Biol4 - Photosynthesis

Question 0

Light-dependant reaction? (7)

Answer 0

~e- enter chlorophyll (PS2)
~light is absorbed by chlorophyll (PS2)
~e- in PS2 become excited
~e- exit PS2 and pass down a chain of electron carriers at successively lower energy levels which releases energy
~ energy released is used to phosphorylate ADP to make ATP
~e- enter chlorophyll (PS1) again excited by photons of light)
~e- exit PS1 and with H+ ions from photolysis of water combine with NADP forming reduced NADP

Question 1

Photolysis? (3)

Answer 1

~Water is split into H+, e- and O2
~as electrons leave PS2 to pass down a chain of electron carriers new electrons from photolysis of H2O can enter PS2
~this allows photolysis to continue

Question 2

Light-independant reaction (5)

Answer 2

~RuBP (ribulose biphosphate) combine with CO2 forming unstable 6C intermediate that immediately splits into 2 x 3C glycerate-3-phosphate molecules
~reduced NADP provides a proton to reduce GP to triose phosphate, reduced NADP is oxidised to NADP
~ATP supplies energy for this reaction
~some TP used to make organic substance e.g. glucose
~ATP supplies phosphate for the process of converting TP to RuBP

Question 3

Why is the concentration of CO2 less in the day than at night? And higher at ground level than amongst the leaves?

Answer 3

~During the day there is light so photosynthesis can occur, during the night respiration occurs
~in (the light independant reaction) of photosynthesis CO2 is absorbed (to combine with RuBP), while respiration releases CO2, hence higher CO2 conc at night
~also in leaves more photosynthesis
~so CO2 is take up by leaves so lower CO2 conc amongst leaves

Question 4

Why is ATP useful in many biological processes? (5)

Answer 4

~phosphorylates compounds
~releases energy in small, manageable amounts
~easily broken down/broken down in one step
~reformed/made again
~Immediate energy compound/makes energy available rapidly

Question 5

Why is more oxygen being supplied to roots useful? (2)

Answer 5

~uptake by roots requires active transport (uptake useful things like nitrates)
~which requires ATP, need aerobic respiration (uses O2)

Question 6

What happens to the amount of C02 absorbed when plant is placed in the dark compared to in the light? (2)

Answer 6

~decreases, less CO2 absorbed

~because light dependent reaction does not occur (barely occurs ask Val) so ATP and reduced NADP not produced

Question 7

What happens to the amount of C02 absorbed when only stroma is isolated from plant? (2)

Answer 7

~Less CO2 absorbed
~because light dependent reaction does not occur so ATP and reduced NADP not produced

(Light dependent reaction takes place in grana(/_ thylakoid membranes?)

Question 8

Where does the light dependent and light independent reactions take place? (2)

Answer 8

~light dependent is in grana/granum (thylakoid membranes?)

~light independent takes place in stroma

Question 9

Why is there less CO2 uptake when the electron transfer chain is prohibited? (2)

Answer 9

~less reduced NADP is formed

~less ATP produced (both used so cycle can recommence

Question 10

Why rise in conc of GP in plant when light switched off? (1)

Answer 10

Because ATP and reduced NADP produced in light dependent reaction
No ATP and reduced NADP = can’t convert GP to TP

Question 12

Explain why there is twice the amount of GP to RuBP when CO2 conc is high (1)

Answer 12

RuBP combines with CO2 to produce 2xGP

Question 13

Explain why carbon used in photosynthesis experiment was radioactively labelled (1)

Answer 13

Allows detection of products

Question 14

Why does amount of glucose in plant decrease after light switched off? (1)

Answer 14

Glucose used up in respiration (not being made to make up for it)
Or converted to starch/cellulose

Question 15

Gross productivity in plants was highest in July as highest temperature, explain why (2)

Answer 15

~high temperature allows enzymes to work faster

~allows more collision/ more e-s complexes to be formed

Question 16

Describe and explain the relationship between light absorption and photosynthesis (2)

Answer 16

~light provides energy for light dependant reaction

~production of reduced NADP (and ATP?)

Question 17

Give one dependant variable you could measure in order to determine the rate of photosynthesis in a plant (1)

Answer 17

~volume of CO2 absorbed

Question 18

Reagent which is blue when oxidised and colourless when reduced is added to a suspension of chloroplasts and exposed to sunlight, the blue colour disappeared, why? (2)

Answer 18

~reagent is reduced by H+ and electrons

~from reduced NADP, reduced NADP changes dye colour

Question 19

Reagent which is blue when oxidised and colourless when reduced is added to a suspension of chloroplasts and small quantities of ADP and phosphate ions were added, then the tube was exposed to sunlight, the blue colour disappeared more quickly, why? (2)

Answer 19

~ADP and Pi needed to produce ATP

~ADP levels are a limiting factor (on production of reduced NADP?)

Question 20

The net productivity of plants was higher in August, which was slightly cooler than the peak temperature in July, use your knowledge of photosynthesis and respiration to suggest why (3)

Answer 20

~photosynthesis less affected by temp increase
~lower energy loss
~respiration slower/less respiration