Unit 10 Diseases and immunity

Question 1

Describe: a pathogen

Answer 1

a disease-causing
organism

Question 2

a transmissible disease

examples of diseases not transmissible

Answer 2

a disease in which the pathogen can be passed from one host to another

e.g., cancer, diabetes

Question 3

How is a pathogen transmitted?

2 ways

Answer 3

(a) by direct contact, including through blood & other body fluids e.g. semen

(b) indirectly, including from contaminated surfaces, food, animals and air [pathogen leaves host & is carried in some way to another, uninfected individual]

Question 4

Ways of transmission, examples - FOUR

Answer 4

1) droplets in air - common cold, influenza

2) food or water - cholera, typhoid, dysentery

3) touching contaminated surfaces - athletes foot, common cold, sal.

4) insect bites - malaria, dengue fever

Question 5

Describe the body defences

1. Mechanical barrier:

Answer 5

define ; structures that make it difficult for pathogens to get past them and into the body

1. Skin - covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab

Question 6

2. Mechanical barrier:

Answer 6

Hairs in the nose - make it difficult for pathogens to get past them further up the nose so they are not inhaled into the lungs

Question 7

3. Chemical barrier:

Answer 7

substances produced by the body cells that trap / kill pathogens before they can get further into the body & cause disease

3. Mucus - made in various places in the body, pathogens get trapped in the mucus and can then be removed from the body (by coughing, blowing the nose, swallowing etc), prevents it reaching the respiratory system

Question 8

4. Chemical barrier:

+ Chemical barrier:

Answer 8

Stomach acid - contains hydrochloric acid which is strong enough to kill any pathogens that have been caught in mucus in the airways and then swallowed or have been consumed in food or water

Another: antibacterial tears

Question 9

Cellular barrier?

Enhanced by…?

Answer 9

5. White blood cells - work to prevent pathogens reaching areas of the body they can replicate in

Phagocytosis (engulfing & digesting pathogenic cells), &

antibody production by lymphocytes [which clump pathogenic cells together so they can’t move as easily (known as agglutination) and releasing chemicals that signal to other cells that they must be destroyed]

Enhanced by vaccination

Question 10

Functions

Lymphocytes

Answer 10

Cells that tag foreign material, antigens, with antibodies, targeting the material for destruction

Question 11

Phagocytes

Answer 11

Engulf foreign material, pathogen, through phagocytosis, digesting it by releasing digestive enzymes

Question 12

Explain the importance of the following in controlling the spread of disease:

How is this done?

Answer 12

(a) a clean water supply

(b) hygienic food preparation

(c) good personal hygiene

(d) waste disposal

(e) sewage treatment

;; It stops pathogens from spreading!

Question 13

Examples of hygienic food preparation

Answer 13

🔗 Keep food cold so bacteria & fungi produce more slowly

🔗 Prepare food hygienically to avoid contamination from pathogens by washing hands well with soap and cleaning work surfaces with products such as bleach to kill pathogens

🔗 Cook food well (long enough at high temp) to kill bacteria & fungi

🔗 Cover food to prevent flies landing on it before eating

🔗 Use separate chopping boards/utensils for cutting uncooked meat

🔗 Wash hands after using the bathroom before handling food

Question 14

Examples of personal hygiene

Answer 14

🔗 Washing w/ soap removes substances which trap pathogens & pathogens themselves from skin

🔗 Use tissues to catch sneezes & coughs

🔗 Dispose of used tissue as soon as possible bc pathogens can still be alive

🔗 Wash hands after using the bathroom

Question 15

Examples of waste disposal

Answer 15

🔗 Waste food = food source for flies that can act as vectors for transmissible diseases & should be disposed of in a sealed container

🔗 Rubbish bins should be covered & removed to the landfill for disposal/burning regularly

🔗 All rubbish should be stored before collection away from human habitation

Question 16

Examples of sanitation

1. clean water supply

Answer 16

🔗 Homes & public places should have plumbing & drains to safely remove faeces & waste which can carry pathogens

Question 17

2. sewage treatment

Answer 17

🔗 Raw sewage should be treated to remove solid waste and kill pathogens before being released into the environment

Question 18

Do pathogens have a specific shape?

Answer 18

each pathogen has its own antigens, which have specific shapes

Question 19

What are antigens?

Answer 19

Antigens are any structure that can be identified by an immune system (usually proteins)

Question 20

Each organism has its own unique antigens. The shape is…

Answer 20

Organism = own antigens.

The shape of the antigen is COMPLEMENTARY to the binding groove on the antibody.

Question 21

What happens next?

Answer 21

Once the ANTIBODY-ANTIGEN COMPLEX is formed, it marks the foreign material/antigens for destruction

by PHAGOCYTES

Question 22

Why do our bodies need to create an antibody that fits the antigen?

Answer 22

specific antibodies have complementary shapes which fit specific antigens

Each pathogen has its own unique antigens.

Question 23

Describe: antibodies

Answer 23

proteins that bind to antigens leading to direct destruction of pathogens

or marking of pathogens for destruction by phagocytes

Question 24

Outline:

Process of vaccination ➡

Answer 24

(a) weakened pathogens or their [specific] antigens are put into the body

(b) the antigens stimulate an immune response by lymphocytes which produce antibodies

Complementary antibody binds to the antigen, tagging it for destruction by phagocytes

(c) memory cells are produced that give long-term immunity, allowing for the antibody to be produced rapidly in the future

Question 25

Explain the role of vaccination in controlling the spread of diseases

Answer 25

🔗 Vaccinations give protection against specific diseases & boost the body’s defence against infection from pathogens without the need to be exposed to dangerous diseases that can lead to death

The level of protection in a population depends on the proportion of people vaccinated

The pathogen in vaccine cannot cause illness but can provoke an immune response

As memory cells have been produced due to vaccine, this immunity is long-lasting

Question 26

Preventing the Spread of Disease:

Explain herd immunity & higher proportion of vaccinated people providing more protection.

