Bio Topic 5 -> Photosynthesis

Describe the light dependent reactions of photosynthesis(5)

• Light excites a pair of electrons in the chlorophyll which leave the photosystem

• The electrons are used in the Electron Transport Chain

• Generating energy for photophosphorylation of ADP → ATP

• Photolysis of water: H2O → 2H+ + ½ O2 + 2e-

• NADP- is reduced to NADPH

Give 2 reasons why a cold solution containing sucrose and a buffer is used for the Hill Reaction(2)

• Cold solution slows enzyme activity

• Buffered solution prevents enzyme denaturation

• Sucrose prevents water from osmosing out of the chloroplasts

Give a reason why a tube in the dark is used in the Hill reaction(1)

• As a control, to ensure the DCPIP doesnt decolourise on its own

• C

What enzyme fixates CO2?

• Rubisco

Explain the relationship between structure and functions of a granum in photosynthesis(3)

• Stacks of thylakoids

• Increases SA

• Thylakoid membranes contain chlorophyll to absorb light

• Contians ATP synthase

In which part of the chloroplast does the reduction of NADP take place(1)

• Stroma

Describe the role of Rubisco in the production of GALP in the light independent reaction(4)

• Enzyme that bonds CO2 to RuBP to form GP in the Calvin Cycle

• GP is converted to GALP

• using ATP and hydrogen ion from NADPH

Describe how the membranes inside the chloroplast are involved in photosynthesis(3)

• Separates the thylakoid space from the stroma

• Thylakoid membrane is where the light dependent reaction occurs

• maintains a high conc grad of H+ ions

• Contains ATP synthase

• Contains the Electron Transport Chain

Where do light independent reactions occur(1)

• Stroma

Describe the roles of the products of the light dependent reactions

• ATP and NADPH

• ATP provides the energy required for the conversion of GP to GALP

• NADPH is used to convert GP to GALP

A decrease in the activity of Rubisco limits the rate of photosynthesis. Why? (2)

• Less CO2 fixed in the Calvin Cycle

• Less GP produced

• Less GP converted to GALP so less hexose sugars produced

• As temp increases, Rubisco activity increases

• As temp increases past 30 degrees, Rubisco activase activity decreases

• So Rubisco activity and Rubisco activase activity are not linked

• Only one species is used in the experiment

How does CO2 reach inside a palisade mesophyll cell from the external atmosphere(2)

• CO2 enters via the stomata

• Passes between spongy mesophyll cells

What does fixation mean (2)

• Carbon from CO2 is converted into a biological molecule

• catalysed by the Rubisco enzyme

Compare and Contrast the cyclic and non cyclic nature of photophosphorylation in the light dependent stage of photosynthesis (4)

Similarities:

• Both photophosphorylate ADP to ATP

• Both use electrons in the Electron Transport Chain

• Both use photolysis to split H20 → 2H+ + ½ O2 + 2e- to provide the electrons

Differences:

• Cyclic only produces ATP whereas non - cyclic produces both ATP and NADPH

Describe the role of the electrons in the light dependent reaction of photosynthesis(4)

• Replace electrons lost by the photosystem

• Be used by the Electron Transport Chain

• to release energy to phosphorylate ADP into ATP

• Electrons and H+ ions help NADP - to convert to NADPH

Describe and explain how the products of the light dependent reaction are involved in the production of GALP(3)

• ATP and NADPH

• ATP provides the energy for the reduction of GP to GALP

• NADPH provides H+ ions for GP to be reduced to GALP

Explain how GALP is used following its production(2)

• 5/6 is used to regenerate RuBP

• 1/6 is used to produce hexose sugars

A - Stroma

B - Lipid droplet

C - Thylakoid space

D - Grana

Where in the diagram is oxygen produced(1)

• Photolysis occurs in the thylakoid space

Explain how oxygen is produced in chloroplasts during photosynthesis(3)

• Photolysis of water

• using light energy

• H20 → 2H+ + ½ O2 + 2e-

Oxygen inhibits the enzyme that catalyses the fixing of CO2. High conc of oxygen, within a chloroplast, can reduce the rate of photosynthesis. Describe and explain the effect of high concs of oxygen on the rate of carbohydrate production in a chloroplast. (3)

• Less CO2 is bonded to RuBP by Rubisco

• Less GP is produced

• Less GP is reduced to GALP

• Less GALP is converted to carbohydrates

• So carbohydrate production will be reduced