biology trial 2012 STAR.pdf

1

964/1 TRIAL EXAMINATION

2012

BIOLOGY

PAPER 1

(One hour and forty five-minutes)

SEKOLAH MENENGAH KEBANGSAAN

TUNKU ABDUL RAHMAN

TRIAL EXAMINATION

Instructions to candidates:

DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO.

There are fifty questions in this paper. For each question, four suggested answers are

given. Choose one correct answer and indicate it on multiple-choice answer sheet

provided.

Read the instructions on the multiple-choice answer sheet very carefully.

Answer all questions. Marks will not be deducted for wrong answers.

This question paper consists of 11 printed pages

© SMKTAR

…………………….. ………………………….

Pn. Vickneswary VN En. Chong Kean Choon

(Guru Penyedia Soalan & ( Penolong Kanan Ketua Bidang Sains & Matematik) Tingkatan Enam)

2

1 Which one of the following compounds is a carbohydrate?

A C3H8O3

B C5H10O5

C C6H12O2

D CH3CH2CH2COOH

2 Both DNA and RNA

A Contain phosphate groups

B Are single stranded molecules

C Have the same five carbon sugar

D Contain the same four nucleotides

3 The concentration of potassium ions in a red blood cell is much higher than it is in the surrounding

blood plasma, yet potassium ions continue to move into the cell. The process by which potassium

ions move into the cell is called

A Osmosis

B Active transport

C Simple diffusion

D Facillitated diffusion

4 Membranes are found as part of all of the following subcellular structures except the

A Ribosomes

B Mitochondria

C Golgi apparatus

D Endoplasmic reticulum

5 The conformation of a protein molecule depends on several different types of bonds and group

interactions. Which of these remain intact when a protein is denatured?

A Ionic bonds

B Peptide bonds

C Hydrogen bonds

D Hydrophobic interactions

3

6 Which one of the following statements is true

A An enzyme acts only once and is then destroyed

B The activity of enzymes is independent of temperature and pH

C Enzymes provide the activation energy necessary to initiate a reaction

D Enzymes lose some or all of their normal activity if their three dimensional structure is

disrupted

7 A parent molecule of DNA containing only radioactive nitrogen 15N is placed in an environment

containing only 14N. After four replications, how many DNA molecules would still contain some 15N?

A 2

B 4

C 6

D 8

8 The “first step” in photosynthesis is the

A Formation of ATP

B Addition of CO2 to a five carbon sugar

C Splitting of water into H and O components

D Energizing of an electron of chlorophyll by a photon of light

9 Which of the following occurs in noncyclic but not in cyclic photophosphorylation?

A Flow of electrons

B Synthesis of reduced NADP

C Absorption of light by chlorophyll

D Synthesis of ATP through a H+ ion gradient

10 In the dark reactions of photosynthesis

A Water is split

B Oxygen is produces

C ATP is synthesized.

D Phosphoglyceraldehyde is synthesized

4

11 When a muscle cell is metabolizing glucose in the complete absence of molecular oxygen, which

one of the following substances is not produced?

A Pyruvic acid

B Acetyl coenzyme A

C Phosphoglyceraldehyde

D Adenosine triphosphate

12 Which one of the following statements concerning glycolysis is false?

A Phosphorylation occurs during the process

B Oxygen is not required for the process to occur

C The end products are carbon dioxide and water

D It proceeds in a step-by-step series of chemical reactions, each catalyzed by an enzyme

13 If two acetyl coenzyme A molecules are fed into the Krebs cycle, how many reduced NAD

molecules are produced?

A 3

B 6

C 12

D 32

14 Autotrophic organisms

A Must digest their nutrients before taking them into the cell

B Require complex organic molecules already synthesized by other organisms

C Synthesize their own organic materials from inorganic materials in the environment

D Require no external energy source since they synthesize their own high energy compounds

15 When the guard cells are turgid

A absisic acid is present in cells

B the osmotic pressure in cells is high

C water has diffused out of cell by osmosis

D cells have a relatively low concentration of potassium ions

16 Which of the following features do all gas exchange systems have in common?

A They are exposed to air

B Exchange surfaces are moist

C They are enclosed in a special chamber

D They are maintained at a constant temperature

5

17 Which of the following mechanisms could raise water to the greatest height in the xylem vessels of

a tall tree?

