u2 c1 Answers

1 Answers to end-of-chapter questions Multiple choice questions 1

B

[1]

2

B

[1]

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C

[1]

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D

[1]

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D

[1]

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C

[1]

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B

[1]

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C

[1]

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A

[1]

10 A

[1]

Structured questions 11 a i • Factor which is least favourable/nearest its maximum value • Which limits the rate of reaction • If factor is increased, it would speed up the process

ii

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• • • • • b

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Carbon dioxide concentration Light intensity Temperature Wavelength of light Mineral ions e.g. magnesium Water

Any point [1] max [2]

3–4 points [2] 1–2 points [1]

Place light at a fixed distance from plant Plants give off O2 in photosynthesis Bubbles of O2 from cut end of plant trapped in flared end capillary tube Bubbles drawn into capillary tube by syringe Length of bubble measured using scale after a fixed period of time e.g. 15 minutes Bubble drawn into syringe so that new bubbles can be pulled into capillary tube Repeat experiment to find average length of bubble Repeat above steps using varying concentration of NaHCO3 Any 8 points [4] Add 0.01 M NaHCO3 into pond water 6–7 points [3] Repeat experiment above 4–5 points [2] Repeat experiment with 0.02 M, 0.05 M, 0.07 M and 0.1 M NaHCO3 1–2points [1]

Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

1

c

ii

• Flatten fronds of Elodea against the central stem • Leave plant for some time to allow shoot to equilibrate to conditions before proceeding with expt. • Cut end of plant should fit into flared end of capillary tube to collect gas • Plant should remain upright to receive maximum light • Temperature of water should be kept constant e.g. 35 °C for each experiment • Ensure it is air and water tight – no leakage • Ensure capillary tube is completely filled with water/no airlocks Any 1 point [1] • Any correct answer Max [2]

i

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A – Light intensity: as light intensity increases, rate of photosynthesis increases

• B – Temperature: light is not limiting because rate does not increase as light intensity increased; rate increased when temperature increased to 30 °C even though [3] concentration of CO2 was kept at 0.14% ii

12

a

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Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses • They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity – more of lightdependent reaction • The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide and heat too. More CO2 = more fixation • An increase in temperature will ensure that enzyme-controlled reactions would proceed at a high rate but the temperature must not exceed the optimum temperature of the enzyme Any 1 point [1] Max [2]

•

Stroma: ATP stalk particle projects into stroma Each correct label [1] Thylakoid lumen: proton pumped into lumen space; high concentration of protons Max [2] present in lumen Reason (each) [1] Any correct answer Max [2]

Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

2

b

i

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• • • • • ii

Place where light-dependent reaction occurs/captures light Found mainly in thylakoids/grana/intergranal membranes Consists of chlorophyll a molecules and accessory pigments Forms a light harvesting cluster and a reaction centre Involved in excitation and transfer of electrons Any correct answer

Any 2 points [1] Each correct label [1] Max [2]

See diagram in a above

iii

Drawing neat/clear [1] Any 3 labels [1] c

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• •

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Light absorbed by antenna system of light harvesting system/complex/pigments Wavelengths absorbed are mainly red and blue light Light energy transferred by resonance to the primary pigment/chlorophyll a in reaction centre Light energy excites electrons of chlorophyll a 5–6 points [3] Excited electrons boosted to a higher energy level 3–4 points [2] 1–2 points [1] Electrons lost from chlorophyll a in reaction centre

d

A cytochrome

e

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• • • • • f

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[1]

Generates ATP synthesis by chemiosmosis Hydrogen ions pumped into lumen from stroma Concentration builds up in thylakoid lumen Electrochemical gradient develops/ proton motive force H+ ions diffuse through channel in ATP stalk particle Energy used to phosphorylate ADP +Pi to form ATP Non-cyclic Involves PSI and PSII ATP, reduced NADP and oxygen formed instead of ATP alone Electrons from photosystems used to reduce NADP Photolysis of water occurs Any correct answer

Biology Unit 2 for CAPE® Examinations

5–6 points [3] 3–4 points [2] 1–2 points [1]

Point 1[1] Any other point [1]

Original material © Cambridge University Press 2011

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13 a

i

Stroma

[1]

ii

Stage 1 – Carbon dioxide fixation/carboxylation Stage 2 – Reduction Stage 3 – Protein synthesis Stage 4 – Regeneration

[1] [1] [1] [1]

iii

Rubisco

[1]

iv

• ATP • Reduced NADP/NADPH

[1] [1]

v

For ATP (1 for each point) [2] For NADPH [1]

b

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No ATP and reduced NADP formed No fixation of CO2 GP cannot be reduced to GALP No sugars and other organic molecules can be formed No respiration

Biology Unit 2 for CAPE® Examinations

Any 4 points [1] Max [4]

Original material © Cambridge University Press 2011

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Essay questions 14 a

i

Drawing neat and clear [1] 2–3 annotations [2] 1 annotation [1] No annotation but with 3 correct labels [1] Max [3] ii

Drawing neat and clear [1] 2–3 annotations [2] 1 annotation [1] No annotation but with 3 correct labels [1] Max [3] iii

Drawing neat and clear [1] 2–3 annotations [2] 1 annotation [1] No annotation but with 3 correct labels [1] Any correct answer

Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

5

b

Photosynthetic pigment: • Light absorbing molecule • Located in the chloroplasts • Absorbs specific wavelengths of light • Different pigments – chlorophyll a, carotenoids • Used in the light-dependent stage of photosynthesis Primary pigment: • Primary pigments found in reaction centre of photosystem • Chlorophyll a • Absorbs wavelengths 700, 680 nm Accessory pigment: • Found in light harvesting antennae of photosystem • Absorbs wavelengths of light not absorbed by chlorophyll a • Carotenoids, chlorophyll b

15 a

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Any 1 point for pigment [1] Max [2]

Any 1 point from primary [1]

Any point accessory [1]

Photons of light collected by light-harvesting system. These light harvesting systems form two photosystems, PSI and PSII • Light energy collected by pigments are passed along the pigment molecules to the reaction centre by resonance transfer • Light energy excites electrons in the reaction centre and these electrons pass to a higher energy level • Electrons are lost from the chlorophyll a in the reaction centre and the chlorophyll a molecule is oxidised • Electrons flowing through the electron transport chains have two possible routes: non-cyclic and cyclic photophosphorylation Non-cyclic photophosphorylation • Process begins in PSII (P680) • Electrons from P680 pass along an electron transport chain (ETC) consisting of plastoquinone (PQ), complex of two cytochromes and some other proteins • These electrons end up in P700 (PSI) • Electron flow is exergonic and provides energy to pump protons from the stroma across the thylakoid membrane into the thylakoid space • A proton /H+ gradient is set up • Proton motive force occurs • Electrons flow through ATP stalk particles down a gradient • Formation of ATP with the use of ATP synthase –chemiosmotic generation • Since chlorophyll a in PSII is still oxidised, the electron hole must be filled for further reactions to occur • Reference to photolysis of water Cyclic photophosphorylation: • Used only for production of ATP • Electrons originate in PSI • Electrons flow from the primary electron acceptor to ETC to P700 • ATP synthesis by chemiosmosis Any 7 points well explained [7]

Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

6

b

Main points: • • •

Occurs in the stroma A series of enzyme catalysed reactions/temperature sensitive Does not depend directly on light but, instead, on the products of the light reactions: ATP and NADPH

Steps 1–5: carbon dioxide fixation/ carboxylation 1. CO2 fixed by RuBP, carbon dioxide acceptor. This molecule is a 5C sugar 2. Carboxylation/fixation 3. Enzyme is rubisco 4. Unstable 6C intermediates 5. Forms 2 molecules of GP (3C), an acid – COOH Steps 6–8: reduction of GP 6. Forms TP/GALP/PGAL, an aldehyde (CHO) by reduction 7. Using ATP which provides energy and reduced NADP from the light reaction to remove oxygen from acid group (COOH) of GP to form an aldehyde (CHO), TP 8. Oxidised NADP and ADP and inorganic phosphate diffuse back (by facilitated diffusion) into the grana for reformation in the light-dependent stage Steps 9–11: regeneration of RuBP 9. Most of TP used to regenerate RuBP 10 molecules of TP = 10 x 3C = 30 carbon atoms 10. Rearrangement of carbon to form pentose sugars (30 carbon atoms form 6 RuMP – ribulose monophosphate) 11. ATP required for the phosphorylation of RuMP to RuBP by adding a phosphate group to RuMP Steps 12: product synthesis TP used in product synthesis to form lipids, amino acids, hexose sugars, starches, DNA, RNA, nucleic acids, chlorophyll etc. The hexose sugars/ glucose may be respired immediately or stored as starch until required 16 a

Any 7 points well explained [8]

i

Synthesis of complex organic material using carbon dioxide and water, and light energy (from sunlight) captured by light-absorbing pigments, such as chlorophyll and other accessory pigments Well explained [2]

ii

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Photosynthesis has two main stages – light-dependent and light-independent Photolysis of water not shown ATP and reduced NADP not shown Reactions of the Calvin Cycle not shown Any correct answer Any 4 points [4]

Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

7

b

i

•

• • • ii

Any 3 points [3]

•

Water is split, providing electrons to replace those lost from chlorophyll a in PSII Water is split into H+ + OHHydroxyl ions provide electrons to stabilise chlorophyll a in PSII 4 OH- − 4e- = 2H2O + O2 The two protons, H+ are used to reduce NADP Oxygen is a by-product Any 3 points [3]

•

Used in light harvesting in photosynthesis Photons of light collected by light harvesting system. These light harvesting systems form two photosystems, PSI and PSII PSI is located in the intergranal membrane and PSII in the grana Each photosystem consists of a reaction centre containing chlorophyll a and a region of several hundred antenna/accessory pigments molecules that funnel energy into chlorophyll a Accessory pigments/carotenoids surround the reaction centre and absorb wavelengths of light not absorbed by the primary pigments/chlorophyll a. They transfer energy to the primary pigments Two photosystems can raise the electrons to a higher energy level for reduction of NADP+ to NADPH + H+ Light energy collected by pigments are passed along the pigment molecules to the reaction centre by resonance transfer Light energy excites electrons in the reaction centre and these electrons pass to a higher energy level 6–7 points [3] Electrons accepted by primary electron acceptor 4–5 points [2] Then passes to electron carriers 1–2 points [1]

• • • • • iii

Source of energy Excites electrons of chlorophyll a in reaction centre For the phosphorylation of ATP And production of reduced NADP

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Biology Unit 2 for CAPE® Examinations

Original material © Cambridge University Press 2011

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