetic organisms as the basic carbon-fixation step.

Carbon concentrating mechanisms

There are many carbon concentrating mechanisms to increase the carbon dioxide levels and the carbon fixation process like C4, CAM, etc.

• Doesn’t happen in all photosynthetic organisms. Rather it happens in conjunction with the C3 cycle in some 4% of angiosperm families.
• Most commonly angiosperm families that witness C4 cycle: Poaceae, Cyperaceae.
• First explained by: Hatch and Slack (hence also called the Hatch and Slack cycle). They worked on the maize plant.
• Role: Endow the ability to efficiently conduct photosynthesis in plants of the semi-arid regions by making them well adapted.
• Mechanism: By separation of photosynthesis stages in 2 types of cells (mesophyll cells and bundle sheath cells). The light reaction is restricted to the mesophyll cells and the CO 2 fixation happens in the bundle sheath cells. This phenomenon is also termed as “chloroplast dimorphism” in C4 plants. The Kranz anatomy is visible here.
• Why does the need arise in the first place? – In semi-arid regions or regions with very hot and dry environmental conditions, plants are forced to close their stomata in order to limit water loss. Under such harsh conditions, the intake of CO 2 decreases during the day as the stomata are forced closed. This might lead to no CO 2 intake and hence no CO 2 fixation (2nd stage of photosynthesis). But the 1st stage of photosynthesis keeps running as it doesn’t depend on stomata opening or closure. This means that a continuous oxygen evolution happens which can lead to oxygen saturation. As we know that RuBisCo enzymes use O 2 gas as substrate too, and this can lead to an increased rate of photorespiration by the oxygenase activity of RuBisCo. This further decreases the carbon fixation. This is a very big issue if not resolved. Hence, for situations like these, carbon concentrating mechanisms have evolved in some families of plants to concentrate and enrich the CO 2 concentration in the leaves of these plants under such conditions.
• Important enzyme for CO 2 concentration: PEP carboxylase
• CO 2 is first added to a three-carbon compound called phosphoenolpyruvate (PEP) in this cycle. This leads to the formation of a four-carbon (4C)  molecule called oxaloacetic acid or malate. This step happens in the mesophyll cells of the leaves.
• After that, these 4C compounds are transferred to the bundle sheath cells where the normal C3 cycle fixes them into glucose molecules.
• This CO 2 concentrating mechanism works on the “principle of separating the RuBisCo enzyme from the O 2 -generating photochemical reactions” in order to reduce the rates of photorespiration and simultaneously increase the rates of CO 2 fixation.
• This increases the photosynthetic capacity of the leaf/leaf photosynthesis.
• When the high light and high-temperature conditions are dominant, C4 plants prove more photosynthetically efficient than C3 plants as they produce more sugar molecules in such conditions.
• Examples of C4 plants: Many crop plants like wheat, maize, rice, sorghum, millet, and sugarcane.
• Number of ATPs required: 12 (for C-enrichment) + 18 (for C-fixation)= 30 ATPS for 1 glucose production
• Number of NADPH required: 18 NADPH for 1 glucose production
• Some plants resort to another mechanism called the CAM cycle in conjunction with the C3 cycle to fix carbon dioxide.
• Examples: xerophytes like cactus photosynthesis, and most succulents.
• Around 16,000 species of plants utilize the CAM mechanism
• Mechanism: Utilize PEP carboxylase to capture carbon dioxide. In contrast to the C4 cycle where there is a “spatial separation of the 2 processes of CO 2 reduction to PEP and PEP fixation to glucose”, CAM plants display a “temporal separation of the 2 listed processes”.

Land plants display different types of photosynthesis based on their requirements and environmental constraints. They are C3, C4 +C3, and CAM+ C3 types of photosynthesis.

Aquatic plants and algae display some extra features in the photosynthetic machinery. These features further refine and define the smooth functioning and efficiency of photosynthesis.

Example: Cyanobacteria photosynthesis – cyanobacteria have carboxysomes  that help in enriching the concentration of carbon dioxide around the RuBisCO enzyme. This directly increases the photosynthetic rates. The distinguished and specially enabled enzyme in the carboxysomes is called “carbonic anhydrase”. The carbonic anhydrase possesses the ability to evolve and release CO 2 from the dissolved hydrocarbonate ions (HCO-). As soon as the CO 2 is released, RuBisCo takes care that it doesn’t go to waste.

Order and Kinetics

There are innumerable reactions and processes involved in the biological mechanism of photosynthesis. Besides the normal flow of photosynthesis, there are some plant-specific and condition-specific additional steps that further complicate the mechanism.

Since every biological mechanism has a lot of enzymes, factors, cofactors, substrates, and entities involved, photosynthesis is no different.

Let’s try to list some kinetics-specific pointers that may help.

As discussed in the overview and starting of this article, the early photosynthetic organisms must have been primarily “anoxygenic” in nature. These bacteria used some other source than water molecules as their primary electron donors. Even the geological evidence aligns with this fact as the early atmosphere of Earth was highly reducing in nature. Some speculated organisms of the early evolutionary phase are :

• Green sulfur bacteria (Electron donor= hydrogen and sulfur)
• Purple sulfur bacteria (Electron donor= hydrogen and sulfur)
• Green nonsulfur bacteria (Electron donor= various amino and other organic acids)
• Purple nonsulfur bacteria (Electron donor= variety of nonspecific organic molecules)

After this, some filamentous photosynthetic organisms are expected to have evolved. This is scaled to be an occurrence of some 3.4 billion years old timeline. It is around 2 million years ago that oxygenic photosynthesis is believed to have evolved.

The modern and more commonly known photosynthesis in plants and most of the photosynthetic prokaryotes= Oxygenic (Electron donor= Water molecules)

Symbiosis and the origin of chloroplasts

There are some animal groups that have the ability to form and establish symbiotic relationships with photosynthetic organisms. By establishing such a relationship, these organisms can directly rely upon their photosynthetic partner for energy and food requirements. Some examples of such animal groups are:

• Sea anemones
• Marine mollusks (example: Elysia viridis & Elysia chlorotica )
• Fungi photosynthesis (Lichens)

When such symbiotic relationships are established, it’s sometimes observed that some genes of the plant cell’s nucleus get transferred to the animal cell . (Observed in some slugs).

Origin of Chloroplasts

Such symbiosis is popularly claimed to be the source of chloroplast evolution. As we notice many similarities between the photosynthetic bacteria and chloroplasts, the evolution of chloroplasts is often hinted to have occurred from these bacteria. Some of the common features between the 2 are:

• Circular chromosome
• Prokaryotic-type ribosome
• A similar set of proteins in the photosynthetic reaction center

It is for all these commonalities the “ endosymbiotic theory ” had been proposed for the evolution of chloroplasts and mitochondria in the eukaryotic cells. According to the endosymbiotic theory, the early eukaryotic cells are believed to have acquired the photosynthetic bacteria by the process of endocytosis). Those early eukaryotic cells after acquiring the photosynthetic bacteria transformed to be self-sustainable and became the “first plant cells”. (Mitochondria photosynthesis is true, they are associated with respiration!)

Photosynthetic eukaryotic lineages

Photosynthetic eukaryotic lineages include:

• Glaucophytes
• Chlorophytes
• Rhodophytes
• Cryptophytes (some clades)
• Haptophytes (some clades)
• Dinoflagellates & chromerids
• Euglenids—clade Excavata (unicellular)

Cyanobacteria and the evolution of photosynthesis

Almost all the prokaryotes carry out anoxygenic photosynthesis in contrast to cyanobacteria, which perform oxygenic photosynthesis. This ability to carry out oxygenic photosynthesis is speculated to have evolved at least 2450–2320 million years ago. The first photosynthetic cyanobacteria might not have been oxygenic as Earth’s atmosphere had no oxygen then.

This topic still requires more scientific study to bring out conclusive results. From the paleontological evidence, it is claimed that the 1st cyanobacteria evolved around 2000 Ma.

For the initial years of the Earth’s oxygen-rich environment (after the oxygen-evolving mechanism evolved), cyanobacteria are claimed to be the “principal primary producers of oxygen”. Even to date, cyanobacteria have been proven vital for marine ecosystems. They’re the primary producers of oxygen in oceans.

Cyanobacteria also fix nitrogen electrons fixation and play a role in biological nitrogen cycles.

Experimental History

We will list the long experimental history in deciphering the extensive photosynthesis process through the ages.

Discovery, Refinements, and Development of the concept

Find out the discovery, refinements, and development of photosynthesis as summarized in the table below:

C3 : C4 photosynthesis research

Several studies were conducted using isotopes of radioactive elements to identify the various aspects of the photosynthetic process. A number of organisms like Chlorella , Stellaria media, Cladophora, Spirogyra, Rhodopseudomonas , sulfur bacteria, green plants like maize, etc have been used to understand the photosynthesis process over the years. Gas exchange studies, isotopic studies, light spectrum studies, radioactive studies, plant anatomical and physiological studies, studies involving roles of carbon dioxide and water, etc have all together opened the gates for our deeper understanding of this topic.

The 3 main factors that directly affect the photosynthesis process are:

• Light irradiance and wavelength
• Carbon dioxide concentration

Temperature

Although there are many more corollary factors, these 3 are the most important ones.

Light intensity (irradiance), wavelength, and temperature

Light is an essential factor for photosynthesis. It directly affects the rate of it. There are 3 different parameters that we should look into:

• Sciophytes : Grow under “diffuse” light. Example: Oxalis
• Heliophytes: Grow under “direct: light. Example: Dalbergia
• Light quality: PAR as previously discussed is the quality or the fraction of light energy that is ‘photosynthetically active’ in nature. It ranges from 400-700nm in wavelength.
• Duration of light: This parameter doesn’t affect the rate of photosynthesis but affects the total photosynthetic output.

