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Photosynthesis is a process in which green plants use energy from the sun to transform water, carbon dioxide, and minerals into oxygen and organic compounds. It is one example of how people and plants are dependent on each other in sustaining life.

Photosynthesis happens when water is absorbed by the roots of green plants and is carried to the leaves by the xylem, and carbon dioxide is obtained from air that enters the leaves through the stomata and diffuses to the cells containing chlorophyll. The green pigment chlorophyll is uniquely capable of converting the active energy of light into a latent form that can be stored (in food) and used when needed.

Photosynthesis provides us with most of the oxygen we need in order to breathe. We, in turn, exhale the carbon dioxide needed by plants. Plants are also crucial to human life because we rely on them as a source of food for ourselves and for the animals that we eat.

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Photosynthesis is a process in which green plants use energy from the sun to transform water, carbon dioxide, and minerals into oxygen and organic compounds. It is one example of how people and plants are dependent on each other in sustaining life.

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http://www.life.illinois.edu/govindjee/encyc/encarta.htm

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https://www.youtube.com/watch?v=3pD68uxRLkM

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Photosynthesis | Photosynthesis in plants | Photosynthesis - Biology basics for children | elearnin

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http://www.factmonster.com/ipka/A0775714.html

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Intermediate

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Let's talk about one of the most important biological processes. Frankly, if this process didn't occur, we probably wouldn't have life on Earth, and I wouldn't be making this video for you, because there'd be no place for me to actually get food. And the process is called photosynthesis. And you're probably reasonably familiar with the idea. The whole idea is plants, and actually bacteria and algae and other things, but we normally associate it with plants. Let me make it in very simple terms. So we normally associate it with plants. And it's a process that plants use, and we might have learned this when we were very young. It's the process that plants use to take carbon dioxide plus some water plus some sunlight and turn it into some sugars or some maybe carbohydrates. Carbohydrates or sugars plus oxygen. Obviously, this has two very profound pieces to it for us as a living species. One, we need carbohydrates or we need sugars in order to fuel our bodies. You saw that in the cellular respiration videos. We generate all of our ATP by performing cellular respiration on glucose, which is essentially a byproduct, or a broken down carbohydrate. It's the simplest one for us to process in cellular respiration. And the second hugely important part is getting the oxygen. Once again, we need to breathe oxygen in order for us to break down glucose, in order to respire, in order to perform cellar respiration. So these two things are key for life, especially for life that breathes oxygen. So this process, other than the fact that it's interesting, that there are organisms around us, mostly plants, that are able to harness actual sunlight. You have these fusion reactions in the sun 93 million miles away, and it's releasing these photons, and some small subset of those photons reach the surface of Earth. They make their way through clouds and whatever else. And then these plants and bacteria and algae are able to harness that somehow and turn them into sugars that we can then eat or maybe the cow eats them and we eat the cow if we're not vegetarians, and we can then use that for energy. Not that the cow is all carbohydrates, but this is essentially what is used as the fuel or the energy for all of the other important compounds that we eat. This is where we get all of our fuel. So this is fuel for animals. Or you know, if you eat a potato directly, you are directly getting your carbohydrates. But anyway, this is a very simple notion of photosynthesis, but it's not incorrect. I mean, if you had to know one thing about photosynthesis, this would be it. But let's delve a little bit deeper and try to get into the guts of it and see if we can understand a little bit better how this actually happens. I find it amazing that somehow photons of sunlight are used to create these sugar molecules or these carbohydrates. So let's delve a little bit deeper. So we can write the general equation for photosynthesis. Well, I've almost written it here. But I'll write it a little bit more scientifically specific. You start off with some carbon dioxide. You add to that some water, and you add to that-- instead of sunlight, I'm going to say photons because these are what really do excite the electrons in the chlorophyll that go down, and you'll see this process probably in this video, and we'll go in more detail in the next few videos. But that excited electron goes to a high energy state, and as it goes to a lower energy state, we're able to harness that energy to produce ATPs, and you'll see NADPHs, and those are used to produce carbohydrates. But we'll see that in a little bit. But the overview of photosynthesis, you start off with these constituents, And then you end up with a carbohydrate. And a carbohydrate could be glucose, doesn't have to be glucose. So the general way we can write a carbohydrates is CH2O. And we'll put an n over here, that we could have n multiples of these, and normally, n will be at least three. In the case of glucose, n is 6. You have 6 carbons, 12 hydrogens and 6 oxygens. So this is a general term for carbohydrates, but you could have many multiples of that. You could have these long-chained carbohydrates, so you end up with a carbohydrate and then you end up with some oxygen. So this right here isn't so different than what I wrote up here in my first overview of how we always imagined photosynthesis in our heads. In order to make this equation balance-- let's see, I have n carbons so I need n carbons there. Let's see, I have two n hydrogens here. Two hydrogens and I have n there, so I need two n hydrogens here. So I'll put an n out there. And lets see how many oxygens. I have two n oxygens, plus another n, so I have three n oxygens. So let's see, I have one n, and you put an n here, and then I have two n, and I think this equation balances out. So this is a 30,000-foot view of what's