B3: Infection And Response

Question 1

What are pathogens and what do they do?

Answer 1

Pathogens are microorganisms that enter the body and cause disease - more specifically, communicable diseases.

Both plants and animals can be infected by pathogens.

Question 2

What are the four types of pathogens?

Answer 2

Bacteria
Viruses
Protists
Fungi

Question 4

What are bacteria and how do they work?

Answer 4

Bacteria are very small cells which can reproduce rapidly inside your body. They can make you feel ill by producing toxins that damage your cells and tissues.

Question 5

Explain what viruses are.

Answer 5

Viruses are not cells, but like bacteria they can reproduce rapidly inside your body. They live in your cells and replicate themselves, causing the cells to burst and releasing all the new viruses. This cell damage is what makes you feel ill.

Question 6

Explain what fungi are.

Answer 6

Fungi come in different shapes. Some are single-celled and other have a body which is made up of hyphae (thread-like structures). These hyphae can grow and penetrate human sling and the surface of plants, causing disease. The hyphae can produce spores, which can be spread to other plants and animals.

Question 7

What are the ways in which pathogens can be spread?

Answer 7

Water - e.g. Cholera

Air - e.g. The influenza virus

Direct Contact - e.g. Athletes foot

Question 8

Explain how measles is caught and what its symptoms are.

Answer 8

Spread through droplets from an infected person’s sneeze or cough.
Symptoms - red skin rash, signs of a fever.
Can sometimes lead to pneumonia or encephalitis.
Most people are vaccinated against measles.

Question 9

Explain how HIV is contracted and what it’s symptoms are.

Answer 9

HIV is spread by sexual contact or by exchanging bodily fluids such as blood.
Initially caused flu-like symptoms.
Often there are no symptoms for years, during this time the virus can be treated with antiretroviral drugs to stop the virus replicating in the body.
If the body’s immune system is badly damaged, it can’t cope with other infections or cancers - at this stage it’s known as late stage HIV infection / AIDS

Question 10

Explain what tobacco mosaic virus is.

Answer 10

TMV is a virus that affects many species of plants, e.g. Tomatoes.
It causes a mosaic pattern on the leaves of plants - parts of the leaves become discoloured.
The discolouration means it is unable to photosynthesise.

Question 11

Give an example of a fungal disease and explain it.

Answer 11

Rose black spot is a fungus that causes purple or black spots to develop on the leaves of rose plants. The leaves then turn yellow and fall off. This prevents photosynthesis from happening. It spreads through the environment in water or by the wind. Gardeners can treat the disease by stripping the plant of its affected leaves and using fungicides.

Question 12

Give an example of a disease caused by a protists and explain it.

Answer 12

Malaria is caused by a protist, part of the malarial protist’s life cycle takes place inside the mosquito. The Mosquitos are vectors, they pick up the protist when they feed on an infected animal. Every time the mosquito feeds on another animal it infects it by inserting the protist into the animal’s blood vessels. Malaria causes repeated episodes of fever that can be fatal. The spread of malaria can be reduced y stopping mosquitoes from breeding. People can be protected from mosquitoes by using insecticides and mosquito nets.

Question 13

Describe the effects of salmonella.

Answer 13

Salmonella is a type of bacteria that causes food poisoning.
Symptoms - fever, stomach cramps, vomiting, diarrhoea l
Symptoms are caused by toxins that the bacteria produce.
You can get Salmonella food poisoning by eating food that’s been contaminated.

Question 14

Explain the effects of gonorrhoea.

Answer 14

Gonorrhoea is a sexually transmitted disease, cause by bacteria and passed on through sexual contact.
Symptoms - pain when urinating, thick yellow or green discharge from the vagina or penis
It was originally treated with antibiotics called penicillin but the bacteria have become resistant to it.
To prevent the spread of this STD people can be treated with antibiotics and should use barrier methods of contraception.

Question 15

Name four ways in which the spread of disease can be prevented.

Answer 15

1. Being hygienic - washing your hands before preparing food
2. Destroying vectors - using insecticides to prevent insects breeding
3. Isolating infected individuals
4. Vaccinations

Question 16

Give some examples of the body’s defence system.

Answer 16

Skin - secreted antimicrobial substances which kill pathogens.
Hair and mucus in nostrils - trap particles that may contain pathogens.
Trachea and bronchi - secrete mucus to trap pathogens.
Stomach - produces hydrochloric acid to kill pathogens that make it that far from the mouth.

Question 17

Explain the three ways in which your immune system can attack pathogens.

Answer 17

1. Consuming them - white blood cells engulf and digest foreign cells (phagocytosis)
2. Producing antibodies - find and destroy foreign cells
3. Producing antitoxins - counteract toxins produced by the invading bacteria

Question 18

Explain how vaccinations work.

Answer 18

A vaccination is an injection of a small amount of dead or inactive pathogens, causing your body to make antibodies to defend against the foreign antigens. Memory cells then make it possible to remember the antibody made in case of another infection.

Question 19

Explain the pros of vaccinations.

Answer 19

Have helped control lots of communicable diseases that were once common in the U.K. (Small pic and polio)

Prevent epidemics

Question 20

Explain the cons of vaccinations.

Answer 20

They don’t always work - sometimes they don’t give you immunity.

You can sometimes have bad reactions to a vaccine (though they are very rare).

Question 21

Explain why antibiotics don’t destroy viruses.

Answer 21

Antibiotics kill or prevent the growth of the bacteria without killing your own body cells. Different antibiotics kill different types of bacteria.

But they don’t destroy viruses; viruses use your body cells to reproduce, making it difficult to develop drugs that destroy just the virus without killing the body’s cells.

Question 22

How can bacteria become resistant to antibiotics.

Answer 22

Bacteria can mutate, causing them to be resistant to an antibiotic. When you treat the infection, only the non-resistant strains of bacteria will be killed. The individual resistant bacteria will survive and reproduce.

To slow the development of resistant strains, it’s important for doctors to avoid over-prescribing antibiotics. It also important that you finish the whole course of antibiotics.

Question 23

Explain the three main stages in drug testing.

Answer 23

1. Preclinical testing on human cells and tissues.
2. Live subject, e.g. Animals
3. Human volunteers

Question 24

What are protists?

Answer 24

Protists are single called eukaryotes. Some are parasites that live on or inside other organisms and can cause them damage. They’re often transferred by a vector which doesn’t get the disease itself, for example an insect that carries the protist.