Carbon dioxide levels and photorespiration

Carbon dioxide concentration is the major factor in determining the rate of photosynthesis. There is no carbon-dioxide enriching system in C3 plants like the C4 plants. So, if you increase the concentration of CO 2 in the system, the photosynthetic rate of C3 plants will increase as the CO 2 concentration increases. On the other hand, the photosynthetic yield of the C4 plant won’t increase in such a scenario.

• CO 2 Compensation Point: A stage in CO 2 concentration when there’s no absorption of CO 2 by the illuminated plant part.

Featuring… “The curious case of RuBisCO and PEP Carboxylase”

Imagine an equal concentration (50-50%) of the two isotopes of carbon, C-12 and C-13, in the form of 12CO 2 and 13CO 2 , made available to both C3 and C4 plants. Now, can you tell which isotope of the carbon will be fixed more or less by the two types of photosynthetic organisms? Can you guess if there would be a “preferable” isotope between the two? Do you think C3 plants will fix the 12CO 2 and 13CO 2 equally or unequally? Or do you think the 12CO 2 and 13CO 2 incorporation would have a biased ratio in any of the two (C3/C4 plants)????

The answer to this lies in the major carbon fixing enzyme involved.

• C3 plants: Major C-fixing enzyme is RuBisCo and RuBisCo has a “discriminatory ability” to preferably fix 12CO 2 and not 13CO2. Hence, you will find more 12CO 2 fixed than 13CO 2 in the C3 plants.
• C4 plants: Major C-fixing enzyme is not RuBisCo but PEP Carboxylase . PEP Carboxylase has “no discriminatory ability”. So, you’ll find an almost equal proportion of 12CO 2 and 13CO 2 getting fixed in C4 plants. So, in comparison to C3 plants, the chances of getting 13CO 2 fixed are more in C4 plants.

Choose the best answer. 

Send Your Results (Optional)

• Rutherford, A.W., Faller, P. (Jan 2003). “Photosystem II: evolutionary perspectives”. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 358 (1429): 245–253. doi:10.1098/rstb.2002.1186. PMC 1693113. PMID 12594932.
• Arnon, D.I., Whatley, F.R., Allen, M.B. (1954). “Photosynthesis by isolated chloroplasts. II. Photophosphorylation, the conversion of light into phosphate bond energy”. Journal of the American Chemical Society. 76 (24): 6324–6329. doi:10.1021/ja01653a025.
• Ehrenberg, R. (2017-12-15). “The photosynthesis fix”. Knowable Magazine. Annual Reviews. doi:10.1146/knowable-121917-115502. Retrieved 2018-04-03.
• El-Sharkawy, M.A., Hesketh, J.D. (1965). “Photosynthesis among species in relation to characteristics of leaf anatomy and CO 2 diffusion resistances”. Crop Sci. 5 (6): 517–521. doi:10.2135/cropsci1965.0011183x000500060010x.
• Earl, H., Said Ennahli, S. (2004). “Estimating photosynthetic electron transport via chlorophyll fluorometry without Photosystem II light saturation”. Photosynthesis Research. 82 (2): 177–186. doi:10.1007/s11120-004-1454-3. PMID 16151873. S2CID 291238.

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Last updated on July 15th, 2022

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Photosynthesis

What is photosynthesis.

It is the process by which green plants, algae, and certain bacteria convert light energy from the sun into chemical energy that is used to make glucose. The word ‘photosynthesis’ is derived from the Greek word phōs, meaning ‘light’ and synthesis meaning ‘combining together.’

Jan Ingenhousz, the Dutch-born British physician and scientist, discovered the process of photosynthesis.

Where does Photosynthesis Occur

Photosynthesis takes place mainly in the leaves of green plants and also in the stems of herbaceous plants as they also contain chlorophyll. Sometimes it also occurs in roots that contain chlorophyll like in water chestnut and Heart-leaved moonseed. Apart from plants, photosynthesis is also found to occur in blue-green algae.

What Happens During Photosynthesis

It involves a chemical reaction where water, carbon dioxide, chlorophyll, and solar energy are utilized as raw materials (inputs) to produce glucose, oxygen, and water (outputs).

Stages of the Process

Photosynthesis occurs in two stages:

1) The Light-dependent Reaction

• Takes place in the thylakoid membranes of chloroplasts only during the day in the presence of sunlight
• High-energy phosphate molecules adenosine triphosphate ( ATP ) and the reducing agent NADPH are produced with the help of electron transport chain

2) The Light-independent or Dark Reaction ( Calvin cycle )

• Takes place in the stroma of chloroplast in the absence of light that helps to fix carbon
• ATP and NADPH produced in the light reaction are utilized along with carbon dioxide to produce sugar in the form of glucose

Factors Affecting the Rate of Photosynthesis

• Intensity of Light: The higher intensity of light increases the rate of photosynthesis
• Temperature:  Warmer the temperature, higher the rate of photosynthesis. The rate is highest between the temperatures of 25° to 35° C, after which it starts to decrease
• Concentration of Carbon dioxide: Higher concentration of carbon dioxide increases the rate of photosynthesis until it reaches a certain point, beyond which no further effects are found   

Although all the above factors together interact to affect the rate of photosynthesis, each of them individually is also capable of directly influencing the process without the other factors and thus called limiting factors.

Importance of Photosynthesis

It serves two main purposes that are essential to support life on earth:

• Producing food for organisms that depend on others for their nutrition such as humans along with all other animals
• Synthesizing oxygen by replacing carbon dioxide in the atmosphere

Ans. Photosynthesis is an endothermic reaction because it absorbs the heat of the sun to carry out the process.

Ans. The oxygen in photosynthesis comes from splitting the water molecules.

Ans. Chlorophyll is the main light-absorbing pigment in photosynthesis.

Ans. The role of water is to provide oxygen in the form of oxygen gas to the atmosphere.

Ans. Sunlight is the source of energy that drives photosynthesis.

Ans. The easiest way to measure the rate of photosynthesis is to quantify the carbon dioxide or oxygen levels using a data logger. The rate of photosynthesis can also be measured by determining the increase in the plant ’s biomass (weight).

Ans. Photosynthesis is an energy-requiring process occurring only in green plants, algae, and certain bacteria that utilizes carbon dioxide and water to produce food in the form of carbohydrates. In contrast, cellular respiration is an energy-releasing process found in all living organisms where oxygen and glucose are utilized to produce carbon dioxide and water.

Ans. Glucose produced in photosynthesis is used in cellular respiration to make ATP.

Article was last reviewed on Tuesday, April 21, 2020

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Photosynthesis

Plants are autotrophs, which means they produce their own food. They use the process of photosynthesis to transform water, sunlight, and carbon dioxide into oxygen, and simple sugars that the plant uses as fuel. These primary producers form the base of an ecosystem and fuel the next trophic levels. Without this process, life on Earth as we know it would not be possible. We depend on plants for oxygen production and food.

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photosynthesis summary

Learn how photosynthesis works and why it’s important.

photosynthesis , Process by which green plants and certain other organisms transform light into chemical energy. In green plants, light energy is captured by chlorophyll in the chloroplasts of the leaves and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds (simple and complex sugars) that are the basis of both plant and animal life. Photosynthesis is crucial for maintaining life on Earth; if it ceased, there would soon be little food or other organic matter on the planet, and most types of organisms would disappear.

Photosynthesis consists of a number of photochemical and enzymatic reactions. It occurs in two stages. During the light-dependent stage (“light” reactions), chlorophyll absorbs light energy, which excites some electrons in the pigment molecules to higher energy levels; these leave the chlorophyll and pass along a series of molecules, generating formation of NADPH (an enzyme) and high-energy ATP molecules. Oxygen , released as a by-product, passes into the atmosphere through pores in the leaves. NADPH and ATP drive the second stage, the “dark” reactions (or Calvin cycle, discovered by Melvin Calvin ), which do not require light. During this stage glucose is generated using atmospheric carbon dioxide.

What is photosynthesis?

Photosynthesis is the process plants, algae and some bacteria use to turn sunlight, carbon dioxide and water into sugar and oxygen.

• Photosynthetic processes
• Photosynthesis equation
• The carbon exchange
• How do plants absorb sunlight?

How does photosynthesis start?

• Location of photosynthesis

Light-dependent reactions

• The Calvin cycle

Types of photosynthesis

Additional resources.

Photosynthesis is the process used by plants, algae and some bacteria to turn sunlight into energy. The process chemically converts carbon dioxide (CO2) and water into food (sugars) and oxygen . The chemical reaction often relies on a pigment called chlorophyll, which gives plants their green color.  Photosynthesis is also the reason our planet is blanketed in an oxygen-rich atmosphere.

Types of photosynthetic processes

There are two types of photosynthesis: oxygenic and anoxygenic. They both follow very similar principles, but the former is the most common and is seen in plants, algae and cyanobacteria. 

During oxygenic photosynthesis, light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to produce carbohydrates . In this transfer, the CO2 is "reduced," or receives electrons, and the water is "oxidized," or loses electrons. Oxygen is produced along with carbohydrates.

This process creates a balance on Earth, in which the carbon dioxide produced by breathing organisms as they consume oxygen in respiration is converted back into oxygen by plants, algae and bacteria.

Anoxygenic photosynthesis, meanwhile, uses electron donors that are not water and the process does not generate oxygen, according to "Anoxygenic Photosynthetic Bacteria" by LibreTexts . The process typically occurs in bacteria such as green sulfur bacteria and phototrophic purple bacteria. 

