1996 Biology Paper I Marking Scheme

CE BIO 1996 Alex Lam

Paper I Marking Scheme & Year Report P.1

1. (a) (i) (1) The major plant group to which maize belongs

produces flowers / fruits while the other group does not ----------------------------------------1

(2) gymnosperm -----------------------------------------------------------------------------------------------1

(ii) (1) To form a new plant/to protect the embryo/for dispersal of the plant ------------------------1

(2) To carry the male gamete ------------------------------------------------------------------------------1

to the female gamete for fertilization -----------------------------------------------------------------1

(iii) dry, small, light (any ONE) ------------------------------------------------------------------------------------1

(iv) Bread mould has branching rhizoids / root-like structures---------------------------------------------1

to provide a large surface area -----------------------------------------------------------------------------1

for secreting digestive enzymes / enzymes to digest the organic food -----------------------------1

and then absorb the digested products --------------------------------------------------------------------1

Effective communication (C) -------------------------------------------------------------------------------1

Total: 10 + 1 marks

1. (a) (i) (1) Some candidates thought that both pine and bread mould do not possess chlorophyll

or seeds.

(2) The sub-group to which pine belongs should be gymnosperm, as stated in the syllabus,

and not conifer. Many candidates could not spell this term correctly.

(ii) (1) Some candidates stated that the seed could be dispersed by wind without pointing out

that the role of the seed is to help in the dispersal of the offspring in order to avoid

overcrowding or to exploit new habitats.

(2) A large number of candidates wrongly stated that the pollen grain is the male gamete

of the plant and that it fertilizes the egg directly. Candidates should be aware that the

role of the pollen grains in reproduction is to produce the male gametes and to carry

them to the female part of the flower for fertilization.

(iv) When answering this part, many candidates did not refer to the features shown in the

diagram that are responsible for obtaining nutrients from the substrate, such as the

branching hyphae that form the rhizoids.



1. (b) (i) (1) artery -----------------------------------------------------------------------------------------------------------1

(2) capillary --------------------------------------------------------------------------------------------------------1

(ii) Blood vessel A has thick wall )

to withstand a high blood pressure )

OR

Blood vessel A has elastic wall ) any ONE set --------------- 1,1

to withstand / maintain a high blood pressure )

OR

Blood vessel A has muscular wall )

to control the blood flow / the diameter of the blood vessel )

The wall of blood vessel B is one-cell thick ---------------------------------------------------------------1

so as to facilitate the exchange of substances between the blood and the tissue cells --------1

(iii) To provide a large surface area to volume ratio ----------------------------------------------------------1

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

(iv) The blood supply to the heart muscle is reduced, -------------------------------------------------------1

so there is less food and oxygen supply to the heart muscle cells ----------------------------------1

The heart muscle cells would die/heart attack would occur -------------------------------------------1


Total: 11+1 marks

1. (b) Candidates made a lot of spelling mistakes, such as 'artery' for the 'artery', 'capillary' for 'capillary',

and 'think wall' for 'thick' or 'thin' wall.

(i) (2) Many candidates did not refer to the information given in the photograph and wrongly

stated that blood vessel B was a vein. This mistake indicates that many candidates

simply answered the question by rote and regurgitated what had been memorised

without thinking.

(ii) Many candidates did not correctly relate the observable feature of the artery wall to its

functional significance. Some of the common misconceptions shown by the candidates are

given below :

- the thick wall maintains a high blood pressure ;

- the muscular wall helps to pump the blood under high pressure.

Such answers indicate that many of the candidates simply memorised information without

understanding. Some candidates erroneously described vessel A/B as having a thick/thin

cell wall. A considerable number of the answers were ambiguous or inaccurate, such as 'the

thick wall enables the artery to accept or adapt to the high blood pressure'.

(iii) Most candidates correctly stated that the biconcave shape of the red blood cells provides a

relatively large surface area. But instead of relating this feature to facilitating the diffusion of

gases, many of them wrongly asserted that it enables the red blood cell to carry more

oxygen.

