GCSE BIOLOGY - INFECTION AND RESPONSE

What is a communicable disease?

A disease caused by a pathogen which can be passed between animals or plants

What is a pathogen?

A disease-causing microorganism

How do bacteria cause disease?

Once inside the body, they divide rapidly by binary fission. They kill cells and produce harmful toxins.

How do viruses cause disease?

They invade and reproduce inside living body cells, leading to cell damage.

Give three ways in which pathogens can be spread.

● By air - flu, tuberculosis and the common cold are spread by droplet infection.
● By water - fungal spores in water spread plant diseases.
● By direct contact - common in plant diseases and sexually transmitted infections.

Give four ways in which the spread of
pathogens can be reduced

● Hygiene - handwashing, disinfectants, tissues.
● Reducing contact with infected individuals - quarantine.
● Removing vectors - use of pesticides and insecticides, removal of habitats.
● Vaccination.

Why is it especially important to prevent the spread of viral diseases?

Scientists have not yet developed cures for many viral diseases.

What is measles?

Measles is a serious viral disease that can cause blindness and brain damage. The main symptoms are a fever and a red skin rash.

How is measles spread?

By air - through the inhalation of droplets from coughs and sneezes.

What is HIV/AIDS?

HIV is a virus which attacks and damages the immune system until it can no longer function properly. AIDS is the condition resulting from a
long-term HIV infection. There is no cure or vaccine for HIV/AIDS.

How is HIV spread?

Direct sexual contact and the exchange of bodily fluids eg. blood, breastmilk.

How can the spread of HIV/AIDS be prevented?

● Use of condoms
● Screening of blood for transfusions
● Not sharing needles
● Bottle-feeding by HIV-positive mothers
● Use of antiretroviral drugs to prevent the development of AIDS

What is tobacco mosaic virus?

A plant pathogen which causes leaf discolouration when cells are damaged. Affected areas cannot photosynthesise, reducing the crop yield. As there is no treatment, farmers grow TMV-resistant crop strains to avoid infection.

How is tobacco mosaic virus spread?

Contact between infected and healthy plants. Insects may act as vectors which transfer the virus between different plants.

What is salmonella?

A type of bacteria found in raw meat, poultry and eggs. If they enter the body via food poisoning, they can affect natural gut bacteria.

What are the symptoms of salmonella food poisoning?

● Fever
● Abdominal cramping
● Vomiting
● Diarrhoea
May be fatal in very young or elderly populations due the
risk of dehydration.

How can the spread of salmonella be limited?

● Vaccinating animals intended for consumption
● Keep raw meat away from cooked meat
● Disinfect hands and surfaces after contact with raw meat
● Thoroughly cook meat

What is gonorrhoea?

A sexually transmitted bacterial infection caused by unprotected sex with an infected individual. Early symptoms include yellow/green discharge from genitals and painful urination, although it may be symptomless.
Its spread can be controlled through the use of antibiotics (no
longer penicillin as many strains are resistant) and using
condoms.

What is rose black spot?

A fungal disease which causes purple or black spots to develop on rose leaves. It reduces the area of the leaf which is available for
photosynthesis and causes leaves to turn yellow and drop prematurely.

How is the rose black spot fungus spread?

Fungal spores are spread by the wind
and in water.

How can the rose black spot fungus be treated?

● Using fungicides
● Destroying infected leaves

What is malaria?

Malaria is a disease caused by protist pathogens. The disease is carried from host to host by mosquitoes, and the protists enter the human bloodstream when they feed. Symptoms include fever and shaking, and it may also be fatal in some cases.

How can the spread of malaria be reduced?

● Using insecticides
● Using insect nets to avoid bites
● Prevent mosquito breeding by removing stagnant water
● Antimalarial drugs

How does the skin prevent pathogens from entering the body?

● Acts as a physical barrier.
● Scab formation after skin is cut/wounded.
● Antimicrobial secretions which can kill pathogens.
● Healthy skin flora compete with pathogens and act as an additional barrier.

How does the respiratory system prevent
pathogens from entering the body?

