2014 PS1 Trial Sk Answers 1

7/24/2019 2014 PS1 Trial Sk Answers 1

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SMK SERI KELEDANG

Trial Examination Semester 1 STPM 2015

Marking scheme

Answers of questions inSection A [15marks]

1. A 2. C 3. A 4. D 5. B

6. D 7. A 8. B 9. C 10. D

11. A 12. C 13. D 14. B 15. D

Answers of questions inSection B [15marks]

16. (a) Companion cell , B: Sieve tube element 2

(b) Structure: The cell is living cell, with thin cellulose cell walls and protoplasm. 1

It consist of sieve elements joined together to form a long tube. 1

Their end walls are perforated forming sieve plates with sieve pores. 1

Function: It allows cytoplasmic connections between the sieve elements and the

flow of liquid from one sieve element to the next element. 1

(c) (i) Mitochondria [if wrong, no mark is given for function] 1

-Provide energy to move sugars and amino acid into the sieve elements 1

(ii) Cell fractionation and differentiation centrifugation method. 1Total(max) : 8 m

17 (a) I: NADH dehydrogenase / Flavoprotein, IV: Cytochrome oxidase (aa3). 2

(b) Electron transport chain / electron transport system. 1

(c)Oxygen is the final electron acceptor, it combines with hydrogen ions to form

water. 1

(d) (i) Chemiosmosis. 1

(ii) The electrochemical proton gradient forces hydrogen ions to diffuse through the

ATP synthase complex, 1

down its electrochemical gradient across the membrane // This potential energy is

used to synthesis ATP. 1

Total(max) : 7 m

Any

two


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Answers of questions inSection C [30marks]

18. a) Explain the roles of proteins in the transport of substances into a living cell. [9 marks]

Answers Marks

P1 Proteins transport substances that cannot pass through thephospholipid bilayers.

P2 Some transmembrane proteins form channels (some are channelproteins).

P3 These channel proteins allow ions or solutes to move across themembrane by facilitated diffusion.

P4 The hydrophilic ion channels allow diffusion of charged ions such asK

+, Na

+, Ca

2+, Cl

-and HCO3

-down their concentration gradient.

P5 Some of the protein channels can open or close, they are called gatedchannels, eg. voltage-gated channels and ligand-gated channels.

P6 Certain proteins form aquaporins in the plasma membrane to increase

the rate of diffusion of water down the water potential gradient.P7 Some other proteins are carrier proteins which transport smallhydrophilic organic molecules like glucose and amino acids throughthe plasma membrane.

P8 Carrier proteins alternate between two conformations to move ions orsolutes across the membrane by facilitated diffusion.

P9 Binding of glucose or amino acid to the carrier protein moleculecauses the carrier protein to change its shape, so glucose or aminoacid molecule is released into the cell.

P10 The channel proteins and the carrier proteins mentioned abovetransport substances down the concentration gradient.

P11 Some proteins act as pump proteins/ carrier proteins for activetransport of ions or solutes against a concentration gradient.

P12 ATP is required in the activity of pump proteins/ carrier proteins inactive transport/ Hydrolysis of ATP and the binding of Pi to theprotein pump changes the protein conformation so substances aretransport across the membrane against the concentration gradient.

P13 Proteins involved in active transport include uniport carriers (whichcarry a single ion or molecule in a single direction), symport carriers(which carry two substances in the same direction) and antiportcarriers (which carry two substances in opposite direction).

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Total(max): 9 m

18. b) Explain the concept of water potential and the importance of water potential values in

determining the direction of water movement at the plant cell membrane. [6 marks]

Answers MarksP1 Water potential is the tendency of a solution to lose water// tendency of

water molecules move out from solution.P2 In pure water, the water molecules have a high free kinetic energy/

high tendency to move very freely.P3 Addition of solutes decreases the water potential // dilute solutions

have lower water potential than pure water.P4 Water potential of a solution can be increased by the application of

Pressure.

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P5 Water potential of pure water (at atmospheric pressure) is 0 kPa.P6 Water potential of solutions have negative values // The greater the

concentration of solutes, the more negative the water potential.P7 Water moves from a region with higher water potential to one with

lower water potential (more negative).P8 Direction of water movement at the plant cell membrane depends on

the water potential of the plant cell and the water potential of itssurrounding.

P9 When the water potential of the surrounding is more negative than thewater potential of the plant cell, water moves out from the cell to thesurrounding(cell undergoes plasmolysis) // When the water potential ofthe surrounding is less negative than the water potential of the plant cell,water moves from the surrounding into the plant cell(cell becomes turgid).

