B3

Pathogens cause disease.

(a) How does the skin defend the human body against pathogens?

physical) barrier

or

stops pathogens entering (blood / body)

How many more bacteria were killed at pH1 than at pH5 in 24 hours?

Complete the following steps.

Calculate the number of bacteria killed at pH1

1968

Describe the trend in the number of people with measles from 1945 to

1975.

Use the figure above.

increases

1

(then) levels off / plateaus

allow (then) stays the same

allow reaches a maximum

between 1956 and 1968

1

(then) decreases

ignore use of numbers of people

if no other mark awarded allow 1 mark for (overall)

decrease

In 1998, a scientific paper was published suggesting a link between condition X

and one type of measles vaccine.

(d) What happened to the percentage of children vaccinated against

measles after the scientific paper was published in 1998?

Use the figure above.

the percentage) decreased

e) Why might the claims made in the scientific paper have affected the

percentage of children vaccinated?

parents were worried their children would get condition X

In 2010, the scientific paper linking condition X and the measles vaccine

was shown to be based on false claims.

What should scientists do with scientific research to help detect false

claims?

) The person who wrote the scientific paper was paid to research the link

between condition X and the measles vaccine.

Why are the claims in the scientific paper likely to be considered not valid?

any one from:

• (the author was) biased

• (the author was) influenced by money

• because the research was not peer reviewed

• there was not enough evidence

• small sample size

+Suggest the reason for the change you described in part (e).

(percentage) decreases

more females were vaccinated (over time)

Malaria is caused by a protist.

The protist is passed from one person to another person by mosquitos.

(a) Which term describes the mosquito?

Vector

Give two features of the malarial protist that show the cell is eukaryotic and

not prokaryotic.

any two from:

• (it has) mitochondria

• (it has a) nucleus

if neither mark awarded, allow 1 mark

for protist has membrane-bound

structures

allow it does not have a loop of DNA

• (it has) no plasmids

Which organism is prokaryotic?

Salmonella

) The malarial protist reproduces asexually.

What is a feature of asexual reproduction?

only one parent is involved

Mitosis occurs in the malarial protist during asexual reproduction.

The protist has 14 chromosomes.

How many chromosomes will each new protist cell have after mitosis?

14

When a person has malaria, the protists destroy red blood cells.

What change would happen in the blood of a person with malaria?

decreased haemoglobin

It is estimated that 210 million people are infected with malaria every year.

Half of these infected people survive the disease.

Calculate how many people would survive the disease in 3 years if the

estimate is correct.

Give your answer in standard form.

The spread of malaria can be controlled by using mosquito nets to avoid

being bitten.

Describe two other ways that people can reduce the chance of being bitten

by mosquitos.

Do not refer to mosquito nets in your answer.

any two from:

• wear long(er) sleeves / clothes

allow reduce bare skin exposure

• use insect repellent or insecticides

allow insect repellent methods such as

citronella candles

• don’t go out in the evening

allow close doors / windows in the

evening

• avoid going to countries / places with malaria / mosquitos

• destroy breeding grounds

allow methods of destroying breeding

grounds such as drain water holes

• release sterile male mosquitos

ignore vaccination / anti-malarial drugs

allow other correct suggestions

percentage / chance (of getting malaria) decreases (with age)

do not accept percentage / chance of

having disorder S

decreases with age

1

2

1

correct use of data such as two pairs of data from the table

HIV (Human Immunodeficiency Virus) is a pathogen.

(a) How is HIV spread from one person to another person?

sexual intercourse

increased (at first)

1

(then) decreased

(c) What could cause a decrease in the number of new HIV cases in the

future?

Tick (✓) one box.

better education on how to prevent the spread of HIV

C) → E → A → B → D

e) When scientists produce a vaccine for a disease the vaccine is tested on

live animals.

What is the next stage in testing the vaccine?

testing on healthy volunteers

A vaccine for HIV is important because it is difficult to develop safe drugs to

destroy viruses.