(iv) Some candidates misinterpreted the question by describing the possible effects of blocking

the vessel on other parts of the body instead of on the heart.



1. (c) (i) (1) short sight --------------------------------------------------------------------------------------------------1

(2) The eyeball might be too long -------------------------------------------------------------------------1

The lens might be too thick ----------------------------------------------------------------------------1

(ii) Large, accurate diagram with smooth lines and parallel incident rays (D) ------------------------1

Title ------------------------------------------------------------------------------------------------------------- �

Presence of an arrow sign --------------------------------------------------------------------------------- �

Focus in front of retina -------------------------------------------------------------------------------------- �

Light rays continue to retina ------------------------------------------------------------------------------- �

Path of light rays from the bus 10m away entering the boy's eye

(iii) Wear a concave lens / have an operation to decrease the curvature of the cornea ------------1

(iv) Cones, which are responsible for colour vision, ---------------------------------------------------------1

cannot function properly in dim light ------------------------------------------------------------------------1

Total : 9 marks

1. (c) (i) Most candidates answered this part correctly.

(ii) The ray diagrams showed a number of mistakes which are also found in some local

textbooks. It is likely that some candidates might have memorised such errors from the

textbooks without genuine understanding. Some of the common mistakes made by the

candidates are illustrated in the following figures :

(1) (2) (3)

(1) The two parallel light rays come from different points on the object.

(2) The light rays stop after converging in front of the retina.

(3) The incident rays from the distant object are diverging instead of being nearly parallel.

The quality of drawing was rather poor; many drawings were too small, untidy and not

in proportion. Most candidates failed to give a title to their drawings.

(iv) Some answers were quite concise and accurate. Many candidates, however, confused the

functions of the rods and of the cones. For example, some stated that rods cannot detect

colour but failed to mention the role of the cones. A small number of candidates wrongly

related the phenomenon to night-blindness.



2. (a) (i) As the plant lost water by transpiration/evaporation, --------------------------------------------------1

it absorbed water from the set-up, -------------------------------------------------------------------------1

so the air bubble moved towards the left.

(ii)

Light intensity

(arbitrary unit)

Rate of water loss

(mm min-1)

10

20

30

40

1.5

2.0

2.5

3.0

Rate of water loss at different light intensities

Results presented in a table with proper headings and units (T) ------------------------------------1

Correct results ------------------------------------------------------------------------------------------ 4 x �

(iii) The rate of water loss increased with an increase in light intensity ---------------------------------1

Reason:

The temperature increased at higher light intensity (1)

so the rate of diffusion of water vapour/evaporation became faster (1)

OR any ONE set -----2

The stomatal pore increased in size at higher light intensity (1)

so the rate of diffusion of water vapour became faster (1)


(iv) Open the tap of the reservoir until the bubble moved to the desired position -------------------1

Total : 9 + 1 marks

2. (a) (ii) Most candidates calculated the rate of water loss correctly and presented their results in a

table. Many, however, did not put down the unit for light intensity.

(iii) Many candidates did not give a satisfactory explanation. They did point out the increase in

stomata! size at higher light intensity, but failed to state that this resulted in a faster rate of

diffusion of water vapour from the leaf.

Instead, they wrongly asserted that the increase in stomatal size led to a higher rate of

photosynthesis or evaporation, which therefore caused a more rapid water loss from the

plant.

15/10 = 1.5

(22-2)/10=2.0

(26-1)/10=2.5

(33-3)/10=3.0



2. (b) (i) Leguminous plants contain nitrogen-fixing bacteria -----------------------------------------------------1

which can change atmospheric nitrogen ------------------------------------------------------------------1

into nitrogenous compounds ----------------------------------------------------------------------------------1

for protein synthesis of the plants ---------------------------------------------------------------------------1


(ii) Vaccination involves the introduction of a

weakened or killed pathogen/antigen into the body -----------------------------------------------1

It stimulates certain white blood cells which will develop a memory for the antigen ------------1

When the body is attacked by similar pathogen / antigen, -------------------------------------------1

it will produce a large amount of antibodies in a short time,

so as to destroy the pathogen ---------------------------------------------------------------------------1

(iii) Birth control serves to limit the increase in population ------------------------------------------------1

Too large a population will lead to faster exhaustion of natural resources, )

destruction of natural habitats and )any TWO... 1, 1

production of larger amount of waste/more serious pollution )

Total : 11 + 1 marks

2. (b) (ii) There were some good answers which were accurate and organised descriptions. A

considerable number of candidates, however, did not distinguish between antibodies and

antigens, or pathogens and the disease.



