1991 Biology Paper I Marking Scheme

CE BIO 1991 Alex Lam

Paper I Marking Scheme & Year Report P.1

1. (a) (i) Cell A Cell C

round shape angular shape )

no cell wall has cell wall )

nucleus : large / nucleus : small / )

irregular-shaped / round / peripherally ) any TWO pairs -------------------- 1,1

lobed / centrally placed nucleus )

placed nucleus )

no vacuole vacuole )

(N.B. No comparison, no mark)

(ii) (1) The cell is a bi-concave disc -------------------------------------------------------------------------1

The central part contains less cytoplasm ---------------------------------------------------------1

(2) this provides a large surface area to volume ratio / shorter diffusion path ----------------1

to facilitate diffusion of gases ------------------------------------------------------------------------1

(iii) to kill / engulf germs -------------------------------------------------------------------------------------------1

(iv) The cell will shrink / become crenated --------------------------------------------------------------------1

because water tends to move out by osmosis ----------------------------------------------------------1

(v) drawing

showing the plasmolysed condition --------------------------------------------------------------------- 1+

quality of drawing e.g. resemblance to the cell shown,

double-lined cell wall ------------------------------------------------------------------------------------ 1 or 0

labels : * cell wall )

* cell membrane )

* cytoplasm ) any TWO labels ---------------------------------------------�, �

* nucleus )

* vacuole )

Total : 12 marks

1. (a) (i) Some candidates produced an answer without referring to the photomicrograph supplied. For example they described the shape of the white blood cell as ‘irregular’ or ‘amoeboid’. This was a clear reflection of mere rote-memory that the white blood cells must be amoeboid. However, in the photomicrograph, the white blood cell could only be described as round or circular. Other candidates thought that all plant cells must have chloroplasts which led them to describe the presence of chloroplasts in the onion epidermal cells. In the photomicrograph, however, the chloroplasts are obviously absent.

(ii) (1) Many candidates could not satisfactorily explain the lighter colour at the central part of the red blood cells. They failed to note that there was less cytoplasm and less haemoglobin there.

(2) Very few candidates could precisely point out the importance of a large surface area to volume ratio in facilitating gaseous exchange.

(iv) Many candidates wrongly explained that the red blood cells after immersion in a concentrated sugar solution would undergo ‘plasmolysis’. They failed to note that ‘plasmolysis’ and ‘flaccid’ are terms commonly used to describe the condition of a plant cell when they loose excessive water resulting in the cell membrane being detached from the cell wall. In the case of crenation in animal cells, the cells simply shrink but do not ‘plasmolyse’.

(v) Most candidates could produce a drawing of a plant cell showing plasmolysis. Many candidates, however, could not produce an accurate drawing of the onion epidermal cell



with the general shape as shown in the photomicrograph. Others used a single line to denote the plant cell wall.



1. (b) (i) (1) iron ---------------------------------------------------------------------------------------------------------1

(2) symptoms associated with anaemia ---------------------------------------------------------------1

(ii) 1700 cm3 (N.B. no unit, no mark) ------------------------------------------------------------------------1

(iii) in human milk ,

- more vitamins good for general health / prevents deficiency diseases ---------- 1+1

(iv) in cow’s milk

- more protein for the production of protoplasm / body growth --------------------- 1+1

- more calcium and / or phosphorus for the growth of bones and teeth ---------------- 1+1

Total : 9 marks

1. (b) (ii) It is encouraging to see that most candidates could correctly extract numerical data from the

question and could readily perform simple calculations to obtain the right answer.

(iii) Many candidates did not refer to the table given and so gave the presence of antibodies as

an advantage of cow’s milk over breast feeding.

(iv) This was the most well answered part of the whole question paper showing students’

increased awareness of the daily applications of human nutrition.



1. (c) (i) Albino -------------------------------------------------------------------------------------------------------------1

- This character is shown in individual 10 but not in )

their parents (individuals 3 and 4) )

- Individual 10 must have received )

one albino allele from either parent ) any THREE ---- 1,1,1

- who must be heterozygous )

- In heterozygous condition, only the )

dominant allele is expressed OR the recessive allele is masked )

(ii) (1)

(individual 6) (individual 10)

D d d

Dd dd

Dd dd

Parent

Gamete

Offspring

(normal) (albino)

Therefore, normal : albino = 1 : 1 ---------------------------------------------------------------------1

(2) � --------------------------------------------------------------------------------------------------------------

1

Total : 9 marks

1. (c) (i) Many candidates could succeed in concluding that albino is the recessive character, but not

many of them could explain their deduction in sentences.