Why is it difficult to develop safe drugs to destroy viruses?

drugs that destroy viruses also damage body tissues

Name one antibiotic

Penicillin

the bacterium is killed (by antibiotic C)

allow there is a zone of inhibition (around antibiotic

C)

1

if the bacterium was resistant, bacteria would be right up to the

(edge of the) antibiotic disc

Suggest why doctors are concerned about antibiotic resistance.

any two from:

• current / available antibiotics do not kill (certain) bacteria

allow current / available antibiotics have no effect

on (certain) bacteria

• diseases become more common

or

there will be some diseases that cannot be cured / treated

ignore more people become ill

• new antibiotics need to be developed which takes time / money

allow some diseases become more difficult to treat

Diseases caused by viruses cannot be treated using antibiotics.

(d) Suggest why viruses cannot be grown on agar.

viruses only exist / reproduce inside (living) cells

Why is it difficult for scientists to develop drugs to destroy viruses?

these) drugs (can) damage (body) cells / tissues

or

it is hard to get (these) drugs into (living) cells

Which disease is caused by a virus that damages white blood cells?

AIDS

Salmonella bacteria cause outbreaks of food poisoning in humans.

To prevent food poisoning in humans, farmers vaccinate their animals against

Salmonella bacteria.

(a) How do Salmonella bacteria in food cause the symptoms of vomiting and

diarrhoea?

bacteria) release / produce toxins

During a food poisoning outbreak, scientists identified the farm where the food

came from.

The farmer had not vaccinated the farm animals against Salmonella bacteria.

(b) The food poisoning outbreak could have been prevented if the farm

animals had been vaccinated.

Explain how:

• the immune systems of animals respond to a vaccination

• the immune response in farm animals prevents an outbreak of food

poisoning in humans.

Vaccination of animal

• (animal’s) white blood cells / lymphocytes produce antibodies

(against Salmonella / vaccine / antigens)

• antibodies are specific / complementary / correct to Salmonella

/ antigens

• (specific) antibodies bind to Salmonella / antigens

Secondary response in animal

• if infected (specific) antibodies are produced quickly or in large

numbers

• (so) white blood cells or antibodies would kill (live) Salmonella

• (so) fewer / no bacteria / pathogens / Salmonella in animals or

in animal products (meat / milk / eggs)

Prevention of food poisoning in humans

• (so) fewer / no bacteria / pathogens / Salmonella eaten or in

(named) food

• (so) number of bacteria never reaches a high enough level for

infection to develop

• (so) fewer toxins produced (in humans).

The scientists incubated the bacteria at 37 °C.

Students in school laboratories incubate bacteria at 25 °C.

Explain why scientists use 37 °C but students must use 25 °C to incubate

bacteria.

(37 °C)

37 °C is human / body temperature

1

Salmonella / bacteria grows best / better at 37 °C

allow (so) bacteria grow best / better at

human body temperature

1

(25 °C)

25 °C reduces / prevents the growth of bacteria that are harmful to

humans / students

What is the purpose of the paper disc with no antibiotic in the figure above?

Acts as a control

The scientists concluded that either antibiotic A or antibiotic B should be

prescribed to patients with food poisoning.

Why should antibiotic A or antibiotic B be prescribed?

) killed the most bacteria

prescribed.

Describe how the results in the figure above could be used to obtain a

quantitative comparison of antibiotics A and B.

measure the diameter / radius of each clear area

h) One year later, there was another outbreak at the farm involving

Salmonella bacteria.

Antibiotic B did not have an effect.

Suggest why antibiotic B no longer had an effect.

bacteria must be resistant (to antibiotic B)

Antibiotics treat food poisoning because they kill Salmonella bacteria

inside the human body.

Some antibiotics work because they damage the bacterial cell wall.

The bacteria die because the cells burst.

Explain why the cells burst.

water enters the (bacterial) cell

1

(water enters) by osmosis

allow (water enters) by diffusion through

a partially / selectively / semi permeable

membrane

do not accept if description of

concentrations is incorrect

(so) damaged / incomplete / no cell wall cannot withstand pressure

(of water)

3.

The protist that causes malaria is passed from one person to another person by

mosquitos.

(a) What term describes an organism that passes a pathogen from one person

to another person?

Vector

The malarial protist is a eukaryotic cell.

Describe three ways the structure of the malarial protist is different from

the structure of a prokaryotic cell.

