Unit 7 - Photosynthesis Flashcards
What is oxidation?
Loss of electrons/hydrogen
What is reduction?
The gain of electrons/hydrogen
What are the steps of the light dependent reaction?
1) Chlorophyll absorbs light and electrons are excited to a higher energy level and leave the chlorophyll (chlorophyll becomes positively charged). This is photoionisation
2) Photolysis - light splits water into electrons, protons and oxygen. The chlorophyll regains its lost electrons from the split water. Oxygen is given off as a waste product
3) Electrons from chlorophyll are passed down a series of electron carriers in the thylakoid membrane, called the electron transfer chain. Via redox reactions. Electrons lose energy. This energy is used to pump protons across the thylakoid membrane forming a proton gradient
4) The protons diffuse back through the thylakoid membrane via ATP synthase down their electrochemical gradient (chemiosmosis). The energy from this forms ATP from ADP and Pi
5) The electron from the electron transfer chain and H reduces NADP to make reduced NADP (NADPH)
Define chemiosmosis?
The movement of ions across a selectively permeable membrane, down their electrochemical gradient (i.e. H+ though ATP synthase)
Photo of the light dependent reaction?
Where does the light independent reaction take place?
In the stroma of chloroplasts
What are the step of the light independent reaction?
1) Carbon dioxide reacts with RuBP
2) Produces 2 molecules of GP
3) Catalysed by rubisco
4) GP reduced to 2 molecules of triose phosphate
5) Using energy from the hydrolysis of ATP
6) Using hydrogen from reduced NADP
7) Triose phosphate converted to organic molecules (1 carbon) such as glucose or amino acids
8) 5 carbons from triose phosphate are used to regenerate RuBP via phosphorylation via ATP.
Photo of the light independent reaction?
How does photosynthesis increase growth of the plant?
-Glucose is produced - repaired to produce ATP which is hydrolysed to release energy.
-Energy used to synthesis new molecules, e.g. DNA replication and protein synthesis/mitosis
-B-glucose used to make cellulose cell walls
-Lipids produced can be used to make phospholipids and form new membranes
-Amino acids used to form proteins/enzymes needed for growth e.g. ATP synthase, enzymes for protein synthesis etc.
In the absence of light, levels of GP increase at first then level off. Explain why?
-ATP and reduced NADP are no longer made in the light dependent reaction
-GP increases as CO2 continues to to react with RuBP to make GP but GP is not reduced to triose phosphate
-GP then levels off as RuBP is not being regenerated
-So GP no longer made as CO2 has no RuBP to react with
What are the 3 limiting factors of photosynthesis?
1) Light intensity
2) CO2 concentration
3) Temperature
How does temperature increase rate of photosynthesis?
Higher temperature means the light independent reaction happens faster, as enzymes such as rubisco have more kinetic energy, so more enzyme-substrate complexes.
How does light intensity increase rate of photosynthesis?
Higher light intensity means more light dependent reaction, so more ATP and NADH produced, so more GP reduced to triose phosphate in light independent reaction.
How does CO2 concentration increase rate of photosynthesis?
Increased CO2 concentration means more light independent reaction as more CO2 reacts with RuBP, so more GP produced, so more GP reduced to triose phosphate.
What would happen to the yield of a crop when the rate of photosynthesis is greater than respiration?
Yield would increase as organic molecules e.g glucose are produced faster than used.
What would happen to plant yield when rate of respiration is greater than photosynthesis?
Yield would decrease as glucose is used faster than produced.
