Photosynthesis Flashcards
(17 cards)
Write an overall equation for photosynthesis.
What are coenzymes?
They transfer chemical molecules during reactions and are continually recycled.
What coenzyme is involved in photosynthesis?
NAPD carries electrons and protons during photosynthesis
Where does the light-dependent reaction occur?
The thylakoids.
How are the thylakoids adapted for the light-dependent reaction?
They contain photosystems which trap light for photosynthesis.
What are photosystems?
They are photosynthesis pigments attached to a protein.
Describe what happens during the light-dependent reaction l.
- Photoionisation: At photosystem I, The chlorophyll absorbs light energy, which excites the electrons. This causes the chlorophyll to lose electrons. The electrons move down the electron transport chain.
- Photolysis of water produces oxygen, protons, and electrons. These electrons are used to replace the ones lost during photoionisation.
- As the electrons move down the electron transport chain they release energy which is used to transport protons from the stroma into the thylakoids
- Chemiosmosis: This created an electrochemical gradient between the stroma and the thylakoids. The protons diffuse down this concentration gradient and back to the stroma. This releases energy to make ATP from ADP and an Inorganic phosphate in a condensation reaction catalysed by ATP synthase.
- At photosystem II, photoionisation happens again, and NAPD accepts the electrons and protons to make NADPH.
Where does the light-independent reaction take place?
The stroma.
Describe the light-independent reaction?
- Ribulose biphosphate combines with carbon dioxide to make a molecule with 6 carbons. This reaction is catalysed by the enzyme rubisco.
- This unstable molecule breaks down into two glycerol-3-phosphate molecules.
- The GP is converted into trios phosphate using the energy released by ATP and hydrogen released by reduced NADP.
- Some of the triose phosphate is used to make useful organic compounds like hexose sugars. The rest is converted back into RuBP using the energy released by ATP.
How many times must the Calvin cycle be repeated to make one molecule of glucose?
- Two molecules of triose phosphate are needed to make one molecule of glucose.
- One out of six molecules of triose phosphate is used to make glucose.
- One Calvin cycle makes 2 triose phosphate molecules. 3 cycles make 6, and one of them is used to make glucose. So six is needed to make 12 triose phosphate molecules and 2 to be used to make glucose.
How does temperature affect the rate of photosynthesis?
The higher the temperature the higher the rate of photosynthesis. This is because the enzymes involved in photosynthesis have more kinetic energy, meaning they move faster, and there are more frequent collisions,s, which lead to the formation of an enzyme-substrate complex. However, if the temperature is too high, the enzymes denature and won’t be able to form a complex, meaning the rate decreases. Also, if the temperature is too high the stomata close to prevent excess water loss and less carbon dioxide enters the leaves.
How does the carbon dioxide concentration affect the rate of photosynthesis?
The more carbon dioxide there is, the more photosynthesis, as carbon dioxide is a substrate used in photosynthesis.
How does water availability affect the rate of photosynthesis?
The more water there is, the more photosynthesis, as carbon dioxide is a substrate used in photosynthesis.
How do light intensity and wavelength affect the rate of photosynthesis?
The higher the light intensity the higher the rate of photosynthesis. This is because more energy is provided for the light-dependent reaction. However, they have to be a certain wavelengths because photosynthesis pigments don’t absorb certain wavelengths of light and instead reflect it.
How does mineral availability affect the rate of photosynthesis?
The more magnesium ions needed the higher the rate of photosynthesis as magnesium is needed to make chlorophyll.
What are the main photosynthesis pigments and their colours?
- Chlorophyll a: blue/green
- Chlorophyll b: yellow/green
- Carotene: orange
What does cyclic phosphorylation stand for?
The electrons that leave the PSI are only used to make ATP ans they circle back once they have reached the end of the electron transport chain. They are not used to make reduced NADP.
