Photosynthesis

Question 1

What is chlorophyll?

Answer 1

• a green pigment found in chloroplasts that absorbs light energy used in photosynthesis

Question 2

What is the stroma?

Answer 2

• contains enzymes, 70S ribosomes, circular DNA
• site of light independent stage

Question 3

What are lamellae?

Answer 3

• membranes in the chloroplast

Question 4

What are thylakoid membranes?

Answer 4

• enclose fluid-filled sacs (thylakoid spaces)
• site of light dependent stage

Question 5

What are grana?

Answer 5

• stacks of thylakoid membranes
• large SA, so faster light dependent reactions
• lots of light absorbed

Question 6

What are the photosynthetic pigments?

Answer 6

Chlorophylls:
- chlorophyll a: yellow-green
- chlorophyll b: blue-green
Carotenoids:
- carotene: orange
- xanthophyll: yellow

Question 7

Explain the absorption spectrum for pigments:

Answer 7

• chlorophyll absorbs red and reflects green light
• carotene absorbs blue light

Question 7

Explain the absorption spectrum for pigments:

Answer 7

• chlorophyll absorbs red and reflects green light
• carotene absorbs blue light

Question 8

What is a photosystem?

Answer 8

• cluster of light harvesting pigments surrounding a reaction centre

Question 9

What is a reaction centre?

Answer 9

• part of photosystem where energy from light is funneled
• contains a pair of chlorophyll a molecules; absorbs energy and emits electrons

Question 10

What wavelength of light do each photosystem absorb?

Answer 10

• photosystem 1: 700nm
• photosystem 2: 680nm

Question 11

What is an action spectrum?

Answer 11

• a graph showing the effect of different wavelengths of light on a process, e.g; the rate of photosynthesis

Question 12

What is an absorption spectrum?

Answer 12

• graph showing the absorbance of different wavelengths of light by a photosynthetic pigment
• more absorption = more photosynthesis

Question 13

What is photophosphorylation?

Answer 13

• production of ATP from light energy

Question 14

What is photolysis?

Answer 14

• splitting of water from light producing H+ ions

Question 15

What is photo activation?

Answer 15

• emission of an electron as a result of absorption of light energy by a photosystem

Question 16

What is cyclic photophosphorylation?

Answer 16

• production of ATP using energy from light involving only photosystem 1

Question 17

What is non-cyclic photophosphorylation?

Answer 17

• production of ATP from light energy involving both photosystems
• also produces reduced NADP

Question 18

What is oxygen-evolving complex?

Answer 18

• enzyme found in photosystem 2
• catalyses breakdown of water using energy from light
• H20 —-> 2H+ + 2e- + 1/2O2
• also know as water splitting complex

Question 19

Outline the process of the Calvin Cycle:

Answer 19

• Ribulose bisphosphate/RuBP (5C) combines with CO2 by the enzyme rubisco
• an unstable (6C) intermediate forms
• then converted to 2x glycerate 3-phosphate/GP (3C)
• 2x GP broken into 2x triose phosphate/TP (3C)
• 1x reduced NADP is oxidized and 2x ATP molecules used
• 5/6 TP used to generate RuBP
• 1/6 TP used to regenerate energy sources, e.g; hexose, fatty acids, acetyl CoA

Question 20

What is a limiting factor?

Answer 20

• when a process is affected by more than one factor
• the factor prevents any further increase in the rate of the process

Question 21

What are the limiting factors of photosynthesis?

Answer 21

• Light
• Temperature
• Carbon dioxide

other factors
- water
- photosynthetic pigments

Question 22

What are the functions and structure of a chloroplast?

Answer 22

thylakoid/grana
- site of light dependent reactions

thylakoid membrane
- large SA to absorb more light
- has pigments, photosystems, electron carriers, ATP synthase

stroma
- contains enzymes (rubisco)
- colourless so light can enter
- water as a reaction medium

DNA/ribosomes
- make chloroplast proteins

starch grains
- store glucose produced from photosynthesis

envelope
- compartmentalization