answers to biology paper 2 stpm trial examination 2010~pahang

964/2

PEPERIKSAAN PERCUBAAN SIJIL TINGGI PERSEKOLAHAN MALAYSIA

NEGERI PAHANG DARUL MAKMUR2010

BIOLOGYPAPER 2

MARKING SCHEME

CONFIDENTIAL* 2

1(a) A : Deoxyribonucleic acid / DNA

B : Nucleotides

C: messenger RNA / mRNA

D: polypeptide

E: RNA polymerase

F: ribosome

1

1

1

1

1

1

6

1(b)

Nucleus

ribosomes

1

1 2

1 ( c ) Aspect Transcription Translation

1

1

1

Any 2

End product mRNA polypeptide

Enzyme RNA polymeraseAminoacyl - tRNA synthetase

TemplateCistron / gene / genetic code on transcribing strand of DNA

Codons on mRNA

TOTAL 10

964/2This Question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL*

CONFIDENTIAL* 3

2 ( a) Light energy ( of wavelength 700nm ) is absorbed by antenna pigments ( of photosystem 1/ P700) and transferred to the reaction centre ( of photosystem 1 / P 700)

High energy electrons are released

1

1 2

2(b) Site of photosystem I and photosystem II/ photosynthetic pigments

High energy electrons pass along electron carriers

Protons / H+ ions pumped into thylakoid space

Chemiosmotic synthesis of ATP

1

1

1

1 Any 3

2(c ) Aspect Cyclic

photophosphorylation

Non- cyclic

photophosphorylation

1

1

1

1

1 Any 3

photosystem Only photosystem I involved

Photosystem I and II are involved

Electron flow cyclic Non -cyclic

First electron donor

Photosystem 1 Water

Last electron acceptor

Photosystem I NADP+

Products ATP ATP, NADPH and O2

2( d ) Both use the electron transport system

Proton gradient created in inter - membrane space

Chemiosmotic synthesis of ATP

1

1

1 Any 2

TOTAL 10


CONFIDENTIAL* 4

3 (a) A : Capillaries / glomerular capillaries

B: Bowman’s capsule

C:podocytes

1

1

1 3

3(b) Diameter of the afferent arteriole is larger than the diameter of the efferent arteriole.

High hydrostatic pressure in the glomerulus

1

1 2

3( c )Plasma contains large protein molecules that are not found in the glomerular filtrate.

These molecules are too large to pass through the basement membrane of the glomerular capillaries

1

1

2

3 ( d )Tightly packed cells increases the rate of reabsorption

Numerous microvilli that increase the surface area for reabsorption

Numerous mitochondria to provide ATP/ energy for active uptake of substances

1

1

1

3

TOTAL 10


CONFIDENTIAL* 5

4(a) RRPP , RRPp, RrPP, RrPp 1 / 0

4(b) Parents ( P ): Phenotypes Rose comb x pea comb

Genotype RRpp x rrPP

Gametes Rp x rP

F1 offspring: Genotype RrPp

Phenotype Walnut comb

Interbreeding of F1: RrPp x RrPp

F1 Gametes RP Rp rP rp RP Rp rP rp

F2 generation

Gametes RP Rp rP rp

RPRRPP

walnut

RRPp

walnut

RrPP

walnut

RrPp

walnut

RpRRPp

walnut

RRpp

rose

RrPp

walnut

Rrpp

rose

rPRrPP

walnut

RrPp

walnut

rrPP

pea

rrPp

pea

rpRrPp

walnut

Rrpp

rose

rrPp

pea

rrpp

single

F2 phenotype ratio: 9 walnut : 3 rose : 3 pea : 1 single comb comb comb comb

1

1

1

1

1

1

1

7

4 (c ) RRPP x RRpp RRPP x Rrpp

11

2

TOTAL 10


CONFIDENTIAL* 6

QUESTIONNUMBER

ANSWER MARKS

5 ( a )

Induced fit hypothesis / lock & key hypothesis 1

Enzyme with a flexible active site / enzyme has a rigid active site

1

Enzyme molecules collide with substrate molecules 1

Substrate binds to the active site of enzyme 1

Enzyme changes shape slightly to enclose substrate in a precise fit / substrate fits exactly into the active site of the enzyme

