AL Bio 2008 Marking Scheme

8/3/2019 AL Bio 2008 Marking Scheme

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Marking Schemes

Paper I Section A

l. (a) r xosmosis(l)

53'Tli:*X'Tiil:$ :i)".d and pointed canines ror klring prey and tearing orr

flesh (l) / large, powerful and sharp-edged molars / carnassial teeth for cutting

flesh and crushing bones

o plants / herbivorous (l):

and molars has sharp vertical ridges for grinding plant materials / incisors are

chisel-like for cutting plants

M_arks

(l)

(b) o the cell may absorb inorganic solutes (e.g. salts) (1) from the extracellular fluid to (3)

. fJ.'J :::.:;ffi'::fl llT'[ff ,ff ,T ll,:'/".,.ease / restorati on of th e ce r r vo r um e

2. (a) (i) o as the site of formation of the polypeptide (l) I fbr transporting the (4)

polypeptide / modification of the polypeptide / as the site of translation(ii) . as the site of formation of the mRNA of amylase (l) / as the site of

transcription / contains genetic information coding for amylase

(iii) . B (l)(iv) . *Golgi apparatus / body (l)

(b) o *mucin (1) / mucus / lysozymeo for lubricating the swallowing of food (1) / sticking food particles together / kills

germs in food

3. (a) . warm temperature / high light intensity promotes groMh of the algae (l). discharge of organic or nutrient-enriched matters to the sea provides nutrients fbr

the growth of the algae (l )

(b) r the harmful algae produce toxins (l) in their cellso the toxins would be taken into shellfish which feed on the algae and eventually

passed to humans along the food chain (l). as the toxins are not metabolized / excreted by the shellfish (l), the toxins may

reach / bioaccumulate to a level that causes poisoning in humans (l)

4. (a) o the storage process allows sufficient time (l) fbr the endogenous proteolytic (2)

enzymes to digest partially the meat tissue (1), leading to tenderization of the meat

(b) . storage at low temperature helps retard microbial growth (l) / prevent spoilage (l)

(2)

(2)

(4)

103

The marking schemes were prepared for markers' reference. They should not be regarded as sets of model

answers. Candidates and teachers who were not involved in the marking process are advised to interpret

their contents with care.

The examination emphasises the testing of understanding, the practical application of knowledge and the use

of processing skills. Candidates are advised to study this document in conjunction with the examiner's

comments on candidates'performance in this booklet.

(4)



6. curve x ( 1)

compared to curve Y, curve X shows thehaemoglobin

startsloading and

unloading oxygen at a lower concentration (1) and it reaches saturation at a lower

oxygen tension (l), indicating a higher affinity for oxygen (l) at low oxygen

tension

this enables the worm to acquire oxygen in the burrows in muddy soil which has a

low oxygen content (l)

due to uncontrolled growth of insulin-secreting cells (l), this pancreatic cancer

probably leads to an excessive secretion of insulin (l)as insulin stimulates the conversion of blood glucose into glycogen by the liver (l)/ uptake of blood glucose by cells, excessive insulin secretion would reduce the

blood glucose to a low level (l)as a result of insufficient blood glucose supplyto the brain (1), the man would feel

dizzy

some tissues of the pancreas secrete protease and lipase (l)they may be removed together with the cancerous tissues. The lack of protease and

lipase would make the digestion of protein and fat difficult (l)

body balance (l)

the position and / or movement of the head (l )

semi-circular canals (l )

hair cells (l)

B (l)

F (l)

c (l)

I

max.2

I

(4)

max. 3

I

(4)

(2)

)

(a).

(b)

(a).

(b)

(c)

(d)

(a).

(b)

(c)

a

o

(4)

(3)

t04



Paper 1 Section B Marks

Hormone level

(arbitrary unit)

Total: 14 marks

10. (a) o

o

o

o

o

correct title (%)

correct choice of axes (%)

correct labelling of axes with units (1%)

correct plotting and joining of points (3)

key I labels for the three line graphs (t/z)

Relationship of the change in blood levels of calcium, hormone X and hormone Y with time

300

254

(6)

Blood calcium

(mmol L-r) 2.2

6

Time (hour)

from hour 0 to hour 4, decrease in blood calcium level resulted in an increase in the

level of hormone X (l)from hour 4 to hour 10, blood calcium level rose and there was a corresponding

decline in the level of hormone X (l)

when the level of hormone X rose, the level of hormone Y also increased (l) (2)

the peak in hormone Y level lagged behind that of hormone X (l)

in the first part, inject hormone X into the blood of rats (l), a rise in the blood (max.4)

level of hormone Y (l) and calcium (l) would show the stimulatory effect ofX on Y and calcium

in the second part, inject hormone Y into the blood of rats (1), there should be

a rise in the blood level of calcium (l) if the hypothesis is correct

(2)b)

(i)c) o

o

(ii) o

o

105



I l. (a) (i)

Marks

chemical M was absorbed from the alimentary canal into the blood of the (2)

pregnant rats (l) and was passed to the F' foetus through the placenta (l)

chemical M treatment had no effect on the viability of the offspring (l) / (3)

number of live offspring born

and no effect on the development of follicles (l) / the number of growing

follicles in the female offspring

but it caused a reduction in sperm count and sperm motility (l) in the male

offspring

Concept for mark award:

o fewer live offspring in sub-group B (l) due to reduced sperm formation (l) /formation of defective eggs / a lower fertilization rate / higher abortion rate Ilower rate of successful implantation

altered sex ratio (l) / more females than males produced, possibly due to

selective adverse effects on sperms with Y chromosome (1

the total number of live offspring produced in sub-group B was smaller than

that in sub-group A (l)this may be due to reduced sperm formation (l) / formation of defective eggs

I a lower rate of fertilization / higher rate of abortion / lower rate ofsuccessful implantation in sub-group B

the sex ratio was altered by a reduction in the number of male offspring (1) /

there were more females than males

possibly because chemical M may have selective adverse effects on sperms

carrying the Y chromosome (l )

sperms or eggs -+ defective

support full development of

support full development of

(ii) .

o

a

(b) (i)

e.g. .

o

a

a

(4)

( ii) Concept for mark award: (any two) 2 x (l +l)o mutation in DNA (l) in sperms I ova / defective

foetus ( I )o malfunctioned / defective placenta (l) -+ cannot

the foetus (l)defects in the maternal physiology (l) + cannot

all the foetuses (l

e.g. Any two of the following: 2 x (l+l) (4)

o there might be mutation in the chromosomal DNA (l) in sperms I ova I

sperms or eggs might be defective, leading to the development of defective

foetus ( I )o the placenta might be malfunctioned I had defects (l) so that it could not

support full development of the foetus (l)o there might be defects in the maternal physiology ( I ) (e.g. intestinal

absorption, circulation), so that the female could not support the

development of all the foetuses and some eventually died (l)

(l bonus mark for pointing out the consequence on F2 arises from the effect of

chemical M on the F1)

106

Total: 13 marks



Marks

(2)

2'(a) (i)

: ;mtilJt? c showed the highest rerative growth rate tyierd at row

phosphate supply (25 and 50 mg per pot) as compared to A and B (l)

(2)ii): ilil:ff:J:: :,:il.ffi.:"J,1il:!',]nun,. phosphate absorption (r)

(iii) o o/s dry weight allows the comparison of the yield of seedlings among (2)

different species (l) whereas the absolute dry weight of seedlings are

inherently different due to differences of the species ( I ), which makes

comparison impossible

(b) (i) (l) . species D showed a higher uptake rate for phosphate (l) than the (3)control, including a higher maximum (l). This could be achieved by

synthesizing additional transport proteins for phosphate (1)

(2) o species E was more efficient in absorbing phosphate at low phosphate (max.3)

concentrations (l) as compared to the controlo the maximum uptake rate remained unchanged (l)o this may be due to a higher efficiency I affinity of the transport proteins

(l) developed in species E in response to phosphate deficiency, but the

number of transport proteins remained unchanged (l)

(ii) . all the transport proteins were saturated with phosphate atany one time (l) / (l)factors other than phosphate concentration became Iimiting

Total: 13 marks

Paper I Section C

13. (a) Any two of the following:. ionizing radiation (l)o chemicals (l). virus (1)

Marks

(2)