(ii) (1) Candidates showed a marked improvement in their ability to draw a genetic diagram.

However, some did not use the given symbols.

--------------------------- 1

--------------------------- 1



2. (a) (i) Starch is still present in these spots as no digestion occurs -----------------------------------------1

enzyme in spot A cannot work in an acidic medium ---------------------------------------------------1

and enzyme in spot B has been denatured by heat ---------------------------------------------------1

(ii) The reddish brown colour indicates starch is absent / digested ------------------------------------1

due to enzymes secreted by bread mould ---------------------------------------------------------------1

(iii) It is a temperature suitable for the enzyme activity in the saliva -----------------------------------1

It is also a temperature suitable for enzyme activity / growth of the bread mould --------------1

(iv) drawing showing reproductive structures ----------------------------------------------------------------1

labels : * sporangium )

* spores )

* sporangiophore ) any FOUR labels ------------------------------------- �,�,�,�

* hyphae / * stolons )

* rhizoids )

* zygospores )

(v) To avoid transmission of diseases such as hepatitis --------------------------------------------------1

Total : 11 marks

2. (a) (i) Some candidates incorrectly explained the lack of digestive activities in saliva after boiling

as due to the enzymes being “killed” by heating.

(iii) Many candidates’ answers were too brief and vague, e.g. saying that saliva (rather than the

enzymes within it) than the enzymes within couid break down starch.

(iv) The term "sporangiophore" was often misspell as "sporangiospore" or "sporangiopore".

Drawings made by candidates of the bread mould were generally of poor quality and the

labels were far from complete.



2. (b) (i) correct choice of axes -----------------------------------------------------------------------------------------1

correct labeling of axes with units --------------------------------------------------------------------------1

correct plotting of all points ----------------------------------------------------------------------------------1

The changes in blood urea concentration with time

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00

7.0

6.0

5.0

4.0

3.0

2.0

1.0

Blo

od u

rea

conc

entr

atio

n (m

g/10

0cm

3 )

Time (hours)

0

(ii) At 0:800 hours, the liver was removed -------------------------------------------------------------------1

no deamination to produce urea ---------------------------------------------------------------------------1

but the kidneys continued to excrete urea in the urine -----------------------------------------------1

Therefore the blood urea concentration decreased

(iii) increase in blood urea ----------------------------------------------------------------------------------------1

as there is no kidney to excrete the urea -----------------------------------------------------------------1

which is continuously formed by the liver ----------------------------------------------------------------1

(iv) storage of blood / vitamin / iron / glycogen /

formation of bile / regulation of blood sugar level, etc. -------------------------------------------------1

Total : 10 marks

2. (b) (i) The graph was well plotted by most candidates although a few still plotted the curve without

using graph paper :

(iii) Some candidates mixed up the deaminating function of the liver with the excretory function

of the kidneys.

(iv) Quite a number of candidates wrongly gave the production of insulin as a function of the

liver



2. (c) (i) (1) green plant and / or decomposers produce carbon dioxide during respiration ----------1

green plants produce oxygen during photosynthesis ------------------------------------------1

(2) water is lost through the plant surface via transpiration ---------------------------------------1

water vapour eventually condenses and returns to the soil ----------------------------------1

(3) the older parts of the plant die or fall off and -----------------------------------------------------1

broken down by decomposers to release the nutrients

back to the soil -------------------------------------------------------------------------------------------1

(ii) animals / consumers ------------------------------------------------------------------------------------------1

(iii) provides an initial supply of nutrients / decomposers -------------------------------------------------1

since recycling of nutrients takes time --------------------------------------------------------------------1

Total : 9 marks

2. (c) (i) (1) Some candidates obviously overlooked the phrase “these supplies are

maintained“ in the question and wrongly stated that to maintain a supply of respiratory

gases in the enclosed system, carbon dioxide was absorbed by green plants for

photosynthesis and oxygen was absorbed for respiration.

