2020 HKDSE Integrated Science Paper 1 Qs. 2, 6 & 8 and Paper 2 Q.2

pancreas

In N, H promotes the conversion of glucose to

glycogen.

H promotes the uptake of glucose by body

cells / muscle cells from blood.

Very good performance.

Satisfactory performance. Candidates

generally knew that hormone H (insulin)

promotes the conversion of glucose to

glycogen. However, some of them

wrongly thought that organ N, in which

this conversion takes place, is the

pancreas.

The performance was poor. Some

candidates did not give ‘another’

process promoted by H as

required by the question. They

quoted the same process, i.e. the

conversion of glucose into glycogen,

in the muscles as the answer.

Some seemingly were unfamiliar

with the functions of H other than

helping convert glucose to

glycogen.

The body cells of type II diabetics have become resistant / insensitive to H, they fail to respond to H and hence are unable to bring a raised blood glucose level back to normal.

Fair. The body cells of type II diabetics are not sensitive to insulin and thus are unable to bring a raised blood glucose level back to normal. Common mistakes made by the candidates included:

• wrongly stating that the pancreas of type II diabetics is insensitive to high blood glucose level, and

• mistakenly thinking that the insulin secreted by type II diabetics cannot function properly.

With no new glucose supply from meals and that H is exerting its effect to reduce the blood glucose level, (1) the glucose level may become too low to provide sufficient energy for the proper functioning of the brain cells. (1)

Satisfactory performance. Most candidates knew that the dizziness is due to a low blood glucose level that results in the brain cells having an insufficient glucose supply. Quite a number of these candidates, however, failed to account for the low blood level in the scenario depicted in the question.

(1)

The results of groups 1 and 2 show

that there is a smaller rise / a slower

rise in glucose level for rats that have

taken food added with E. (1)

E lowers blood glucose level / reduces

fluctuation of blood glucose level. (1)

(2)

The results of groups 3 and 4 show

that for rats which are unable to

produce H, the change in glucose level

is similar regardless the rats have

taken food added with E or not. (1)

This shows that E is unable to

regulate blood glucose level in rats

which are unable to produce H.

(3)

E is useful to type II diabetics only.

(1+)

E may achieve its effect by enhancing

the sensitivity of the receptors / body

cells / target cells / target organs to H

or E may enhance the activity of H. (1)

Satisfactory performance. Most candidates recognised that rats that had taken food added with E showed a smaller rise in blood glucose level. However, many of them did not provide an explanation based on the tabled information.

Satisfactory performance.

While a lot of candidates realised that E is useful to diabetics who can produce insulin, quite a number of them did not suggest the action of E.

Some candidates suggested actions that do not require the presence of insulin, e.g. E prevents the absorption of glucose into the blood. These suggestions are not consistent with the results.

The removal of both limpets and sea urchins relieved the seaweed from being heavily consumed by both

these consumers. The curve that shows (the greatest) increasing seaweed cover over the 18 months should

be the one corresponding to Area 3, in which both limpets and sea urchin had been removed. (1)

OR

The seaweed is being heavily consumed when both limpets and sea urchins live in such area. The curve that

shows a (much) reduced seaweed cover over the 18 months should be the one corresponding to Area 4, in

which neither limpets nor sea urchin had been removed. (1)

3

4

Good performance.

Sea urchins have a greater effect on limiting seaweed cover. (1)

The seaweed cover was much lower in the area where only limpets

had been removed (i.e. sea urchins were present) than that in the

area where only sea urchins had been removed (i.e. limpets were

present). (1)

Good performance.

amount of sunlight / temperature of the seawater (1)

As the photosynthetic rate is affected by this factor (1), the

growth of seaweed is affected.

Satisfactory performance.

Some candidates overlooked the requirement of giving a factor ‘apart from the organisms present in the habitat’ and wrongly suggested red tides. Some candidates gave vague answers such as water pollution.

third / 3rd trophic level (1)

secondary consumer (1)

Fair. Many candidates failed to point out that the otter is the secondary consumer in the food chain shown. Just stating that otters serve as the ‘predator’ did not successfully describe the precise role of otters in this food chain.