The Photosynthesis equation

Though both types of photosynthesis are complex, multistep affairs, the overall process can be neatly summarized as a chemical equation.

The oxygenic photosynthesis equation is: 

6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O

Here, six molecules of carbon dioxide (CO2) combine with 12 molecules of water (H2O) using light energy. The end result is the formation of a single carbohydrate molecule (C6H12O6, or glucose) along with six molecules each of oxygen and water.

Similarly, the various anoxygenic photosynthesis reactions can be represented as a single generalized formula:

CO2 + 2H2A + Light Energy → [CH2O] + 2A + H2O

The letter A in the equation is a variable, and H2A represents the potential electron donor. For example, "A" may represent sulfur in the electron donor hydrogen sulfide (H2S), according to medical and life sciences news site News Medical Life Sciences . 

How is carbon dioxide and oxygen exchanged?

Plants absorb CO2 from the surrounding air and release water and oxygen via microscopic pores on their leaves called stomata. 

When stomata open, they let in CO2; however, while open, the stomata release oxygen and let water vapor escape. Stomata close to prevent water loss, but that means the plant can no longer gain CO2 for photosynthesis. This tradeoff between CO2 gain and water loss is a particular problem for plants growing in hot, dry environments. 

How do plants absorb sunlight for photosynthesis?

Plants contain special pigments that absorb the light energy needed for photosynthesis.

Chlorophyll is the primary pigment used for photosynthesis and gives plants their green color, according to science education site Nature Education . Chlorophyll absorbs red and blue light and reflects green light. Chlorophyll is a large molecule and takes a lot of resources to make; as such, it breaks down towards the end of the leaf's life, and most of the pigment's nitrogen (one of the building blocks of chlorophyll) is resorbed back into the plant,  When leaves lose their chlorophyll in the fall, other leaf pigments such as carotenoids and anthocyanins begin to show. While carotenoids primarily absorb blue light and reflect yellow, anthocyanins absorb blue-green light and reflect red light, according to Harvard University's The Harvard Forest .

Related: What if humans had photosynthetic skin?

Pigment molecules are associated with proteins, which allow them the flexibility to move toward light and toward one another. A large collection of 100 to 5,000 pigment molecules constitutes an "antenna," according to an article by Wim Vermaas , a professor at Arizona State University. These structures effectively capture light energy from the sun, in the form of photons.

The situation is a little different for bacteria. While cyanobacteria contain chlorophyll, other bacteria, for example, purple bacteria and green sulfur bacteria, contain bacteriochlorophyll to absorb light for anoxygenic photosynthesis, according to " Microbiology for Dummies " (For Dummies, 2019). 

It was previously hypothesized that just a small number of photons would be needed to kickstart photosynthesis, but researchers never successfully observed this first step. However, in 2023, scientists discovered that photosynthesis appears to begin with a single photon. 

The researchers set up an experiment where a photon source spat out two photons at a time. One was absorbed by a detector, while the other hit a bacteria's chloroplast equivalent. When the second photon hit, photosynthesis began. 

After performing the test over 1.5 million times, the researchers confirmed that just one photon is needed to start photosynthesis.

Where in the plant does photosynthesis take place?

Photosynthesis occurs in chloroplasts, a type of plastid (an organelle with a membrane) that contains chlorophyll and is primarily found in plant leaves. 

Chloroplasts are similar to mitochondria , the energy powerhouses of cells, in that they have their own genome, or collection of genes, contained within circular DNA. These genes encode proteins that are essential to the organelle and to photosynthesis.

Inside chloroplasts are plate-shaped structures called thylakoids that are responsible for harvesting photons of light for photosynthesis, according to the biology terminology website Biology Online . The thylakoids are stacked on top of each other in columns known as grana. In between the grana is the stroma — a fluid containing enzymes, molecules and ions, where sugar formation takes place. 

Ultimately, light energy must be transferred to a pigment-protein complex that can convert it to chemical energy, in the form of electrons. In plants, light energy is transferred to chlorophyll pigments. The conversion to chemical energy is accomplished when a chlorophyll pigment expels an electron, which can then move on to an appropriate recipient. 

The pigments and proteins that convert light energy to chemical energy and begin the process of electron transfer are known as reaction centers.

When a photon of light hits the reaction center, a pigment molecule such as chlorophyll releases an electron.

The released electron escapes  through a series of protein complexes linked together, known as an electron transport chain. As it moves through the chain, it generates the energy to produce ATP (adenosine triphosphate, a source of chemical energy for cells) and NADPH — both of which are required in the next stage of photosynthesis in the Calvin cycle. The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. This splitting of water molecules releases oxygen into the atmosphere.

Light-independent reactions: The Calvin cycle

The Calvin cycle is the three-step process that generates sugars for the plant, and is named after Melvin Calvin , the Nobel Prize -winning scientist who discovered it decades ago. The Calvin cycle uses the ATP and NADPH produced in chlorophyll to generate carbohydrates. It takes plate in the plant stroma, the inner space in chloroplasts.

In the first step of this cycle, called carbon fixation, an enzyme called RuBP carboxylase/oxygenase, also known as rubiso, helps incorporate CO2 into an organic molecule called 3-phosphoglyceric acid (3-PGA). In the process, it breaks off a phosphate group on six ATP molecules to convert them to ADP, releasing energy in the process, according to LibreTexts.

In the second step, 3-PGA is reduced, meaning it takes electrons from six NADPH molecules and produces two glyceraldehyde 3-phosphate (G3P) molecules.

One of these G3P molecules leaves the Calvin cycle to do other things in the plant. The remaining G3P molecules go into the third step, which is regenerating rubisco. In between these steps, the plant produces glucose, or sugar.

Three CO2 molecules are needed to produce six G3P molecules, and it takes six turns around the Calvin cycle to make one molecule of carbohydrate, according to educational website Khan Academy.

There are three main types of photosynthetic pathways: C3, C4 and CAM. They all produce sugars from CO2 using the Calvin cycle, but each pathway is slightly different.

C3 photosynthesis

Most plants use C3 photosynthesis, according to the photosynthesis research project Realizing Increased Photosynthetic Efficiency (RIPE) . C3 plants include cereals (wheat and rice), cotton, potatoes and soybeans. This process is named for the three-carbon compound 3-PGA that it uses during the Calvin cycle. 

C4 photosynthesis

Plants such as maize and sugarcane use C4 photosynthesis. This process uses a four-carbon compound intermediate (called oxaloacetate) which is converted to malate , according to Biology Online. Malate is then transported into the bundle sheath where it breaks down and releases CO2, which is then fixed by rubisco and made into sugars in the Calvin cycle (just like C3 photosynthesis). C4 plants are better adapted to hot, dry environments and can continue to fix carbon even when their stomata are closed (as they have a clever storage solution), according to Biology Online. 

CAM photosynthesis

Crassulacean acid metabolism (CAM) is found in plants adapted to very hot and dry environments, such as cacti and pineapples, according to the Khan Academy. When stomata open to take in CO2, they risk losing water to the external environment. Because of this, plants in very arid and hot environments have adapted. One adaptation is CAM, whereby plants open stomata at night (when temperatures are lower and water loss is less of a risk). According to the Khan Academy, CO2 enters the plants via the stomata and is fixed into oxaloacetate and converted into malate or another organic acid (like in the C4 pathway). The CO2 is then available for light-dependent reactions in the daytime, and stomata close, reducing the risk of water loss. 

Discover more facts about photosynthesis with the educational science website sciencing.com . Explore how leaf structure affects photosynthesis with The University of Arizona . Learn about the different ways photosynthesis can be measured with the educational science website Science & Plants for Schools .  

This article was updated by Live Science managing editor Tia Ghose on Nov. 3, 2022.

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Daisy Dobrijevic joined  Space.com  in February 2022 as a reference writer having previously worked for our sister publication  All About Space  magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the  National Space Centre  in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K.

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• chasmogamous
• cleistogamous
• efflorescence
• in flower idiom
• multi-headed
• palynological

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• What is Photosynthesis

When you get hungry, you grab a snack from your fridge or pantry. But what can plants do when they get hungry? You are probably aware that plants need sunlight, water, and a home (like soil) to grow, but where do they get their food? They make it themselves!

Plants are called autotrophs because they can use energy from light to synthesize, or make, their own food source. Many people believe they are “feeding” a plant when they put it in soil, water it, or place it outside in the Sun, but none of these things are considered food. Rather, plants use sunlight, water, and the gases in the air to make glucose, which is a form of sugar that plants need to survive. This process is called photosynthesis and is performed by all plants, algae, and even some microorganisms. To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight.

Just like you, plants need to take in gases in order to live. Animals take in gases through a process called respiration. During the respiration process, animals inhale all of the gases in the atmosphere, but the only gas that is retained and not immediately exhaled is oxygen. Plants, however, take in and use carbon dioxide gas for photosynthesis. Carbon dioxide enters through tiny holes in a plant’s leaves, flowers, branches, stems, and roots. Plants also require water to make their food. Depending on the environment, a plant’s access to water will vary. For example, desert plants, like a cactus, have less available water than a lilypad in a pond, but every photosynthetic organism has some sort of adaptation, or special structure, designed to collect water. For most plants, roots are responsible for absorbing water. 

The last requirement for photosynthesis is an important one because it provides the energy to make sugar. How does a plant take carbon dioxide and water molecules and make a food molecule? The Sun! The energy from light causes a chemical reaction that breaks down the molecules of carbon dioxide and water and reorganizes them to make the sugar (glucose) and oxygen gas. After the sugar is produced, it is then broken down by the mitochondria into energy that can be used for growth and repair. The oxygen that is produced is released from the same tiny holes through which the carbon dioxide entered. Even the oxygen that is released serves another purpose. Other organisms, such as animals, use oxygen to aid in their survival. 