A Mass flow

B Root pressure

C Cytoplasmic streamimg

D Transpirational pull and cohesion

18 The driving force that moves blood in veins back to the heart is

A Active transport

B Beating of the heart

C Closing of one-way valves

D Skeletal muscle contraction

19 The production of urine by the cells of the mammalian kidney requires energy, which is used mainly

to

A Actively pump water into the urine

B Filter the blood into Bowman’s capsule

C Actively reabsorb solutes from the urine

D Actively reabsorb water water from the loop of Henle

20 The vertebrate liver carries out all of the following functions except

A Secretion of bile

B Metabolism of amino acids

C Removal of urea from the blood

D Regulation of blood glucose level

21 The term ‘homeostasis’ is best defined as

A Adaptation to a harsh environment

B Maintenance of constant body temperature

C The maintenance of a constant internal environment

D The maintenance of constant salt concentration in the body

6

22 Which of the following statements most accurately describes what is happening during nerve

repolarization.

A K+ ions are flowing into the cell

B Na+ ions are flowing into the cell

C K+ ions are flowing out of the cell

D Na+ ions are flowing out of the cell

23 Which one of the following statements is false concerning the axon in a resting stage?

A The membrane is relatively impermeable to sodium ion

B Potassium ions are in higher concentration inside the axon than outside

C The membrane has a positive charge on the outside and a negative charge on the inside

D The membrane is highly permeable to large negatively charged organic ions and allows them

tom leak out

24 All of the following are functions of the sympathetic nervous system except

A Erection of hairs on the skin

B Dilation of intestinal capillaries

C Acceleration of the rate of heartbeat

D Decrease of peristalsis of the digestive tract

25 Plant hormones, in contrast to most animal hormones

A Are required in large amounts

B Are not produced in specialized glands

C Do not coordinate activities of the organism

D Always stimulate and never inhibit various processes

26 A polypeptide hormone affects muscle but not liver cells. The most likely reason is that

A Liver cells do not make cAMP

B Liver cells do not contain enzymes

C Liver cells lack a receptor for that hormone

D Liver cells do not have adenylate cyclase in their plasma membrane

27 The memory cells of the immune system

A Are produced by the thymus

B Produce circulating antibodies

C Are nonspecific, each reacts to a variety of antigens

D Are responsible for response upon second exposure to an antigen

7

28 A clone of activated B lymphocytes may give rise to all of the following except

A T cells

B Plasma cells

C Memory cells

D Circulating antibodies

29 In plants, the gametophyte generation is produced by

A Mitosis of sporophyte cells

B Haploid spores that divide by mitosis

C The formation of four gametes by meiosis

D Fertilization of an egg cell by a sperm cell

30 The endosperm of a flowering plant is triploid because

A Two male nuclei fuse with one female nucleus

B Two polar nuclei fuse with one sperm nucleus

C One normal gamete fuse with a diploid gamete

D Two synergid nuclei fuse with one sperm nucleus

31 In most embryos, the archenteron

A Is filled with mesoderm

B Is formed by invagination

C Eventually forms the neural tube

D Usually disappears during gastrulation

32 Which one of the following sets of structures is derived primarily from mesoderm?

A Eye, brain, spinal cord

B Blood, skeleton, muscle

C Epidermis, hair, fingernails

D Lining of gut, lining of lungs, liver

33 Identify the organ in an insect that produces the juvenile hormone.

A Thoraxic gland

B Corpus allatum gland

C Neurosecretory cells

D Corpus cardiacum gland

8

34 Select the correct statement regarding the growth of human brain, sex organs and the whole body.

A The organs' growth is allometric.

B The organs' growth is isometric.

C Growth of every organ is unlimited.

D Every organ growth has a sigmoid growth curve.

35 Cystic fibrosis is inherited as a simple recessive. Suppose a woman who carries the trait marries a

normal man who does not carry it. What percent of their children would be expected to have the

disease?

A 0%

B 25%

C 33%

D 50%

36 Among white human beings, when individuals with straight hair mate with those with curly hair,

wavy-haired children are produced. If two individuals with wavy hair mate, what phenotypes and

ratios would you predict among their offspring?