1

Enzyme –substrate complex formed 1

Stressing & distortion of bonds of the substrate 1

Bonds break & new bonds are formed 1

Activation energy reduced 1

Substrate converted into products 1

Products are released from the enzyme 1

Enzyme can be reused 1

Rate of reaction increases 1

*Diagram showing enzyme & substrate molecule, enzyme- substrate complex, enzyme & products // sketch graph showing reduction of activation energy

*1

Maximum [ any 7points + *1 mark for diagram/sketch graph ]

Accept either induced fit hypothesis or lock & key hypothesis

8


CONFIDENTIAL* 7

QUESTIONNUMBER

ANSWER MARKS

5 ( b )

Competitive inhibitor has similar/ same shape to the natural substrate

1

Competitive inhibitor competes with substrate for the active site on the enzyme

1

When competitive inhibitor combines with enzyme, no products are formed

1

When natural substrate combines with enzyme, enzyme-substrate complex formed & subsequently products are formed

1

Vmax has the same value 1

Km increases 1

Example: malonate competes with succinate for the active site on the enzyme, succinate dehydrogenase

1

Effect of competitive inhibitors can be reduced by increasing the substrate concentration.

1

*Sketch graph of V vs [S] // Lineweaver –Burk plot of

1/V vs 1/ [S]

*1

Maximum [ any 6 points + *1 mark for sketch graph ] 7

QUESTION ANSWER MARKS964/2This Question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL*

CONFIDENTIAL* 8

NUMBER

6 ( a )

Krantz anatomy // Vascular bundle surrounded by 2 layers of cells , columnar mesophyll palisade cells and bundle sheath cells.

1

In mesophyll cells 1

Carbon dioxide combines with phosphoenolpyruvate to form oxaloacetate / C4 compound

1

Using the enzyme phosphoenolpyruvate carboxylase 1

PEP carboxylase has a high affinity for CO2 1

Oxaloacetate is reduced to malate using NADPH 1

Malate is shunted through the plasmodesmata into the bundle sheath cells

1

Malate is oxidized to pyruvate & carbon dioxide using NADP+ 1

CO2 concentration in stroma of chloroplast is increased 1

CO2 enters the Calvin cycle producing organic molecules 1

Pyruvate diffuses into mesophyll cells 1

Pyruvate is phosphorylated to regenerate phosphoenolpyruvate

1

Energy / ATP used 1

Example: maize/ sugar cane 1

*Labelled diagram of Hatch Slack pathway *1

Maximum [any 12 points + *1 mark for diagram] 13

6 ( b )

High CO2 concentration inhibits photorespiration 1

increases the rate of photosynthesis 1

Enzyme PEP carboxylase has a high affinity for CO2 1

Maximum ( any 2 points ) 2


CONFIDENTIAL* 9

QUESTIONNUMBER

ANSWER MARKS

7 (a ) In skeletal muscles, glycogen store is converted to glucose 1

Glucose is converted to pyruvate during glycolysis 1

During anaerobic respiration, pyruvate is reduced to lactate by NADH + H+

1

Lactate is transported by the blood from the muscles to the liver

1

In the hepatocytes, lactate is oxidized to pyruvate using NAD+ 1

Pyruvate is converted to glucose -6 –phosphate and then to glucose

1

Glucose is converted to glycogen & stored in the liver 1

Glucose can be transported back to the muscles & used for cellular respiration

1

Importance:

prevents an increase in lactic acid / H+ concentration in muscles

1

Prevents a decrease in pH which will affect most metabolic reactions that are catalysed by enzymes

1

Reduces muscle fatigue 1

Maximum [ any 6 points on Cori cycle + 1 point for importance] 7


CONFIDENTIAL* 10

QUESTIONNUMBER

ANSWER MARKS

7 (b ) Occurs in the liver 1

Excess amino acids undergo deamination 1

Amino group is converted to ammonia 1

From cellular respiration, CO2 is produced 1

CO2 combines with NH3 , in the presence of water & ATP to form carbomyl phosphate

1

Carbomyl phosphate combines with ornithine to form citrulline 1

Citrulline combines with asparate, NH3 and ATP to form

argininophosphate

1

Argininophosphate cleaves to form arginine and fumarate 1

Arginine is hydrolysed to form urea & ornithine 1

Urea is transported by the blood to the kidneys to be excreted 1

Importance:

Ammonia is toxic and must be excreted 1

Prevents an increase in CO2 concentration/ H+ concentration / decrease in pH

1

so that optimal conditions maintained for metabolic reactions / homeostasis

1

Maximum [ any 7 points on the Ornithine cycle + any 1 mark for importance ]

8

QUESTION ANSWER MARKS


CONFIDENTIAL* 11

NUMBER8 ( a ) Maintenance of a constant internal environment 1

Internal environment refers to the tissue fluid that surrounds the cells

1

Maintain optimal physical & chemical conditions for metabolic reactions

1

Through negative feedback mechanisms 1


8 ( b ) Activation of the cyclic AMP system 1

Non- steroid hormone is not soluble in lipid and cannot diffuse through the plasma membrane

1

Non- steroid hormone acts as the first messenger 1

Hormone combines with receptor at the cell surface membrane, leading to a conformational change in the receptor

1

Hormone – receptor complex binds to the G protein . 1

G protein binds with GTP 1

G protein stimulates adenylyl cyclase . 1

Adenylyl cyclase converts ATP to cyclic AMP 1

c AMP acts as the second messenger 1

Cascade effect occurs 1

c AMP catalyses the conversion of inactive protein kinase to active protein kinase

1

Active protein kinase catalyses the conversion inactive phosphorylase to active phosphorylase

1

Active phosphorylase catalyses the conversion of glycogen to glucose

1

Fast manifestation 1

Effect last for a short duration 1

Example: epinephrine / adrenaline 1

*Diagram *1

Maximum : [ any 12 points + *1 mark for diagram ] 13


CONFIDENTIAL* 12

QUESTIONNUMBER

ANSWER MARKS

9 ( a ) High reproductive potential 1

leading to overproduction of individuals of a species 1

Struggle for existence 1

leading to competition 1

Variation exists within a population 1

Survival of the fittest by natural selection 1

Best adapted survive, reproduce & pass on the genes to the next generation

1

After many years, new species is formed from pre-existing species via natural selection

1

Maximum: any 5 points 5


CONFIDENTIAL* 13

QUESTIONNUMBER

ANSWER MARKS

9 ( b ) ( i )

( ii )

( iii )

Fossil record of horses :

increase in body size 1

Number of digits reduced to 1 on each foot 1

Thicker & stronger bones 1

Teeth modified for grazing 1

Sub -Total 4

Pentadactyl limb:

Homologous structures

1

Modified structures that share a basic pattern as the common ancestor but may have different forms & functions

1

Occupy different ecological niches / example 1

Sub -Total 3

Comparative embryology

Early embryological development of vertebrates reflects evolutionary origins / Ontogeny recapitulates phylogeny

1

Adult stages are different but show certain structural similarities in embryonic stages

1

Example: fish-like stages with pharyngeal gill slits in the

embryological development of fish, chicken, man

1

Sub -Total 3

Total: 10


CONFIDENTIAL* 14

QUESTIONNUMBER

ANSWER MARKS

10 ( a ) Development that can continue indefinitely 2 / 0

Uses renewable resources

Minimizes the use of non-renewable resources

Conservation of the environment

Maximum [ all 4 points included ] 2

10 ( b ) ( i ) Replanting programmes : replanting the trees in areas that have been logged

1

Stop traditional ‘slash & burn’ forest clearance in shifting

cultivation

1

Limit licenses for logging activities 1

Enforcement of laws and surveillance to prevent illegal logging 1

Creating more forest reserves to avoid the complete destruction of forests

1

Selective logging : control the trees that are logged in terms of diameter and species

1

Recycling of paper helps to reduce the number of trees being cut down

1

Educational Awareness programmes 1

Maximum : [ any 5 points ] 5

10b ( ii ) Crop rotation to prevent depletion of nutrients 1

Prudent use of herbicides, pesticides, 1

encourage use of biological control 1

Soil improvement method – application of organic fertilizers 1

Irrigation of water deficient soils 1

Contour farming on hill slopes 1



CONFIDENTIAL* 15

10b ( iii) Limiting areas for fishing 1

Permissible mesh size of nets 1

Introduce closed seasons so that fish can reproduce & fish population can be maintained

1

Stop illegal fishing methods eg: fish bombing 1

Maximum [ any 3 points ] 3


CONFIDENTIAL* 16


answers to biology paper 2 stpm trial examination 2010~pahang

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