Answer 26

If a large enough percentage of the population is vaccinated, it provides protection for the entire population because there are very few places for the pathogen to breed - it can only do so if it enters the body of an unvaccinated person = herd immunity

Spread of contagious disease is contained.

Question 27

What happens otherwise?

Answer 27

If the number of people vaccinated against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection

bc more likely to come across people who are infected and contagious, increases:

🔗 the number of infections
🔗 the number of people who could die from a specific infectious disease

Question 28

What does herd immunity do?

Answer 28

prevents epidemics and pandemics from occurring in populations = the reason that many vaccinations are given to children

Question 29

Is the goal of a vaccination programme always just to control the disease?

Example?

Answer 29

No; sometimes, its aim is to eradicate certain dangerous diseases

Like smallpox in 1980 [by WHO since 1950s]

Question 30

Describe: active immunity

Answer 30

defence against a pathogen by antibody production in the body

Question 31

How is active immunity gained?

What ways? With what cells?

Answer 31

after an infection by a pathogen

or by vaccination

Memory cells are produced.

Question 32

Describe: Passive immunity

Example?

Answer 32

passive immunity: a [fast-acting,] short-term
defence against a pathogen by antibodies acquired from another individual,

including mother to infant, across the placenta [through blood] and in breast milk

Question 33

Explain the importance of breast-feeding for the
development of passive immunity in infants

Answer 33

Importance for newborns:

get all antibodies from the mother; it helps the very young to fight off infections until they are older and stronger and their immune system is more responsive

Question 34

Are memory cells produced in passive immunity?

Answer 34

memory cells are NOT produced in passive immunity

Question 35

Describe: cholera

Answer 35

a disease caused by a
bacterium which is transmitted in contaminated water

Question 36

What does the cholera bacterium do?

Explain

Answer 36

The cholera bacterium produces a toxin

that causes secretion of chloride ions into the small intestine,

causing osmotic movement
of water into the gut,

causing diarrhoea, dehydration and loss of ions from the blood

Question 37

Why do we always feel more sick from first infections?

Answer 37

It takes our body many days to create antibodies that will fit an antigen if we have never been exposed to it [& if any, it’s slow]

The second time our body is exposed to it, it recognises the antigen much faster & can start producing antibodies

[First infection w/ new pathogen: more risky, symptom causing]

Question 38

Explain how cholera causes diarrhoea (4)

Answer 38

cholera releases toxin

toxin causes more chloride released into small intestine

lowering water potential in lumen

osmosis into the lumen

diarrhoea is loss of watery faeces

can lead to death due to loss of salts and dehydration

Question 39

Describe how diarrhoea is treated (2)

Answer 39

oral rehydration therapy

drink mixture of sugar and salt

replace lost water

Question 40

(b) Explain what would happen if a kidney from a person with blood group A was
transferred into the body of a person with blood group O.

Answer 40

kidney would be rejected ;

(lymphocytes produce anti-A) antibodies ;

(antibodies) attach to blood vessels ;

Question 41

Describe how antibodies provide protection from diseases caused by viruses and
bacteria.

Answer 41

attach to virus / bacteria / antigens ;

prevent movement around the body and entry into cells ;

stop division ;

neutralise, toxins ;

clumping bacteria tgt to help phagocytes engulf virus / bacteria ;

Question 42

Explain what is meant by the term antibiotic. [2]

Answer 42

drug / chemical / substance ;

produced by microorganisms ;

that kills / stops, growth of, bacteria

Question 43

Explain why

(i) only a few bacteria grew in dish B compared with dish A, [1]
(ii) more bacteria grew in C than in B. [1]

Answer 43

i) (most) were killed by the antibiotic

ii) (only) resistant bacteria in C

Question 44

Fig. 4.1 shows the effect of an antibiotic on a species of disease-causing bacterium.
Suggest why antibiotics should not be used too often.

Answer 44

resistant bacteria survive / not killed ;

eventually, all / many, become resistant ;

antibiotic no longer effective ;

Question 45

Explain the possible effect of the X-rays on the bacteria. [3]

Answer 45

X-rays caused mutations ;
change in DNA ;
ref to, gene / allele ;
mutation causes antibiotic resistance

Question 46

State two ways in which the structure of a bacterium differs from the structure of a
virus.

Answer 46

cell wall

flagellum

Question 47

Human Immunodeficiency Virus (HIV) infects cells of the immune system.

Describe the effects of HIV on the immune system. [4]

Outline how the human immunodeficiency virus (HIV) affects the immune system. [3]

Answer 47

HIV infects lymphocytes ;

[[T helper (lymphocytes / cells) ;]]

fewer antibodies produced ;
infected cells not killed (by immune system) ;
phagocytes less effective ;

increased susceptibility to / longer recovery time for, (infectious)
diseases

///// ref. to invasion of lymphocytes ;
so no production of antibodies ;
ref. to decrease in body’s ability to fight infection ;

Question 48

Explain why it is important for newborn babies to have antibodies. [3]

Answer 48

📍 any 3 from:

provides (passive) immunity;

protects against illness and pathogens ;

immune system of babies not yet developed;

bc antibodies stop pathogens entering cells ;

Question 49

Some mothers bottle-feed their newborn babies with formula milk rather than breast-feed.

Describe four advantages of breast-feeding, other than providing antibodies. [4]

Answer 49

bonding/AW, with mother;
it’s free/‘cheap’;
sterile/no risk of infection;
body temperature;
no preparation/easily available;