A 3 curly: 1 wavy

B 3 wavy: 1 straight

C 1 curly: 1 wavy: 1 straight

D 1 straight: 1 curly: 2 wavy

37 Knowledge of the blood-type genotypes of a certain couple leads us to say that if they were to have

many children, the ratios of the children’s blood types would be expected to approximate ½ type A

and ½ type B. It follows that the blood types of the couple are

A AB and O

B AB and A

C AB and B

D AB and AB

38 The exchange of parts between nonhomologous chromosomes is called

A Duplication

B Polyploidy

C Transformation

D Translocation

9

39 Identify the sequence that is the most serious when the triplet code ATTGCC is changed.

A ATTGCA

B ATCGCC

C ATTTGCC

D ATTTCCCGCC

40 Identity the process that causes aneuploidy.

A Segregation

B Crossing over

C Recombination

D Non-disjunction

41 Calculate the gene frequency of the recessive allele in a population, if 6 babies out of 2400 born

suffer from a recessive disease of colon impasse?

A 0.5

B 0.05

C 0.25

D 0.40

42 Select the reason that most clearly explains why certain mutant genes cannot be eliminated from

the gene pool.

A mutant genes are recessive and are carried by heterozygous individuals.

B mutant genes have potential value for the survival of future generations.

C genetic drift causes the mutant genes to spread throughout a population.

D mutant genes are dominant and are carried both by homozygous and heterozygous

individuals

43 Identify the assumption based on which works the Hardy-Weinberg law.

A Small population, no mutation, random mating.

B Large population, no mutation, random mating.

C Large population, no mutation, non-random mating.

D Small population, mutation occurs, random mating.

10

44 In the lactose operon system in E.coli, the repressor is

A Lactose

B A protein

C A short length of DNA

D A product of a structural gene locus

45 The sugar lactose induces synthesis of the enzyme lactase. What happens when an E.coli cell runs

out of lactose?

A Repressor binds to the operator

B Repressor binds to the promoter

C RNA polymerase attaches to the promoter

D RNA polymerase attaches to the repressor

46 A plasmid is

A A virus that infects bacteria

B A portion of a bacteriophage

C A fragment of bacterial chromosome

D Self-replicating nonchromosomal circle of DNA

47

A genetic engineer prepares DNA fragments from two species and mixes them together. Two of the

many fragments are shown below. Which one of the following statements is correct?

--------------------------- TTCC--------------------------------

----------------------------------ATGC -------------------------------

A No sticky ends were produced

B The two fragments shown above will join by complementary base pairing

C The two fragments were prepared by two different restriction endonucleases

D A single restriction endonuclease was used to cut at different locations in the two types of

DNA

48 Two plants which belong to different families must also belong to different

A orders

B genus

C classes

D phylum

11

49 In which one of the following ways do viruses resemble cellular organisms? Viruses

A Divide by mitosis

B Can undergo mutation

C Exhibit aerobic respiration

D Have an extensive endoplasmic reticulum

50 Which one of the following is not typical of insects?

A Compound eyes

B Pincer like chelicerae

C One pair of antennae

D Body divided into a head, thorax and abdomen

12

ANSWER SCHEME

1 B 11 B 21` C 31 B 41 B 2 A 12 C 22 C 32 B 42 A 3 B 13 B 23 D 33 B 43 B 4 A 14 C 24 B 34 A 44 B 5 B 15 B 25 B 35 A 45 A 6 D 16 B 26 C 36 D 46 D 7 A 17 D 27 D 37 A 47 C 8 D 18 D 28 A 38 D 48 B 9 B 19 C 29 B 39 C 49 B 10 D 20 C 30 B 40 D 50 B

CONFIDENTIAL Name: …………………………………….

TRIAL 964/2 CONFIDENTIAL

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1

964/2 TRIAL EXAMINATION 2012 BIOLOGY

PAPER 2 (Two and a half hours)

SEKOLAH MENENGAH KEBANGSAAN

TUNKU ABDUL RAHMAN TRIAL EXAMINATION

Instructions to candidates:

Answer all the questions in Section A in the spaces

provided.

Answer any four questions from Section B. For this

section, write your answers on the answer sheets provided.

Begin each answer on a fresh sheet of paper. Answers should

be illustrated by large, clearly labeled diagrams wherever

suitable.

Answers may be written in either Malay or English.

Arrange your answers in numerical order and tie the answer sheets.

This question paper consists of 10 printed pages© SMKTAR

…………………….. ……………………

Pn. Vickneswary VN En. Chong Kean Choon

(Guru Penyedia Soalan) (Penolong Kanan Tingkatan 6)

For examiner’s use 12345678910

Total



2

2

Section A [40 marks]

Answer all the questions in this section.

1. The diagram below is of a plant cell as seen under an electron microscope.

(a) Name the structures A–D.

