Photosynthesis Flashcards
What is the aim of photosynthesis?
To reduce carbon dioxide to form carbohydrates.
Briefly, how does the reduction of carbon dioxide in photosynthesis happen?
Hydrogen ions from water reduce it. And the energy needed for this reacton comes from ATP produced from light energy.
Where does photosynthesis occur?
In the chloroplasts -> light-independent stage is in the stroma; light-dependent in the thylakoids.
Discuss the different structures in the chloroplasts.
There are 4 main ones.
- The lamella is the membrane which is arranged in fluid-filled sacs called thylakoids; with photosynthetic pigments embedded in them.
- The thylakoids are where the light-dependent reactions take place. They contain enzymes, protein molecules and possess an electron transport chain.
- The thylakoids fold up into stacks called grana. They hold ATP synthase in place and allow for pigments to be arranged for efficient light absorption. they also increase surface area for the same reason.
- The stroma is the watery material in the chloroplast. It contans enzymes for the Calvn cycle and contains 70s rbosomes and circular DNA, as well as stores carbohydrates produced as starch grains.
Define pigments as well as naming the different kinds found in chloroplasts and the parts of the light spectrum they are most and least active in.
A pigment is a subtance that absorbs some wavelenghts and reflects others. In leaves they are used to absorb light energy to drive reactions in the lght-dependent stage.
There are two types in chloroplasts
1. Chlorophyll- A and B; most act. in blue-violet, B in red regions.
2. Carotenoids- carotene and xanthophyll; most act. in blue-violet regions.
State the wavelengths in which the rates of photosynthesis are highest and lowest
Highest: 450 and 660-680
What are the two stages of photosynthesis and what do they entail.
The light-dependent and independent stage.
* The light-dependent stage involves photolysis (the splitting of water into hydrogen and oxygen by light energy).
* The energy from the hydrogen is used to make ATP through phosphorylation , and then NADP attaches to it to form reduced NADP which is necessary for the light independent stage.
- In the light-independent stage, energy from the ATP and hydrogen from the reduced NAD are used to reduce carbon dioxide and produce carbohydrates.
What molecules are produced in the light-dependent stages?
ATP and NADP
What are the two means by which ATP can be produced in the light-dependent stage and briefly discuss them.
Cyclic phosphorylation: involves the excitation of an electron called photoactivation, through the absorption of light energy in photosystem I. The passage of this electron from electron carrier to the other causes the electron to lose energy; of which protons are moved from the stroma, through the thylakoid membrane to the thylakoid space to form a chemostatic gradient of protons. Through this chemiosmosis takes place- the prootns pass through ATP synthase through facilitated diffusion and Pi is added to ADP.
Non-cyclic phosphorylation: Photosystem II receives an electron through the process of photolysis. It gets excited through light energy and is transferred to photosystem I; (but in this, the energy is used to phosphorylate ATP, through the same dynamic that happens in the cylic level i.e. chemiosmosis from protons moving into the thylakoid lumen etc.) At the same time, photoactivation occurs in photosystem I and is transported through electron carriers and its energy as well as the hydrogen ions from hydrolysis is used to reduced NADP.