going on in photosynthesis. But when you dig a little deeper, you'll see that this doesn't happen directly, that this happens through a bunch of steps that eventually gets us to the carbohydrate. So in general, we can break down photosynthesis. I'll rewrite the word. We can break down photosynthesis-- and we'll delve deeper into future videos, but I want to get you the overview first-- into two stages. We can call one the light reactions. Or sometimes they are called the light-dependent reactions, and that actually would probably be a better way to write it. Let me write it like that. Light dependent means that they need light to occur. Light-dependent reactions. And then you have something called the dark reactions, and that's actually a bad name, because it also occurs in the light. Dark reactions, I wrote in a slightly darker color. And the reason why I said it's a bad name is because it still occurs in the light. But the reason why they probably called it the dark reaction is that you don't need light, or that part of photosynthesis isn't dependent on photons to occur. So a better term for it would have been light-independent reaction. So just to be clear, the light reactions actually need sunlight. They actually need photons for them to proceed. The dark reactions do not need photons for them to happen, although they do occur when the sun is out. They don't need those photons, but they need the byproducts from the light reaction to occur, so that's why it's called the light-independent reaction. They occur while the sun is out, but they don't need the sun. This needs the sun, so let me make it very clear. So this requires sunlight. This requires photons. And let me just make a very brief overview of this. This'll maybe let us start building a scaffold from which we can dig deeper. So the light reactions need photons, and then it needs water. So water goes into the light reactions and out of the other side of the light reactions. We end up with some molecular oxygen. So that's what happens in the light reactions, and I'm going to go much deeper into what actually occurs. And what the light the actions produce is ATP, which we know is the cellular or the biological currency of energy. It produces ATP and it produces NADPH. Now, when we studied cellular respiration, we saw the molecule NADH. NADPH is very similar. You just have this P there. You just have this phosphate group there, but they really perform similar mechanisms. That this agent right here, this molecule right here, is able to give away-- now let's think about what this means-- it's able to give away this hydrogen and the electron associated with this hydrogen. So if you give away an electron to someone else or someone else gains an electron, that something else is being reduced. Let me write that down. This is a good reminder. OIL RIG. Oxidation is losing an electron. Reduction is gaining an electron. Your charge is reduced when you gain an electron. It has a negative charge. So this is a reducing agent. It gets oxidized by losing the hydrogen and the electron with it. I have a whole discussion on the biological versus chemistry view of oxidation, but it's the same idea. When I lose a hydrogen, I also lose the ability to hog that hydrogen's electron. So this right here, when it reacts with other things, it's a reducing agent. It gives away this hydrogen and the electron associated with it, and so the other thing gets reduced. So this thing is a reducing agent. And what's useful about it is when this hydrogen, and especially the electron associated with that hydrogen, goes from the NADPH to, say, another molecule and goes to a lower energy state, that energy can also be used in the dark reactions. And we saw in cellular respiration the very similar molecule, NADH, that through the Kreb Cycle, or actually more importantly, that through the electron transport chain, was able to help produce ATP as it gave away its electrons and they went to lower energy states. But I don't want to confuse you too much. So the light reactions, you take in photons, you take in water, it spits out oxygen, and it spits out ATP and NADPH that can then be used in the dark reactions. And the dark reactions, for most plants we talk about, it's called the Calvin Cycle. And I'll go into a lot more detail of what actually occurs in the Calvin Cycle, but it takes in the ATP, the NADPH, and it produces-- it doesn't directly produce glucose. It produces-- oh, you probably saw this. You could call it PGAL. You could call it G3P. These all stand for-- let me write these down-- this is phosphoglyceraldehyde. My handwriting broke down. Or you could call it glyceraldehyde 3-phosphate. Same exact molecule. You can almost imagine it as-- this is a very gross oversimplification-- as three carbons with a phosphate group attached to it. But this can then be used to produce other carbohydrates, including glucose. If you have two of these, you can use those two to produce glucose. So let's just take a quick overview again because this is super important. I'm going to make videos on the light reactions and the dark reactions. Those will be the next two videos I make. So photosynthesis, you start with photons. All of these occur when the sun is out, but only the light reactions actually need the photons. The light reactions take photons-- we're going to go into more detail about what actually occurs-- and it takes in water. Oxygen gets spit out. ATP and NADPH get spit out, which are then used by the dark reaction, or the Calvin Cycle, or the light-independent reaction, because these still occur in the light. They just don't need photons. So they're the light-independent reaction. And it uses that in conjunction-- and we'll talk about other molecules that are used in conjunction. Oh, and I forgot a very important constituent of the dark reaction. It needs carbon dioxide. That's where you get your carbons to keep producing these phosphoglyceraldehydes, or glyceraldehyde 3-phosphate. So that's super important. It takes in the carbon dioxide, the products from the light reactions, and then uses that in the Calvin Cycle to produce this very simple building block of other carbohydrates. And if you remember from glycolysis, you might remember that this PGAL molecule, or this G3P-- same thing-- this was actually the first product when we split glucose in two when we performed the glycolysis. So now we're going the other way. We're building glucose so that we can split it later for energy. So this is an overview of photosynthesis, and in the next couple of videos, I'm actually going to delve a little bit deeper and tell you about the light reactions and the dark reactions and how they actually occur.