2. (c) (i) to close the opening of the trachea / to prevent food

from entering the trachea during swallowing ------------------------------------------------------------1

(ii) *peristalsis ---------------------------------------------------------------------------------------------------------1

(iii) It contains protease --------------------------------------------------------------------------------------------1

to digest protein into short peptides / amino acids / polypeptides ----------------------------------1

It is alkaline -------------------------------------------------------------------------------------------------------1

to neutralize the acid from the stomach/to provide a suitable pH for the

functioning of protease ---------------------------------------------------------------------------------------1

(iv) The faeces will become more watery ---------------------------------------------------------------------1

because less water is absorbed if a large part of D is removed ------------------------------------1

(v) - breakdown of excess amino acids/formation of urea )

- storage of iron / vitamin A / Vitamin D / glycogen ) any TWO -------------------- 1,1

- regulation of blood sugar level )

Total : 10 marks

2. (c) (iii) Most candidates mentioned the presence and action of protease in the pancreatic juice, but

only a small number indicated the alkaline nature of the juice and its significance.

(iv) This part was generally well answered, showing that the candidates could apply their

knowledge to explain a novel situation.

(v) A common misconception of the candidates was that deamination of proteins or amino acids

forms urea. This indicates that the candidates just memorised the term 'deamination' without

understanding its exact meaning. For the CE level, it is sufficient and appropriate for the

candidates to understand that the liver breaks down excess proteins or amino acids to form

urea. Introducing the term 'deamination' does not help their understanding and, in fact, may

result in misconceptions.



3. (a) (i) Spherical fruits --------------------------------------------------------------------------------------------------1

In cross B, some offspring must have received an allele for spherical fruits and

an allele for pear-shaped fruits from their parents / heterozygous ---------------------------------1

All daughter plants have spherical fruits -------------------------------------------------------------------1

Therefore, the allele for pear-shaped fruits must be masked by the allele for

spherical fruits ----------------------------------------------------------------------------------------------------1


(ii) Let F represents the allele for spherical fruits

f represents the allele for pear-shaped fruits ------------------------------------------------ 1 or 0

(1) Ff -------------------------------------------------------------------------------------------------------------1

(2) FF ------------------------------------------------------------------------------------------------------------1

(iii)

× ff

Offspring

Gamete

Parent ff

f(F) f

ff

Pear-shaped fruit

Plant with pear-shaped fruit

Plant with pear-shaped fruit

Format (F) --------------------------------------------------------------------------------------------------- 1 or 0

(iv) Sexual reproduction ----------------------------------------------------------------------------------------- 1+

because the self-cross involves the fusion of two gametes/fertilization ----------------------------1

Total : 12 + 1 mark

3. (a) (i) Most candidates did not make a sound, logical deduction based on the results of the genetic

crosses. In general, candidates' communicative skills, as shown in this part, was far from

satisfactory.

(ii) Many candidates did not give a proper definition of the symbols used for the alleles. The

most common error was using a letter to represent the character instead of the allele for that

character.

(iii) The quality of most candidates' genetic diagram was satisfactory.

(iv) Some candidates stated wrongly that the self-cross was a kind of asexual reproduction

because it involved only one parent. Some answered correctly that the self-cross was a

sexual process but wrongly explained that variation occurred in the offspring. This was not

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true in the context of this question.



