DBADD

1C2B3D4D5C6B

Answers

Objective Questions

78910ll

Structured Question(a) (i) Nucleus

(ir) DNA consists of 2 polynucleotide chains that

(b) (i) Nucleotide(ii) Tvpe of nitrogenous base(iii)

are coiled together

,F

(c) Gene

(d) (i) Reproductive cell(ii) Chemical substance such as the mustard gas

Essay Question(a) o Enz--vmes accelerate biochemical reactions but are not

the experiment. As such, enzymes are required only inchanged at the end ofsmall quantities in the

body.o The action of the enzymes is specific. that

reaction that involves certain substrates.ts each enz_yme onlS'catalyses the

c Enzymes exhibit protein characteristics such as being sensitive towardschanges in temperature. Enzymes are destroyed at a temperature of 60"c andthe enzymatic action is stopped. At a low temperature of 10.c, the enzymaticaction is slorv. Enry-mes react at the rnaximum level at the opiirrlo-temperature.

o The erzymatic action is influenced by the medium pH. Each enzvme reacts atthe maximum level at its optimum pH.

r The same enzyme catalyses the reverse reaction.

Exampie: Starch + water amylase t maitose

amr-laseMaltose ' > starch*water

(b) Purpose: To siudy the effect of temperature on the enz),rne activity

Apparatus/Material: -

Procedure.I 5 rnl of saliva is collected and diluted by adding 5 ml of distilled water into

a small beaLer.2 Test tubes labelled P, Q, R, S and T are prepared.

is poured into each test tube.5 nrl ofstalch suspension

3 Each test tube is placed in the water bath at temperatures of 5oc, 2g"c,37'C,45oC and 60"C.

4 After that. I ml of saliva solution is added into each test tube and thestopwatch is started immediately. The content of each tube is stirred and adrop of the contents is removed at I minute interr,'als to be tested with iodinesolution. This step is repeated until the iodine solution does not changecolour.

Result:

Conclusion:The action of the enzyme is influenced bv temperature. Enzymatic action is

llo-tl ut low temperatures, and increases u'ith the increase in temperature until37"c. The enzymatic action is at ihe maximum at 37"c. Aft-er 37.c. theenzyrnatic action decreases and stops at 60"C.

Testtube

---- Time\---\ {minute)

Temperature---r.-(oC)

1 2 3 4 5 6 7 8 o 10

P t

o 28R 37e 45T 60

Objective Questions1D2B3C4B5A6B7C8B

Structured Question(a) X: spindle fibre

Y: chromosomeZ: centromere

Answers

9tntl,11

1213

t415

CA

BBBAB

(b)

(c)

4

At the anaphase stage. the centromere divided and the chromatid separates, and thechromosome is pulled by the spindle fibre at the centromere.

Essay Question(a) 1 Mitotic cell division process

2 Before mitosis begins, the cell is in the interphase stage/state of rest. The acii1.ecell nucleus/chromosome experiences replication/doubling of DNA/nucleusmembrane is seen clearl,v/chromosome is like a granule/chromatin/long and finecoil/there is an increase rn ihe number of mitochondriaichloroplast/organille

3 FIGURE (a)

AFcellwallll t'4 lll nuctear membranett=-%f nucleus

Shows the following cell characteristics: clear nucleus membrane, chromosomelooks like a granule/chromatir,.,tong and fine coil/chiomatin netrvork. hasnucleus

At the prophase siage, the chromosorne thickens/shortens anrl looks like twoidentical coils/alike/sister chromatids/alike/double helix joined at the centromere

The nucieus membrane slowly disappears/spindie fibre is formed al the end of theprophase

l0

6 FIGURE (b) (early/end prophase)

nuclear membranebreak downcentromeie

chromosome

r Shows the following cell characteristics: chromosome thickens and shortens-chromatid ioins at the centromere, no nucleus

At the metaphase stage, the chromosomes/chromatids are arranged at theequatorial plane and is held by the spindle fibre at the centromere

FIGURE (c)

r Shows the follou'ing cell characteristics: the chromosomes/chromatids arearranged at the centre/fibre equatorial plane, fibres are formed

At the anaphase, each chromatid pair starts to separate at the centromere and ispulled tou'ards opposing cell poles as a result of the contraction of the spindle fibre

FIGURE (d)

o Shows the following cell characteristics: the chromatid pair separates at thecentromere, the chromatid is pulled towards the opposing poles, the centromereis orientated towards the pole

The spindle starts to disappear and the nucleus membrane is reformed/trvodaughter cell nuclei are formed

At the telophase, c1'toplasm division/cl.tokinesis produces two diploid daughtercells/that has the same number of chromosomes as the parent cell

FIGURE (e)

I Shows the following cell characteristics: cell plate is formed at the middle,nucleus membrane exists, chromosome lengthens/coils/form coils

ll

I2

13

(b) (i) The process of producing a new individual from a parent without involvingfertilisation between gametes.

(iD . Cell division through mitosis on the multi-cell organism can increase thenumber of cell for grou,ttr, and to replace damaged or dead cells.

o unicellular organisms (Amoeba sp. and pqramecium sp.), reproduces bysplitting into two through mitosis.

e Division through mitosis maintains the number of diploid chromosomes in thedaughter cell, and as such, the new organism that is formed will have the samecharacteristics as the parent.

. Mitosis is used in agriculture to produce flowering plants arrd fruit plants in alarger quantity and at a higher qualiqv.