If we were to write a formula for photosynthesis, it would look like this: 

6CO 2 + 6H 2 O + Light energy → C 6 H 12 O 6 (sugar) + 6O 2 

The whole process of photosynthesis is a transfer of energy from the Sun to a plant. In each sugar molecule created, there is a little bit of the energy from the Sun, which the plant can either use or store for later. 

Imagine a pea plant. If that pea plant is forming new pods, it requires a large amount of sugar energy to grow larger. This is similar to how you eat food to grow taller and stronger. But rather than going to the store and buying groceries, the pea plant will use sunlight to obtain the energy to build sugar. When the pea pods are fully grown, the plant may no longer need as much sugar and will store it in its cells. A hungry rabbit comes along and decides to eat some of the plant, which provides the energy that allows the rabbit to hop back to its home. Where did the rabbit’s energy come from? Consider the process of photosynthesis. With the help of carbon dioxide and water, the pea pod used the energy from sunlight to construct the sugar molecules. When the rabbit ate the pea pod, it indirectly received energy from sunlight, which was stored in the sugar molecules in the plant. 

Humans, other animals, fungi, and some microorganisms cannot make food in their own bodies like autotrophs, but they still rely on photosynthesis. Through the transfer of energy from the Sun to plants, plants build sugars that humans consume to drive our daily activities. Even when we eat things like chicken or fish, we are transferring energy from the Sun into our bodies because, at some point, one organism consumed a photosynthetic organism (e.g., the fish ate algae). So the next time you grab a snack to replenish your energy, thank the Sun for it! 

This is an excerpt from the  Structure and Function  unit of our curriculum product line, Science and Technology Concepts TM  (STC). Please visit our publisher,  Carolina Biological , to learn more. 

[BONUS FOR TEACHERS] Watch "Photosynthesis: Blinded by the Light" to explore student misconceptions about matter and energy in photosynthesis and strategies for eliciting student ideas to address or build on them.

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• What is Photosynthesis

What Is Photosynthesis?

“Photosynthesis is the process used by green plants and a few organisms that use sunlight, carbon dioxide and water to prepare their food.”

The process of photosynthesis is used by plants, algae and certain bacteria that convert light energy into chemical energy. The glucose formed during the process of photosynthesis provides two important resources to organisms: energy and fixed carbon.

Read on to explore what is photosynthesis and the processes associated with it.

Site of Photosynthesis

Photosynthesis takes place in special organelles known as chloroplast. This organelle has its own DNA, genes and hence can synthesize its own proteins. Chloroplasts consist of stroma, fluid, and stack of thylakoids known as grana. There are three important pigments present in the chloroplast that absorb light energy, chlorophyll a, chlorophyll b, and carotenoids.

Also Read: Photosynthesis Process

Types of Photosynthesis

There are two different types of photosynthesis:

• Oxygenic photosynthesis
• Anoxygenic photosynthesis

Oxygenic Photosynthesis

Oxygenic photosynthesis is more common in plants, algae and cyanobacteria. During this process, electrons are transferred from water to carbon dioxide by light energy, to produce energy. During this transfer of electrons, carbon dioxide is reduced while water is oxidized, and oxygen is produced along with carbohydrates.

During this process, plants take in carbon dioxide and expel oxygen into the atmosphere.

This process can be represented by the equation:

6CO2+ 12H2O + LIGHT ENERGY → C6H12O6 + 6O2 + 6H2O

Anoxygenic Photosynthesis

This type of photosynthesis is usually seen in certain bacteria, such as green sulphur bacteria and purple bacteria which dwell in various aquatic habitats. Oxygen is not produced during the process.

The anoxygenic photosynthesis can be represented by the equation:

CO2 + 2H2A + LIGHT ENERGY → [CH2O] + 2A + H2O

Also Read:  Difference between Photosynthesis and Respiration

Photosynthesis Apparatus

The photosynthesis apparatus includes the following essential components:

Pigments not only provide colour to the photosynthetic organisms, but are also responsible for trapping sunlight. The important pigments associated with photosynthesis include:

• Chlorophyll: It is a green-coloured pigment that traps blue and red light. Chlorophyll is subdivided into, “chlorophyll a”, “chlorophyll b”, and “chlorophyll c”. “Chlorophyll a” is widely present in all the photosynthetic cells. A bacterial variant of chlorophyll known as bacteriochlorophyll can absorb infrared rays .
• Carotenoids: These are yellow, orange or red-coloured pigments that absorb bluish-green light. Xanthophyll and carotenes are examples of carotenoids.
• Phycobilins: These are present in bacteria and red algae . These are red and blue pigments that absorb wavelength of light that are not properly absorbed by carotenoids and chlorophyll.

Plastids are organelles found in the cytoplasm of eukaryotic photosynthetic organisms. They contain pigments and can also store nutrients. Plastids are of three types:

• Leucoplast: These are colourless, non-pigmented and can store fats and starch.
• Chromoplasts: They contain carotenoids.
• Chloroplasts: These contain chlorophyll and are the site of photosynthesis.

Antennae is the collection of 100 to 5000 pigment molecules that capture light energy from the sun in the form of photons. The light energy is transferred to a pigment-protein complex that converts light energy to chemical energy.

Reaction Centers

The pigment-protein complex responsible for the conversion of light energy to chemical energy forms the reaction centre.

Also Read: Photosynthesis

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What Is Photosynthesis?

The photosystem, the process.

Photosynthesis is the process used by plants to convert sunlight into chemical energy that can be used to fuel the plants’ growth. The process is fueled by the sun and powered by the chloroplasts in the plants’ leaves. The process begins with the sun’s light energy breaking down water molecules into oxygen and hydrogen. The oxygen is released into the air and the hydrogen is used to power the conversion of carbon dioxide into glucose, which is the plant’s food.

Plants, like every other organism, need energy to live, grow and repair. Unlike heterotrophs –  animals that consume food to synthesize energy – plants or autotrophs are self-reliant — they can make their own food, and therefore energy, by using the resources available in their surroundings. The resources include sunlight, water and carbon dioxide, and this incredible process is called  photosynthesis.

The process is known as photo synthesis because, while water and carbon dioxide are the major ingredients required to cook the food, it is light that ignites the stove, and sunlight is the most abundant light that illuminates the planet.

A photosynthetic organism using the energy of photons ( photo-) , makes its own food (- synthesis ).

Recommended Video for you:

A plant is essentially a highly efficient solar panel. It is replete with molecular structures that have evolved to soak up and absorb as much sunlight as possible.

These structures are in separate compartments of the cell called chloroplasts. Inside the chloroplasts are small towers of discs called grana, each disc is called thylakoid. In the membrane or lining of the thylakoids are a dense grid of various light absorbing molecules, the most notable of them, chlorophyll. The pigments, like any other pigments, absorb light of certain wavelengths and reflect the rest.

This is how pigments or colors are radiated. Majority of plants are green because they (the abundance of chlorophyll) reflect wavelengths that we associate with green while absorbing wavelengths that fall into the red and blue zones. But there are other pigments that absorb different wavelengths in the visible spectrum. Carotenoids are pigments that absorb in the blue to green wavelengths, reflecting orange, yellow and red wavelengths.

This is why leaves take on shades from orange to red during autumn , as they start losing their chlorophyll come at that time of the year. Some deep-sea algae (rhodophyta) are red in color due to a photosynthetic pigment called phycoerythrin and phycocyanin which absorb in blue to green region and reflect back red wavelengths.

These pigments are part of larger protein machines called photosystems. Plants have two photosystems – photosystem I (PSI) and photosystem II (PSII), each having a key chlorophyll-a molecule embedded in it, along with other accessory pigments. These accessory pigments collect light energy and pass it onto the main chlorophyll-a molecule. The photosystems are the main light harvesting machines in the chloroplasts that convert light energy to chemical energy that the cell can use to do build its food. Some algae and photosynthetic bacteria only have single photosystems.

Solar energy is used by the chloroplast to trigger a chemical reaction between the two reactants – water and carbon dioxide.

Also Read: Why Are Plants Red In Color At The Bottom Of The Ocean?

A plant obtains water from its roots through osmosis . From there, the water ascends through the stem and is transported to every part of the plant that requires it for a myriad of processes other than photosynthesis.

To ensure that plant doesn’t dry out due to evaporation, they evolved special pores, called stomata about 400 million years ago. Stomata allowed them to respire, exchanging gases like oxygen and carbon dioxide. However, the crucial development of pores came at the expense of losing water unnecessarily

The stomata inhale carbon dioxide exhaled by animals, which reacts with water in the presence of sunlight to create sugar (glucose), their food. However, the reaction unfolds in two parts.

The first part is called a light-dependent or simply, a light reaction, in which light breaks down water to produce oxygen molecules. These molecules are the same oxygen molecules that we breathe. They are exhaled through the stomata and dispersed into the air. The light energy absorbed by a pigment can be either simply dissipated as heat or be converted into another form of energy. We witness the latter in plants. The light reaction converts solar energy into chemical energy; the reaction also produces ATP (Adenosine Tri-Phosphate) and NADP + (Nicotinamide Adenine Dinucleotide Phosphate), organic compounds that become sources of energy for subsequent metabolic processes.

When light breaks down water at PSII. This releases two protons (H+) and oxygen, and two energized electrons which the chlorophyll-a in PSII accepts. These electrons are passed from PSII to other middle protein structures, like cytochrome bf, to PSI. There these two electrons get energized at PSI due to light energy captured by the photosystem’s chlorophyll-a. These electrons are them funneled to making NADPH from NADP+.