A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]

(b) State concisely how each of the following structures would be involved in the

process of protein synthesis.

Mitochondria

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



3

3

Ribosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Endoplasmic reticulum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Golgi body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [4]

(d) Name the carbohydrates in the cell above which are found:

(i) in the cell wall; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) as a storage compound in the cell; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (iii) as a component of ribosomes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]



4

4

2. Diagram shows the regular organization of thick and thin filaments in a striated

muscle.

a) i. State the theory used to describe muscle contraction.

.................................................................................................................

[1]

ii. State what happens to the following areas during muscle contraction

A band:

.............................................................................................................

H zone:

.............................................................................................................

I band:

.............................................................................................................

[2]

B



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5

b) The actin filament is made up of actin protein, tropomyosin and troponin,

whereas the myosin filaments are made up of myosin heads and tails.

Each named structure has a specific function during muscle contraction.

Explain the function of the following structures during muscle contraction

i. Calcium ions

..........................................................................................................

..........................................................................................................

..........................................................................................................

ii. Troponin

..........................................................................................................

..........................................................................................................

..........................................................................................................

iii. Tropomyosin

..........................................................................................................

..........................................................................................................

..........................................................................................................

iv. Myosin head

..........................................................................................................

..........................................................................................................

..........................................................................................................

[4]



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3. The diagram below shows an outline of the stages involved in aerobic respiration

(a) Name A, B, C and D.

A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[3]



7

7

(b) Identify all the steps involved in glycolysis by drawing a box around them on

the diagram.

[1]

(c) Precisely where do the Krebs cycle and the electron transport chain occur

in a mammalian cell?

Krebs cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electron transport chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]

(d) (i) Indicate, by writing a letter E on the diagram, where ATP is used in

respiration.

[1]

(ii) Indicate, by writing ATP on the diagram, the two stages, not including the

electron transport chain, where ATP is produced during respiration.

[1]

(iii) Indicate on the diagram, using the correct names, where other

respiratory substrates from the breakdown products of lipids enter the

aerobic respiration pathway.

[2]

(e) Describe what happens to pyruvate in anaerobic conditions in mammalian

cells.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . [3]



8

8

4. The diagram shows the body’s response to an invading pathogen.

Pathogen enters body

Pathogen invades cells and multiplies

It destroys different types of cells

Destroys pathogen

Has special receptors which attach to antigens

Special cells in the blood

Secrete antibodies

Destroys pathogen

Patient recovers

a) Suggest the type of pathogen described in the diagram. Explain your

choice.

………………………………………………………………………………………

………………………………………………………………………………………

……………………………………………………………………………………….

[2]

b) i. Name the special cells in the blood involved in this response.

………………………………………………………………………………………

[1]



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ii. Where else in the body would these cells be found?

………………………………………………………………………………………

[1]

iii. Name the two different types of cells which are produced by the

special cells in the blood.

1………………………………………………………..

2………………………………………………………..

[2]

c) Explain the importance of memory cells in the response to an infection.

………………………………………………………………………………………

………………………………………………………………………………………

………………………………………………………………………………………

………………………………………………………………………………………

[3]

d) Old people are offered vaccination against influenza. Suggest why a

different vaccine is given to these people each year.

………………………………………………………………………………………

………………………………………………………………………………………

………………………………………………………………………………………

………………………………………………………………………………………

[3]



10

10

Section B [60 marks]

Answer any four questions in this section

5. a) Differentiate between types of enzyme inhibitors.

[8]

b) Describe the role of DNA in protein synthesis.

[7]

6. a) Explain the countercurrent multiplier mechanism in the nephron.

[8]

b) Describe the adaptive features of xerophytic plants that enable them to live in

their habitat

[7]

7. a) With the aid of a diagram, describe the events that are involved in the

development of a fertilized egg upto an embryo with three germ layers.

[10]

b) Outline the role of hormones during complete metamorphosis of a butterfly.

[5]

8. a) Name the three main requirements for the germination of seeds and explain why

each is necessary.

[9]

b) Describe how food reserves are mobilised during germination.

[6]

9. a) Deletion of a base from a DNA molecule is usually more severe as compared to

substitution of a base with another base. Explain this statement.

[5]

b) Sickle cell anaemia and Down’s Syndrome are caused by mutation. For each

disorder explain the type of mutation involved.