3. (b) (i) Urea is present in the blood but not in the solution ----------------------------------------------------1

It diffuses into the surrounding solution -------------------------------------------------------------------1

(ii) (1) Because only a small volume of blood enters the kidney )

machine per unit time. ) any ONE --------------------1

To allow time to remove most of the urea from the body )

(2) To remove urea which is continually produced / harmful )

at high concentration ) any ONE --------------------1

To remove excess salts taken up in the diet )

(iii) (1) All useful substances in the glomerular filtrate are reabsorbed back

into the blood along the kidney tubule -------------------------------------------------------------1

(2) As the solution contains the same concentration of glucose, amino

acids and minerals as the normal plasma, -------------------------------------------------------1

there is no net movement of these substances from the blood into

the solution -----------------------------------------------------------------------------------------------1

(iv) Not many people are willing to donate their kidneys after their death ----------------------------1

The kidney transplanted must match with the tissue of the patient --------------------------------1

Total: 9 marks

3. (b) (i) Some candidates could not distinguish diffusion from osmosis and answered that 'urea goes

out of the blood by osmosis'.

(ii) (1) Most candidates did not point out precisely that the kidney machine could only treat a

small volume of blood of the body at a time. Many wrongly stated that 'a long time was

required for urea to diffuse across the dialysis tubing in the kidney machine'.

(iii) (2) Some candidates answered this question accurately by comparing the solute

concentrations of the circulating solution and plasma, showing an understanding of the

mechanism of the kidney machine. A number of candidates wrongly stated that 'the

circulating solution was isotonic with the normal plasma', or 'no osmosis occurs'.



3. (c) (i) (1) food + oxygen � carbon dioxide + water (+ energy) ------------------------------------- 1 or 0

(2) oxygen ------------------------------------------------------------------------------------------------------1

(ii) The water level in limb X would rise -----------------------------------------------------------------------1

Reasons:

The live grasshoppers take up oxygen during respiration -------------------------------------------1

and give out carbon dioxide which is absorbed by the sodium hydroxide solution ------------ I

As a result the air pressure inside flask A becomes lower than that in flask B ------------------1


(iii) To eliminate the error caused by changes in environmental temperature/pressure -------------1

(iv) The rise in the water level is faster/ the water level rises higher -----------------------------------1

because the rate of respiration of grasshoppers is faster at a higher temperature ------------1

Total : 9 + 1 marks

3. (c) (i) (1) Some candidates did not follow the instruction; they wrote a chemical equation for

respiration instead of using a word equation.

(2) Although the question referred to a standard experiment in biology, most candidates

wrongly stated that the set-up measured the change in the amount of carbon dioxide

instead of oxygen.

(ii) Most candidates answered this part correctly, although many of them asserted that the

set-up measured change in the amount of carbon dioxide in (i)(2). This suggests that these

candidates actually did not understand the principle of the investigation, but simply

answered from rote memory using information given in textbooks or by teachers. Some

common mistakes were detected in the candidates' explanations, e.g. the consumption of

oxygen by respiration results in a drop in air volume in flask A; heat released from

respiration of the grasshoppers causes the air in flask A to expand.

(iii) Most candidates mentioned that flask B was a control but did not explain its use. Very few

candidates correctly stated that the presence of flask B was to eliminate the error caused by

changes in environmental temperature or pressure during the experiment.



4. (a) (i) As the water potential of the sucrose solution is lower than that of the distilled water, -------1

water passes through the potato ---------------------------------------------------------------------------1

into sucrose solution, ------------------------------------------------------------------------------------------1

causing the level to rise.


(ii) Osmosis occurs when two solutions of different concentrations are separated,

by living tissue -------------------------------------------------------------------------------------------1

which serves as a selectively permeable membrane ------------------------------------------------- I

(iii) Large, clear drawing with smooth lines (D) -------------------------------------------------------------- I

* Labels (any three): cell wall, cell membrane, cytoplasm ----------------------------------- � X 3

(optional: starch grains, nucleus, vacuole)

Title ------------------------------------------------------------------------------------------------------------- �

Signs of plasmolysis and turgidity (S) ---------------------------------------------------------------------1

(iv) The cell membrane of potato cells became freely permeable/was destroyed

after boiling --------------------------------------------------------------------------------------------------- 1 +

so sucrose can diffuse out to the distilled water --------------------------------------------------------1

Total: 11+1 marks

4. (a) (ii) The poor performance on this question shows that the candidates were still quite weak in

drawing conclusions by comparing the results of two set-ups with reference to the different

set-up conditions.