Do not refer to size in your answer.

any three from:

allow converse for prokaryotic cells

allow eukaryotic for protist

• protist / it has mitochondria

• protist / it has (a) nucleus or protist DNA / genetic material is

not free in the cytoplasm

if neither mark awarded, allow 1 mark

for protist has membrane-bound

structures

ignore genetic information

• protist / it does not have a single loop of DNA / genetic material

ignore genetic information

• protist / it does not have plasmids

• protist / it does not have a cell wall

During one stage of malaria infection, the malarial protists enter red blood

cells and cause them to burst.

Explain why the bursting of red blood cells causes tiredness.

less oxygen carried (in blood)

allow less oxygen carried (to cells)

ignore reference to number of red blood

cells unqualified

do not accept no oxygen carried

1

less energy released from respiration

The malarial protist reproduces sexually and asexually during a life cycle.

Complete Table 1 to give three differences between sexual reproduction

and asexual reproduction.

One difference has been completed for you.

One drug for treating malaria prevents mitosis occurring in the malarial

protist.

The drug stops the synthesis of new DNA bases in the cell.

Suggest how the drug prevents mitosis occurring.

no bases so) DNA replication cannot occur

having disorder S reduces incidence / percentage of malaria

allow having disorder S reduces chance

of getting malaria

allow having disorder S protects against

malaria

1

as age increases a lower percentage of children with disorder S get

malaria until age 10, then the percentage increases

Human immunodeficiency virus (HIV) is a pathogen.

(a) Give one way HIV can spread from one person to another person.

any one from:

• sexual contact / intercourse

allow intercourse unqualified

ignore kissing

• exchange of body fluids

Describe the trends shown in the table above between 2010 and 2018.

(number of cases) in women decreases then increases, then

decreases

1

(number of cases) in men increases then decreases

Suggest one reason for the change in the number of new HIV cases

between 2014 and 2018.

any one from:

• better education (into prevention of spread of HIV)

allow increased awareness about HIV

• condoms more widely available or condoms easier to

source or condoms cheaper

ignore contraception / protection unqualified

• new / better drugs (to prevent HIV infection / spread)

allow PrEP / anti-retrovirals stop the virus being

passed on

ignore new treatments

do not accept antibiotics

• better / more testing / identification (of people with HIV)

Calculate the ratio of new cases of HIV in women to new cases of HIV in

men in 2018.

Give your answer to 3 significant figures.

In the UK population the total number of women is greater than the total

number of men.

The data in the table in part (a) is used to compare the proportions of new

cases of HIV in the population for men and women.

Suggest how the data could be presented differently so that a more valid

comparison can be made.

any one from:

• calculate as a percentage

• give the numbers per 100 000 people

Scientists have been working to produce a vaccine for HIV for many years.

(f) Explain how a vaccine for HIV could work to prevent a person developing

HIV infection.

inactive HIV / virus is injected (into bloodstream / muscle / body)

allow dead HIV / virus is injected (into bloodstream /

muscle / body)

allow (named) part of HIV / virus is injected (into

bloodstream / muscle / body)

1

white bloods cells produce antibodies (against inactive virus)

allow lymphocytes produce antibodies (against

inactive virus)

do not accept phagocytes produce antibodies

(against inactive virus)

1

(if infected with HIV) correct / specific antibodies are produced

quickly

1

antibodies destroy the (active) virus / HIV

A person with late stage HIV infection has AIDS.

Scientists have produced monoclonal antibodies for HIV.

The monoclonal antibodies can prevent a person infected with HIV developing

AIDS.

(g) Describe how the monoclonal antibody for HIV can be produced.

HIV / antigen / protein injected into mouse

1

extract / collect (mouse) lymphocytes that make a specific antibody

to HIV / antigen / protein

allow other correct small mammals eg rat

allow extract specific lymphocytes from someone

with HIV for 2 marks

lymphocytes are combined with tumour cell to create a hybridoma

allow lymphocytes are combined with a myeloma /

cancer cell to create a hybridoma

1

1

(hybridoma) cloned to create many cells that produce the antibody

alternative route

HIV / antigen / protein injected into mouse (1)

lymphocytes from mouse are combined with a

tumour cell to create a hybridoma (1)

the hybridoma that makes the specific / correct

antibody is isolated (1)

(hybridoma) cloned to create many cells that

produce the antibody (1)

Scientists use monoclonal antibodies to test for the presence of anabolic steroids

in an athlete’s urine.

To produce monoclonal antibodies, a mouse lymphocyte is combined with a

tumour cell.