[10]

10. Describe the steps in gene cloning by using plasmid as a vector.

[15]



11

11

ANSWER SCHEME

1.a) A- cell wall

B- chloroplast

C- pit

D- vacuole/ cell sap

b)

Mitochondria

- generates energy/ ATP

- used during

translation to synthesise mRNA

transcription to synthesise protein

transcription to synthesise tRNA- amino acid complex.

Ribosomes

- contain P site and A site for binding of activated tRNA-

amino acid complex

- bind mRNA between small and large subunit

- coordinate the codon of mRNA with the anticodon of tRNA

to synthesise protein

- translation of mRNA into a protein

Endoplasmic

reticulum

- transports protein synthesized by ribosome

- modifies the protein by adding functional groups

- forms transport vesicles containing the modified protein

Golgi body

- receives modified protein from transport vesicle on the cic

end

- modifies, sorts and repackages proteins into enzymes

- forms secretory vesicles containing enzymes

c) i. - cellulose

ii. - starch

iii. – pentose sugar/ ribose



12

12

2. a) i. sliding filament theory

ii. A band- same length

H zone- smaller

I band – smaller

b)

Calcium ions - bind to troponin

- bind to myosin head and activate ATPase

Troponin - troponin attached with Calcium displaces

tropomysosin

Tropomyosin - Displaced tropomyosin exposes myosin binding site on

actin protein

Myosin head - Mysosin head attached with Calcium ion becomes

cocked/ has high energy configuration

- Binds to the actin to form cross bridge



13

13

3.a) A- carbon dioxide

B- acetyl coenzyme A

C- oxygen

D- water

b) & d)

c) Krebs cycle- matrix of mitochondria

ETC- inner membrane /cristae of mitochondria

e) - NADH oxidises to become NAD+ and release 2H

- the 2H reduces pyruvate

- into lactic acid

(b)

E(d)i

ATP

ATP

(d)ii.

(d)ii.

glycerol

Fatty acid

(d)iii

(d)iii



14

14

4. a) – virus

- only virus requires a host cell to multiply

- only virus is non-specific where it can infect different type of cells

b)i. leucocytes

ii. lymphatic system @ tissue fluid

iii. B lymphocytes & T lymphocytes

c) – memory cells recognize antigen that have previously infected the body

- the cells are able to immediately initiate an immune response

- by producing specific antibodies and killer T cells

- providing the body with immunity against the antigen

d) - influenza is a viral disease

- the virus frequently mutates

- so memory cells from previous infections will be unable to recognize the new

virus

- people cannot develop an immunity towards influenza

- different vaccine enables them to be immune to the new versions of the virus



15

15

1. a) Differentiate between types of enzyme inhibitors.

[8]

COMPETITIVE INHIBITOR NON-COMPETITIVE INHIBITOR

P1 Structure of inhibitor is similar to the

structure of a normal substrate

molecule

P2 Structure of inhibitor is different

compared to the normal substrate

P3 Inhibitor competes with substrate

for the enzyme’s active site

P4 Inhibitor does not compete for the

active site of the enzyme instead it

binds to an allosteric site/

disulphide bridge on the enzyme

P5 When inhibitor binds to the active

site, no biochemical reaction occurs

so the rate of reaction reduces

P6 When inhibitor binds to the active

site/ disulphide bridge it causes the

active site of the enzyme to change

shape.

So the enzyme is unable to form an

enzyme-substrate complex and the

rate of reaction reduces

P7 The rate of reaction (Vm) remains

constant, whereas the substrate

concentration to maintain ½ Vm

(Km) increases in the presence of

an inhibitor

P8 The rate of reaction (Vm) reduces

but substrate concentration to

maintain ½ Vm (Km) remains

unchanged

P9 The inhibition is reversible when

substrate concentration is

increased

P10 The inhibition is reversible only if

the inhibitor leaves the allosteric

site.