(2) Many candidates neglected the fact that, within the enclosed system, the major source

of water vapour came from the transpiration of the green plants rather than from the

moist soil.

(3) Very few candidates correctly mentioned that the dead bodies of plants would undergo

decay to give inorganic nutrients.

(iii) Despite comments in previous examiners* reports, many candidates still held the

misconception that humus is a direct source of inorganic fertilizer rather than dead decaying

organic matter.



3. (a) (i) (1) to prevent oxygen in air dissolving into the solution -----------------------------------------------1

(2) to provide sufficient carbon dioxide in the tube --------------------------------------------------1

(3) the relative light intensity is inversely proportional

to the (square of) distance of the lamp away from

the test-tube ----------------------------------------------------------------------------------------------1

(4) 1

0 05 1

T = −. min ----------------------------------------------------------------------------------------1

T = 1

0.05 min

T = 20 min (no unit, no mark) ----------------------------------------------------------------------1

(5) the rate of photosynthesis increases with

increasing light intensity up to a certain point, ---------------------------------------------------1

beyond which the rate levels off ---------------------------------------------------------------------1

(ii) Points to note for in the diagram :

soda lime / conc. KOH / conc. NaOH solution in

an enclosed container to absorb CO2- --------------------------------------------------------------------1

lime water / hydrogen carbonate indicator in an

enclosed container to check the absence of CO2 ------------------------------------------------------1

correctly linked glass tubings and rubber tubings ------------------------------------------------------1

dye solution in container with an air outlet ---------------------------------------------------------------1

(N.B. No mark is to be awarded if the set-up is not workable.) soda lime

air in

air out

OR

dye solution lime water /hydrogen carbonate indicator

conc. KOH /NaOH solution

Total : 11 marks

3. (a) (ii) This part of the question was set to test candidates’ ability to design an experimental set-up

for hypothesis testing. Many candidates failed to draw a workable set-up either because

they wrongly positioned the relevant reagents or they blocked the delivery tube at the outlet.



3. (b) (i) X - * pseudopodium -------------------------------------------------------------------------------------------1

Y - * contractile vacuole --------------------------------------------------------------------------------------1

(ii) the pseudopodia extend to engulf / surround food particles -----------------------------------------1

and form a food vacuole in the cytoplasm ---------------------------------------------------------------1

(iii) (1) Rate of discharge = 6 [60/10s](discharges per minute) -------------------------------------1

(2) Water potential of the medium around )

A is higher than that around B )

OR ) any ONE ------------------------------------1

Water potential of A is lower than that of B )

Therefore, water enters into cytoplasm of A more quickly ------------------------------------1

and contractile vacuole (Y) discharge more frequently ----------------------------------------1

Total : 8 marks

3. (b) (i) "Contractile" was often misspell as "contratile" or "contracile". "Vacuole" was often misspell

as "vacule". Some candidates in the Chinese version mistook structure Y as a food vacuole.

(iii) (2) Candidates’ explanations involving water potential to explain the different rates of

discharge of contractile vacuoles under different external media revealed their good

grasp of the concept.



3. (c) (i) * cartilage ring --------------------------------------------------------------------------------------------------1

to prevent collapse of the trachea / to allow free passage of air -----------------------------------1

(ii) (1) * pleural membrane / * pleura ------------------------------------------------------------------------1

(2) because air leaks in / increases pressure between pleura -----------------------------------1

the lung recoils / collapse due to its own elasticity ----------------------------------------------1

(iii) muscle C relaxes -----------------------------------------------------------------------------------------------1

(iv) (1) to provide a short distance for diffusion -----------------------------------------------------------1

(2) to provide a large surface area for diffusion ------------------------------------------------------1

(3) to dissolve the respiratory gases for diffusion to occur ----------------------------------------1

(v) dust particles cannot be removed from the respiratory

tract / more dust particles enter the lungs ----------------------------------------------------------------1

thereby reducing the surface area for gaseous exchange -------------------------------------------1

Total : 11 marks

3. (c) (i) "Cartilage" was sometimes wrongly spelt as "cartinage".

(ii) (1) "Pleural" was often misspell as "pleual" or "pleral". "Membrane" was often misspell as

"membrance". Many candidates were unsure about the function of the pleural cavity.