(d) What type of cell is created when a mouse lymphocyte and a tumour cell

combine?

monoclonal antibody is complementary / specific to HIV antigen

allow correct description of complementarity

1

1

monoclonal antibodies attaches to (all the) HIV antigens

1

(so) HIV cannot bind to (human) cell

or

(so) HIV genetic material cannot enter (human) cell

allow white blood cells or phagocytes identify

(monoclonal) antibodies and engulf / destroy

(antibody bound) HIV

alternative route

monoclonal antibody is complementary / specific to

HIV antigen (1)

monoclonal antibody with (anti-retroviral) drug

attached attaches to the HIV antigens (1)

drug destroys the virus or drug destroys genetic

material (1)

allow ‘the virus’ for HIV throughout

Scientists use monoclonal antibodies to test for the presence of anabolic steroids

in an athlete’s urine.

To produce monoclonal antibodies, a mouse lymphocyte is combined with a

tumour cell.

(d) What type of cell is created when a mouse lymphocyte and a tumour cell

combine?

hybridoma

Describe how scientists make monoclonal antibodies using the cell created

when a mouse lymphocyte and a tumour cell combine.

any three from:

• (cell) is cloned

ignore name of cell

• many (identical) cells are produced

allow many clones are produced

• all the cells make the same antibody

• the antibody is (collected and) purified

f) What property makes a monoclonal antibody useful in detecting the

presence of an anabolic steroid in urine?

a monoclonal antibody only binds to the anabolic steroid

The end of the test strip is dipped in urine.

The urine moves up through the test strip.

The test area and the control area contain a dye.

The dye turns blue when monoclonal antibodies bind to it.

(g) Suggest the purpose of the control area in the test strip.

to show that the test is working

+Which athlete has tested positive for anabolic steroids in their urine?

evidence

no blue / visible dye (in control area)

allow no line(s) (in control area) allow

no colour change (in control area)

1

reason

(because) no (free) monoclonal antibodies bound to control area

or

(because) there were no (free) monoclonal antibodies on the end of

the (test) strip

(i) D

In the past many drugs were extracted from plants.

(c) Aspirin is a painkiller.

Which plant does aspirin originate from?

willow

The scientists usually extract chemical A from the berries of the deadly

nightshade plant.

Suggest one reason why berries are used instead of leaves or roots.

any one from:

• (berries are) easy to access / pick

ignore berries are not underground

• easier to extract chemical

• taking berries will not harm the plant

A deadly nightshade plant has chlorosis (yellow leaves).

The mass of chemical A found in the leaves of the plant is 60% of the mass

shown in the table above.

(e) Calculate the mass of chemical A in 200 g of the leaves with chlorosis.

Give your answer in mg

(0.6 × 1.2 =) 0.72

1

(0.72 × 2 =) 1.44

1

1.44 × 1000

allow conversion of a correct mass

calculated for berries / roots

1

1440 (mg)

Suggest one reason why the leaves of the deadly nightshade plant have

chlorosis.

lack of chlorophyll

allow lack of chloroplasts

• lack of magnesium (ions)

Chemical A has not been tested in large-scale clinical trials in the UK.

(g) It is important for drugs to be tested in clinical trials before the drugs are

approved for use by the public.

Give two reasons why.

There are many online reports making claims about the effects of chemical A.

Some of these reports are biased.

(h) Suggest one reason why a report making claims about the effects of

chemical A may be biased.

________________________

writers / companies may get) financial gain

or

(competitor may suffer) financial loss

some leaves, the green parts become yellow because of an ion deficiency.

(d) Which ion is deficient in a plant with yellow leaves?

Magnesium

Give the scientific term that describes the yellow colour of the leaves

Chlorosis

Hornets are insects that sting other animals and cause pain.

Hornet moths do not sting other animals.

Suggest how mimicry helps the hornet moth survive.