While passing these energized electrons, protons (H+) were taken from outside the thylakoid to its inside. This creates a gradient of H+, more inside than outside. This electrochemical gradient fuels the production of ATP. This happens because of a protein machine called ATP synthase. H+ from inside can return to the outside only by passing through ATP synthase. When H+ pass through ATP synthase, it converts ADP to ATP. This is how light and water create energy for the cell.

One of these processes is the next part of the reaction itself. The two sources of energy fuel the light-independent or dark reaction. The energy breaks down the carbon dioxide molecules and reorganizes the constituents to form a molecule of glucose. The chloroplast then harvests energy by breaking down that glucose, just how mitochondria in animal cells produce energy by breaking down the food they consume. Photosynthesis as a combination of the two reactions can be summarized with this expression:

But if plants can produce ATP through photosynthesis, then why do they need to respire? First, photosynthesis can only happen in the daytime, when there is sun around to provide light. Plants still need energy when there is no light. Second, glucose is important molecule for the cell. It can be broken down or built up to make many other biomolecules like DNA , RNA, proteins, and even fats.

In this manner, we share a deep and indispensable symbiotic relationship with plants. The byproduct, or put more impolitely, the waste product exhaled by plants gives us life, whereas carbon dioxide, the waste product that we exhale, gives plants their life. American biologist and one of my favorite science communicators, Lynn Margulis, called this innocuous act of breathing, spirituality.

However, she believes that “the connection doesn’t stop at the exchange of gases in the atmosphere… The fact that we are connected through space and time shows that life is a unitary phenomenon, no matter how we express the fact.”

Also Read: How Do Plants Excrete?

• PHOTOSYNTHESIS - www2.estrellamountain.edu
• What is Photosynthesis.

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.

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photosynthesis

[ foh-t uh - sin -th uh -sis ]

• the complex process by which carbon dioxide, water, and certain inorganic salts are converted into carbohydrates by green plants, algae, and certain bacteria, using energy from the sun and chlorophyll .

/ ˌfəʊtəʊsɪnˈθɛtɪk; ˌfəʊtəʊˈsɪnθɪsɪs /

• (in plants) the synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll
• the corresponding process in certain bacteria

/ fō′tō-sĭn ′ thĭ-sĭs /

• The process by which green plants, algae, diatoms, and certain forms of bacteria make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using energy captured from sunlight by chlorophyll, and releasing excess oxygen as a byproduct. In plants and algae, photosynthesis takes place in organelles called chloroplasts . Photosynthesis is usually viewed as a two-step process. First, in the light reactions , the energy-providing molecule ATP is synthesized using light energy absorbed by chlorophyll and accessory pigments such as carotenoids and phycobilins, and water is broken apart into oxygen and a hydrogen ion, with the electron of the hydrogen transferred to another energy molecule, NADPH. The ATP and NADPH molecules power the second part of photosynthesis by the transfer of electrons. In these light-independent or dark reactions , carbon is broken away from carbon dioxide and combined with hydrogen via the Calvin cycle to create carbohydrates. Some of the carbohydrates, the sugars, can then be transported around the organism for immediate use; others, the starches, can be stored for later use.
• Compare chemosynthesis See Note at transpiration
• Use by green plants of the energy in sunlight to carry out chemical reactions , such as the conversion of carbon dioxide into oxygen . Photosynthesis also produces the sugars that feed the plant.

Derived Forms

• ˌphotosynˈthetically , adverb
• photosynthetic , adjective

Other Words From

• pho·to·syn·thet·ic [ foh-t, uh, -sin-, thet, -ik ] , adjective
• photo·syn·theti·cal·ly adverb
• non·photo·syn·thetic adjective

Word History and Origins

Origin of photosynthesis 1

A Closer Look

Compare meanings.

How does photosynthesis compare to similar and commonly confused words? Explore the most common comparisons:

• chemosynthesis vs. photosynthesis
• photosynthesis vs. cellular respiration
• photorespiration vs. photosynthesis

Example Sentences

Specifically, he was interested in the protein-based "reaction centers" in spinach leaves that are the basic mechanism for photosynthesis—the chemical process by which plants convert carbon dioxide into oxygen and carbohydrates.

Algae and plants use photosynthesis to turn sunlight into food.

According to the Washington Post, this happens because as the days shorten and turn frigid, it’s not worth it for some trees to expend energy to conduct photosynthesis.

In a steady state, most of the energy captured by photosynthesis is used up by the furnace of respiration and metabolism burning on Earth’s surface by its infrared layer of life.

There’s no sunlight beneath half a mile of ice, so of course there’s no photosynthesis.

Nevertheless, it was required, and at least it was more fun than studying algebra or photosynthesis.

Re-solarizing the food chain should be our goal in every way—taking advantage of the everyday miracle that is photosynthesis.

As the microbes moved toward the light to carry out photosynthesis, they projected the image of the stencil.

Timiriazeff, in his Croonian Lecture, was the first to see the connexion between photosynthesis and the Lagado research.

On the other hand, their ancestors, the green or yellow mastigota, form new plasm by photosynthesis like true cells.

There the miracle of life consists merely of the chemical process of plasmodomism by photosynthesis.

Like von Baeyer's hypothesis, this assumes that formaldehyde and oxygen are the first products of photosynthesis.

In general, starch is the final product of photosynthesis in most green plants; but there are many exceptions to this.

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What is photosynthesis?

April 28, 2020 By Emma Vanstone Leave a Comment

Green plants make sugar for growth by a process called photosynthesis . Photosynthesis is a process where light energy is converted to chemical energy in the form of sugars. It’s a process that provides the main source of oxygen in the atmosphere and is essential for almost all life on Earth.

Photosynthesis made simple

Plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of glucose.

The glucose molecules created by photosynthesis act as fuel for cells and are used for cellular respiration and fermentation.

Photosynthesis Equation

Carbon dioxide + water  (and light ) ———> glucose and oxygen

Where does photosynthesis happen?

Photosynthesis takes place in chloroplast cells, which contain a substance called chlorophyll. It is chlorophyll, which gives plants their green colour.

Chloroplasts are one of the organelles in a plant cell. We made a jelly model of plant cell to learn about organelles and plant cell structure.

Sunlight is also needed to make chlorophyll. If plants are kept in the dark, they can’t make chlorophyll and will have yellow leaves! You can see this in our multicoloured cress caterpillar .

What affects the rate of photosynthesis

Four factors affect the rate of photosynthesis . The faster it occurs, the more the plant grows.

Light  – the more light there is, the faster photosynthesis occurs.

Water  – lack of water slows photosynthesis down.

Temperature  – photosynthesis works best at around 30 degrees Celsius.

Carbon dioxide levels  – photosynthesis is faster if there is more carbon dioxide in the air.

Plants make the energy to grow through a process called respiration . This uses the sugar produced by photosynthesis and oxygen.

How are leaves adapted for photosynthesis?

Leaves are green as they contain lots of chlorophyll, which absorbs sunlight.

They are thin and have a large surface area. This means they can absorb a lot of sunlight, and gases such as oxygen and carbon dioxide can pass in and out of the leaf easily.

Leaves have veins – xylem and phloem, which transport water, minerals and sugars around the plant.

Do only plants photosynthesise?

Plants, algae, and some types of bacteria use photosynthesis to create energy.

A large percentage of the Earth’s oxygen comes from phytoplankton in the oceans, which contain chlorophyll and use photosynthesis to create energy.

What is chlorophyll?

Chlorophyll is a green pigment which absorbs energy from blue and red light waves and reflects green light waves, which is why plants look green!

Chlorophyll in a plant is found in an organelle called a chloroplast. This is where photosynthesis occurs.

Why is photosynthesis important?

Photosynthesis also allows plants to make energy for growth and repair, and it has an important ecological impact.

Plants incorporate the carbon from carbon dioxide into organic molecules ( carbon fixation ). This creates a carbon source for animals who cannot create their own and also removes carbon dioxide from the air, slowing down the rate at which it builds up in the atmosphere.

Photosynthesis also creates oxygen, which is needed for most life on Earth!

Do you have more questions? You might find the answers in my collection of science questions for kids .

Last Updated on January 26, 2024 by Emma Vanstone

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I will give tons of points to the perfect answer. What is the meaning of life?

Answer: The meaning of life is multiple things.

Explanation: Experiencing things you've dreamed of figuring yourself out like if your part of LGBTQ+ and having a family finding love working towards retirement spending everyday with the person you love and giving a helping hand to those in need.  

Related Questions

The classification of some organisms has changed. Which new process is used to reclassify organisms? A. Organisms are now given Latin-based scientific names. B. Structures are now examined at the molecular level. C. Organisms are now divided into three kingdoms. D. Structures are now used to classify organisms.

C. Organisms are now divided into three kingdoms.

Explanation:

In the early 1860s, a German scientist named Ernst Haeckel suggested using a three kingdom system of classification. Haeckel's three kingdoms were Animalia, Plantae, and Protista.

Which statement correctly describes the process of photosynthesis? A. The mitochondria use oxygen, water, and sunlight to produce sugars and carbon dioxide. B. The chloroplasts use carbon dioxide, water, and sunlight to produce sugars and oxygen. C. The chloroplasts use oxygen, water, and sunlight to produce sugars and carbon dioxide. D. The mitochondria use carbon dioxide, water, and sunlight to produce sugars and oxygen.

the equation for photosynthesis is:

carbon dioxide + water ---> glucose +oxygen

                                     (light)

The statement that correctly describes the process of photosynthesis is that chloroplasts use carbon dioxide , water, and sunlight to produce sugars and oxygen. The correct option is B.