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Overview of photosynthesis. What photosynthesis accomplishes, why it's important, and how the light-dependent and light-independent reactions work together. Photosynthesis is usually represented by the equation 6 CO2 + 6 H2O + light --> C6H12O6 + 6 O2. During this process, organisms such as plants go through the light-dependent and light-independent reactions to convert carbon dioxide and water into sugars and oxygen.

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Advanced

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(Image credit: KPG_Payless | Shutterstock)

Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight and turn it into chemical energy. Here, we describe the general principles of photosynthesis and highlight how scientists are studying this natural process to help develop clean fuels and sources of renewable energy.

Types of photosynthesis

There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. The general principles of anoxygenic and oxygenic photosynthesis are very similar, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria.

During oxygenic photosynthesis, light energy transfers electrons from water (H ₂O) to carbon dioxide (CO ₂), to produce carbohydrates. In this transfer, the CO ₂ is "reduced," or receives electrons, and the water becomes "oxidized," or loses electrons. Ultimately, oxygen is produced along with carbohydrates.

Oxygenic photosynthesis functions as a counterbalance to respiration by taking in the carbon dioxide produced by all breathing organisms and reintroducing oxygen to the atmosphere.

On the other hand, anoxygenic photosynthesis uses electron donors other than water. The process typically occurs in bacteria such as purple bacteria and green sulfur bacteria, which are primarily found in various aquatic habitats.

"Anoxygenic photosynthesis does not produce oxygen - hence the name," said David Baum, professor of botany at the University of Wisconsin-Madison. "What is produced depends on the electron donor. For example, many bacteria use the bad-eggs-smelling gas hydrogen sulfide, producing solid sulfur as a byproduct."