(it looks like the hornet so) predators / animals are tricked / deceived

(by the colouring) and so avoid eating it

less absorption of water

◦ less water so lower rate of photosynthesis

◦ so less glucose produced

◦ for respiration / energy release

◦ so less cellulose produced so fewer cells

walls / cells made

◦ so fewer amino acids produced to make new

proteins

◦ cells lose turgidity

less absorption of (named) ions / minerals

◦ fewer nitrates so fewer proteins made for growth

◦ fewer magnesium ions so less chlorophyll produced

◦ so lower rate of photosynthesis

• damage to phloem

◦ less transport of sugars to root cells

◦ for respiration / energy release

• damage to xylem

◦ less water transported (to cells)

◦ fewer nitrates reach cells

◦ so fewer proteins made for growth

◦ fewer magnesium ions reach cells

◦ so less chlorophyll produced

◦ less magnesium / chlorophyll so lower rate of

photosynthesis

• less anchorage

Mitosis

genetic material / DNA / chromosomes is doubled / replicated /

copied / duplicated

1

the (replicated) chromosomes are pulled / moved apart

the (replicated) chromosomes are separated

1

cytoplasm divides into two (cells)

or

cell membrane divides to form two cells

allow two new nuclei form

allow the nucleus divides (into two)

1

the set of chromosomes in each new cell are identical (to one

another)

Suggest one reason why viruses are not classed as cells.

any one from:

• they do not have a cell membrane

do not accept they do not have a cell

wall

• they do not have cytoplasm

• they do not have a nucleus

• they do not have mitochondria (like most eukaryotic cells)

• they do not have ribosomes

Tobacco mosaic virus (TMV) causes disease in plants.

TMV affects the rate of photosynthesis in plants.

(f) Which part of a plant shows discolouration caused by TMV?

Leaf

Explain why a high level of TMV infection reduces growth in a plant.

less chlorophyll

so) less glucose / starch / protein made

Q2.

The human body can defend itself against microorganisms that cause disease.

Viruses are one type of microorganism that cause disease.

(a) Name one type of microorganism that causes disease in humans.

Do not refer to viruses in your answer.

any one from:

• bacteria

• fungi

• protists

Which two defence systems prevent microorganisms infecting the human

body?

Tick (✓) two boxes.

hydrochloric acid is produced by the stomach

1

1

the skin is a barrier covering the whole body

How is the measles virus spread from one person to another?

by coughs / sneezes

allow ‘by droplets in the air’

f) (from day) 10 (to day) 18

(g) 14 (days)

(h) any one from:

• they had been vaccinated

• they already had antibodies

• they were immune

ignore they were resistant

• they had had it before

• they did not get any / enough virus from infected child

ignore they wore a mask unqualified

• they did not play (much) with the infected child

(i) antibiotics do not kill viruses

How will the poisonous berries help the deadly nightshade plant to survive?

will stop animals / herbivores eating it

Which type of defence mechanism are the berries?

chemical

Suggest how the gorse plant is adapted to defend itself.

thorns / spikes / spines / prickles (to stop animals / herbivores eating it)

The green leaves of the gorse plant make glucose for the plant to use.

What are two uses of glucose in the gorse plant?

for respiration

to store as starch

A student wanted to show that the leaves of a gorse plant contain glucose.

The student crushed the leaves to extract the liquid from the cells.

Describe the method the student could use to test the liquid from the cells

for glucose.

Include the result if glucose is present.

add Benedict’s (solution / reagent to the liquid)

boil / heat

(if glucose is present the blue) colour changes to yellow / green /

orange / brown / (brick) red

The roots of the gorse plant have bacteria that turn nitrogen gas into nitrate

ions.

Explain why nitrate ions are needed by the gorse plant.

(nitrate ions are needed) to make proteins / amino acids

allow to make chlorophyll / DNA / ATP /

nucleic acid

1

which are needed for growth / enzymes / new cells

The roots of gorse plants can be infected by honey fungus.

The honey fungus produces tiny spores underground.

Suggest how the honey fungus spores travel from the roots of an infected

gorse plant to the roots of a healthy gorse plant.

in / on the (soil) water

A drug can be extracted from gorse seeds.

Doctors want to trial the drug from gorse seeds to see if it can treat diarrhoea.

(h) Which two factors must the doctors test the drug for in the trial?

dosage

toxicity

Mosquitoes carry a pathogen that causes malaria.

