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Biology Unit 2 for CAPE Examinations Original material Cambridge University Press 2011 1

1 Answers to end-of-chapter questions

Multiple choice questions

1 B [1]

2 B [1]

3 C [1]

4 D [1]

5 D [1]

6 C [1]

7 B [1]

8

C[1]

9 A [1]

10 A [1]

Structured questions11 a i Factor which is least favourable/nearest its maximum value

Which limits the rate of reaction Any point [1] If factor is increased, it would speed up the process max [2]

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

b i Place light at a fixed distance from plant Plants give off O 2 in photosynthesis Bubbles of O 2 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. 15minutes

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 NaHCO 3 Add 0.01 M NaHCO 3 into pond water Repeat experiment above Repeat experiment with 0.02 M, 0.05 M, 0.07 M and 0.1 M NaHCO 3

34 points [2]12 points [1]

Any 8 points [4]67 points [3]45 points [2]12points [1]

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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 correct answer

c i A Light intensity: as light intensity increases, rate of photosynthesis increases

B Temperature: light is not limiting because rate does not increase as lightintensity increased; rate increased when temperature increased to 30 C even thoughconcentration of CO 2 was kept at 0.14%

ii Farmers can use their knowledge of these limiting factors to increase crop growth ingreenhouses

They may use artificial light so that photosynthesis can continue beyonddaylight hours, or in a higher-than-normal light intensity more of light-dependent reaction

The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide and heattoo. More CO 2 = 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 temperatureof the enzyme

12 a

Stroma: ATP stalk particle projects into stroma Thylakoid lumen: proton pumped into lumen space; high concentration of protons

present in lumen Any correct answer

Any 1 point [1]Max [2]

[3]

Each correct label [1]Max [2]

Reason (each) [1]Max [2]

Any 1 point [1]Max [2]

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b i 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

ii See diagram in a above

iii

c 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 Excited electrons boosted to a higher energy level Electrons lost from chlorophyll a in reaction centre

d A cytochrome [1]

e 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 +P i to form ATP

f 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

Any 2 points [1]

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

56 points [3]34 points [2]12 points [1]


Point 1[1]An other oint [1]

Each correct label [1]Max [2]

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13 a i Stroma [1]

ii Stage 1 Carbon dioxide fixation/carboxylation [1]Stage 2 Reduction [1]Stage 3 Protein synthesis [1]Stage 4 Regeneration [1]

iii Rubisco [1]

iv ATP [1] Reduced NADP/NADPH [1]

v

b No ATP and reduced NADP formed No fixation of CO 2 GP cannot be reduced to GALP No sugars and other organic molecules can be formed No respiration

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

Any 4 points [1]Max [4]

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Essay questions

14 a i

ii

iii

Drawing neat and clear [1]23 annotations [2]

1 annotation [1] No annotation but with

3 correct labels [1]Max [3]



3 correct labels [1]

Max [3]



3 correct labels [1]Any correct answer

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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 Photons of light collected by light-harvesting system. These light harvestingsystems form two photosystems, PSI and PSII

Light energy collected by pigments are passed along the pigment molecules to thereaction centre by resonance transfer

Light energy excites electrons in the reaction centre and these electrons pass to ahigher energy level

Electrons are lost from the chlorophyll a in the reaction centre and the chlorophylla 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 someother 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 waterCyclic 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 point accessory [1]

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

Any 7 points wellexplained [7]

Any 1 point from primary [1]

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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 15: carbon dioxide fixation/ carboxylation1. CO 2 fixed by RuBP, carbon dioxide acceptor. This molecule is a 5C sugar2. Carboxylation/fixation3. Enzyme is rubisco4. Unstable 6C intermediates5. Forms 2 molecules of GP (3C), an acid COOH

Steps 68: reduction of GP6. Forms TP/GALP/PGAL, an aldehyde (CHO) by reduction7. 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), TP8. Oxidised NADP and ADP and inorganic phosphate diffuse back (by facilitated diffusion)

into the grana for reformation in the light-dependent stage

Steps 911: regeneration of RuBP9. Most of TP used to regenerate RuBP

10 molecules of TP = 10 x 3C = 30 carbon atoms10. 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 synthesisTP 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 i Synthesis of complex organic material using carbon dioxide and water, and lightenergy (from sunlight) captured by light-absorbing pigments, such as chlorophyll andother accessory pigments Well explained [2]

ii 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]

Any 7 points wellexplained [8]

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b i Source of energy Excites electrons of chlorophyll a in reaction centre For the phosphorylation of ATP And production of reduced NADP Any 3 points [3]

ii Water is split, providing electrons to replace those lost from chlorophyll a in PSII

Water is split into H+

+ OH-

Hydroxyl ions provide electrons to stabilise chlorophyll a in PSII 4 OH - 4e - = 2H 2O + O 2 The two protons, H + are used to reduce NADP Oxygen is a by-product Any 3 points [3]

iii 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 funnelenergy 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 forreduction of NADP + to NADPH + H +

Light energy collected by pigments are passed along the pigment molecules tothe reaction centre by resonance transfer

Light energy excites electrons in the reaction centre and these electrons pass toa higher energy level

Electrons accepted by primary electron acceptor Then passes to electron carriers


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