(b) ward:

Any two of the following explanations: 2x (l,l) (accept other correct alternatives)

o gene as allelic pairs (l) -+ recessive mutation masked by the effect of the normal

allele ( I ). degenerative nature of the genetic code (l) + mutation in one base may not cause (4)

a change in the amino acid coded (l) / normal gene product can still be produced

o most mutations are repaired (l) -+ normal mRNA can still be formed (l)o the active site of the gene product may not be altered much (l) -+ normal

functionirrg of the gene product is maintained (l)

e.g. Any two of the following explanations: 2x (l,l)o genes usually occur as allelic pairs on homologous chromosomes (1), mutation in

one allele, if recessive, would not cause harm because the normal allele can still

form the gene product (1)

o several codons code for the same amino acid (l) / due to the degenerative nature

of the genetic code, mutation in one base may not lead to a change in the amino

acid coded (l) / normal gene product can still be produced in some cases

(4)

t07



(c)

o most mutations are repaired by substituting I replacing the changed nucleotide(s)with the correct nucleotide(s) (l), so the normal mRNA can still be formed (l)

o changes in a few amino acids may not alter the conformation of the active site ofthe gene product (l), so the mutation may not affect the functioning of the gene

product (l)


o relate the response of B cells upon vaccination to antibody production (l)r relate the response of T cells uDon vaccination to T cell oroliferation (l

(2)

e.g. r B cells lead to antibody production; due to the poor immune response of SCIDbabies, the number of B / plasma cells formed after vaccination is very small (l) /no humoral immune response will be elicited, resulting in a low antibody level in

the plasma

- ---r -)'---'-- -o --- - "-r ^- (2)

o f cells also fail to proliferate (1) / no cell-mediated immune response will be

elicited, resulting in the low level of T cells


o XSCID is sex-linked (l); so once the male inherits one recessive allele on the Xchromosome (l ), he will develop the disease

r ADA SCID develops only when a person is homozygous for the mutated allele (max. 3)(l), the chance is lower (l)

o mutation leading to XSCID may occur at a higher frequency than that of ADASCID in a oooulation ( I

e.g. o XSCID is sex-linked (1) / the mutated allele for XSCID is carried on the Xchromosome; once the male inherits a copy of the mutated allele on the Xchromosome (l), he will develop the disease as there would not be another normalallele to offset the effect of the mutated allele

. whereas in ADA SCID, individuals would only develop the disease when they (max. 3)

inherit two copies of the mutated allele from the parents (l) / are homozygous forthe mutated allele, thus the chance of developing the disease is lower (l)

e besides, the mutation leading to XSCID may occur at a higher frequency than that

ofADA SCID in a population (l), resulting in a higher incidence of the former

(d)

(e) Somatic gene therapv Germ-line gene therapvo

the change only occurs inthe

manipulated body cells and their

daughter cells of the treated

individual

othe

changeswill affect all the cellsof the offspring

r the changes are not inheritable and

affect only the individual who

undertakes the therapv

o the changes will be inherited in allmembers of the subsequent

senerations

. does not change the genome of thepopulation

. may lead to changes in the genome

of the population

(*Any two of the above comparison)

Concept for mark award: (accept other reasonable answers)

r take in more refined food that lacks dietary fibre (l) -+ higher chance of colon /rectal cancer (1)

o have a more stressful lifestyle (1) -+ increase the chance of cancer developmento lack physical exercise (l) + higher chance of obesity (1) -+ increase the chance

of cancer development'^D'^-' (max' 5)

. reach older age (1) -+ higher chance of accumulating mutations in cells (l),leading to cancer development

. medical advancement / better preventive measures (1) -+ death rate due to other

diseases is lower (l

108

(f)



e.g. o people in developed countries take in more refined food that lacks dietary fibre(l), leading to a higher chance of colon /rectal cancer (l)

o people in developed countries have a more stressful lifestyle (l) which may

increase the chance of cancer development. people in developed countries generally lack physical exercise (1), resulting in a

[t"T:Omr.of obesity (l), which may increase the chance of cancer

(max. 5)

o people in developed countries can reach an older age (l), thus have a higher

chance of accumulating mutations in cells (l), leading to cancer development

o due to medical advancement / better preventive measures (1), the death rate due to

other diseases is lower in developed countries (l)(accept other reasonable answers)

(g) Any two of the following: (accept other correct alternatives) (2)

o coronary heart diseases (l). hypertension (l)o atherosclerosis ( 1)

o constipation (l)o scurvy (l)o night-blindness (1)

Total: 20 marks

Paper 2 Section A

L (a) Nucleotide number 20 A is changed to T (l)

(b) Concept of mark award:[base sequence being the same as the coding sequence (l) except T is replaced by U

(l)l

AUG GUG CAC CUG ACU CCU GUG GAG

Marks

(l)

(2)

(c) Met Val His Leu Thr Pro Val Glu (2) (2)

(d) (i) : ;:'T)''Ji,'*l'l[t'?#ll",T'L'r",::3.'ti'5ltoo which can be

recognized by the restriction enzyme (l); the B-chain gene is thus cut into

two DNA fragments (l) of different lengths / masses (l bm) between C and@)

' iJd{ l.1iffi,1itrjl#sr:TfiiT:f:h:H:,i$ H*::

(ii)lii,f;:1"i#:;i##*1,T""

be AS (r) / heterozvsous because thev haveQ)

(iii) Parent AS x AS

GameteAsASl

Offspring AA AS AS SS I

Offspring normal sickle-cell trait sickle cell anaemia I

phenotype

Format of genetic diagram (parent, gamete and offspring indicated) I

The chance for the couple to have a child with sickle-cell trait is 214 :'/r.(l)(5)

109



(e) Concept for mark award:

r advantage of sickle-cell trait outweighs disadvantage of being

malarial prevalent areas (l)o malarial infection as selection agent (l)o preferential survival of individuals with sickle-cell trait (l). reproduction to pass the S allele to subsequent generations (1), hence a rise in

proportion of individuals with sickle-cell trait from one generation to another (1)

o reasons for fewer cases of sickle-cell trait in areas with low incidence of malaria:

e (l)

in malarial prevalent areas, the survival advantage brought by sickle-cell traitagainst malarial infection outweighs the disadvantages of being mildly anaemic

(t)malarial infection acts as a selection agent for people with sickle-cell trait (1)

people with sickle-cell trait have a higher chance to survive and reproduce (l),passing the S allele to the subsequent generations (l)the proportion of individuals within a population having sickle-cell trait increases

from one generation to another (l), making the trait more common in the

population

in areas with low incidence of malaria, people with sickle-cell trait would not

have such a selection advantage (l), instead being mildly anaemic is a

disadvantage ( I ), thus the trait is less common in these areas

rate of glycolysis would be higher under anaerobic conditions (l)because ATP production is lower in anaerobic conditions (l)the inhibitory effect of ATP on enzyme E is lower (l) and hence the conversion

of intermediates A to B would be faster ( I )

competitive inhibitor competes with the substrate for the active site of the

enzyme, thus with inhibitor concentration kept constant (l), increasing

substrate concentration will remove the inhibitory effect of the

competitive inhibitor (l) / lead to the attainment of the same maximal

reaction rate

fluoride inhibits glycolysis ( I )

it would prevent / inhibit the uptake of plasma glucose by red blood cells

for glycolysis (l)as a result, the plasma glucose level would not be changed (l) /would not

decrease / the plasma glucose level so determined would not be lower than

the actual level

pyruvate will be reduced by NADH to lactate ( I )

this will regenerate NAD (l) for sustaining glycolysis

anaemlc

e.g.

