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.
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. 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. Basically, with photosynthesis, plants are helping produce the oxygen that all living things need to breathe and survive. As we learned earlier, the glucose will be used by the plant as energy.
The oxygen and water will be released back into the atmosphere to help other living things. During photosynthesis, plants use light energy to combine carbon dioxide and water to produce glucose, oxygen, and water. Photosynthesis is important because it provides plants with the energy they need to survive. It also releases needed oxygen and water back into the atmosphere. Are you studying clouds in your science class?
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Chloroplasts have a double membrane envelope composed of an outer membrane and an inner membrane. Within the double membrane are stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane is chlorophyll, a pigment that absorbs certain portions of the visible spectrum and captures energy from sunlight.
Chlorophyll gives plants their green color and is responsible for the initial interaction between light and plant material, as well as numerous proteins that make up the electron transport chain.
The thylakoid membrane encloses an internal space called the thylakoid lumen. Learning Objectives Describe the main structures involved in photosynthesis and recall the chemical equation that summarizes the process of photosynthesis.
In plants, the process of photosynthesis takes place in the mesophyll of the leaves, inside the chloroplasts. Chloroplasts contain disc-shaped structures called thylakoids, which contain the pigment chlorophyll. Chlorophyll absorbs certain portions of the visible spectrum and captures energy from sunlight.
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