(2) Most candidates could correctly explain the collapse of the lungs when punctured by

pointing out the difference in pressure on both sides of the pleura. Some merely

explained this in terms of the leaking out of pleural fluid or simply the leakage of air.

Most candidates failed to note that during expiration, the lungs will recoil or collapse

due to their own elasticity.

(iv) (1) Few candidates could relate the one-cell thick feature to the short distance needed for

diffusion of respiratory gases.



4. (a) (i) (1) It would be easier to observe any changes in the water level in the glass tubing -------1

(2) to suck up the water column through the rubber tubing ---------------------------------------1

and then close the rubber tubing with the screw clip -------------------------------------------1

(ii) germinating sees used up oxygen in the glass container for respiration -------------------------1

and released carbon dioxide --------------------------------------------------------------------------------1

which was absorbed by conc. KOH -----------------------------------------------------------------------1

As the gas in the glass container became less the gas pressure reduced, ----------------------1

the higher atmospheric pressure would force the water level up to position A ------------------1

(iii) the volume of oxygen used up in respiration was equal

to the volume of carbon dioxide released ----------------------------------------------------------------1

Total : 9 marks

4. (a) (i) (1) Many candidates suggested that setting the initial water level near the middle of the

glass tubing could make it easier to observe the results, without stating what the

results were i.e. they did not mention any changes in the water level within the tubing.

(2) Rather than saying 'to suck up' a column of water, many candidates tended to say 'to

pump up'. Still far too many candidates omitted the very important step of closing the

screw clip after sucking the water column up.

(ii) This part of the question was well answered showing candidates' improvement in explaining

the phenomenon of gaseous exchange during seed germination. Many candidates, however,

could not clearly point out that the rise in water level inside the glass tubing was due to the

greater atmospheric pressure on the outside.



4. (b) (i) 6016

2.

× = 75 (beats per minute) ---------------------------------------------------------------------------1

(ii) (1) X ------------------------------------------------------------------------------------------------------------1

(2) X can produce greater pressure / force to proper

blood to all parts of the body -------------------------------------------------------------------------1

(iii) (1) to prevent the backflow of blood into the auricles / atria ---- )

when the ventricle are contracting -------------------------------- )

OR any ONE set ---------- 1+1

to prevent the blackflow of blood into the ventricles ---------- )

when the ventricles are relaxing ----------------------------------- )

(2) (I) closed ----------------------------------------------------------------------------------------------1

(II) At time A, the ventricular pressure is increasing -----------------------------------------1

thus forcing the valves to close --------------------------------------------------------------1

(iv) From left ventricle : * aorta -----------------------------------------------------------------------------------1

From right ventricle : * pulmonary artery -----------------------------------------------------------------1

blood in aorta contains more oxygen than that

in the pulmonary artery ---------------------------------------------------------------------------------------1

Total : 11 marks

4. (b) (iv) "Aorta" was often wrongly spelt as "arota". "Pulmonary" was often wrongly spelt as

"pulmonry".



4. (c) (i) (1) * testis -----------------------------------------------------------------------------------------------------1

(ii) (1) * meiosis --------------------------------------------------------------------------------------------------1

(2) the chromosomes number of the egg is half of that of the parent cell ---------------------1

so that the normal chromosome number is restored after fertilization / in the zygote --1

(iii) oviduct / fallopian tube ----------------------------------------------------------------------------------------1

(iv) * mitosis ----------------------------------------------------------------------------------------------------------1

(v) (1) * umbilical cord ------------------------------------------------------------------------------------------1

(2) carries oxygen / nutrients to the foetus ------------------------------------------------------------1

(vi) (1) any discontinuous variation of man e.g. tongue

rolling ability, eye colour, blood group, etc. ---------------------------------------------------1

(2) any continuous variation of man e.g. height, weight etc. --------------------------------------1

Total : 10 marks

4. (c) (ii) (2) Many candidates could not fully explain the significance of meiosis in terms of

maintaining constant chromosome numbers over successive generations. Many

candidates wrongly claimed that meiosis gives rise to haploid offspring rather than

haploid gametes. Others wrongly stated that meiosis could reduce the chromosome

numbers of the “offspring” by half.

(v) (2) Many candidates described the embryo or foetus as the baby.