(max.4)

(max. 4)

Total: 20 marks

Marks

o

a

2. (a) o

o

a(4)

(b) (i)

( ii)

(i) o

a

(c)

(2)

(3)

(2\


. red blood cells as oxygen carrier (l)o absence of mitochondria -> lack of Krebs cycle and electron transport

chain (l) / oxidative metabolism

. little / no oxygen consumed due to lack of Krebs cycle and electron

transport chain (l) I amount of oxygen carried in red blood cells is

rved

(3)

( ii)

ll0



e.g. . red blood cells serves in oxygen transport (l). a lack of mitochondria implies a lack of Krebs cycle and electron transport

chain (l) / oxidative metabolism in the cells

o this results in little / no oxygen consumption (l) / helps to preserve the

amount of oxygen carried in red blood cells


o G6PD deficiency results in a reduction in NADPH formation ( I )

o membrane integrity cannot be maintained (l) / RBCs are more likely to ,

burst (3)

o haemoglobin released to plasma is more likely to be broken down (l) /number of RBCs decreases

(3)

(d) (i)

e.g. o glucose-6-phosphate dehydrogenase deficiency brings about a reduction in

the formation of NADPH (1)

. with insufflrcient NADPH, membrane integrity cannot be maintained (l) /the red blood cells are more likely to burst

. haemoglobin released into plasma is more likely to be broken down (l) /haemoglobin level would drop / number of red blood cells would

decrease, resulting in symptoms of anaemia

(ii) . reducing property ( I )

(iii) Two examples. one from anlz two of the following categories: (2 x 1)

o ATP /ADPo NAD / NADHo NADP / NADPH

o FAD / FADHo mRNA / tRNA / rRNA(accept other correct answers)

Total: 20 marks

Marks

3. (a) o photosynthetic activities is higher in summer (1) than in winter as the daylength

is longer / air temperature is higher (# I ) and plant growth is faster (# I )o this will consume more carbon dioxide in air (#l), thus lower the atmospheric (3)

carbon dioxide concentration(# : any two out of the 3 points)


o example of the human activity (l)o source of methane: from organic matter (l)

(3)

o methane produced by anaerobic respiration (l

e.g. Any one of the following sets:

. domestic wastes are dumped in landfills (1)

o organic matters (l) in the wastes are decomposed by anaerobic bacteria (l),forming methane

OR. more livestock such as cows are reared byhumans for food (1)

. anaerobic bacteria (l) decompose organic matters (l) in the gut of cows to

produce methane which is then released to the environment

ORo in rice cultivation (1), flooded fields favour the anaerobic activity of soil bacteria

(l) which decompose organic matter (1) in soil and release methane

(3)

(l)

(2)

(b)

lll

(3)



(c)

(d)

carbon dioxide and methane absorb heat radiated from the Earth surface (l) and

re-radiate the heat back to the Earth (l), thus heat builds up in the lower

atmosphere (l) / near the Earth surface, resulting in global warming

Any one of the following sets: (l+l). more intense rainstorms (1) / typhoons or hurricanes / higher rainfallo these changes rvould result in physical destruction of crops in fields (1) la loss of

arable land due to flooding / mudslides

ORo heat waves / intensified droughts / drier summers ( l)o these changes would impair crop growth (l) / result in a loss of arable land

An), two of the following: (accept other reasonable answers)

Invasive species may:

. cofflpetewith

local speciesfor

resources (l). transrnit diseases that may kill local species (l). be potential predators of local species (1)

. lead to the decline / extinction of local species (l)o become prey of local species, which will then increase in population (l)

warmer conditions favour bacterial growth (l), cholera is caused by a kind ofbacteria wliich is transmitted through contaminated food / water (l)warmer conditions favour the breeding i activity of mosquitoes (l), which is the

vector of the malarial pathogen (l)

baleen whales feed only on krill (l), so if the number of krill declines greatly, the

u'hale population rvould drop as a result of food shortage (l)penguins have food sources (e.g. zooplanktons) other than krill (1), the nurrber

of these organisms may increase as a result of the decline of krill (l), thus the

penguin population is less affected

off of vesicles

(l) due to membrane

of this hydrophobic ( l)

(max.2)

Total: 20 marks

Marks

max. 4

max. 4

(max. 6)

(2)

(e)

Paper 2 Section B

(0

(2)

(4)

1u)

(4)

(a). Concept for mark award:

. how phospholipids lead to membrane fluidiry (2) and hence support functions

invagination of membrane (l) / endocy'tosis / budding

exocy,tcsis (1) and intracellular vesicular transport

fusion ( l)horv phospholipids form a bilayer (l) and the importance

bilayer to membrane function:

substances ( I )

oteins ( I

the phospholipids molecules in the membrane are capable of slight lateral

movements ( I ), giving fluidity ( 1) to the membrane

vesicles from ER and Golgi apparatus

contained in vesicles by exocy4osis (1), and the intracellular vesicular transport

of materials (l) e.g. transport of proteins in vesicles from RER to the Golgi

apparatus

)

r.5.

n2

max.4



due to the hydrophobic nature (l) of the fatty acid chains, phospholipid

molecules spontaneously form a bilayer (l) in aqueous surroundings

compartmentalization (1) and can help restrict the entry / exit of ionsand

polar molecules (l), thus establishing gradients of charges / concentration

across membranes

proteins (1) so that they can exert their respective functions

at the leaf-end of the sieve tubes, active loading of sugars from the mesophyll

cells into the sieve tubes occurs (l), making this end the source; this would lower

the water potential (l) of this part of the sieve tubes and water enters the sieve

tubes by osmosis from the xylem ( l), raising the pressure potential at the source

0)at the root / the fruits / active growing regions / storage organs, unloading ofsugars from the sieve tubes to the surrounding cells occurs (1), making this end

of the sieve tube the sink; this rvould increase the water potential (l) of this part

of the sieve tubes and water leaves the sieve tubes by osrnosis (l) along with the

sugars, lowering the pressure potential at the sink (l)a hydrostatic pressure gradient (l) is set up between the source and the sink,

forcing a mass florv of solution along the sieve tubes ( I ), thus transportine

orsanic food from the source to the sink

Relating features of the myofibril to the sliding-filament hypothesis:

. filaments are observed in the myofibril (l)o the actln (thin) filaments and the myosin (thick) filaments inter-digit with one

another (l). during muscle contraction, actin filaments slide over myosin filaments (#l) to

bring about an overall shortening of the length of the muscle fibre (l) I

myofibril, while the length of the filaments remains unchanged (1)

max.4

(r""^i)

(b)

e.g. max. 3

max. 3

2

('"r-i)

(c)


o how loading of sugars at the source end of the sieve tubes results in a rise in the max. 3

pressure potential (4)

o how unloading of sugars at the sink end of the sieve tubes results in a drop in the max.3

pressure potential (4)

o the subsequent set up of a hydrostatic pressure gradient between the source and )the sink (1) to drive the mass flow of solution containing the organic food (l)

(max. 6)


Relating features of the rnyofibril to the sliding-filament hypothesis:

. filaments observed in the myofibril (l)r filaments inter-digit (l) with one another

o relate these features to the sliding-filament hypothesis (3)

Changes irr the regions of the myofibril during contraction:. decreases in length of the light band (2)

o increases in length of the dark ends of the dark bands (2) and decrease in length

of the H-zone in the dark bands (2) max' 6

. no change in length of dark bands (1)

. decrease in leneth of sarcomere (1) / distance between two Z lines

(max. 8)

e.g.

ll3



Changes in the regions of the myofibril during contraction:

o due to the sliding of the actin filaments into the myosin filaments (#1), the light

band of the myofibril, which makes up of actin filaments only (l), decreases in

length (1)

o the dark ends of the dark bands, which represent the overlapping regions of the max. 6

actin and myosin (1), increase in length (1); the H zone of the dark band, which

is the region of myosin only (1), decreases in length or even disappears (1)

o there would be no change in the length of the dark bands (l)o the overall lensth of the sarcomere decreases (l) / distance between two Zlines

shortens

(# marks to be awarded once only)(max. 8)

5. (a) Reflexes Tropism

o response

internal st

s elicited by external or

muli

. response is elicited by external

stimuli

r stimuli involved mav or mav not be

unilateral

o stimuli involved are unilateral

. messages involved are

electrochemical in nature (1)

. messages involved are chemical in

nature (l)o most are non-directional responses o directional responses, either

towards or away from the stimuluso quick responses o slower responses

o Don-Rrowth responses o flroMh responses

Marks

II

1I

l, I

I

I

I

max.6

max.7

Significance:. protection against danger ( I ) I

damage

photoreceptors from damage by

strong light (1)

objects protects the skin from

being burnt / cut (l)

protects the eyes from

mechanical damage (1)

o adjustment to changes in internal

environment for optimum body

function (l) / for homeostasis

response to increased carbon

dioxide level in arterial blood so

as to speed up the removal ofcarbon dioxide (1)

o as reactions to perform body

functions (1)

muscle tone in maintaining

posture ( I )

to prepare for digestion in

mouth (l

Significance:o to position its body parts so as to

obtain adequate supply of light,

nutrients, water (l) for better

groMh and survival ( I )

or

o phototropism helps to bring leavestowards light for more food

production (l) / photosynthesis, forproper growth and development ofshoot (l)