The inhibition is irreversible when

the inhibitor binds to the disulphide

bridges



16

16

b) Describe the role of DNA in protein synthesis. [7]

P1. DNA contains the genetic code

P2. DNA provides the template for transcription

P3. The genetic code in DNA is transcribed (copied) onto an mRNA

P4. RNA polymerase attaches to a promoter located at the beginning of a gene

on the DNA

P5. The polymerase unwinds the DNA double helix by splitting the hydrogen

bonds between the double strands

P6. Free nucleotides in the nucleoplasm will then pair with the exposed

nucleotides on the 3’ 5’ DNA strand

P7. Cytosine will pair with guanine and vise versa, thymine will pair with

adenine and uracil of RNA will pair with adenine of DNA

P8. Transcription continues until a terminating sequence like ATT, ATC @ ACT

appears

P9. RNA polymerase leaves the DNA, and the double strands become a helix

again

P10. The transcribed genetic information on mRNA will then be translated

by a tRNA at the ribosomes to synthesize a protein

2. a) Explain the countercurrent multiplier mechanism in the nephron. [8]

P1. The mechanism occurs at the Loop of Henle P2. Mechanism involves optimal absorption of water into the peritubular

capillaries P3. Descending limb is permeable to water, impermeable to NaCl P4. Water from the glomerular filtrate in the descending limb leaves the

tubule into the interstitial space osmotically P5. The interstitial space has high osmotic concentration due to the

secretion of Na+ at the ascending limb P6. NaCl which remains in the tubule causes the osmotic concentration of

the filtration within the tubule to increase P7. The osmotic concentration at the loop tip is at its highest osmotic

concentration



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P8. Thin ascending limb is permeable to NaCl, impermeable to water P9. The thin ascending limb releases NaCl into the interstitial space

leading to increase in the osmotic concentration of the interstitial space P10. Thick ascending limb is impermeable to both water and NaCl so it

secretes Cl- actively P11. To balance the ions, Na+ shifts out of the tubule passively P12. Water remains within the tubule to form urine

b) Describe the adaptive features of xerophytic plants that enable them to live in their habitat

[7] P1. Xerophytic plants survive in arid conditions (desserts & artic regions) where

they have difficulty to obtain sufficient water

P2

Plants have twisted stems to

achieve smaller surface area

This helps plants reduce water loss

via transpiration

P3 Thick & succulent stems For water storage

P4

Has parencyma cells with high

osmotic pressure To absorb more water by osmosis

P5 Leaves modified into thorns for

smaller surface area To reduce water loss by transpiration

P6Shallow & widely spread roots

To absorb water over a large area

from soil surface

P7

Stomata are sunken, less, as crypt

like depression or only on lower leaf

surface

To reduce water loss by transpiration

P8 Dark reaction of photosynthesis is by

CAM pathway

To ensures stoma closes during day

so

water loss by transpiration in daytime

is minimised

P9 Vegetative reproduction So that reproduction is Independent

of water



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P10

Leaves with thick cuticle &

lignificationSince wax is impermeable to water it

helps minimise water loss

P11

Stems carry out photosynthesis

since they have chlorenchyma cells

Otherwise photosynthesis by leaf

would cause stomata to open and so

water loss will increase

3. a) With the aid of a diagram, describe the events that are involved in the development of a fertilized egg upto an embryo with three germ layers.

[10]

P1. Zygote will undergo cleavage

P2. Zygote will do rapid mitotic cell divisions without

intervening growth periods

P3. Repeated division by mitosis forms a solid

multicellular ball called morulla

P4. The morulla cells move to the side of the ball

P5. Forming a liquid filled cavity in the centre

(blastocoels)

P6. The structure is called a blastula

P7. The blastula undergoes gastrulation

P8. Invagination occurs at the vegetal pole

P9. The blastocoel shrinks and a new cavity called

archenteron is formed

P10. The blastula is now two-layered with an

ectoderm & endoderm



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P11. The cells on the posterior proliferate and

migrate to form the third layer that is mesoderm

P12. This three-layered structure is called a

gastrula

P13. Various regions of the three germ layers

develop into the basis of organs

b) Outline the role of hormones during complete metamorphosis of a butterfly.

[5] P1. As a larva, high levels Juvenile hormone levels inhibit ecdysone

P2. So ecdysis of the larvae skin occurs as the larva grows in size

P3. After some time levels of JH reduces to almost equal ecdysone

P4. This stimulates formation of pupa skin

P5. As a pupa JH level becomes nil and ecdysone is now uninhibited

P6. Ecdysone stimulates transcription & translation of genes for adult structure

formation



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4. a) Name the three main requirements for the germination of seeds and explain why each is necessary.