Photosynthesis is the process of producing food, nutrition, and energy. It is done by plants and algae because only they contain chlorophyll. Those organisms containing chlorophyll can perform photosynthesis.

It is a chemical process and the process involves, carbon dioxide , water, and sunlight, and it produces sugar and oxygen as a byproduct. The oxygen is released, whereas the sugar gives the energy.

The process can be described as chloroplast absorbing the sunlight for plants, and the process can only occur in the presence of light or sunlight.

Thus, the correct option is B. The chloroplasts use carbon dioxide, water, and sunlight to produce sugars and oxygen.

To learn more about photosynthesis , refer to the below link:

https://brainly.com/question/1757345

Which of these statements is true of ATP? A. It stores energy as glucose. B.It stores energy for cellular processes. C. It converts sunlight into chemical energy. D. It contains less stored energy than ADP.

A. It stores energy as glucose.

Hope this helps!

A watershed, also known as a drainage basin, is an area of land where water drains to a central point like a lake river or an ocean. natural vegetation in the landscape, helps maintain the natural flow of Regine of water and rapid change in water level in lakes and wetlands. imagine a position of a wetland that has changed as scenes in the image. predict what will happen to the natural flow of water is natural vegetation as replaced by impervious surfaces A) groundwater flows increase to its endpoint causing flooding B) runoff will increase and less water will penetrate the soil to become groundwater C) groundwater will puddle up and remain in one place instead of flowing to a central point D) impervious surfaces such as roads and parking lots will divert water flow and it will not reach its endpoint ​

B) runoff will increase and less water will penetrate the soil to become groundwater.

D) impervious surfaces such as roads and parking lots will divert water flow and it will not reach its endpoint

The runoff will increase and less water will penetrate into the soil to become groundwater if natural vegetation is replaced by impervious surfaces. The natural vegetation helps to lower the speed and intensity by absorbing large amount of water. Due to this absorbing, there is an increase occur in the concentration of groundwater level which increases underground water reserves for the coming generations. These impervious surfaces also act as a barrier that diverts water and prevents the water to reach to its ending point.

B is the correct answer.

Morning glories are flowering vines that will climb up a trellis or other support by wrapping tendrils around it. What kind of tropism causes the morning glories to twine around the support this way? A. phototropism, because the light pulls the morning glories upwards B. gravitropism, because gravity helps the morning glories orient themselves in space C. thigmotropism, because the morning glories twine around the support when they touch it D. nutrotropism, because the curliness of the morning glories depends on the nutrients in the soil PLEASE help me and quick

pretty sure its c also nice pfp 0_0

What is a scientific theory? The sentences above help to describe a scientific theory. One sentence is not quite accurate though. Choose the sentence that needs to be modified and make the necessary modification so it may be included in the description of a theory. A) D. A scientific theory has a simple basis: an experiment done to test a hypothesis. B) C. Theories are descriptions, often mathematical descriptions of natural phenomenon; A. A scientific theory is based on a scientific investigation that supports a hypothesis. D) B. When new information does not support a scientific theory, the theory may be revised or sometimes rejected.

Original sentence: When new information does not support a scientific theory, the theory  may be revised or sometimes rejected.  

New changed sentence: When the results of the experiment do not support a hypothesis, the hypothesis must be revised or rejected to state a new scientific theory.

The scientific theory is a conceptual framework used to explain facts or phenomena and to make predictions.

The theory is fundamental to science because it allows scientists to organize and understand observations.

The construction of a theory begins with a hypothesis. The scientist believes that a phenomenon occurs in a certain way, so he/she performs observations under the scientific method to prove that his/her hypothesis is valid or not valid. The systematization of the observations and the empirical data collected might derive from a scientific theory that explains the analyzed phenomenon.

A scientific theory is a knowledge that has been contrasted in several ways.

How do blood vessels change during vasodilation? O A. They shrink to decrease body temperature. B. They expand to decrease body temperature. C. They expand to increase body temperature. D. They shrink to increase body temperature.

D. They shrink to increase body temperature

if wrong sorry ya based on my syllabus

Which organisms represents a secondary consumer?

Either small fish or zookplanton

What's the answer please??????????

species IV is the one most closely related

act gca ccc

act gca ccg

its just one letter off

A large community of plants and animals that occupy a district region of the world is a

____ The bristle worm living with the hermit crab. A. Mutualism B. Commensalism C. Parasitism

A. Mutualism

Mutualism The bristle worm living with the hermit crab.

What is the role of the nervous system in the body? A.To protect other organs and tissues B.To send messages using blood cells C.To gather and respond to information D. To transport oxygen and carbon dioxide

Is the classification system of domains and kingdoms the only system that scientists have ever used to classify organisms??? Answer nowww

Aristotle developed the first system of classification of animals based off of appearances and habitats.

Explanation: Hope this help :D

Hi. Is this correct?????

Yes, that is correct.

HELP Which of the following is a correctly described example of negative feedback? A thermostat controls the temperature at random times of the day by producing heat every 2 hours regardless of how warm the room is. B thermostat turns on and off throughout the day to keep the temperature approximately the same or at a set point. C thermostat steadily increases the temperature throughout the day.

Please help, any unnecessary answers will be reported. Thanks :)

The one all the way over to the left, the dark blue one. I hope this helps!

Answer: first one

Explanation: The brain uses the nerves to tell the muscles when to move. The nerves also deliver information on what to do in a fight or flight case

who would win in fight an elephant or a rhino

Yeah a rhino is an aggressive animal but soo

Research shows that an elephant is the largest animals on earth u can cross check.

my explanation is not that good but surely an elephant will win

In an early experiment, it was found that a mouse in a sealed glass jar soon died, but if a plant was included in the jar, the mouse lived much longer. Explain theses results.

The correct answer is - mouse produces carbon dioxide which is used by the plants for photosynthesis that in turn produces oxygen that is used for cellular respiration.

A mouse can not live in a sealed container or jar for a long time whereas with a plant in a closed and sealed jar mouse can live longer. This is due to the fact that in absence of the plant there is no oxygen for the mouse to get perform cellular respiration.

in a jar with a plant, the mouse lives longer because the plant still produces oxygen by the process of photosynthesis which is used by the mouse for cellular respiration and produces carbon dioxide that is taken by the plant.

A(n)\ is a system composed of living organisms and their interaction with the surrounding environment, where the main focus is the interaction and relationship between species . 1.habitat 2.biome 3.environemnt 4.ecosystem

what can a scientist conclude about two sperate rock layers that hold ammonite fossils of the same species?

that specis lived for a long time

The mountain ash produces a bright red berry fruit. How has the mountain ash tree evolved in order to allow its seeds to be spread far from their source? A. The leaves are brightly colored and attract animals to the plant, B. The seeds are in berries that are eaten by birds and dropped as waste away from the plant C. The seeds are lightweight so animals can pick them up and carry them back to their nests D. The seeds have light stems that allow them to be carried by the wind,

The correct answer is - B. The seeds are in berries that are eaten by birds and dropped as waste away from the plant.

The mountain ash trees contain red berries fruits that attract birds and other organisms. These birds eat these berries and eat berries and fly over the hills or mountains and after digesting they drop the seeds of these berries with the digestive waste. These berries grow on the mountains far from the original source as birds carry them by flying away after eating.

Thus, the correct answer is option B.

Match each of the five levels of organization to their proper definition. a group of tissues that work together to perform specific activities for an organism a group of cells that are similar in structure and function a living thing that carries out the processes of life the basic unit of life for all organisms a group of organs that work together to perform specific activities for an organism

3. Organism

5. Organ System

which type of muscle do you control voluntarily

Plzz help. Finding answers from smart people plzz. Will give Brainiest.

1) According to the diagram, divergence among mammals took place about 75 mya.

2) Scientists are able to determine common ancestors by studying molecular data.

3) Darwin's theory of evolution by natural selection states that animals change over long periods of time.

4) Scientists are closesly studing how genes reorganize themselves.

5) Some scientists, however, think new species evolve quickly.

6) Still, among scientists, the principles of natural selection remain unchanged and highlight how animals evolve.

7) The main tool for the study of evolution is careful observation of fossils and the anatomy of animals.

8) Scientists also study animal embryology .

9) What no one doubts is the wide diversity among organisms on Earth.

10) The divergence that took place among mammals helps us understand why whales and dolphins are mammals and not fish.

Fun fact: Uh, I happen to discover a whole packet of answer keys, not just for this but also for other assignments and stuff. (O.O)

Most of the rocks we study were formed in what era? A. Paleozoic B. Cenozoic C. Precambrian D. Mesozoic?

I think that answer A is correct

Which would register a drop in air pressure? A.) a drop in temperature B.) going down a mountain C.) going up a mountain D.) a heavy rainstorm I think it’s d but I’m not sure :’(

Drop in air pressure takes place when one goes up a mountain .

• Altitude is associated with air pressure, that is, with an elevation in altitude, there is a drop in air pressure .

• That is why when one goes up the mountain, the person feels a drop in air pressure.

• The air pressure is indicated with the help of an instrument called altimeter.

• There are two reasons of the drop in air pressure with altitude, that is, gravity and density .

• The high altitude regions like mountains are generally much colder than the regions closer to the sea due to low air pressure.

Thus, the correct answer is option C.

To know more about:

https://brainly.com/question/21751143

what is the probability for a child to inherit one of the two alleles from her dad?? a: 100% b: 50% c: 0% d: impossible to know

We get one allele from each parent, one from mom and one from dad. Hope it helps :)

Cells and transport proteins are physically prevented from passing through the filtration membrane. This has the following effect on filtration: Cells and transport proteins are physically prevented from passing through the filtration membrane. This has the following effect on filtration: increased osmotic pressure in the filtrate that draws plasma through the membrane decreased osmotic pressure in the filtrate that increases the amount of filtration increasing osmotic pressure in the glomerular capillaries that reduces the amount of filtration neutral change in osmotic pressure with no effect on filtration

The correct answer is ''increasing osmotic pressure in the glomerular capillaries that reduces the amount of filtration.''