. geotropism helps to bring root into

the soil for nutrient and water

absorption (l) and for anchorage

(l). hydrotropism helps to bring roots to

areas of the soil with hieher water

content (l)

max.4

n4



(b)

dilation of pupil under dim

conditions allows more light to

reach the retina (l )when distended by food

peristalsis of intestine increases

to help movement of food inside

(l)max.4

(max. I l)

Any four of the following: (max. 4)

. it has to be synthesized within presynaptic neurones ( I )

o it has to be found in vesicles present in presynaptic terminals (l) / knobs

r it has to be released by presynaptic stimulation (l)o it can bind specifically to the post-synaptic receptors (l)

o it can induce post-synaptic potential (1)r it has to be metabolically degraded (l)

o reptiles are restricted ecologically such that they are more numerous in tropicalareas (l) and are rare in habitats with extreme low temperatures, such as the

polar regions (1)

. because being ectotherms, reptiles gain heat mainly from the environment (l)and the tropics are warmer (1), thus suitable for their survival

o mammals are more widely distributed ecologically (l) lcan be found from the

tropics to the polar regions, because they can generate body heat (l) and can

maintain a constant body temperature irrespective to changes in the external

temperature ( I )

(max. 5)

Marks

max. 8

(c)

e.g.

6. (a)

lI

It'(n.-10)


o contrast ecological distribution of reptiles and mammals:

e relate the ecological distribution of reptiles to their dependence on environmental(max' 5)

heat (l) and the variation in temperature in different regions of the Earth (1)

r relate the ecological distribution of mammals to their ability of generating

metabolic heat ( I ) and maintaining a constant body temperature ( I


For the comparison part:. similarities in terms of:

establishing a close relationship with host / mother; and having a large

surface area for absorption (l)o differences in terms of:

for food absorption

Reasons supporting the relationship being a kind of parasitism:

o foetus depends of the mother for food (1)

. cite example(s) to illustrate how the foetus brings harm to the mother (l)

Reasons against the relationship being a kind of parasitism:

o relationship is not between two species (1

ll5



e.g. Tapeworm Foetus

o both obtains digested food from the host / mother (l) by diffusion (l)o both are living inside the host / mother (1) / establish a very close relationship

with the host / mother

o absorbs food through its body

surface (l) / no specialized organ forfood absorptron

. absorbs food at the placenta (l) /across the chorionic villi / presence

of a specialized organ for food

uptake

a both have a large surface area for food absorption ( I )

r the elongated and flattened body (1)

helps to provide the large surface

area

o ho transport system to facilitate food

absorption ( I )

o the numerous finger-like chorronrc

villi (l) help to provide the large

surface area

o food absorbed is quickly

transported away from the placentaby the umbilical vein (l) and this

helps to maintain the concentrationgradient for continuous diffusion

0)max. 8

Considered as parasitism:

o foetus is dependent on mother for provision of food ( I ). it may bring harm to mother e.g. causes weakening of teeth and bones of the

mother due to the uptake of calcium from these structure ( l), add stress to Imother's backbone due to its weieht. etc.

Not considered as parasitism:o relationship is not between two different species (1)

(tr.* l0)

o continual stimulation of the nipples (l) by suckling. send nerve impulses to the hypothalamus (l)o rvhich stimulates the pituitary gland (1), resulting in an increase in prolactin

secretion (l) and oxytocin secretion (l) (max.6)

o prolactin stimulates the mammary glands to produce milk ( l)r ox),tocin stimulates contraction of smooth muscle of mammary gland (l),

resulting in milk ejection

r in photosynthesis, carbon dioxide and water (l) is assimilated to form glucose (l)I 3-C intermediate / triose phosphate

e nitrate (l) / ammonium ions and the carbon skeleton derived from glucose (l) / (max.4)

3-C intermediate are used for synthesizing amino acids (l)r amino acids are then condensed / polymerized to form proteins (1)

(b)

(c)

ll6



Paper 2 Section C

The assessment of essay is divided into2 areas, i.e. content and style.

Marks

Content (max. 15)

Ideas / concepts and mark allocation suggested in the marking scheme will give markers some

guidelines in assessing essays in this section. Nevertheless these ideas / concepts should not be

treated as the only acceptable answers. Markers should exercise their professional expertise in

judging alternative options / viewpoints given by candidates which they consider relevant and

appropriate. Markers are requested to go through a number of live scripts (with answers

relevant but not stated in this marking scheme) and come up with suggested alternative

answers for discussion at the markers' meeting. The chief examiner should be ccnsulted in

case ofdoubts on accuracy.

Stvle

Marks on style is based on the following:

(max. 5)

Criteria on effective communication

Marksawarded

Clarity of expression

Logical and

systematicpresentation

Marksawarded

Relevance to

the question

J

Easy to understand,

fluent, good command

of language

Well structured

showing coherence ofthought and

orsanization of ideas z No or little irrelevantmaterial

2

Language used is

understandable, some

inappropriate use ofwords

Most answers are

organised, some

reoetitions of ideas

I

Irrelevant materials

obscure some minor

ideas

Markers have to

spend some time and

effort to understand

Answers a bit

disorganised, but

paragraphing is

evident, repetitions

are prominent

0

Irrelevant material

burying the major

ideas required by the

questionLanguage used ls

incomprehensible

Just paragraphs

shown, ideas are not

coherent and

systematic

Answers chaotic,

showing no attempt

to organize thoughts

n7



7.

Paper 2 Section C


Knowledge on cycling of nutrients:o harvesting of crops disrupts natural cycling of nutrients (2)

. need to replenish soil nutrients by:

o enhance microbial activities involved in the nutrient cvcline

Knowledge on interdependence of organisms:o parasites / pathogens of crops (l) and its importance:

diseases (1), crop rotation to break life cycle of pathogens / parasites ((1)to protect the crop from infection (1)

o feeding relationship of other organisms (pests) and the crop plants (1) and its

importance:

parasitism / predation (2); crop rotation to break life cycle of pest ((l)o competition and its importance:

o mutualism and its importance e.g. legumes with nitrogen-fixing bacteria and theiruse (#3), keeping bees in orchards for pollinating fruit trees (l)

e.g. Knowledge of cycling of nutrients:

o due to constant harvesting, nutrients locked in the harvested plant parts are

removed from the field / not recycled to the soil (l), resulting in a gradual

depletion of soil nutrients (1)

to replenish the soil nutrient supply, farmers may

form to the soil

as organic fertilizers (l); they will be decomposed by soil bacteria (l) and the

minerals locked inside will be released / recycled (1) for crop growth

crop; roots of legumes are known to harbour some nitrogen-fixing bacteria

(#l) which fixes atmospheric nitrogen into ammonia / organic nitrogen (#l);when the organic nitrogen is decomposed, it will increase the nitrate content

of the soil (#l)

with the knowledge of the microbial activities involved in the cycling of nutrients,

farmers can plough the earth to aerate the soil (l) so as to encourage the activities

of putrefying bacteria and nitrifying bacteria (l) which together help to recycleorganic nitrogen to nitrates (l) and discourage the activity of denitrifying bacteria

(l) which convert nitrates to nitrogen gas (1)

Marks

max. 9

max. 9

5

JJ^t r Iff)-r I

(max.l5)

max. 9

2

118



Knowledge of interdependence of organisms: max. 9

.understandingthatthereare@(l)ofcropplants,farmers/scientists can study and identify the parasites / pathogens and their routes of 5

transmission (1) / biology, so as to develop control measures to protect the crops

from infection (@l), thus raising the yield:

pathogens / vectors of diseases

o understanding that there are organisms that feed on crop plants (l), farmers can:

protect the crops from damage (@1) / secondary infection, thus increasing the

yield;

parasitism / predation in which the parasite / predator of the pest is

introduced to control the population of the pest (l) (e.g. using the bacteria

Bacillus thuringensls to control the pest of cotton plants);

o concept of competition:

themselves for space, light, water and nutrients, farmers would plant crops

with sufficient spacing in between (l) / remove weaker plants;

and the crop (l), farmers may apply herbicides to control the growth of weeds

( I ) which compete with crop plants for nutrients / light / space I water

. concept of mutualism:

(#l), farmers may grow legumes in fields so that the bacteria fixes #3

atmospheric nitrogen into ammonia I organic nitrogen (#l); when the organic

nitrogen is decomposed, it will increase the nitrate content of the soil (#l);

pollinate their flowers for fruit formation (l)I

(max. l5)

(# , @ and ( each denotes similar points where marks are to be awarded once only)

ll9



8. Concept for mark award:

Reasons for decline in death caused byinfectious diseases

Biological principles

q,)

c)

F

e discovery and mass production ofantibiotics / antiviral agents / drugs

(l). advancement in diagnostic

techniques / medical knowledge /science allows quick identificationof the pathogens ( I )

o to kill pathogens quickly and

effectively ( I )o to reduce the number of viable

pathogens in the community, thus

lowering the chance of transmission(2\

q)

. application of antibiotics / antiviralagents / drugs to animals with close

contact to humans ( l)

o to prevent the spread of pathogens

from the animals to humans (l )

o advances in medical knowledge /science for understanding

transmission routes (l )

o quarantine (l) / isolation of persons

who might have been infected or

exposed to the pathogens

o to break the transmission link ofpathogens ( I )

. improved personal hygiene (l)

. improvement in food and water

hygiene ( l) i specific example. improvement in environmental

hygiene (l) / specific example

o to prevent spreading pathogens in the

human wastes to the environment /water systems (l)

o to control disease vectors (1)

o to reduce the viability of pathogens

in the envirc''nment ( I )

o lmlnuntzailon programmes

established and improvement irr

vaccine development (2)

o to induce the development ofirnmunity against the diseases, hence

reduce the number of infected

individuals and the chance ofdisease transmission (3)

Marks

max. 9

max. 6

(max. 15 )

e.g.

challenges in coming years:

comrnodities ) easy spread of diseases around the world (2)

wild areas ) transmission of pathogens in wild animals / soil to humans (2)

max. I I

Reasons for the decline in death due to

infectious diseases

Biological principles

q)

q)L,

o discovery and mass production ofdifferent types of antibiotics (l) I

antiviralagents

/ more effectivedrugs

o advancement in diagnostic

techniques / medical knowledge /science (e.g. DNA sequencing)

allows quick identification of the

pathogens for follow-up treatment(l)

o antibiotics, antiviral agents and new

drugs help to kill pathogenic

bacteria and viruses in patientsquickly and effectively ( I ), thus

reducing the death rate

as infected persons can recover

faster, the number of viablepathogens harboured in the

community is thus reduced ([1), and

the chance of disease transmission is

lowered (#l )

120



0)

. some of the antibiotics / antiviral

agents / drugs are also applied to

animals which may have close

contacts with humans ( I )

o this helps to prevent the spread ofpathogens from these animals to

humans (1)

. advances in rnedical knowledge iscience allorv scientists to better

understand the transmission routes

of the pathogens (1)

o quarantine (l) / isolation of persons

who might have been infected or

exposed to the pathogens

o this allows people to employ

different methods to break the

transmission link (l) and hence

prevent the spread ofthe pathogens

. improved personal hygiene (l)

. improved food and water hygiene (l)/ proper treatment of drinking water /proper food processing and storage

. improved environmental hygiene (l)i sewage treatment of domestic

wastes before discharging into any

water system / proper drainage and

solid waste disposal

o these help prevent the spread ofpathogens in the human wastes via

the environrnent lwater systems (l)o improved environmental hygiene

helps control the breeding of diseasevectors (l) such as mosquitoes and

rats

o this would reduce the viability ofpathosens in the environment ( I )

o inrmunization / vaccination:

been established in rvhich young

clrildren receive vaccinations

against some common

infectious diseases during the

early years of childhood (l), e.g.

polio. measles, TB

developed e.g. vaccines for flu(l) / hepatitis B

vaccinations can induce the body to

develop immunity against the

diseases (l), hence the number ofinf-ected individuals are reduced (l) ithe population of the pathogens in

the community is reduced(O, and so

is the chance of disease transmission

r#r\

Note: # and ( each denotes similar points which are to be awarded once only

challenges in coming years:

increase in antibiotic resistance among the pathogens (l); infections by these

resistant strains are difficult to treat and if not controlled properly it may

cause an epidemic I a surge in that particular disease and its associated death

toll(l

)

H5Nl infection, people do not have immunity against these new strains (l)and thus rnany people would be infected

commodities (l) facilitates the spread of diseases around the world (l)

areas (l), this provides opportunities for pathogens in wild animals / the soil

to transmit to humans (l)

malaria and cholera

max. 9

max. 6

max.I I

t2l

(max. l5)



Candidates' Performan ce

In 2008,5413 candidates took the English-version papers and209l candidates took the Chinese-version papers,

an increase of about 2lo/o compared with last year. The performance of candidates was satisfactory in general.

Basic understanding and application of knowledge were observed in questions based on familiar topics in the

curriculum. However, in certain questions candidates failed to read and analyse the questions carefully to

understand the contexts described and to getthe gist of the questions, and candidates tended to give memorised

answers. As in previous examinations, candidates taking the English-version papers were handicapped by an

inability to express themselves clearly and precisely. Misspelling of biological terms was also common.

Paper I

All questions in this paper were compulsory. The performance of candidates is summarized in the table below:

Question Number Performance in General

Section A

o.l - 9 Satisfactory

Section B

Q.l0Q.1lQ. l2

Satisfactory

Fair

Satisfactory

Section C

Q.l3 Satisfactory

Section A

The performance in this section was generally satisfactory especially for the matching type question. Manycandidates had a good grasp of biological facts but were weak in applying this knowledge to daily examples.

Some candidates misunderstood the requirements of the questions and recalled too many details which were

irrelevant to the questions. Comments on the performance in individual questions are as follows:

Q.l (a) Many candidates did not read the question carefully and mistook the cells for plant cells.

They put down plasmolysis instead of osmosis.

(b) Candidates were asked to interpret the graph and explain the changes in the cell volume.

Many of them had the misconception that water will be regained because of the drop in water

potential inside the cell. In fact at equilibrium there should be no difference in the waterpotential between the solution and the cell.

Q.2 (a) This question required candidates to identify organelles in the diagram provided and to state

their functions. The performance was satisfactory.

(b) Candidates were tested on their knowledge of secretory substances produced by the salivaryglands. The performance was unsatisfactory. Instead of naming a secretory substance,

many candidates gave saliva/lysosome as the answer.

Q.3 (a) The performance was fair. A number of candidates just stated the factors that cause red tides

without describing their effects on algal groMh.

(b) The question tested candidates' understanding of how toxins produced by the algae might pose

a health risk to humans. The performance was unsatisfactory. About half of the candidates

failed to associate the risk with the harmful algal bloom. Instead they gave heavy metals and

bacterial contamination as the cause of the risk, suggesting memorization.

133



Q.4

Q.5

Q.6

Q.7

Q.8

Q.e

(b)

(a) Candidates were asked about the tenderizing process in daily life application. Half of the

candidates applied their understanding of rneat tenderizers to this unfamiliar situation.

However, most of them did not point out that the storage process also allows time for theprotease to work.

Many candidates wrongly stated that the temperature was optimum for enzyme activities.

Candidates also wrongly said that 'low temperatures can prevent microbial growth'.

The performance was fair. Candidates had no problem in deducing the diets but the reasoning was

poor. Most of them did not describe the special feature of the teeth and their functions.

The performance was very good. Nevertheless, the meanings of the answers were often distorted by

wrong grammar and inaccurate expressions. For example, 'the afhnity of haemoglobin for oxygen'

was written as 'the affinity for haemoglobin to oxygen', using the wrong prepositions. Some

candidates also carelessly answered that 'the worm' or 'curve X' has a higher oxygen affinity, insteadof the 'haemoslobin'of the worm.

The performance was generally good but still many candidates expressed the action of insulin

wrongly as if it converted glucose to glycogen directly.