Good performance.

Many candidates showed a

good understanding of the

pyramid of number and

were able to draw a curve

that showed the otter

population being lower than

that of sea urchins.

Quite a number of

candidates also realised

that the cyclical rise and

fall of the otter population

should lag behind that of

the sea urchin as otters are

the predators of sea

urchins. Some candidates,

however, drew a curve that

showed only one of these

two features.

lower populatoin

rise lag behind

BW ; Bw (1)

During gamete production by meiosis, (1)

the independent assortment of homologous

chromosomes allows alleles to be

segregated, which results in forming

gametes of different genotypes. (1)

The performance was poor.

Candidates who gave ‘BBWw’ as the

answer were unable to differentiate an

individual’s genotype from the genotype

of a gamete, which is either ‘BW’ or

‘Bw’ in this case. Those who gave

incorrect answers such as ‘Ww’ or ‘BB’

seemed to have a poor understanding

of meiosis, which is involved in the

production of gametes.

These candidates failed to realise the

consequence of the segregation of the

independently assorted homologous

chromosomes during meiosis, i.e. only

one of the paired alleles would be

found in a gamete.

For the non-belted red pig, all gametes produced are of the genotype bw. (1)

As fertilization is random, there is an equal chance of these gametes (of genotype bw) to fertilise with the gametes of the genotype BW and those of the genotype Bw. (1)

50% (1)

The performance was poor.

Most of the candidates knew that the

expected percentage is 50.

They, however, failed to recognise

that it is the randomness of

fertilisation that accounts for the

equal chance that a gamete bearing

the genotype bw to fuse with a gamete

bearing the genotype BW or to fuse

with a gamete bearing the genotype

Bw.

Allow the two parent pigs to breed until there is at a least a pair of F1 non-

belted black pigs, which are of opposite sex. (1)

Allow these F1 non-belted black pigs to mate and use F2 non-belted black

pigs (already with the genotype BBww) for further breeding. (1)

Poor.

Although quite a number of

candidates knew that they had

to get a pair of pigs with the

genotype BBww to establish a

pure bred line, they failed to

point out how pigs with this

particular genotype could be

identified morphologically

among the F1 offspring.

Some gave irrelevant

answers such as writing a

lengthy account of the

chance of getting a pair

of F1 pigs with the

required genotype.

In addition, some

candidates may have

misunderstood the

question and gave

answers such as ‘cloning’

or ‘DNA recombinant

technology’. They

seemed to have confused

these technologies with

‘breeding’.

The production of pure bred pets will cause the loss of alleles which are

not artificially selected for (1) and thus reduces biodiversity (1) in terms of

the gene pool.

Fair.

Many candidates

knew that

biodiversity might be

reduced. Yet, very

few of them could

attribute the reduction

in biodiversity to the

loss of alleles.

Q (1+) It is unicellular and has

cell wall. (1)

Satisfactory performance.

The majority of candidates were

able to identify Q to be a bacterium.

While many of them correctly used

the fact that bacteria possess cell

wall (and hence the non-cellular

virus R could be ruled out) in

explaining their answer, the

explanation offered by some

candidates reveals a misconception

that viruses do not have DNA.

These candidates did not know

that the genetic material in some

viruses is DNA.

In addition, very few candidates

realised that bacteria are single

celled. Candidates with such

knowledge would have known that

the multicellular P is not a

bacterium.

Not a unique characteristic

The B cells that recognise the antigens on the invaded bacteria (1) are activated

and developed into plasma cells. (1)

The plasma cells will then produce antibodies to fight against the invaded

bacteria. (1)

Fair.

Some candidates seemed to have

confused the function of B cells

with that of T cells and

erroneously suggested that killer

cells were involved.

Some candidates mixed up the

functions of the B cells, plasma

cells and memory cells. They

gave wrong answers such as

‘antibodies are produced by the

B cells or the memory cells’,

‘plasma cells are activated to

give B cells’.