Osmotic pressure is understood to be the force that must be applied to a solution when the flow of solvent needs to be stopped by means of a membrane with semi-permeable characteristics.Colloidal osmotic pressure in glomerular capillaries: it is the pressure exerted by proteins in the blood, which tends to recover the filtered water. To generate and maintain glomerular filtration, filtration pressure is required. That is, glomerular filtration is a physical phenomenon regulated by hemodynamic changes that affect the glomerulus and, although it is the initial excretion mechanism, it is not the exclusive regulator. Water, ions and some nutrients are mainly reabsorbed in the proximal tubule by different mechanisms. The water will follow a passive transport process by osmotic drag. The activity of the tubule is highly dependent on maintaining a fluid osmotic pressure similar to that of plasma. Since proteins and other elements that participate in the maintenance of the plasma osmotic pressure do not cross the glomerular barrier, in the tubule, the isoosmotic pressure with the plasma is fundamentally conditioned by the content of water and salt (dissociated as chlorine and Na +) of the ultrafiltered.

Cells and transport proteins are physically prevented from passing through the filtration membrane for this the correct answer is to increase osmotic pressure in the glomerular capillaries that reducing the amount of filtration.

That is, glomerular filtration is a bodily phenomenon regulated with the aid of using hemodynamic modifications that have an effect on the glomerulus and, even though it is the preliminary excretion mechanism, it isn't the different regulator .

Thus it is clear that the above answers are well explained.

To learn more about the filtration membrane refer to the link :

https://brainly.com/question/3420464

Which plant tissue has air spaces in it? A: Palisade cells B: Waxy cuticle C: Upper epidermis D: Spongy mesophyll

Which statement can be best supported by the fossil record

Many organisms that lived in the past are now extinct .

please mark me as brainliest

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Discovery of 'dark oxygen' deep in the ocean could rewrite the origins of life

Our understanding of the origins of life itself faces a potentially drastic overhaul following a startling discovery deep on the seafloor.

Marine researchers were surveying a mountain range in the depths of the Pacific Ocean when they noticed something strange.

Instruments deployed by the team kept registering a rise in oxygen levels and yet, the area they were analysing – more than 4,000 metres (13,000 feet) down – was in complete darkness, meaning oxygen production should have been impossible.

After all, we are taught that this essential building block of life comes from plants and phytoplankton, which harness sunlight to break down carbon dioxide and water and release O2 – a process known as photosynthesis.

So with no light, there should have been no oxygen.

Indeed, Professor Andrew Sweetman, of the Scottish Association for Marine Science, who led the expedition admitted : “When we first got this data, we thought the sensors were faulty because every study ever done in the deep sea has only seen oxygen being consumed rather than produced.”

He continued in a statement : “We would come home and recalibrate the sensors, but, over the course of 10 years, these strange oxygen readings kept showing up.”

It was only after different methods of oxygen detection offered up the same results that Sweetman and his colleagues knew they "were onto something ground-breaking and unthought-of.”

They soon realised that potato-sized metallic deposits strewn across the seafloor were releasing oxygen in complete darkness and without any help from living organisms.

The production of this deep-sea oxygen, which Sweetman and his team dubbed “dark oxygen,” represents the first time scientists have ever observed oxygen being generated without the involvement of organisms.

In so doing, it fundamentally challenges what we know about the creation of life on Earth, and our quest for life beyond our planet.

The results of Sweetman’s investigations were published on Monday (22 July) in the journal Nature Geoscience .

They suggest that the small metallic deposits, found in the Pacific's Clarion-Clipperton Zone (CCZ), produce oxygen via seawater electrolysis. This process involves the splitting of sea water into oxygen and hydrogen in the presence of an electric charge.

Researchers believe that this charge may come from the difference in electric potential that exists between metal ions within the nodules. This then leads to a redistribution of electrons, according to the study.

Polymetallic nodules like these are common on the so-called ocean's abyssal plains – flat regions of the seafloor between 3,000 and 6,000 metres (10,000 and 20,000 feet) below the ocean surface, as Live Science notes.

They predominantly consist of iron and manganese oxides, but they also contain metals including cobalt, nickel and lithium.

In addition, they feature rare earth elements , such as cerium, that are essential components of electronics and low-carbon technologies.

Sweetman and his fellow biochemists, originally set out to study the potential impact on the seafloor ecosystem of mining these nodules in the CCZ – an abyssal plain which spans some 4.5 million square kilometres (1.7 million square miles) between Hawaii and Mexico.

In order to carry out their assessment, the team measured changes in oxygen concentrations using special experimental chambers positioned at multiple locations.

Typically, the deeper you go in the ocean, the more oxygen levels drop. This is because less light is available, meaning there are fewer photosynthetic organisms and therefore lower oxygen production.

And yet, instead of the expected decrease in oxygen, the data showed steady emissions from the seabed.

This extraordinary discovery undercuts the long-held belief that Earth's oxygen is only naturally produced through photosynthesis (and, to a far lesser extent, oxidising ammonia).

As a result, scientists are having to rethink how life began on Earth some 3.7 billion years ago.

"For aerobic life to begin on the planet, there has to be oxygen and our understanding has been that Earth's oxygen supply began with photosynthetic organisms," Sweetman explained.

"But we now know that there is oxygen produced in the deep sea, where there is no light. I think we therefore need to revisit questions like: where could aerobic life have begun?"

In addition, his team’s findings raise new concerns about the mining of polymetallic nodules, given that these could represent a vital source of oxygen for deep-sea ecosystems.

"Through this discovery, we have generated many unanswered questions,” Sweetman concluded.

“And I think we have a lot to think about in terms of how we mine these modules, which are effectively batteries in a rock."

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'Disgusted' MrBeast breaks silence on Ava Tyson's 'unacceptable acts'

Now the ap has had to debunk the jd vance couch story, controversial ‘alien mummies’ found to have ‘non-human fingerprints’, what is skibidi toilet and why is michael bay making a movie about it, first map of earth's lost continent has been published, scientists work out how greenland sharks can live to 500 years old, stripper shares 'scary truth' about men on stag dos, male elephants use deep rumbles to signal when it is time to go, man creates website to shame airlines after girlfriend loses luggage, all of the cool things the apple vision pro can do, public asked to help name zoo’s new baby giraffe, the 'world's most expensive holiday' will set you back £1.3 million, trump ally tells reporter emily maitlis she needs her 'head examined', young people are officially the unhappiest of all age groups.

Scientists discover lumps of metal producing 'dark oxygen' on ocean floor, new study shows

Oxygen is being produced over 13,000 feet underwater without photosynthesis, but how.

"Dark oxygen" is being produced deep in the ocean, and scientists are baffled by the strange phenomenon, according to a new study.

In science class, kids learn that plants need sunlight to do photosynthesis and create the oxygen we breathe. But, oxygen is being produced on the abyssal seafloor, which is so deep that sunlight cannot reach it, according to a  study published on Monday in the journal Nature Geoscience.

Not only is oxygen being produced, but plants aren't creating it.

Instead of green, photosynthesizing plants, the oxygen is created by metallic “nodules” that look like lumps of coal. But, instead of heating a grill, they’re splitting H2O (water) molecules into hydrogen and oxygen.

New study: Prehistoric crystals offer clues on when freshwater first emerged on Earth, study shows

Faulty readings

The phenomena was first observed in 2013, when the lead scientist of the study, Andrew Sweetman, a professor at the Scottish Association for Marine Science, was studying the Clarion-Clipperton Zone , an area between Mexico and Hawaii. He believed his equipment was faulty when it showed that oxygen was being made on the dark sea floor, reports CNN .

“I basically told my students, just put the sensors back in the box," Sweetman, who also leads the institution’s seafloor ecology and biogeochemistry group, told CNN. "We’ll ship them back to the manufacturer and get them tested because they’re just giving us gibberish. And every single time the manufacturer came back: ‘They’re working. They’re calibrated.’”

Sweetwater ignored the readings because he'd only been taught that you can only get oxygen from photosynthesis, according to the BBC .

“Eventually, I realized that for years I’d been ignoring this potentially huge discovery,” Sweetman told BBC News.

What produces the ocean's oxygen?

Around half of the Earth's oxygen comes from the ocean , states the National Oceanic and Atmospheric Administration, NOAA.

Scientists attributed the production to the following:

• Oceanic  plankton
• Drifting plants
• Some bacteria

All the organisms listed are capable of photosynthesis, thus creating oxygen. But they wouldn't be able to do that so deep underwater.

Mining companies want to collect oxygen-producing modules

The modules, which form over millions of years, are made of ingredients needed to create batteries: lithium, cobalt and copper, according to the BBC. And mining companies are interested in collecting them.

However, Sweetman's new study raises concerns about the risks involved in collecting these deep-sea minerals.

What is Harris' stance on Israel? Plus, takeaways from Biden's Oval Office speech

Good morning. You're reading the Up First newsletter.  Subscribe  here to get it delivered to your inbox, and  listen  to the Up First podcast for all the news you need to start your day.

Today's top stories

President Biden made a rare Oval Office address last night to discuss his decision to end his bid for reelection. He also laid out plans for the next six months of his presidency. Biden said he didn’t want to drop out of the presidential race, but the stakes were just too high to risk. Here are four takeaways from his speech.

