Photosynthesis

Question 1

Give 5 reasons why ATP is useful

Answer 1

1- releases energy in small manageable amounts
2- broken down in one step
3- immediate energy compounds
4- phosphorylate other compounds making them more reactive
5- reformed again

Question 2

what is NADP

Answer 2

a co-enzyme molecule which acts as a hydrogen acceptor, becoming reduced NADP

Question 3

What is photosynthesis

Answer 3

a process in which chlorophyll absorbs a range of different wavelengths of light energy and convert it into chemical potential energy.

Question 4

where does LDR take place and what does it form

Answer 4

• specifically in the granum
• forms ATP and NADPH

Question 5

describe the 8 steps of LDR

Answer 5

1- chlorophyll absorbs light energy via photoionisation
2- which excites electrons to a higher energy level (chlrpyl is oxidised)
3- electrons move along the carriers
4- energy released by electrons used to form an electro-chemical gradient
5- H+ diffuse through ATP Synthase (not A-T)
6- Photophosphorylation; providing energy to join ADP + Pi to form ATP
7- Photolysis of water produces two protons, two electrons and 1/2 oxygen. (occurs in thylakoid psace)
8- NADP reduced by electrons

Question 6

chemiosmotic theory

Answer 6

the movement of ions usually protons across a membrane down an electrochemical gradient, established through REDOX and activation of proton pumps

Question 7

herbicide-weed killer questions

Answer 7

• less/no ATP
• Or less/no reduced NADP

Question 8

fluorescence- when an ETC is not available for excited electron. WHY?

Answer 8

because the excited electrons cannot lose energy via the ETC so releases the energy as light or heat

Question 9

in plants, ATP is produced in the LDR.
suggest why this is not a plants only source of ATP (4)

Answer 9

1- plants dont photosynthesis in the dark
2- not all parts of the plants photosynthesise (roots)
3- plants require more ATP than is produced in the LDR
4- ATP used in active transport

Question 10

Describe the effect of introducing an herbicide on the ETC (4)

Answer 10

• reduced transfer of protons across thylakoid membrane / reduced chemiosmotic gradient
• so less ATP produced
• so less reduced NADP produced
• so L-IR slows / less reduction of GP to triose phosphate

Question 11

describe the light independent reaction which take place in the stroma

Answer 11

1- carbon fixation: carbon dioxide combines with ribulose biphpsphate RuBP
2- produces two GP molecules
3- reduction: x2 GP reduced to 2x triose phosphate
4- using reduced NADP
5- using energy from ATP
6- triose phosphate converted into glucose/RuBP/ other organic substances
( AA, pyruvate, cellulose, DNA)
- Most Triose phosphate is used to regenrate RuBP

Question 12

give 3 limiting factors for photosynthesis

Answer 12

1- carbon dioxide concentration
2- light intensity and wavelengths
3- temperature

Question 13

the concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours.

describe these changes and explain where they occur (5)

Answer 13

• high concentration of carbon dioxide in darkness
• no photosynthesis in the dark
• in dark plants and other organisms respire
• in light, rate of photosynthesis greater than rate of aerobic respiration
• decrease in CO2 concentration with height
• at ground level fewer leaves