The question tested candidates' knowledge of the digestive function of the pancreas. The

performance was satisfactory. Some answers took on a wrong direction by following up on

part (a). These candidates explained wrongly in terms of pancreatic hormones and blood

glucose level.

The performance was good. Some candidates mistook the hairs of hair cells for the receptors.

The performance was satisfactory.

(a)

(b)

Section B

The objectives of questions in this section are to assess candidates' capability to analyse and interpret data, and

to utilize conceptual ideas and theories to explain phenomena and make predictions. In general, candidates'

performance was satisfactory. Of the three questions, Questions l0 and 12 were better answered than QuestionI L It is important to note that the candidates' innovative thinking remained weak as most of them did not

know how to design an experiment to test a hypothesis.

Q l0 (a) Good in general. A number of candidates did not write an appropriate title for the graph and did

not use an appropriate scale for plotting the graph. Some of them plotted the curves separately in

different graphs.

(b) Good in general. Some candidates did not mention clearly the 'time periods' during which the

changes of blood calcium level and hormone X level occurred.

(c) ( i) Fairly good. Since the question mentioned that an increase in hormone X level would bring

about a rise in blood calcium, some candidates wrongly thought thata decrease in hormone X

level would also bring about a drop in blood calcium.

(ii) Poor. Most candidates did not know how to design an experiment to test the hypothesis

stated in the question.

Q I I (a) (i) This part is supposed to be very direct and simple but the candidates' performance was only

fairly good. A number of candidates did not mention that chemical M has to be absorbed

from the small intestine into blood before it can reach the foetus via the placenta.

(ii) Good in general, but some candidates did not know the meaning of 'viability'

134



(b) (i) Good in general, but only a few candidates mentioned the term 'sex ratio'. Instead, most

candidates used a number of words to paraphrase the meaning of the 'sex ratio', but theexplanations provided for the observed change in the 'sex ratio' were not appropriate.

Very poor. Most could not explain that the effect of chemical M on the offspring was due to

the induced changes of the gametes from their parents.

( ii)

Q 12 (a) (i) Very good performance.

Very good performance.

Very poor. Most candidates did not know how to present their idea correctly; they oftenanswered in terms of 'data accuracy' instead of 'for data comparison'. This type of question

has been asked previously, but the performance in 2008 was very poor. This may show that

some candidates did not have a good grasp of scientific data handling.

(b) (i) Good in general, but some candidates mistook the independent variable on the x-axis as

'time'. Hence in part (2), some inappropriate terms such as initially / finally / at first llaterwere used.

(ii) Fairly good, but the concept of the 'limiting factor' was not well understood.

Section C

Thistext-response question was setto assess candidates'understanding of the application of biologyto daily life

and the contribution of biology to the modern world. After identifying and synthesizing relevant informationfrom the text, candidates were expected to communicate their ideas clearly and logically. Candidates'performance was satisfactory in general. They could have performed better if more attention had been directedto understanding the questions, especially for parts (c) and (d). Candidates who opted for the Chinese versionof the paper expressed their ideas more effectively and accurately, particularly in part (f). Comments on the

performance in individual parts are as follows:

Q.13 (a) Good. Many candidates were able to state two different types of agents that can induce gene

mutation. However, some stated examples of the agents instead of the types.

(b) Fair. Candidates were weak in applying knowledge and concepts in genetics to explain why mostmutations do not result in any important changes in body traits.

(c) Satisfactory. Many candidates were able to relate SCID to poor immune responses.

Nevertheless, some candidates had difficulty in presenting the correct immune responses of T and B

cells.

(d) Fair. Candidates merely stated the phenomenon instead of explaining the mechanism underlyingwhy more individuals suffer from XSCID.

Fair. Many candidates pointed out that changes resulting from germ-line gene therapy are

inherited in subsequent generations, but those resulting from somatic gene therapy are not.

However, they often failed to give another difference as requested.

Satisfactory. Many candidates stated the reasons why cancer remains one of the top killer diseases

in developed countries, though they often failed to elaborate on the reasons logically and clearly.

Candidates attempting the Chinese version of the paper performed better in this sub-question.

Good. Many candidates stated the effects on health of insufficient vitamins and dietary fibre in thediet. However, some candidates failed to identifo the diseases which are chronic in nature

according to the question.

( ii)

( iii)

(e)

(0

(e)

135



Paper 2

Candidates were to attempt any two questions

The performance of candidates is summarized

in both section A and section B, and any one question in section C.

in the table below:

(E)

(c)Engl ish-vers ion cand idates

Chinese-vers ion cand idates

Section A

In this section, candidates were tested on their understanding of the concepts and their ability to apply these

concepts. They were also tested on their ability to extract information provided in the questions to ansue:'

them. The overall performance of candidates was satisfactory. There were candidates who performed verr

well and showed a thorough understanding of the biological concepts and were able to applythem in answerinq

the questions. However, there were also many candidates who were weak in applying concepts. Candidates

of the English-version paper and those of the Chinese-version paper alike had problems in conveying their ideas

clearly.

Q.l In general, candidates performed satisfactorily in this question.

Very good. Most candidates were able to answer this part correctly, giving both the location of the

mutation and the change from the 'A' nucleotide to the 'T' nucleotide. However, some candidates

put down the nucleotide number but not the mutation. These candidates did not understand the

requirement of the question, especially the meaning of identify'.

Very good. Most of the candidates who got this wrong gave the sequence of the opposite strand

This suggests that they did not understand the concepts of 'anti-parallel' and transcription. Ir:

transcription, mRNA is synthesized on the template strand. Therefore, the sense of the mRNA is

anti-parallel to the template strand and the mRNA has the same sense as the non-template strand

The non-template strand is the same as the coding strand. The sequence of the mRNA is thus the

same as the coding DNA sequence with just the 'T' nucleotides changed to 'U'.

Very good except that a few candidates made careless mistakes in the translation of one or t\\'c

codons.

(a)

(b)

t36

Question Number Popularity Performance in General

Section A

Q.1

Q.2

Q.3

78% (E) t 72% (C)

6t% (E) t 4s% (c)

6t% (E) t 83% (C)

Satisfactory

Quite good

Fair

Section B

Q.4

Q.5

Q.6

83% (E) t 70% (C)

4e% (E) t se% (c)

68% (E) t 70% (C)

Satisfactory

Satisfactory

Fair

Section C

Q.7

Q.8

33% (E) t 2s% (C)

67% (E) t7s% (C)

Fair

Good

(c)



(d) (i) Satisfactory. In this part, candidates were tested on restriction enzyme digestion and DNAgel electrophoresis. Most knew that the DNA sample 'J' was cut by the restriction enzyme

into two parts and they correctly pinpointed the restriction site. Some candidates answered

that the DNA sample was cut into two 'strands'. This implies either an inaccurate use ofbiological terms or a poor understanding of the concept of restriction enzymes in DNA

technology. Very few candidates managed to answer that the two bands derived from 'J'were of different sizes and even fewer candidates answered that 'J' was homozygous for the

[A] allele. Many candidates did not communicate their ideas in a straightforward and direct

manner when they attempted to explain the observed results.

(ii) Satisfactory. In this part, candidates need to analyse DNA gel electrophoresis results and to

deduce the genotypes of the unknown samples. Many candidates answered correctly by

matching the DNA bands in the unknown samples 'M' and 'P' to the known samples 'J' and

'K'. However, many answered wrongly by deducing the genotypes of the parents from the

baby's genotype. These candidates did not understand the concept of DNA fingerprint

analysis and they were not aware of the general significance of the known samples orstandards in experiments.

(iii) Satisfactory. Most candidates gave the correct genetic diagram and managed to deduce all

the possible genotypes of the offspring. However, many of them did not relate the

genotypes to the correct phenotypes, despite the fact that the relevant information was

provided in the question. As a result, they mixed up 'sickle-cell trait' and 'sickle-cell

anaemia', failing to get the correct phenotypes and consequently the correct probability.

(e) Unsatisfactory. Most candidates had only a superficial understanding of the concept of selection

and were unable to express their ideas properly. Many candidates explained in length why people

with sickle-cell trait were more resistant to malarial infection, which was totally irrelevant. Most

candidates failed to point out that the [S] allele was passed from one generation to another. Onlyvery few candidates answered that malaria serves as the selection agent.