• 🎧 This is a monumental moment for Biden as it marks the beginning of the end of his long career in public life, NPR’s Tamara Keith tells Up First . In his remaining time, Biden plans to continue fighting for reproductive and civil rights, trying to lower costs and speaking out against extremism and political violence. As his time winds down, Keith says he will be remembered for what happens in the November election . If Vice President Kamala Harris wins, he'll be remembered as "the rare president who put his party and country above his own ego." If she loses, he'll be the person who removed former President Donald Trump from office and then ushered him back in.

Israeli Prime Minister Benjamin Netanyahu defended his administration's war efforts yesterday in his first address to the U.S. Congress since the Oct. 7 Hamas attacks. He called on the U.S. to stand with Israel, urged Congress to fast-track additional military aid and vowed that his country would do “whatever it must” to defeat Hamas. Dozens of Democratic lawmakers boycotted the speech, and thousands of protesters marched outside the Capitol. Netanyahu is expected to meet separately with Biden and Harris today and with former President Donald Trump tomorrow. The Israeli prime minister's visit comes at a crucial time in American politics, as Harris looks to strike a delicate balance on Israel ahead of the 2024 election.

• 🎧 NPR’s Asma Khalid says that multiple people have told her that Harris shows a greater degree of empathy for Palestinian civilians than Biden. She was also one of the earlier people in the administration to show a less dismissive response to the pro-Palestinian protests in the U.S. Some Democrats who voted uncommitted during the primaries are now willing to give Harris a chance . But that doesn’t mean they will certainly vote for her. Khalid says that as Harris runs for president, she will need to avoid alienating Israel supporters while winning back some of the young, progressive brown and Black voters that Biden alienated with his actions.

In the upcoming election, Harris faces the fundamental challenge of holding together the broad coalition that Biden won in 2020. The problem: They have very different views on some issues. Aspects of her record, especially her time as a prosecutor in California, are under scrutiny. Here's what one Democrat and one Republican in Pittsburgh have to say about the issue.

• 🎧 Morning Edition host Steve Inskeep has been speaking with voters in the swing state of Pennsylvania. A variety of people shared with him their split views on Harris' prosecution record. A Democratic activist says many people who live in suburbs like her appreciate Harris' emphasis on public safety. In a historically Black neighborhood, another person tells Inskeep they have mixed feelings about who Harris has incarcerated in the past. Sometimes civil rights groups and activists have clashed over her decisions. To hold together the Democratic coalition, she needs people who support law and order and those who are skeptical of it.

Today's listen

This year, the annual Tiny Desk Contest received nearly 7,000 entries. Even though there could only be one winner , there was no shortage of talent displayed. NPR Music’s Bobby Carter, who has produced Tiny Desks for some legendary hip-hop artists such as Mac Miller and Noname, breaks down some of his favorite entries. Carter talks about how hip-hop acts stepped up their submissions this year and the versatility of the entries.

• 🎧 Listen to these up-and-coming rappers .

Life Advice

Tweens might not be getting enough sleep due to how they use their electronic devices before bedtime. Scientists looked at nearly 9,400 11- and 12-year-olds for the Adolescent Brain Cognitive Development Study, a long-term study of brain development and child health in the U.S. Researchers asked tweens and their parents detailed questions about how they used screens around bedtime and how well they slept. Then a follow-up was done a year later. Here’s how parents can help their kids have better quality sleep.

• 💤 No screens for an hour before bedtime.
• 💤 Turn phones all the way off at night. Don’t just put it on vibrate.
• 💤 Resist the urge to check your phone if you wake up in the middle of the night.
• 💤 Keep phones in another room at bedtime.

3 things to know before you go

• The International Olympic Committee chose Salt Lake City for the 2034 Winter Olympics , but it could be too soon to celebrate. The IOC threatened to reject the city's bid yesterday in an attempt to crush U.S. inquiries into Chinese sports doping.
• Chipotle’s CEO is reminding workers to give customers big scoops after TikTokers suggested their servings have shrunk .
• Researchers believe they have discovered “dark oxygen,” or oxygen not made through photosynthesis, being created on the Pacific Ocean floor. The discovery potentially challenges commonly held beliefs about how oxygen is produced on Earth.

This newsletter was edited by Suzanne Nuyen .

Copyright 2024 NPR

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What is Harris' stance on Israel? Plus, takeaways from Biden's Oval Office speech

Brittney Melton

Biden's Oval Office Address, Harris and Gaza, Pennsylvania Voters

Good morning. You're reading the Up First newsletter.  Subscribe  here to get it delivered to your inbox, and  listen  to the Up First podcast for all the news you need to start your day.

Today's top stories

President Biden made a rare Oval Office address last night to discuss his decision to end his bid for reelection. He also laid out plans for the next six months of his presidency. Biden said he didn’t want to drop out of the presidential race, but the stakes were just too high to risk. Here are four takeaways from his speech.

U.S. President Joe Biden delivers an address from the Oval Office of the White House on July 14, 2024 in Washington, D.C., to call for a calming of political rhetoric a day after a shooting in Butler, Pa., left former President Trump injured at a campaign rally. Erin Schaff/Getty Images hide caption

• 🎧 This is a monumental moment for Biden as it marks the beginning of the end of his long career in public life, NPR’s Tamara Keith tells Up First . In his remaining time, Biden plans to continue fighting for reproductive and civil rights, trying to lower costs and speaking out against extremism and political violence. As his time winds down, Keith says he will be remembered for what happens in the November election . If Vice President Kamala Harris wins, he'll be remembered as "the rare president who put his party and country above his own ego." If she loses, he'll be the person who removed former President Donald Trump from office and then ushered him back in.

Israeli Prime Minister Benjamin Netanyahu defended his administration's war efforts yesterday in his first address to the U.S. Congress since the Oct. 7 Hamas attacks. He called on the U.S. to stand with Israel, urged Congress to fast-track additional military aid and vowed that his country would do “whatever it must” to defeat Hamas. Dozens of Democratic lawmakers boycotted the speech, and thousands of protesters marched outside the Capitol. Netanyahu is expected to meet separately with Biden and Harris today and with former President Donald Trump tomorrow. The Israeli prime minister's visit comes at a crucial time in American politics, as Harris looks to strike a delicate balance on Israel ahead of the 2024 election.

• 🎧 NPR’s Asma Khalid says that multiple people have told her that Harris shows a greater degree of empathy for Palestinian civilians than Biden. She was also one of the earlier people in the administration to show a less dismissive response to the pro-Palestinian protests in the U.S. Some Democrats who voted uncommitted during the primaries are now willing to give Harris a chance . But that doesn’t mean they will certainly vote for her. Khalid says that as Harris runs for president, she will need to avoid alienating Israel supporters while winning back some of the young, progressive brown and Black voters that Biden alienated with his actions.

In the upcoming election, Harris faces the fundamental challenge of holding together the broad coalition that Biden won in 2020. The problem: They have very different views on some issues. Aspects of her record, especially her time as a prosecutor in California, are under scrutiny. Here's what one Democrat and one Republican in Pittsburgh have to say about the issue.

• 🎧 Morning Edition host Steve Inskeep has been speaking with voters in the swing state of Pennsylvania. A variety of people shared with him their split views on Harris' prosecution record. A Democratic activist says many people who live in suburbs like her appreciate Harris' emphasis on public safety. In a historically Black neighborhood, another person tells Inskeep they have mixed feelings about who Harris has incarcerated in the past. Sometimes civil rights groups and activists have clashed over her decisions. To hold together the Democratic coalition, she needs people who support law and order and those who are skeptical of it.

Today's listen

A view of NPR's Tiny Desk. NPR hide caption

A view of NPR's Tiny Desk.

This year, the annual Tiny Desk Contest received nearly 7,000 entries. Even though there could only be one winner , there was no shortage of talent displayed. NPR Music’s Bobby Carter, who has produced Tiny Desks for some legendary hip-hop artists such as Mac Miller and Noname, breaks down some of his favorite entries. Carter talks about how hip-hop acts stepped up their submissions this year and the versatility of the entries.

• 🎧 Listen to these up-and-coming rappers .

Life Advice

The large study looked at 11- and 12-year-old children, and 72% of them have their own cell phone. Sladic/E+/Getty Images hide caption

Tweens might not be getting enough sleep due to how they use their electronic devices before bedtime. Scientists looked at nearly 9,400 11- and 12-year-olds for the Adolescent Brain Cognitive Development Study, a long-term study of brain development and child health in the U.S. Researchers asked tweens and their parents detailed questions about how they used screens around bedtime and how well they slept. Then a follow-up was done a year later. Here’s how parents can help their kids have better quality sleep.

• 💤 No screens for an hour before bedtime.
• 💤 Turn phones all the way off at night. Don’t just put it on vibrate.
• 💤 Resist the urge to check your phone if you wake up in the middle of the night.
• 💤 Keep phones in another room at bedtime.

3 things to know before you go

International Olympic Committee President Thomas Bach speaks during the 142nd session of the IOC in Paris on Wednesday, ahead of the Paris 2024 Olympic Games. Ludovic Marin/AFP via Getty Images hide caption

• The International Olympic Committee chose Salt Lake City for the 2034 Winter Olympics , but it could be too soon to celebrate. The IOC threatened to reject the city's bid yesterday in an attempt to crush U.S. inquiries into Chinese sports doping.
• Chipotle’s CEO is reminding workers to give customers big scoops after TikTokers suggested their servings have shrunk .
• Researchers believe they have discovered “dark oxygen,” or oxygen not made through photosynthesis, being created on the Pacific Ocean floor. The discovery potentially challenges commonly held beliefs about how oxygen is produced on Earth.

This newsletter was edited by Suzanne Nuyen .