Biology 2000 Paper I Marking Scheme

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~PI..eBD2000 CE Biology Paper I Marking Scheme

FOR TEACHERS' USE ONLYMarks

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(i) The cells of A and the cells of the foetus are fonned by mitosisof the zygote "".""'"

(ii) (1)(2)

female IA spenn ca"ying an X chromosome Ifused with an egg, which always contains an X chromosome ".'.'" Ito fonn a zygote I offspring with two X chromosomes. '... I

thus resulting in a female foetus

(iii) There are 3 chromosomes 21 / an extra chromosome is present

(iv) The foetus may be expelled out of the uterus I miscarriage ' I

(v)))) any)

Blood from A to the foetus hashigher oxygen contenthigher nutrient contentlower carbon dioxide contentlower urea content(accept other correct answers)

Total: 10 marks

,(.(b) (i) Tissue A is .palisade mesophyll Tissue B is .spongy mesophyll

,

I

1

(ii)

(iii)

Number of chloroplasts in region 1 is 20; while that in region 2 is 12 IRatio of chloroplast density in region 1 to that in region 2 is 5:3 I

,: " 0 o.'_0. This allows."thc leaf to carry out pho~synthcsis ,at a higher rate 1

because tissue A has a higher ~ensityofchloroplasts 1and it is located in the upper layer of the leaf :. 1so its cells are under direct illumination I can receive more sunlight thanthe cells oftissueB 1

Effective communication (C) 11

(iv) Put the stem ofa leafy shoot in a dye solution for some time ~..~ Cut cross sections of the stem and the leaf """' ".""""'"

Examine the sections under the microscope Cell type C would be stained by the dye '

Total: 12 + 1 marks

-.( I. (c) (i) Oxygen in the tidal air diffuses through'the residual air '..." ""'... 1and dissolves in the water film lining the air sac 1It then diffuses across the walls of the air sac and the capilla[): into the blood... 1

I Effective communication (C) i I

(I) The volume of tidal air will increase ..' '..' ".'...""."...'.'.'." 1(2) The oxygen uptake in the blood becomes faster I

(ii)

(iii)

because the distance of diffusion of oxygen from the tidal air)to the water film is reduced )

or because the surface area of the air sac for diffusion of ) anyone 1oxygen is increased )

Particles I Tar deposit on tii~ ~all of the air ~c 1thus reduce the rate ofdiffiisionofoxygen ..., 1(accept other correct anSWers) ..". t.,: .,1,:... '~!'. .:'

Total: 8 + 1 marks

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20OO-CE-Brn I":. .,..

two

-H'B...g FOR TEACHERS' USE ONLY2000 CE Biology Paper 1 Marking Scheme .Marks

2. (a) (i) The daily energy intake of Jane is 6620 kJ """ '" I

which is less than her daily energy requirement IThus she has to consume I mobilize the fall food reserve in her body : I

~t;o ~~:;;:=~~~~h t ,

L-~=::~:~=~ .--!-l(ij) Amino acids are broken down in the liver Ito form carboh~drafC I a part without nitrogen (and urea) ".'" '.'.' Iwhich will be oxidized/used in respiration to release energy I

(iii) anaemia '."" """'" "." ". I

(iv) Rub a piece of ham on a filter paper mA translucent spot will remain after drying I

Immerse the paper in an organic solvent and the spot will disappear 1 anyOR one

Add alcohol to a piece ofham and obtain a clear solution m setAdd water to the clear solution IThe solution will turn milky 1

" .A + I marks

.(b> I(i)

-(ii)

.u..I: auFrom I to S units of light intensity, the size of the pupil decreases

with increasing light intensity However, when the light intensity is above S units,

the size of the pupil will remain unchanged with increasing light intensity This response helps to prevent excessive light entering the eye... '" so that the light-sensitive cells of the retina may not be damaged light-sensitive cells / photorcceptors -+ sensory neurone / optic nerve

-+ associatinn neurnn.c in .-+ motor neurone / nerve -+ iris muscle

( If: mark for each tenn) Deduct If: mark if there is no arrow sign. Because all the light entering the eye is absorbed by the retina and the choroid As a result no light is reflected out of the eye through the pupil

(iii)

3

I(iv)

ITotal: 9 marks

Advantage:

The chance of pollination I fertilization is higher )Less wastage of pollen grains ) anyone IDesirable characters of the parent are more likely to be transmitted)to the offspring )

Disadvantage:Less genetic variation (accept other con-ect answers) I

Remove the anthers from the flower before they are mature IUse a brush to dust pollen grains of another pea flower onto the stigma of this flower ICover the flower with a plastic bag to prevent further pollination ". ...' I

Effective communication (C) 1

(I) Green pod colour is dominant to yellow pod colour Ior The allele for green pod colour is dominant to the all~le for yellow pod colour

(2) Let G represent the allele for green pods Iand g represent the allele for yellow pods

F, Gg X Gg I

It~ It~Gamete C(;:~~a 1

Fz GG Gg Gg gg t' Y. "'

gree~ POd: yello7 pod } I

Deduct 1 mark for leaving out the labels ofF., gamete and Fz..