5. (a) (i) (1) it contracts ---------------------------------------------------------------------------------------------------1

(2) (I) * elbow joint / * hinge joint -------------------------------------------------------------------------1

(II) it allows movement in one plane / 180° only -------------------------------------------------1

(ii) Man X :

the motor / relay neurone / assoication neurone / intermediate nueorne was damaged -------------1

so that no impulses could be transmitted to the

effector muscle arm to produce the response ----------------------------------------------------------1

Man Y :

the sensory neurone / receptor was damage -----------------------------------------------------------1

so that no impulses from the receptor could be

transmitted to the brain for producing the painful feeling ---------------------------------------------1

since Y could move his hand voluntarily therefore the

motor neurone was still functioning ------------------------------------------------------------------------1

Man Z :

the relay neurone / assoication neurone / intermediate nueorne to the brain the spinal cord above the

arm level was damage ----------------------------------------------------------------------------------------1

no impulses could be carried to the brain ----------------------------------------------------------------1

since Z can withdraw his hand therefore the reflex arc

was not damage ------------------------------------------------------------------------------------------------1

Total : 11 marks

5. The highly disappointing results in this question demonstrated that candidates are still weak in applying

their knowledge in the nervous system to explain neural responses.

(a) (ii) Most candidates were weak in understanding the location and functions of the different

types of neurones (sensory, relay and motor) in the nervous system. Many candidates

mixed up the motor or sensory areas of the brain with the sensory or motor neurones in the

neural pathway and failed to distinguish nerve fibres from nerves. Others were confused

about the meanings of reflex actions and voluntary actions. Many did not realise that a

nerve impulse would be sent to the brain from the reflex arc involved in the withdrawal

action.



5. (b) (i) to activate the enzymes in seeds / to help rupturing the

seed coat / to soften the seed coat / other suitable answer -----------------------------------------1

(ii) (1) weight with all water removed -----------------------------------------------------------------------1

(2) dry weight gives a more accurate measurement

of the amount of organic matter present /

measurement on fresh weight shows greater variation -----------------------------------1

water content is affected by different environmental conditions -------------------------1

(iii) to minimize error due to individual variation / death / unsuccessful germination ---------------1

(iv) (1) retarding / slowing growth -----------------------------------------------------------------------------1

(2) no effect on growth -------------------------------------------------------------------------------------1

(v) (1) cotyledons provide food reserve for germination ------------------------------------------------1

therefore early removal of cotyledons resulted in less growth

(2) food reserve in cotyledons would have been used up -----------------------------------------1

seedlings would have developed leaves for photosynthesis ---------------------------------1

therefore removal of cotyledons had no effect on growth

Total : 10 marks

5. (b) (ii) (1) Some candidates could not relate growth to an increase in dry mass.

(iii) Many candidates could not realise the importance of using large samples, particularly of

biological specimens, to arrive at more reliable results. They only stated that a large sample

size could give more accurate results' but could not explain why.

(iv) (1) The functions of cotyledons during the initial stage of germination was not clear to

many candidates. They did not realise that removal of cotyledons on the 4th day of

germination could lead to "retarded growth" but not "zero growth".



5. (c) (i) 2.8 × 1010 kg (no unit, no mark) ---------------------------------------------------------------------------1

(ii) particles ----------------------------------------------------------------------------------------------------------1

(iii) to reduce the number of motor vehicles, -----------------------------------------------------------------1

because they produce the greatest total amount

pollutants / carbon monoxide / hydrocarbons per year -----------------------------------------------1

or other suitable answers

(iv) particles - irritation of the respiratory tract / reduce the efficiency of gaseous exchange -----1

carbon monoxide - decreases oxygen carrying capacity of blood ---------------------------------1

(v) it dissolves in raindrops / water -----------------------------------------------------------------------------1

increases the acidity of water and affects lives there -------------------------------------------------1

(vi) hot water / radioactive wastes / carbon dioxide / other suitable answer ----------------------------1

Total : 9 marks

5. (c) (iii) Many candidates did not refer to the bar chart given in the question and simply regurgitated

what they had learnt from textbooks.

(iv) Many candidates could grasp the idea of blockage of respiratory surfaces by particles while

a few could point out the "irritating" function of particles to the respiratory system.

1991 Biology Paper I Marking Scheme

Documents

Transcript of 1991 Biology Paper I Marking Scheme