● Nose - has hairs and mucus which trap pathogens.
● Trachea and bronchi - have mucus that traps pathogens. Ciliated cells move mucus to the mouth so it can be swallowed.

How does the stomach prevent pathogens
infecting the body?

● Secretes hydrochloric acid - kills any pathogens present.

How does phagocytosis protect us against disease?

White blood cells (phagocytes) ingest and destroy pathogens so they cannot infect more cells.

How does antibody production protect us
against disease?

White blood cells produce antibodies which are complementary to a specific antigen on a pathogen. The binding of antibodies to antigens causes pathogens to clump together, making them easier to destroy. In the case of a second infection, the correct antibodies can be
produced rapidly, preventing the person getting the same disease again.

How does antitoxin production protect us
against disease?

Antitoxins bind to toxins released by pathogens and neutralise them.

What is a vaccination?

Contains a dead or inactivated form of the pathogen which stimulates white blood cells to produce complementary antibodies to the pathogen. In the case of a second infection, memory cells can rapidly
produce the correct antibodies and prevent illness.

What is herd immunity?

If a sufficiently high proportion of a population are immune to a disease (especially through vaccination), the spread of this disease will be limited.

What are the advantages of vaccinations?

● They have eradicated many deadly diseases eg. smallpox.
● Many epidemics can be prevented by vaccinations.
● Herd immunity protects those who cannot have vaccinations.

What are the disadvantages of vaccinations?

● Not guaranteed to work - might not protect against multiple strains of a pathogen.
● May be side effects or adverse reactions.

What drugs are used to cure some bacterial diseases?

Antibiotics - they can kill bacterial pathogens inside the body

How do antibiotics work?

Antibiotics eg. penicillin kill bacterial pathogens inside the body, but do not kill human cells. Whilst some antibiotics kill a wide range of bacteria, it is important that the right antibiotic is used for specific
bacteria.

Why can antibiotics not be used to treat viral diseases?

Antibiotics have no effect on viral pathogens as they live inside the host’s (human) cells. Therefore, it is difficult to design drugs that would kill the virus and not destroy human cells at the same time.

What is antibiotic resistance?

Antibiotic resistance occurs when mutations lead to individual bacteria being resistant to an antibiotic. These bacteria are able to survive, reproduce and pass on their alleles, leading to a greater proportion of antibiotic-resistant bacteria. This is concerning as some types of bacteria are becoming resistant to all known antibiotics, so the diseases that they cause cannot be cured.

How can we prevent antibiotic resistance?

● Avoid overuse and unnecessary use of antibiotics
- eg. antibiotics are often used for viral infections.
● Finish antibiotic courses - to ensure all bacteria is killed.

What effect do painkillers have on infectious diseases?

Painkillers can only treat the symptoms but do not kill pathogens.

What plant is the heart drug digitalis extracted from?

Foxgloves

What painkiller originates from a compound found in willow bark?

Aspirin

What antibiotic was discovered by Alexander Fleming from a type of mould?

Penicillin

What are the four qualities of a good medicine?

● Effective
● Safe
● Stable
● Able to be taken in and removed easily

What three main factors are tested for when developing new drugs?

● Toxicity
● Efficacy
● Dose

How is preclinical testing carried out?

In a laboratory - uses cells, tissues and live animals

How is clinical testing carried out?

Uses healthy volunteers and patients. Firstly, the drug is tested at a low dose on healthy people - then tested on patients and on a larger scale to find the optimum dose. Often, one group receive a placebo
(not the test drug) and the other group receive the actual drug, in order to assess its efficacy.

What is the difference between a single-blind and a double-blind trial?

In a single-blind trial, only the doctor knows whether the patient is receiving the drug or the placebo. In a double-blind trial, neither the patient nor the doctor knows. Double-blind trials help remove bias on the part of the doctor.

What is a peer review?

Where the results of drug trials are checked over by scientists knowledgeable in this field.

Where the results of drug trials are checked over by scientists knowledgeable in this field.

● Antibodies that are clones from one parent cell
● Specific to one type of antigen

Describe how monoclonal antibodies are
produced

1. Specific antigen injected into an animal (e.g. mouse).
2. B-lymphocytes producing complementary antibodies extracted.
3. B-lymphocytes fuse with myeloma cells to form hybridoma cells - these cells can divide and produce antibody.
4. Hybridoma cells cultured.
5. Monoclonal antibodies collected and purified.