(a) What type of pathogen causes malaria?

a protist

b) Lower percentage of people with malaria when using (mosquito) nets

C)any one from:

• some people who use (mosquito) nets have malaria

data from only one area / part of Africa

• size of group too small or sample size too small or only 476

people

allow correlation does not imply

causation

• only 50 people did not use (mosquito) nets

or

uneven group sizes (nets vs. no nets)

• no other information about people considered

allow examples of information not

considered e.g. age, other medical

issues such as sickle cell, whether

taking anti-malarial medication,

vaccination

ignore ref to other factors unqualified

• people may have lied about using (mosquito) nets

88-91

e) Use of mosquito nets has helped to reduce the number of deaths from

malaria each year.

Suggest one other reason for the reduced number of deaths from malaria

each year.

any one from:

• improved health care

allow examples of improved health care

such as more / cheaper / new

treatments / vaccinations / antibiotics

• use of mosquito control methods

allow descriptions such as spraying of

insecticides / repellent or draining water

holes or preventing mosquitoes from

breeding

• changing behaviour to avoid being bitten (by mosquitoes)

allow descriptions such as wear long

clothing or avoid going out at dusk

Describe how the human body:

• prevents pathogens from entering

• defends itself against pathogens inside the body. (6)

prevents pathogens from entering

skin

• tough / dry / dead outer layer

• skin acts as a barrier

• sebum / oil on (surface of) skin

• sebum / oil repels pathogens

scabs form over cuts or scabs form a barrier

• platelets are involved in forming clots / scab

stomach

• contains (hydrochloric) acid

• (HCl) kills bacteria

• in food or in swallowed mucus

eyes

• produce tears

• contains enzymes to kill bacteria

• tears are antiseptic

breathing system

• trachea / bronchi / nose produce mucus

• mucus is sticky

• (mucus) traps bacteria

• (mucus) carried away by cilia

defends itself against pathogens inside the body

• immune system / white blood cells (WBCs)

• WBCs engulf pathogens

• antitoxins are produced

• (antitoxins) neutralise toxins / poisons (produced by pathogen)

• antibodies are produced

• (antibodies) help destroy pathogens

• memory cells (are formed)

• (memory cells give a) more rapid response if pathogen

re-enters

man has the following symptoms:

• yellow discharge from his penis

• pain when urinating.

(a) The man has a bacterial infection.

What is the most likely cause of the man’s symptoms?

gonorrhoea

The man took a full course of antibiotics.

The man’s symptoms did not improve.

Why did the antibiotics not cure the symptoms?

the bacteria are resistant to the antibiotics

Using a condom can stop the bacteria being passed to another person

during sexual intercourse.

Suggest a different way the man could avoid passing the bacteria on to

someone else

abstain from sex(ual intercourse)

allow abstinence

or

wash hands after touching penis / urinating / using the toilet

ignore wash hands unqualified

Compare the effectiveness of the three antibiotics at killing the different

types of bacteria.

Indicative content:

qualitative statements

• 3 works best on A

• 1 works best on B

• 2 works best on C

• 1 is least effective on A

• 3 is least effective on B

• 3 is least effective

or has no effect on C

quantitative statements

• 1 kills more of B and C compared to A

• 2 kills more of C than A / B

• 3 kills more of A than B and C

• 2 kills the same amount of A and B

• 2 and 3 killed similar amounts of B

• C are resistant to 3

• only 2 worked well on all of the bacteria

• for A, 3 works best, 2 is next and 1 is least effective

• for B, 1 works best, 2 is next and 3 is least effective

• for C, 2 works best, 1 is next and 3 is least effective

e)sample E

f) 15+12+13+16/4

Or

56/4

14

g)an answer of 140 000 scores 3 marks

an incorrect answer for one step does

not prevent allocation of marks for

subsequent steps

(area = 0.1 × 0.1 =) 0.01

allow 1 × 10−2

(volume = 0.01 × 0.01 =) 0.0001

allow 1 × 10−4

1

1

(number = 14 =) 140 000

0.0001

allow ecf from part (f)

allow 1.4 × 105

do not accept 14 × 104

area=0.01

Volume=0.0001

Number=140,000

h)Q

(i)

allow reverse argument

(bacteria) could make humans ill

allow (bacteria) cause infection /

disease

or

(bacteria) could kill humans

allow (bacteria) cause appropriately

named disease

or

(bacteria) could release toxins

ignore harmful

Eating food containing Salmonella bacteria can cause illness.

(a) Two symptoms of infection by Salmonella are vomiting and diarrhoea.

What causes these symptoms?

(a) toxins / poisons (secreted by / from / in bacteria)