Summary What is Light Reaction? Light reactions of photosynthesis take place in the thylakoid membranes of chloroplasts.
The Calvin cycle Video transcript In the last video we learned a little bit about photosynthesis.
And we know in very general terms, it's the process where we start off with photons and water and carbon dioxide, and we use that energy in the photons to fix the carbon. And now, this idea of carbon fixation is essentially taking carbon in the gaseous form, in this case carbon dioxide, and fixing it into a solid structure.
And that solid structure we fix it into is a carbohydrate. The first end-product of photosynthesis was this 3-carbon chain, this glyceraldehyde 3-phosphate.
But then you can use that to build up glucose or any other carbohydrate. So, with that said, let's try to dig a little bit deeper and understand what's actually going on in these stages of photosynthesis.
Remember, we said there's two stages. The light-dependent reactions and then you have the light independent reactions. I don't like using the word dark reaction because it actually occurs while the sun is outside.
It's actually occurring simultaneously with the light reactions. It just doesn't need the photons from the sun.
But let's focus first on the light-dependent reactions. The part that actually uses photons from the sun. Or actually, I guess, even photons from the heat lamp that you might have in your greenhouse. Remember, reduction is gaining electrons or hydrogen atoms.
And it's the same thing, because when you gain a hydrogen atom, including its electron, since hydrogen is not too electronegative, you get to hog its electron. So this is both gaining a hydrogen and gaining electron. But let's study it a little bit more. So before we dig a little deeper, I think it's good to know a little bit about the anatomy of a plant.
So let me draw some plant cells. So plant cells actually have cell walls, so I can draw them a little bit rigid. So let's say that these are plant cells right here. Each of these squares, each of these quadrilaterals is a plant cell. And then in these plant cells you have these organelles called chloroplasts.
Remember organelles are like organs of a cell. They are subunits, membrane-bound subunits of cells.
And of course, these cells have nucleuses and DNA and all of the other things you normally associate with cells. But I'm not going to draw them here. I'm just going to draw the chloroplasts.The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions.
Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis?
Photosynthesis is frequently described in two stages– the light dependent process, which requires light, and the light independent process, which does not require light. Overview The light dependent process occurs in the thylakoid membranes of the chloroplast. In light-independent reactions (the Calvin cycle), carbohydrate molecules are assembled from carbon dioxide using the chemical energy harvested during the light-dependent reactions. Key Terms photosystem: Either of two biochemical systems active in chloroplasts that are part of photosynthesis. In the light-dependent reactions of photosynthesis, the energy from light propels the electrons from a photosystem into a high-energy state. In plants, there are two photosystems, aptly named Photosystem I and Photosystem II, located in the thylakoid membrane of the chloroplast.
In light-independent reactions (the Calvin cycle), carbohydrate molecules are assembled from carbon dioxide using the chemical energy harvested during the light-dependent reactions.
Key Terms photosystem: Either of two biochemical systems active in chloroplasts that are part of photosynthesis. Photosynthesis is frequently described in two stages– the light dependent process, which requires light, and the light independent process, which does not require light.
Overview The light dependent process occurs in the thylakoid membranes of the chloroplast. Photosynthesis occurs via two main reactions: light-dependent and light-independent reactions. In the light-dependent reaction, adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) are generated via proton motive force and the electron transport chain (Figure 1).
The production of ATP via photosynthesis is called photophosphorylation.
Light dependent capture energy from the sunlight for reactions that occur in the thylakoids, light independent use energy from the light dependent reactions to make sugars in the chloroplasts Light (photo) synthesis (put together).
The light INDEPENDENT reaction takes the energy and electron carriers from the previous reaction and uses them to turn carbon dioxide into glucose.
This reaction doesn't need light but it will cease if it uses up all the chemical energy. This reaction happens in the stroma of the chloroplast.