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

Oxygenic photosynthesis is written as follows:

Here, six molecules of carbon dioxide (CO ₂) combine with 12 molecules of water (H ₂O) using light energy. The end result is the formation of a single carbohydrate molecule (C ₆H ₁₂O ₆, or glucose) along with six molecules each of breathable oxygen and water.

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

The letter A in the equation is a variable and H ₂A represents the potential electron donor. For example, A may represent sulfur in the electron donor hydrogen sulfide (H ₂S), explained Govindjee and John Whitmarsh, plant biologists at the University of Illinois at Urbana-Champaign, in the book " Concepts in Photobiology: Photosynthesis and Photomorphogenesis" (Narosa Publishers and Kluwer Academic, 1999).

(Image credit: Shutterstock)

The photosynthetic apparatus

The following are cellular components essential to photosynthesis.
Pigments
Pigments are molecules that bestow color on plants, algae and bacteria, but they are also responsible for effectively trapping sunlight. Pigments of different colors absorb different wavelengths of light. Below are the three main groups.

Chlorophylls: These green-colored pigments are capable of trapping blue and red light. Chlorophylls have three subtypes, dubbed chlorophyll a, chlorophyll b and chlorophyll c. According to Eugene Rabinowitch and Govindjee in their book "Photosynthesis"(Wiley, 1969), chlorophyll a is found in all photosynthesizing plants. There is also a bacterial variant aptly named bacteriochlorophyll, which absorbs infrared light. This pigment is mainly seen in purple and green bacteria, which perform anoxygenic photosynthesis.

Carotenoids: These red, orange or yellow-colored pigments absorb bluish-green light. Examples of carotenoids are xanthophyll (yellow) and carotene (orange) from which carrots get their color.

Phycobilins: These red or blue pigments absorb wavelengths of light that are not as well absorbed by chlorophylls and carotenoids. They are seen in cyanobacteria and red algae.

Plastids
Photosynthetic eukaryotic organisms contain organelles called plastids in their cytoplasm. The double-membraned plastids in plants and algae are referred to as primary plastids, while the multiple-membraned variety found in plankton are called secondary plastids, according to an articlein the journal Nature Education by Cheong Xin Chan and Debashish Bhattacharya, researchers at Rutgers University in New Jersey.

Plastids generally contain pigments or can store nutrients. Colorless and nonpigmented leucoplasts store fats and starch, while chromoplasts contain carotenoids and chloroplasts contain chlorophyll, as explained in Geoffrey Cooper's book, " The Cell: A Molecular Approach" (Sinauer Associates, 2000).

Photosynthesis occurs in the chloroplasts; specifically, in the grana and stroma regions. The grana is the innermost portion of the organelle; a collection of disc-shaped membranes, stacked into columns like plates. The individual discs are called thylakoids. It is here that the transfer of electrons takes place. The empty spaces between columns of grana constitute the stroma.

Chloroplasts are similar to mitochondria, the energy centers of cells, in that they have their own genome, or collection of genes, contained within circular DNA. These genes encode proteins essential to the organelle and to photosynthesis. Like mitochondria, chloroplasts are also thought to have originated from primitive bacterial cells through the process of endosymbiosis.

"Plastids originated from engulfed photosynthetic bacteria that were acquired by a single-celled eukaryotic cell more than a billion years ago," Baum told Live Science. Baum explained that the analysis of chloroplast genes shows that it was once a member of the group cyanobacteria, "the one group of bacteria that can accomplish oxygenic photosynthesis."

In their 2010 article, Chan and Bhattacharya make the point that the formation of secondary plastids cannot be well explained by endosymbiosis of cyanobacteria, and that the origins of this class of plastids are still a matter of debate.
Antennae
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 "antennae," 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.

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, for example, 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.
Reaction centers
The pigments and proteins, which convert light energy to chemical energy and begin the process of electron transfer, are known as reaction centers.

The photosynthetic process

The reactions of plant photosynthesis are divided into those that require the presence of sunlight and those that do not. Both types of reactions take place in chloroplasts: light-dependent reactions in the thylakoid and light-independent reactions in the stroma.