(iii) The quality of drawing was poor. Various cellular features were not drawn in the right way,

e.g. the cell wall wrongly represented as a single line, the cell membrane in a turgid cell

incorrectly shown as detached from the cell wall, and the vacuole and cytoplasm incorrectly

positioned. There were a lot of spelling mistakes on the labels. Most candidates did not give

an appropriate title for their drawings.

(iv) Many answers were incomplete with the candidates simply saying that the boiled potato was

no longer selectively permeable, without pointing out specifically that the tissue became

freely permeable after boiling. Some candidates erroneously stated that 'the sucrose

solution (rather than sucrose) diffuses out to the distilled water'.



4. (b) (i) (1) competition -----------------------------------------------------------------------------------------------1

(2) predation and competition ---------------------------------------------------------------------- 1 or 0

(ii) The shorter period of daylight would result in a lower photosynthetic activity -------------------1

so the algal population would decrease ------------------------------------------------------------------1

(iii) DDT is leached into the sea from farming areas in other regions ----------------------------------1

It is absorbed by microscopic algae -----------------------------------------------------------------------1

DDT or microscopic algae are carried by oceanic currents to the South Pole region ---------1

As penguins feeds on squids, while squids feed on shrimps,

and shrimps feed on algae,. ----------------------------------------------------------------------------------1

and DDT cannot be metabolized or excreted by the organisms, -----------------------------------1

so it accumulates up the food chain into the body of penguin.


Total: 9 + 1 marks

4. (b) (i) (2) Most candidates mentioned predation but left out competition as a type of relationship

between the squid and the sea bird.

(iii) Most answers failed to include a clear, organised explanation for the concentration effect of

DDT along the food chain. Some candidates did not even mention the role of the algae or

the non-biodegradable nature of DDT There was a general lack of communicative skills

shown by the candidates in answering this question.



4. (c) (i) (1) The skin temperature increased ----------------------------------------------------------------------1

(2) Vasodilation occurs in the arterioles of the skin ---------------------------------------------------1

so that more blood bringing heat flows to the skin -----------------------------------------------1

(ii) (1) The body temperature remains constant -----------------------------------------------------------1

(2) Sweating ----------------------------------------------------------------------------------------------------1

As the room temperature was higher than the body temperature, ---------------------------1

heat could not be lost by conduction / convection / radiation ----------------------------------1

so sweating was the main way of heat loss.

(3) Evaporation of sweat is too slow to lose heat effectively ---------------------------------------1

while the body absorbs heat from the environment ----------------------------------------------1

Thus the body becomes overheated ----------------------------------------------------------------1

Total : 10 marks

4. (c) (i) (2) Some candidates did not seem to understand what was meant by physiological

change. Some wrongly stated that vasodilation occurs in the capillaries instead of the

arterioles of the skin. Many did not point out the significance of vasodilation of the skin

in causing a rise in skin temperature.

(ii) (2) Although most candidates knew that heat loss from the body could occur in different

ways, they did not understand the significance of these ways in different situations. For

instance, heat cannot be lost from the body by conduction or radiation when the room

temperature is higher than the body temperature. As a result, many candidates did not

point out correctly that sweating is the main way to lose body heat under the specified

condition.

(3) Some candidates erroneously stated that sweating is very slow when the relative

humidity of a room becomes high. As body heat cannot be removed efficiently by the

evaporation of sweat in such a situation, sweat production actually increases. Only a

small number of candidates mentioned the consequence of a rise in body temperature.

Very few pointed out that the body actually absorbs heat from the surroundings in such

a situation.

1996 Biology Paper I Marking Scheme

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