Photosynthesis

Question 1

Differences between cyclic & non-cyclic photophosphorylation

Answer 1

Cyclic: only PSI involved, H20 not required, O2 not evolved, NADPH not synthesised

Non-cyclic: PSI & PSII involved, H20 required for photolysis to replace chlorophyll e-, O2 is evolved, NADPH synthesised

Question 2

what is the use of having cyclic & non-cyclic photophosphorylation

Answer 2

Non-cyclic is used more as it produces the reactants for the light independent reactions
Cyclic is used to synthesis additional ATP to meet cell energy demands

Question 3

state the 2 main processes of photosynthesis & their purposes

Answer 3

Light-dependent stage: photophosphorylation to produce ATP to meet cell energy demands

Light-independent-stage: Calvin cycle to synthesis useful organic biomolecules such as sugars, amino acids, fatty acids

Question 4

what 3 things to plants use glucose for

Answer 4

sucrose (disaccharide)
starch (storage polysaccharide)
cellulose (B-glucose polysaccharide for cells walls)

Question 5

outline the light-dependent stage for NON-CYCLIC photophosphorylation

Answer 5

1. Photolysis of H2O to 1/2O2 + 2e- + 2H+
2. p680 wavelength light absorbed by PSII excited pair of e- in chlorophyll molecule
3. e- move to higher energy level, leaving the chlorophyll & are accepted by the first carrier of the ETC
4. e- from photolysis replace the lost e-
5. e- move along ETC: energy released used to pump H+ into thylakoid SPACE - conc. increases
6. e- diffuse down electrochemical gradient facilitated by ATP synthase
7. the movement of protons through ATP synthase drives synthesis of ATP from ADP & Pi = chemiosmosis
8. e- accepted by PSII at end of ETC, then when p700 wavelength absorbed they are excited & accepted by NADP –> NADPH

Question 6

outline the light-dependent stage for CYCLIC photophosphorylation

Answer 6

1. p700 wavelength light absorbed by PSI excites pair of e- in chlorophyll; e- leave & reduce an e- carrier
2. e- pass along ETC, releasing energy
3. energy released by ETC used to pump H+ into thylakoid space- conc. build up
4. protons diffuse back into stroma facilitated by ATP synthase; this movement drives ATP synthesis from ADP & Pi = CHEMIOSMOSIS
5. e- return to original PSI chlorophyll (no photolysis needed to replace)

Question 7

outline the light-independent stage

Answer 7

CARBON FIXATION:
CO2 diffuses through stomata, cell wall & chloroplast envelope

CALVIN CYCLE:

1. RuBisCo enzyme catalyses CO2 to combine with Ribulose Bisphosphate (RuBP; 5C) to form an unstable 6C
2. unstable 6C breaks down to 2 GP (glycerate 3-phosphate)
3. 2GP reduced to 2 triose phosphate (TP) using 2H from 2 NADPH (generated by LDS)
4. 1/6 of TP used to synthesis organic molecules
5. 5/6 converted back to RuBP using Pi from ATP (1 ATP->ADP for every 2 TP(3c) to produce RuBP (5c)

Question 8

For every 6CO2 used, how many RuBP are needed, and how many GP, therefore TP are produced?
How many TP are used to regenerate RuBP?

Answer 8

6RuBP(5C) + 6CO2–> 12 GP(3c) (36 C in total)

12GP phosphorylated by 12 ATP & oxidised by 12 NADP
–> 12 TP (3C)

2 TP used for organic molecule synthesis
10 TP phosphorylated by 5 ATP –> 5 RuBP regenerated

Question 9

structure of chloroplast

Answer 9

envelope (double membrane) with an inter membrane space between inner & outer membrane

inside = fluid filled matrix: STROMA containing enzymes, loop of DNA & small ribosomes similar to prokaryotic for localised therefore quicker enzyme synthesis

Grana are stacks of thylakoid membranes
grant are linked by intergranal lamellae

Question 10

where do the LDS and LIS occur?

Answer 10

LDS is in grana

LIS is

Question 11

why is the grana specialised for photosynthesis

Answer 11

stacked thylakoid membranes increase surface are

has electron carriers, ATP synthase & photosystems that contain the photosynthetic pigments to trap sunlight energy

Question 12

what type of nutrition is photosynthesis and why

Answer 12

autotrophic nutrition, as:

sunlight energy used to synthesise organic molecules

Question 13

what is the relationship between respiration and photosynthesis?

Answer 13

photosynthesis produces O2 & glucose
= the reactants of respiration

respiration produces CO2 and H2O
= the reactants of photosynthesis

Question 14

define compensation point & compensation period

what makes the period different and why?

Answer 14

photosynthesis & respects occur @ equal rate so no net gain/loss of carbohydrate

compensation period = time taken to reach this point

varies with plant species as shade plants reach the compensation point sooner; have a shorter period ,
whereas sun plants require high intensity to reach the CP
exposure to light after darkness

Question 15

what term describes animals, fungi, etc that ingest plants to obtain organic molecules, rather than photosynthesise?

Answer 15

heterotrophs

Question 16

suggest why ocean plants have photosynthetic systems for red light, but land plants for blue light?

Answer 16

it has a longer wavelength so penetrates down to the ocean floor

Question 17

why does chlorophyll b appear yellow-green but chlorophyll a appears green

Answer 17

chlorophyll b absorbs 500nm light (red) but reflect blue & yellow

chlorophyll a absorbs 680/700nm light (blue) but reflects red, yellow & blue light