[9]

Main

requirements

for the

germination

of seeds

Why each is necessary

Water P1. Water diffuses into seed micropyle to help cells expand and

soften seed coat for germination

P2. Water stimulates the embryo to synthesise giberellin which

activates hydrolytic enzymes at aleurone layer

P3. Water helps transport hydrolytic enzymes to cotyledon,

products of hydrolysis to seed embryo

P4. Water is involved in the hydrolysis reactions of food storage

breakdown

P5. Water is involved in vacuolisation process that enables cell

elongation for plumule and radicle growth

Temperature P6. Most seeds require optimal temperature (wheat 1-35º C @

Corn 5-45° C) for biochemical reactions to occur in the embryo

P7. Some seeds require extremely high temperatures to stimulate

gibberellin synthesis which then helps seeds germinate after a

forest fire

P8. Some seeds require long cold periods to stimulate gibberellin

synthesis so as to germinate after winter and during spring

Oxygen P9. Oxygen is only necessary once the testa ruptures to carry out

aerobiosis to generate energy

Light P10. Exposure to sunlight is necessary for small seeds to

ensure that the seed is close enough to the soil surface for

easy germination



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b) Describe how food reserves are mobilised during germination. [6] P1. Food reserves such as starch, proteins & lipids

P2. are stored at the cotyledon/ endosperm

P3. Hydrolytic enzymes at the aleurone layer

P4. become activated by gibberellin

P5. These enzymes hydrolyse starch into glucose, protein into amin o

acids and lipids into glycerol and fatty acids

P6. These nutrients are transported/ translocated by water to the

developing embryo

P7. The Embryo uses the nutrients for energy synthesis, construction

of new cells or enzyme synthesis

5. a) Deletion of a base from a DNA molecule is usually more severe as compared to substitution of a base with another base. Explain this statement.

[5]

P1. Deletion leads to a frame shift mutation

P2. The whole genetic code from the place of mutation is altered

P3. A new DNA sequence will be transcribed and translated into a totally

different protein.

P4. Substitution leads to a point mutation

P5. Only the genetic code at the point of mutation is altered

P6. The DNA sequence will be transcribed and translated into a slightly

different protein



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b) Sickle cell anaemia and Down’s Syndrome are caused by mutation. For

each disorder explain the type of mutation involved. [10]

Sickle cell anemia (5m)

Down’s syndrome (5m)

P1. Gene mutation/ gene

substituition mutation

P2. The sixth genetic code for the

synthesis of -globulin in

haemoglobin is CTT

P3. But during mutation the nitrogen

base T is substituted with A so

the triplet code is now CAT

P4. During transcription &

translation glutamic acid (triplet

code CTT) is replaced with

valine (triplet code CAT)

P5. An acidic & negatively charged

amino acid is replaced with a

hydrophobic amino acid

P6. This causes the biconcave

structure of the RBC to become

distorted into a sickle shape.

P7. The sickle cell carries less O2,

gets stuck in capillaries,

obstructs blood flow & is easily

destroyed by phagocytes

P1. Chromosomal mutation/

Aneuploidy/ Trisomy

P2. Chromosome number is not

an exact multiple of the haploid set.

P3. This mutation is due to non-

disjunction of chromosome 21

during Anaphase of either meiosis I

or II

P4. A gamete with 24

chromosomes/ 2 chromosomes 21

will be formed

P5. When this gamete is fertilized

by a normal gamete containing 23

chromosomes/ 1 chromosome 21

P6. A zygote with 47

chromososmes/ 3 chromosome 21

will be formed

P7. The child will be retarded



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6. Describe the steps in gene cloning by using plasmid as a vector. [15] P1. isolate both the gene to be cloned and the plasmid from E.coli that is

to be used as the vector

P2. Select a vector that contains a restriction site as well as antibiotic

resistance site

P3. mix the gene and plasmid with a restriction enzyme such as ECoR1

P4. the enzyme cuts the DNA and plasmid at the bond between G and A

along the sequence GAATTC/ palindromic sequence

P5. sticky ends will form on both the DNA and plasmid

P6. when both the cut DNA & plasmid are mixed together, the sticky

ends complement each other

P7. and bind with hydrogen bonds according to complementary base

pairing

P8. DNA ligase is added to this mixture so that phosphodiester bonds

form between the DNA and plasmid

P9. and an rplasmid is constructed

P10. The rplasmid is mixed with E.coli and Ca2+

P11. so that the cell membrane becomes competent/ more porous

and enables the rplasmid to be taken up

P12. a transgenic bacteria is produced

P13. The bacteria is cultured in a complete medium added with

penicillin

P14. Only bacteria that have transformed with the rplasmid will survive

since they contain the penicillin resistant site

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