topic 5

Question 1

Location of light dependent reaction

Answer 1

Thylakoid membranes of chloroplast

Question 2

Location of light independent reaction

Answer 2

Stroma of chloroplast

Question 3

Thylakoid membranes

Answer 3

Folded membranes containing photosynthetic proteins (chlorophyll)
embedded with transmembrane electron carrier proteins involved in the LDRs

Question 4

Chlorophyll

Answer 4

Located in proteins on thylakoid membranes
mix of coloured proteins that absorb light
different proportions of each pigment lead to different colours on leaves

Question 5

Advantage of many pigments

Answer 5

Each pigment absorbs a different wavelength of visible light
many pigments maximises spectrum of visible light absorbed
maximum light energy taken in so more photoionisation and higher rate of photosynthesis

Question 6

Light-dependent reaction (LDR)

Answer 6

First stage of photosynthesis occurs in thylakoid membranes uses light energy and water to create ATP and reduced NADP for LIR
involves photoionisation of chlorophyll, photolysis and chemiosmosis

Question 7

Photolysis

Answer 7

Light energy absorbed by chlorophyll splits water into oxygen, H+ and e-

Question 8

Products of photolysis

Answer 8

H+
Picked up by NADP to form
reduced NADP for LIR e-
passed along chain of
electron carrier proteins oxygen
used in respiration or diffuses out leaf via stomata

Question 9

Photoionisation of chlorophyll

Answer 9

Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll some of the energy released is used to make ATP and reduced NADP

Question 10

Chemiosmosis

Answer 10

Electrons that gained energy move along a series of electron carriers in thylakoid membrane release energy as they go along which pumps proteins across thylakoid membrane electrochemical gradient made protons pass back across via ATP synthase enzyme producing ATP down their conc. gradient

Question 11

What happens to protons after chemiosmosis

Answer 11

Combine with co-enzyme NADP to become reduced NADP reduced NADP used in LIR

Question 12

Products of LDR

Answer 12

ATP (used in LIR)
reduced NADP (used in LIR) oxygen (used in respiration / diffuses out stomata)

Question 13

Light independent reaction (LIR)

Answer 13

Calvin cycle
uses CO2, reduced NADP and ATP to form hexose sugar occurs in stroma which contains the enzyme Rubisco temperature-sensitive

Question 14

Calvin cycle

Answer 14

Carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP) which is a 3-carbon compound. This reaction is catalysed by the enzyme rubisco.
GP is reduced to triose phosphate (TP) using energy from ATP and by accepting a H from reduced NADP.
Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances.
The rest of the molecule is used to regenerate RuBP, with the energy released from the hydrolysis of ATP.

Question 15

Producing hexose sugar in LIR

Answer 15

Takes 6 cycles
glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose) can be converted to glycerol to combine with fatty acids to make lipids

Question 16

Limiting factors of photosynthesis

Answer 16

Light intensity CO2 concentration temperature

Question 17

How light intensity limits photosynthesis

Answer 17

If reduced, levels of ATP and reduced NADP would fall
LDR limited - less photolysis
and photoionisation
GP cannot be reduced to TP in LIR

Question 18

How temperature limits photosynthesis

Answer 18

LIR inhibited - enzyme controlled (Rubisco)
up to optimum, more collisions and E-S complexes
above optimum, H-bonds in tertiary structure break, active site changes shape - denatured