Q.2 Overall, candidates performed quite well in this question.

(a) Most candidates realized that the rate of glycolysis is higher in anaerobic respiration, but they were

weak in explaining why this is so. Many candidates explained why the rate would be lower in

aerobic respiration instead of explaining why it should be higher in anaerobic respiration. This

demonstrated their weakness in conveying their ideas properly. Many candidates also tended to

write down whatever they remembered about aerobic and anaerobic respiration, failing to grasp the

gist of the question.

(b) (i) The question asked candidates to outline the principle of an experiment but many candidates

gave the procedures instead. Many candidates used 'amounts' in place of 'concentrations'

and gave rather vague and indirect statements like 'the reaction rate would be faster'and 'the

inhibition becomes lower'. This probably reflects their inadequate understanding of the

;"rH:,of inhibition'as well as their weakness in communication using precise scientific

(ii) Most candidates answered vaguely that the results would be 'more accurate', because

glycolysis would be inhibited by the addition of fluoride. They failed to state precisely the

;fffi #j,1??.1 m'ff ;'1, JT, ij; "j.: il i:l: l? ;l

".#." il ;jJ,l: r#' :i, h

m e n'1 i o n'fh e

(c) o il#,nTft*r;fuJi*#TH lfffij;1'tl#'::'y,"ffi;"ff*TilixT,""i;

(ii) Performance was poor. Most candidates failed to answer correctly and said that the lack of

#i{il:i# iilii:**:*;:fl:: # f1# #tr ::'r:"ff :lyffi r"T:

137



(d) Very good performance. However, some candidates confused the concepts of 'reduction' and

'oxidation' in part (ii). In part (iii), most candidates answered correctly, but some just gave any

biological molecules they knew, ranging from fatty acids, proteins, lipids, amino acids and evenenzymes. This indicates a poor application of knowledge about nucleotides.

Q.3 This question was based on a familiar context but the overall performance of candidates was less than

satisfactory. In general, candidates showed a lack of in-depth learning and the ability to apply concepts

and basic knowledee to different scenarios.

(a) Satisfactory. However, many candidates did not write precisely and concisely, either in English or

Chinese.

(b) Performance was quite poor. Only a few candidates correctly pointed out that methane is formed

from anaerobic fermentation of organic maffers. Most candidates wrongly thought that methanewas generated from the burning of fossil fuels.

(c) Fair performance. Many candidates obviously lacked a clear concept of the greenhouse effect.

They wrote that methane and carbon dioxide absorbed radiation/light/heat from the sun and this

made the earth warmer. Terms like'light','energy'and'radiation'were loosely used, Only a

few candidates managed to answer correctlv that 'heat' was reflected back to the earth's surface.

(d) Fair performance. Many candidates mistook'melting of polar ice'and'increase in the number ofpests'as a climatic change.

(e) Satisfactory. However, a few candidates answered the effects on the ecosystem rather than the

effects on the local species per se.

(f) Fair. Many candidates mixed up the two diseases and answered as if they were transmitted in a

similar way. Many lacked the basic knowledge that cholera is caused by a bacterium and that the

mosquito is the vector for malaria.

(g) Performance was satisfactory. Most candidates gave the correct explanation but only a few ofthem rvere able to point out that the supply of alternative food sources for penguins might increase.

Section B

This section required candidates to present answers in paragraph form. The use of table format in 'compareand contrast' type of questions was permitted, but candidates were not allowed to present their answers only in

'point-form'.

Q.4 The overall performance of candidates in this question was satisfactory.

(a) Quite a number of candidates failed to discuss the various membrane functions based on the

properties of the membrane. They simply regurgitated everything they had learned on this topic.

(b) Many candidates did not indicate that the transport of food by mass flow occurs in the sieve tubes ofthe phloem. An enclosed structure (e.g. a pipe or a sieve cell) is essential for the build-up of a

hydrostatic pressure gradient. Incorrect spelling of the term 'phloem'was common.

(c) The performance in this part was the best among the three parts. Some candidates mixed up the

two terms'sarcomere' and'sarcolemma'.

Q.5 (a) The overall performance of candidates in this part was satisfactory. However, many failed to make

comprehensive comparisons between the two types of responses, for example the direction of the

response and the sources of stimuli. Most candidates gave relevant examples to explain the

significance of reflex and tropism.

138



Q.6 (a)

Candidates' performance in this part was satisfactory. Many of them knew the action of a

neurotransmitter and were able to point out certain criteria for a substance to be considered as a

neurotransmitter. However, some of them misunderstood the question; they wrongly answered this

part by describing detailed experimental procedures.

The performance in this part was fair. Many candidates did not compare the heat source forreptiles and mammals. This reflected that they did not understand the concept of ectotherm and

endotherm. Many candidates wrongly stated that reptiles prefer to live in water and did not knowthat most reptiles are terrestrial.

The performance of candidates in this part was fair. Most candidates failed to give specificdifferences in terms of the sites of absorption of digested food and the ways to enhance the

efficiency of food absorption. Quite a number of candidates wrote a lengthy comparison of the

means of attachment of the two organisms, immune responses and other irrelevant differences. In

the second part of this question, most of the candidates did not consider the foetus-motherrelationship from different perspectives and their comments on whether or not this relationship was

parasitism were inadequate.

This part was well-answered. Most candidates had a good understanding of the concept and

mechanism of lactation.

(c) The performance of candidates in this part was fair. A lot of candidates gave a lengthy descriptionon the details of the Calvin cycle, Krebs cycle and I or translation. They were weak in puttingdown succinctly the key concepts of how inorganic substances are assimilated to form proteins.

Section C

In general the performance of candidates in question 8 was beffer than that in question 7. A considerable

number of candidates answered question 7 by recalling information about the nutrient cycles without any

reference to the measures adopted by the farmer. In contrast, fewer irrelevant materials were included in the

answers to question 8.

Q.7 There were excellent as well as grossly unsatisfactory answers, reflecting a wide range of abilities among

candidates. Apparently some of the candidates did not read the question carefully, or failed to

understand the gist. Thus a substantial part of the answer was merely a regurgitation of facts pertaining

to the water cycle, carbon cycle and nitrogen cycle. There was little or no mention of how farmers makeuse of the knowledge of nutrient cycling and interdependence of organisms in their farming practice to

enhance crop production. Instead, some candidates presented detailed descriptions of photoautotrophs,

chemoautotrophs, herbivores, carnivores, omnivores, parasitism, commensalism and predation. Other

candidates suggested measures to increase crop growth, such as providing adequate water supply,

appropriate light intensity, using greenhouses, applying lime to soil and the use of hydroponics. Allthese were not related to the two ecological concepts stated in the question. The introduction ofpredators of denitrifying bacteria to the soil to reduce denitrification, and the addition of putrefuing

bacteria to facilitate decomposition and nitrification, were often mentioned. Some candidates had an

erroneous concept of nitrogen fixation. Others mixed up the roles of nitrogen-fixing bacteria and

nitrifying bacteria. Some candidates quoted examples to illustrate symbiosis, predation and parasitism,

which were inappropriate in the context of the question e.g. lion and rabbit for predator-preyrelationship.

Misspelling was sometimes detected in words like 'leguminous', 'nodule', 'pesticide' and 'predator'.

(b)

(c)

(b)

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Q.8 This was a much more popular question than question 7. The performance of candidates was on the

whole quite good, probably due to the wealth of information from mass media regarding food,

environmental and personal hygiene and the high incidence of influenza before the examination. Mostmaterials in the answers were relevant, with the exception of excessively lengthy discussion about the

primary and secondary immune response to vaccination. Some candidates erroneously proposed the use

of gene therapyto treat infectious diseases in general, and organ transplants to treat hepatitis in particular.

A few candidates failed to differentiate between antibiotics and antibodies. Very few pointed out that

administration of vaccines or antibiotics to animals can reduce the spread of pathogens from animals to

humans. Some candidates held the following misconceptions: (i) antibiotics can be used to eliminate

viruses, (ii) antibiotics produce mutations in bacteria leading to antibiotic resistance, and (iii) cancers are

infectious diseases. Instead of writing on the discovery / development of new therapeutic agents like

antibiotics and vaccines, many candidates attributed the reduced incidence of infectious diseases simply

to the affluence of developed countries. The following words were sometimes misspelt: condom,

hygiene, mutation, transmission and wound.