Total: 11 + I marks

(i)

(ii)( -"

(iii)

2000-CE-BIO 1-9 .-

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.R Pi ~ ftiJi ~ fJD2000 CE Biology Paper 1 Marking Scheme

FOR TEACHERS' USE ONLYMarks

3. (a) (I) Blood capillary (2) Its wall is one-cell thick I the diameter of the lumen is

slightly greater than or similar to that of a red blood cell The pressure of blood in A is higher than the pressure of

the fluid surrounding the muscle cells This forces the plasma except the plasma protein out of A Drawing (D): clear and accurate diagram. double line for capillary wall,

biconcave RBC "",."",.,.",.,.,."""",.,.."..,."",Labels (L): any three of the following labels and title; '/z mark each

(i) 1+

(ii)

(iii)lYJ.lYJ.

nucleuscell of capillary wall/capillary wall

red blood celllumen I blood plasma I blood

A section alon~ line BC

{ (iv) (small intestine) -+ hepatic portal vein -+ liver -+ hepatic vein -+ vena cava-+

heart -+ pulmonary artery -+ (lung) (Yz mark for each term) j Deduct Yz mark if there is no arrow sign. I

Total: 10 marks

3

(i)

(ii)

(iii)

(iv)

(

Diabetes is caused by the absence of certain substance(s) Iwhich can be found in the pancreas I

To detennine whether the substance in the pancreas extract effective intreating diabetes is a protein I

ora fat , I

Symptoms of diabetes would remain IThis is because protease in the alimentary canal Iwill digest the active substance which is protein in nature I

In the diabetic person, the pancreas cannot produce enough insulin... 1Thus the liver cannot convert excess glucose in the blood into glycogen 1His blood glucose concentration remains high 1leading to a high level of glucose in the glomerular filtrate 1The kidney tubules cannot reabsorb all the glucose from the filtrate ,. Ithus glucose is excreted in the urine

I Effect~ve communication (C) i I

Total: 12 + 1 marks

(i)

(ii)

(iii)

The water potential of the cell sap of cell A is greater than that ofthe sucrose solution 1

Water moves out of the cell by osmosis 1The vacuole shrinks in size 1pulling the cytoplasm/cell membrane away from the cell wall 1

I ~jfec~ve co;;;:'unicatwn (C) .--!JThe water potential of the cell sap of cell B may be the same flower than

that of the surrounding solution 1(accept other reasonable answers)

(I) Adjust the positinn nfthe slide until cell A is at the centre ofthe field of vision 1

(2) Adju~ the diaphra~m / condenser to increase the illwninationof the slide 1

rum the ad_iustment knob until the cell is in focus 1Total: 8 + 1 marks

R ~.R ~ ft~ ~ IJU2000 CE Biology Paper 1 Marking Scheme

FOR TEACHERS' USE ONLYMarks

4. (a) (i) The amylase converts starch into maltose.

(ii) To ensure that sufficient amount of maltose is produced

(jij) When the temperature increases from O.'70°C. the amylase activity increases..., 1When the temperatures increases from 70-90°C. the amylase activity decreases. 1The optimum temperature for the activity of barley amylase is 70°C 1

(iv) Keep the mixture at very low temperature (below IO.C) The amylase is inactive at this temperature "."""'.'.'.""".".".""

but it is not denatured I destroyed ...".

(v) After incubating the mixture at a given temperature for a fixed period of time,

perform the Benedict's test Measure the amount of red precipitate / reducing sugar formed ", "

Total: 10 marks

4. (b) (i) (1) High concentration of suspended solids reduces the light intensityin water I

Thus the rate of photosynthesis of the producers decreases... Iand this leads to a drop in the population of the producers I

I Effective communication (C)- --11

SiteD I

:~~( ~

(2)

(ii) (1) The greater the amount of organic pollutants in water. the higherthe bacterial population 1

because the organic pollutants provide food 1for the growth I multiplication of bacteria I

(2) Site C ,

(3) Slow water current in the harbourThere is sewage outfall at this siteLarge human population

)) anyone ) .

(iii) To protect endangered species (accept other correct answers)

Total: 10 + I marks

4. (c) (i) When perfonning heavy exercise, rate of sweat production was faster

This was because large amount of heat was generated by the body

during exercise The body temperature started to increase and this stimulated the increase in sweat production

I

(~II

I

(ii)

(iii)

When the person is performing exercise, a large amount of water in thebody was lost in the form of sweat 1

The water potential of the blood / plasma was lowered 1Thus a greater proportion of water was reabsorbed from the glomerular filtrate.. 1

hence less urine was produced

I Effective communicat;on (C) 11

(I) The lining of the air sacs or respiratory tract is moist / covered witha water film 1

Water in the water film evaporates into the air of the air sac Irespiratory tract 1and is lost during exhalation

because the rate and depth of breathing was increased .., Iso greater amount of air was exhaled from the lungs per unit time Ileading to an increased rate of water loss through exhalation

Total: 10 + I marks

(2)