Light-dependent reactions (also called light reactions): When a photon of light hits the reaction center, a pigment molecule such as chlorophyll releases an electron.

"The trick to do useful work, is to prevent that electron from finding its way back to its original home," Baum told Live Science. "This is not easily avoided, because the chlorophyll now has an 'electron hole' that tends to pull on nearby electrons."

The released electron manages to escape by traveling through an electron transport chain, which generates the energy needed to produce ATP (adenosine triphosphate, a source of chemical energy for cells) and NADPH. The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. As a result, oxygen is released into the atmosphere.

Light-independent reactions (also called dark reactions and known as the Calvin cycle): Light reactions produce ATP and NADPH, which are the rich energy sources that drive dark reactions. Three chemical reaction steps make up the Calvin cycle: carbon fixation, reduction and regeneration. These reactions use water and catalysts. The carbon atoms from carbon dioxide are "fixed," when they are built into organic molecules that ultimately form three-carbon sugars. These sugars are then used to make glucose or are recycled to initiate the Calvin cycle again.

(Image credit: PNNL, QuickBird satellite)

Photosynthesis in the future

Photosynthetic organisms are a possible means to generate clean-burning fuels such as hydrogen or even methane. Recently, a research group at the University of Turku in Finland, tapped into the ability of green algae to produce hydrogen. Green algae can produce hydrogen for a few seconds if they are first exposed to dark, anaerobic (oxygen-free) conditions and then exposed to light The team devised a way to extend green algae's hydrogen production for up to three days, as reported in their 2018 study published in the journal Energy & Environmental Science.

Scientists have also made advances in the field of artificial photosynthesis. For instance, a group of researchers from the University of California, Berkeley, developed an artificial system to capture carbon dioxide using nanowires, or wires that are a few billionths of a meter in diameter. The wires feed into a system of microbes that reduce carbon dioxide into fuels or polymers by using energy from sunlight. The team published its design in 2015 in the journal Nano Letters.

In 2016, members of this same group published a study in the journal Science that described another artificial photosynthetic system in which specially engineered bacteria were used to create liquid fuels using sunlight, water and carbon dioxide. In general, plants are only able to harness about one percent of solar energy and use it to produce organic compounds during photosynthesis. In contrast, the researchers' artificial system was able to harness 10 percent of solar energy to produce organic compounds.

Continued research of natural processes, such as photosynthesis, aids scientists in developing new ways to utilize various sources of renewable energy. Seeing as sunlight, plants and bacteria are all ubiquitous, tapping into the power of photosynthesis is a logical step for creating clean-burning and carbon-neutral fuels.
Additional resources:

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(Image credit: KPG_Payless | Shutterstock) Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight and turn it into chemical energy. Here, we describe the general principles of photosynthesis and highlight how scientists are studying this natural process to help develop clean fuels and sources of renewable energy.

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https://www.youtube.com/watch?v=2xNwZCk2CHY

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http://www.livescience.com/51720-photosynthesis.html

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Photosynthesis | Photosynthesis in plants | Photosynthesis - Biology basics for children | elearnin

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http://photosynthesiseducation.com/photosynthesis-for-kids/

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https://www.youtube.com/watch?v=C1_uez5WX1o

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https://youtu.be/yHVhM-pLRXk

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just click play video.

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Thanks awesome video

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Photosynthesis Equation Song - Biology Lesson

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basic video

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Photosynthesis Quiz- Basic

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The process of photosynthesis is very beneficial to both human beings and plants. The process helps plants to produce energy and oxygen that is used by humans. Did you understand the topic? Test your understanding of the process by giving the multiple choice questions below a try. Best of luck!

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https://www.youtube.com/watch?v=eo5XndJaz-Y

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The simple story of photosynthesis and food - Amanda Ooten

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Vegetation Transformation: Crash Course Kids #5.2

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In this free online science interactive, students explore how a plant's environmental conditions affect its growth and development.

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Interactive Concepts in Biochemistry - Interactive Animations

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Illuminating Photosynthesis - NOVA | PBS

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Explore how photosynthesis works by helping the process along in this game.