Some candidates wrote in great

detail on how memory cells

would trigger a secondary

immune response and/or the

secondary immune response.

Unfortunately, these are

irrelevant to the question.

• The dose of the antibiotic taken may have killed the non-resistant bacteria

making the symptoms disappear, but may not be sufficient to kill all the

bacteria resistant to the antibiotic prescribed. (1)

• Without the competition of the non-resistant bacteria, these antibiotic resistant

bacteria would grow and reproduce rapidly, and increase in number. (1)

• This practice may thus accelerate the problem of antibiotic resistance, /

making this antibiotic ineffective in treating pharyngitis in the future. (1)

Satisfactory

performance.

Candidates in

general understood

very well that not

completing the

course of antibiotic

treatment would

accelerate the

problem of

antibiotic

resistance.

The rapidly growing polyp starts to invade / has invaded the colon to cause damage.

Very poor performance. It seems

that candidates were unable to

make use of the hint in the question

that polyps are abnormal tissue

masses capable of growth in

answering the question. Most of the

candidates gave characteristics of

cancers that are common to polyps

and cancerous mass, e.g. growth of

cells in an uncontrolled manner or

the development of tumours. They

did not realise that an invasive

growth of a polyp into the colon is a

sign of the polyp having turned

cancerous.

breast self-examination / palpation of breast

Satisfactory performance. Some

candidates were not familiar with the

correct name of the screening test.

Instead of ‘breast self-examination’,

these candidates gave vague answers

such as cancer screening,

checking/touching one’s breast, etc.

Unlike colon which is located deep inside our body and that an examination of the

colon requires a medical procedure, a person can perform a preliminary screening of

the breast located on body surface easily. (1)

This may explain the observation that the percentage of breast cancer diagnosed at

early stages are higher than / about 2 times that in colorectal cancer. (1)

Fair.

Candidates were expected to

recognise from the given information

that the percentage of breast cancer

diagnosed at early stages is higher

than that of colorectal cancer, and to

offer an explanation with reference to

the locations of the two organs in the

human body. Some candidates did not

compare the percentages of detection

of the two types of cancers.

Some gave explanations such as it is

more difficult to detect colorectal

cancer than breast cancer or the

screening of colorectal cancer needs

to be done in hospital, without

referring to the locations of the two

organs.

Starting from 50, the incident

rate of colorectal cancer

starts to rise with age in both

male and female.

Well answered.

Well answered.

Most candidates

knew that the

development of

colorectal cancer is

related to the food we

eat. A few candidates

wrongly thought that

it is related to the

consumption of

alcohol. In fact, the

latter is more related

to the development of

liver cancer.

a high fat and/or low fibre diet

cancer: lung cancer (1+)

carcinogen: tar (1) Satisfactory performance.

While most candidates

correctly pointed out that

lung cancer is highly

correlated with smoking,

many did not realise that tar

is the related carcinogen.

Many candidates wrongly

thought the related carcinogen

was nicotine, which is more

related to the addiction to

smoking.

A low total sperm count and low percentage of motile sperms suggests a lower fertility.

As compared to sperm parameters of people carrying mobile phone in handbags, carrying

mobile phones in trouser pockets may have caused a lowering of total sperm count (1) as

well as a lowering of the percentage of motile sperms. (1)

This may be because the distance of the mobile phone is farther from the testes when it is

carried in handbag and that the intensity of electromagnetic radiation is diminishing with

the square of the distance (the inverse square law). (1)

Fair.

Quite a number of candidates were

able to recognise from the given

information that carrying a mobile

phone in one’s trouser pocket has a

greater effect both on the total sperm

count in an ejaculate and on the

percentage of motile sperms. Some,

however, stated only one of these

effects.

Candidates in general were weak at

offering an explanation for these

effects. Some candidates realised

that these effects are related to the

difference in distance of the mobile

phone from the testes. Yet, they

failed to point out that the intensity of

radiation received by the testes

decreases with their distance from the

mobile phone.