Paper 4 Practical Examination

Q.l Identification of unknown plant tissues using the iodine, biuret and Benedict's tests.

This is a typical and straightforward food test question. Candidates would most likely be able to

guess the identity of the tissues by looking at their appearance and texture; yet many of them failed to

deduce the identities of the tissues based on the results of the food tests. Most of the candidates did

not tabulate their results properly.

Q.2 Botanical spot

The candidates'techniques for sectioning of plant materials and slide preparation were not satisfactory.

Drawings and labelling based on the prepared slides were also poor. Most candidates were unable to

compare and contrast the morphology of the specimens by using appropriate biological terms in their

descriptions.

Zoological spot

Most of the candidates were able to identiff the specimens using the key provided. Some apparently

lacked training in using the microscope. Many candidates did not put a title on their drawings.

Q.3

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TEACHER ASSESSMENT SCHEME SUPERVISOR'S REPORT

ADVANCED LEVEL BIOLOGY

In the 2008 A-level Biology Examination,7483 candidates from 4ll schools participated in the Teacher

Assessment Scheme (TAS). The TAS schools were divided into 24 groups. A coordinator was assigned to

monitor the assessment work of the teachers in each TAS group. Based on the review of sampled student

reports submitted by individual schools, the coordinator provided feedback to the TAS teachers about the

quality of their assessment and made recommendations to the TAS Supervisor on the moderation of the TAS

scores of individual schools.

This year, most candidates were able to achieve satisfactory standards in the practical skills assessed by the

Scheme, and the teachers involved were able to assess their students according to the guidelines in the TAS

Handbook. Specific comments on the candidates' performance in individual assessment areas of the Schemeare given below.

Area A - Practical skills and abilities

The general performance of the candidates in Area A was satisfactory. However, teachers tended to be lenient

in area Al (Abilities to organize and perform practical work), and some awarded exceptionally high scores or

even full scores in this area to their students, whose performance in other areas such as A2 and B was rather

poor.

The standard of high power (HP) drawings was not satisfactory. The most common and serious problem is that

students tended to draw too many cells in their HP drawings, which failed to show any cellular details. Itappears that many candidates did not understand the purpose of making HP drawings. Furthermore, they had

difficulty in interpreting cellular structures as observed under high power magnification, which is cognitively

more demanding than making whole-specimen or low-power drawings.

These problems can be illustrated by the following HP drawings made by candidates:

t4l



Cross section oF Heltqnthus stem, H.P. G2AO)

Oastric glandoF stomqch ,T.5. (4 x Lo)

In the high power drawings of the leaf and stem shown above, a large number of cells were drawn but no

cellular details, such as the cell wall, cytoplasm, nucleus and vacuole, are shown. As a result, the differences

between the cell types are not presented explicitly. In the high power drawing of the gastric gland, the different

types of cells and their nuclei are also poorly represented.

Teachers can help their students to improve in this area by alerting them to the requirement and importance of a

HP drawing, together with constant feedback on the quality of their drawings.

Other common weaknesses found in candidates'biological drawings are listed as follows:

o incomplete titles;

r low-power drawings being too diagrammatic, resembling textbook diagrams rather than actual specimens;

r individual cells shown in low-power drawings;

. annotations lacking a specific focus or too simple for advanced-level work.

Furthermore, some candidates only made a minimal number of drawings throughout the AL course.

Consequently, they had few opportunities to improve their drawing skills. On the other hand, more and moreteachers made good use of the TAS as an opportunity for assessment for learning. By providing constant

feedback on students'work, these teachers ensured that their students learn from their mistakes and make steady

improvement throughout the AL course.

Area B - Reporting of investigatory work

In Area B 1 (Quality of the written accounts on the design and method of investigation), teachers in general

demonstrated good and consistent marking standards. The candidates wrote a clear and comprehensive

procedure, and many demonstrated an understanding of the purpose of a hypothesis and different types of

variables.

However, the following weaknesses in Area B 1 were prevalent among candidates:

. no principle of design;

. great elaboration on theories or biological principles that were not relevant to the design of the

investigation;

. no diagram for the experimental set-up;

r confusion about the concepts of hypothesis, prediction and assumption;

. no consideration of independent and dependent variables or the need for a control;

. precautions being too general and not relevant to the investigation concerned.

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The following extracts from students'reports illustrate some of the common problems:

Extract 1:

Aim: To investigate the effects of different chemicals on the permeability of cell membrane of beetroot cells.

Hypothesis: Cell membranes are mainly composed of phospholipids, proteins and cholesterol. If a solvent

can dissolve the main components of the cell membranes, the pigment inside will leak out into the solvent.

Hence, the more damage the solvent can do to the cell membrane, the more pigment will leak out, and the

darker the solvent will become.

Variables: dependent variable - colour of solvent

Independent variables - choice of solutions as solvents, volume of solution, size of beetroot discs.

In order to study the effects of different chemicals on the permeability of cell membrane of beetroot cells, it is

not necessary to put forward a hypothesis. Rather, the 'hypothesis' stated in Extract I is the theoretical

background that should be considered in designing the investigation. There is some confusion in the conceptof independent variable, which should be different chemicals. The volume of solutions used and the size ofbeetroot discs should be the controlled variables.

Extract 2:

Objective: To investigate the eflect of light intensity on the rate of photosynthesis

Hypothesis: The rate of photosynthesis is directly proportional to the light intensity.

Assumptions: Assume the bubbles are equal in size. Assume all the cells in Hydrilla are alive, and the

oxygen Hydrilla produced would not dissolve in water.

This investigation also does not require a hypothesis. The 'hypothesis' stated above is a prediction of the result.

Making such a prediction is undesirable as the students may become biased by the preconception when theycollect the data.

The concept of 'assumptions' is difficult for students. In the above example, we are not sure whether the size

of bubbles is the same throughout the experiment, but making the assumption that bubbles size is equal is

necessary when comparing the rate of photosynthesis in different light intensities. This implies that theconclusion may be wrong if it turns out that the bubbles vary in size. However, it is not necessary to assume

that'all cells are alive'and 'oxygen would not dissolve in water'.

Extract 3:

Aim: To determine the water potential of cell sap in red onion epidermal cells at incipient plasmolysis.

Hypothesis: When the concentration of the outside solution is the same as that of the cell sap, there should be

no net water flow in or out of the cell ....

Assumptions:

Assume that the water potential of different cells in the epidermis is similar to each other.

Assume there is enough time for the reaction to occur.

Variables: Independent variables - concentration of sucrose solution, duration of experiment.

Dependent variables - number of plasmolysed cells.

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As illustrated by this example, some students could not distinguish between water potential and osmotic

potential. This investigation should be concerned with finding the osmotic potential of the cell sap of plant

cells. Again, this investigation does not require the formulation of a hypothesis. The independent variableshould be the concentrations of sucrose solution only, and not the duration of the experiment. The dependent

variable should be the percentage of plasmolysed cells rather than the number of plasmolysed cells.

The general performance of the candidates in Area 82 (Quality of the recording and presentation of results) was

satisfactory. However, the following problems were common in the candidates'reports:

r tables or graphs lacking a meaningful title;r joining points with straight lines instead of a smooth curve to produce a graph for estimating a biological

value:

. no repeated collection of data to reduce sampling error.

In Area 83 (Quality of the interpretation of the results and conclusion), candidates were generally weak indiscussing the trends or relationships as shown by the experimental data. The main weaknesses include:

. describing the experimental results with little interpretation;

r focusing on the errors of the experiment and means of improvement;

. stating the overall trend with little reference to the actual data obtained;

I drawing conclusions with no reference to the aim of the investigation.

Concluding remarks

Most teachers demonstrated a good understanding of the requirements of the TAS and a good standard ofassessment, although some teachers were a bit lenient. There is, however, a tendency for teachers to make a

minimal number of assessments in the whole AL course, particularly in Area A2 and Area B. Such a practice

greatly reduces the practical experience of the students and also has a negative impact on the effect of the TAS

as a means of assessment for learning.

Documents

AL Bio 2008 Marking Scheme