photosynthesis

Question 1

What is the overall equation of photosynthesis?

Answer 1

6CO2 + 6H2O ——> C6H12O6 + 6O2

Question 2

What are the 2 stages of photosynthesis?

Answer 2

Light dependent and light independent

Question 3

Where does the light dependent stage occur?

Answer 3

Thylakoid membrane

Question 4

What is the first stage of photosynthesis?

Answer 4

Light dependent stage

Question 5

What does the light dependent stage require?

Answer 5

Light

Question 6

What happens in the photolysis of water?

Answer 6

• Light energy is absorbed by chlorophyll
• Splits water into oxygen, H+ and e-

Question 7

What is the equation for the photolysis of water?

Answer 7

H2O —> 1/2O2 + 2e- + 2H+

Question 8

What happens to the H+ produced in the photolysis of water?

Answer 8

The H+ is picked up by NADP to form NADPH

Question 9

What happens to the e- produced in the photolysis of water?

Answer 9

The e- are passed along a chain of electron carrier proteins

Question 10

What happens to the oxygen produced in the photolysis of water?

Answer 10

Either used for respiration or diffuses out of the leaf via the stomata

Question 11

What is the photoionisation of chlorophyll?

Answer 11

• Light energy is absorbed by the chlorophyll
• Electrons are excited and move up an energy level to leave chlorophyll
• Chlorophyll is ionised by light

Question 12

What happens when electrons have gained energy?

Answer 12

They move along a series of proteins embedded within the thylakoid membrane

Question 13

What happens when the electrons move along the proteins in the membrane?

Answer 13

• They release energy
• Some energy is used to pump protons across the chloroplast membranes

Question 14

What does moving protons across the chloroplast membranes do?

Answer 14

Creates an electrochemical gradient

Question 15

How do protons move across the membrane?

Answer 15

They pass through the enzyme ATP synthase, producing ATP

Question 16

What do the protons do once they have moved across the membrane?

Answer 16

Combine with the co-enzyme NADP to become reduced NADP (NADPH)

Question 17

Where does the light independent reaction occur?

Answer 17

Stroma

Question 18

What catalyses the light independent reaction?

Answer 18

RuBisCo

Question 19

Where is RuBisCo found?

Answer 19

Stroma

Question 20

Why is the light independent reaction temperature sensitive?

Answer 20

Because of the enzymes

Question 21

What does the Calvin cycle do?

Answer 21

Uses CO2, NADPH and ATP to form a hexose sugar

Question 22

What happens first in the Calvin cycle?

Answer 22

• CO2 reacts with RuBP to form GP

Question 23

How many molecules of GP are formed when CO2 reacts with RuBP?

Answer 23

TWO

Question 24

What is RuBP?

Answer 24

Ribulose biphosphate

Question 25

What is GP?

Answer 25

Glycerate-3-phosphate

Question 26

What catalyses the first stage of the Calvin cycle?

Answer 26

RuBisCo

Question 27

What happens second in the Calvin cycle?

Answer 27

GP is reduced to TP

Question 28

What is TP?

Answer 28

Triose phosphate

Question 29

How is GP reduced to TP in the second stage of the Calvin cycle?

Answer 29

- Using energy from ATP - Accepting a H+ from reduced NADP

Question 30

What happens in the Calvin cycle after GP has been reduced to TP?

Answer 30

1/6 carbons from TP leave the cycle each turn to be converted into useful organic substances

Question 31

What are useful organic substances?

Answer 31

Substances that contain carbon

Question 32

What happens in the Calvin cycle to the rest of the molecule?

Answer 32

- The rest of the molecule (5 carbons) is used to regenerate RuBP - With the energy from ATP

Question 33

How many carbons in RuBP?

Answer 33

5

Question 34

How many carbons in GP?

Answer 34

3

Question 35

How many carbons in TP?

Answer 35

3

Question 36

What is a limiting factor?

Answer 36

Any factor that reduces the rate of photosynthesis

Question 37

What are the limiting factors for photosynthesis?

Answer 37

- Temperature - Light intensity - CO2 concentration

Question 38

Why does the rate of photosynthesis increase as light intensity increases?

Answer 38

- Greater light intensity means more light energy is absorbed by the plant - Faster LDR stage occurs - Produces more ATP and NADPH for the Calvin cycle

Question 39

Why does the rate of photosynthesis increase as [CO2] increases?

Answer 39

- CO2 is required for the LIR stage - More CO2 means faster Calvin cycle

Question 40

What is it called when CO2 is combined with RuBP?

Answer 40

Carbon fixation

Question 41

Why does the rate of photosynthesis increase as temperature increases?

Answer 41

- Rate increases with temperature due to enzymes - Rate decreases if temperature exceeds a certain value due to enzyme denaturation

Question 42

Describe what happens during photoionisation in the light-dependent reaction.

Answer 42

- Chlorophyll absorbs light - Electrons are lost and move to electron transport chain

Question 43

Explain why heat stress decreases the light-dependent reaction of photosynthesis.

Answer 43

- Less ATP - Less NADPH

Question 44

Explain why a decrease in the activity of the enzyme RuBisCo would limit the rate of photosynthesis.

Answer 44

- Less CO2 reacts with RuBP - Less GP

Question 45

Where precisely is RuBisCo found in a cell?

Answer 45

Stroma

Question 46

How does Atrazine affect the rate of photosynthesis in weeds?

Answer 46

- Reduced transfer of protons across thylakoid membrane - Less ATP produced - Less NADPH produced - LIR slows

Question 47

Why do weeds treated with Atrazine give off small amounts of heat?

Answer 47

Energy is released for excited electrons

Question 48

Describe how crop plants use light energy during the light-dependent reaction.

Answer 48

- Excites electrons (electrons removed from chlorophyll) - Electrons move along electron transport chain, releasing energy - Energy used to join ADP and Pi to form ATP - Photolysis of water produces protons, electrons and oxygen - NADP reduced by electrons

Question 49

Explain the relationship between stomatal opening and photosynthesis.

Answer 49

- Stomata allow uptake of CO2 - CO2 used in photosynthesis