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Total(max): 6 m

19. a) With a suitable example, explain in detailed about three types of cofactors. [9 marks]

i) Prosthetic Groups [3 m]

A prosthetic group is a non-protein organic molecule that binds tightly on apermanent basis to the protein part of the enzyme (apoenzyme). 1

The prosthetic group is involved in the catalytic function of the enzyme. 1

Haem is present in the enzyme catalase which catalyses hydrogen peroxide intooxygen and water. // Haem is found in the prosthetic group of cytochromes whichare electron carriers. It takes part in oxidation-reduction reactions. 1

Maximum: 3 marksii) Coenzymes [3 m]

Coenzymes are small, non-protein organic molecules. 1 They bind loosely and temporarily to the active site of the enzyme. 1

The coenzymes readily detach and help to transfer chemical group, atoms orelectrons from one enzyme to another. 1

Many coenzymes are derivatives of vitamins especially group B vitamins, NAD(nicotinamide adenine dinucleotide) for example is formed from niacin // Otherexamples include NADP and CoA. 1

It is a coenzyme for a number of dehydrogenase enzymes and acts as ahydrogen acceptor. 1

Succinate dehydrogenaseSuccinate + NAD+ --> Fumarate + NADH + H+

(coenzyme)Maximum: 3 marks

iii) Enzyme Activators [3 m]

Activators are inorganic ions such as Ca2+, Zn2+, Mg2+, Fe2+and Cl-. 1

They may attach temporarily to the enzyme and change its active site to make theshape more suitable for a reaction to take place. 1

The ion may also bind the enzyme and substrate together. 1

Calcium ions are needed to activate thrombokinase which converts prothrombin tothrombin in blood clotting. // Chloride ions increase salivary amylase activity. 1

Maximum: 3 marks

Total(max) : 9 m


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19. b) Tabulating the differences between cellular respiration in animal cells under sufficient

oxygen supply condition and condition with sufficient oxygen but in presence of high partial

pressure of carbon monoxide. [6 marks]

Condition with sufficient oxygen With sufficient oxygen and highpartial pressure of carbon monoxide

Marks

P1 Aerobic respiration occurs (incytoplasm and mitochondria).

Anaerobic respiration occurs (only incytoplasm).

1/0

P2 38 molecules of ATP areproduced from one glucosemolecule.

2 molecules of ATP are producedfrom one glucose molecule.

1/0

P3 Complete oxidation of glucosecan occur.

Incomplete oxidation of glucoseoccurs.

1/0

P4 The respiration involvesglycolysis, link reaction, Krebscycle and electron transportchain.

The respiration only involvesglycolysis. Link reaction, Krebs cycleand the electron transport chain arenot involved.

1/0

P5 Carbon dioxide and water areproduced.

lactate are produced // no carbondioxide and water are produced.

1/0

P6 Respiration in this condition isnormal for the animal cells tocarry out cell activities.

Prolonged respiration in thiscondition causes damage to thecentral nervous system and heartand even death.

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Total(max): 6 m


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20. a) Explain why C4plant is more efficient in photosynthesis compared to C3pant.

. [9 marks]

Answers Marks

Formation of ATP during photosynthesis [max: 6 m]P1 C4plant (leaf) has Krantz anatomy that is not found in C3plant. //concentric arrangement of 2 layer of cells, mesophyll cells and bundle sheathcell around vascular bundle in C4plant(leaf), but not in C3plant.P2 PEP carboxylase (in the chloroplast of mesophyll cell) has higher affinityfor CO2compared to RUBP carboxylase/Rubisco in C3 plant. // PEPcarboxylase in C4plant has lower Km than that of Ribisco in C3plant.PEPcarboxylase.P3 PEP carboxylase (in mesophyll cell) enable very efficient absorption ofcarbon dioxide even at low carbon dioxide concentrations.P4 PEP carboxylase fix atmospheric CO2forming 4 carboncompound/oxaloacetate in mesophyll cell that does not occurs in C3plant.

P5 this concentrates CO2in bundle sheath cell (where Calvin cycle occurs).P6 reduction/decarboxylation of malate into pyruvate releases/produces ahigher level of CO2 concentration in CO2 fixation (in bundle sheath cell.)P7 this reduced photorespiration in C4plant that often occurs in C3plant.P8 CO2 fixation occurs twice at same time (spatial CO2 fixation) in 24hours/all the time.P9 although only fewer and smaller chloroplast in mesophyll cells, but thegranum is large/active granal activities(to produce ATP and NADH).P10 there are many/abundant chloroplasts in bundle sheath cell with highgranal activities to produce ATP and NADPH (that needed in Calvin cycle/foodproduction).

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Total(max): 9 m

20. b) Explain the importance of ATP and NADPH in photosynthesis. [6 marks]

Answers Marks

P1 ATP and NADPH are used in the light-independent reactions/ Calvincycle (in the stroma).

P2 - ATP is important to reduce carbon dioxide into carbohydrate.P3 In Calvin cycle, ATP donates a phosphate to glycerate 3-phosphate to

form glycerate 1,3-bisphosphate.P4 NADPH donates hydrogen atoms to glycerate 1,3-bisphosphate in the

formation of glyceraldehydes 3-phosphate.P5 Glyceraldehyde 3-phosphate (triose phosphate) are used for

biosynthesis of organic molecules such as carbohydrates, proteins andlipids.

P6 ATP is also needed in the regeneration of ribulose bisphosphate(RuBP), the carbon-acceptor.

P7 ATP donates a phosphate to ribulose phosphate to form ribuloseBisphosphate.

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Total(max): 6 m

2014 PS1 Trial Sk Answers 1

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