Photosythesis

Question 1

What is meant by oxidation and reduction?

Answer 1

• Oxidation is the loss of electrons/ hydrogen
• Reduction is the gain of electrons/ hydorgen

Question 2

State the chemical equation for photosynthesis

Answer 2

carbon dioxide + water = glucose + oxygen

Question 3

Describe the structures in a chloroplast

Answer 3

• outer membrane
• inner membrane
• granum
• thylakoid membrane (where light dependent reaction occurs)
• thylakoids
• stroma

Question 4

What are the names of the 2 stages of photosynthesis?

Answer 4

light dependent reaction
light independent reaction (calvin cycle)

Question 5

Where in the chloroplast does each stage of photosynthesis take place?

Answer 5

Light dependent reaction= thylakoid membrane
Light independent reaction= stroma

Question 6

Describe the steps of the light dependent reaction

Answer 6

1. Photoionisation
   - Chlorophyll absorbs light
   - Electrons are excited to a higher energy level and lost from chlorophyll- photoionisation
2. Photolysis
   - Light splits water into electrons, protons and oxygen- photolysis
   - The chlorophyll regains its lost electrons from the split water
   - Oxygen is given off as a waste product
3. The electron transfer chain
   - 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
   - Energy is used to pump protons across the thylakoid membrane forming a proton gradient
4. Formation of ATP
   - The protons diffuse back through the thylakoid membrane via ATP synthase down their electrochemical gradient (chemiosmosis)
   - The energy from this forms ATP from ADP + Pi
5. Reducing NADP
   - The electron from the electron transfer chain and H reduce NADP to make reduced NADP (NADPH)

Question 7

Name the 2 products made in the light dependent reaction used in the light independent reaction

Answer 7

ATP and reduced NADP

Question 8

Describe the reactions which occur in the light independent reaction

Answer 8

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 hydrogen from reduced NADP
6. Using energy from the hydrolysis of ATP
7. Triose phosphate converted organic molecules such as glucose, amino acids
8. 5 carbons from triose phosphate is used to regenerate RuBP via phosphorylation by ATP

Question 9

What is the name of the enzyme which catalyses the reaction between CO2 and RuBP?

Answer 9

Rubisco

Question 10

Explain the term limiting factor

Answer 10

a factor that will stop the reaction rate getting any higher. If this increases, rate increases

Question 11

Describe how photosynthesis may be measured

Answer 11

Measure the volume/ concentration of oxygen produced over time

Question 12

Describe and explain how temperature affects the rate of photosynthesis

Answer 12

• higher temperature, light independent reaction happens faster
• enzymes have more kinetic energy
• more enzyme- substrate complexes form

Question 13

Describe and explain how carbon dioxide concentration affects the rate of photosynthesis

Answer 13

• more CO2, more light independent reaction
• more CO2 reacts with RuBP
• more GP produced
• more GP reduced to triose phosphate

Question 14

Describe and explain how light intensity affects the rate of photosynthesis

Answer 14

• higher light intensity, light dependent reaction happens faster
• more ATP and NADPH produced
• more GP reduced to triose phosphate in light independent reaction