Outline the uses of monoclonal
antibodies

● Detection of pathogens
● Location of cancer cells and blood clots
● Treatment of cancer
● Used in pregnancy test kits

What are myeloma cells?

Type of tumour cell

Outline the uses of monoclonal
antibodies

● Detection of pathogens
● Location of cancer cells and blood clots
● Treatment of cancer
● Used in pregnancy test kits

What do pregnancy kits test for?

hCG in urine

What does a pregnancy test consist of?

A stick containing monoclonal antibodies (mAbs) specific to hCG:
● mAbs attached to a blue bead (free to move)
● mAbs fixed to the test stick

Describe what happens to the test stick if
a woman is pregnant

● hCG in urine binds to mAbs attached to a blue bead.
● mAbs with hCG diffuse up dipstick.
● mAbs fixed to the stick bind to hCG.
● Blue line forms.

Describe what happens to the test stick if
a woman is not pregnant

No hCG in urine so a blue line is not formed.

What is the advantage of using monoclonal antibodies to test for pathogens?

● Specific to one particular antigen
● Very accurate
● Quick results

Why can monoclonal antibodies be used
to target cancer cells?

● Cancer cells have specific antigens called ‘tumour markers’ on their membranes.
● mAbs are specific to one type of antigen so can be targeted to ‘tumour markers’ without damaging other cells.

Describe how monoclonal antibodies can
be used to diagnose cancer

● mAbs tagged to a radioactive substance.
● mAbs injected into the patient’s bloodstream.
● mAbs bind to ‘tumour markers’ on cancer cells.
● Emitted radiation is detected using a specialised scanner enabling doctors to determine the location of cancer cells.

How can monoclonal antibodies be used
to target drugs to cancer cells?

● mAbs attached to an anti-cancer drug.
● mAbs injected into the patient’s bloodstream.
● mAbs bind to ‘tumour markers’ on cancer cells.
● Anti-cancer drug destroys cancer cells.

Why are cancer treatments that use
monoclonal antibodies favoured over
traditional treatments?

● Radiotherapy and chemotherapy target rapidly dividing cells.
● Healthy cells (e.g. hair follicle cells, bone marrow cells) are damaged as a consequence, producing unpleasant side effects.
● mAbs only target cancer cells, reducing damage to normal cells.

How can monoclonal antibodies be used
to locate blood clots?

● mAbs tagged to a radioactive substance.
● mAbs target and bind to specific proteins in blood clots.
● Radiation emitted by mAbs is detected, enabling the location of blood clots to be identified.

How do aphids cause damage to plants?

They use their sharp mouthparts to extract sap from the plant phloem, weakening the plant. They are also vectors who can transfer pathogens from diseased plants to healthy plants.

How can we reduce the number of aphids?

● Chemical pesticides
● Biological pest control - using ladybirds

Why do plants need a good supply of nitrate ions?

Nitrate ions are required to convert sugars into proteins which are required for the plant to grow. As a result, the growth of the plant will be stunted if there is not an adequate supply of nitrates.

Why do plants need a good supply of magnesium ions?

Magnesium ions are required to synthesise chlorophyll, which absorbs light energy during photosynthesis. As a result, the leaves cannot photosynthesise properly and they turn yellow (chlorosis).

What are the symptoms of disease in plants?

● Stunted growth (lack of nitrate ions)
● Spotted leaves (eg. rose black spot fungus)
● Decay/rotting
● Growths
● Malformation of stems/leaves
● Discolouration
● Presence of pests

What are three ways in which plant disease can be identified?

● Reference to a gardening website or manual
● Laboratory testing
● Monoclonal antibody test kits

Give examples of physical defence
responses used by plants

● Cellulose cell walls
● Tough waxy cuticle on leaves
● Outside layer on stems/bark on trees
● Leaf fall

Give examples of chemical defence
responses used by plants

● Antibacterial chemicals
● Poisons

Give examples of mechanical defence
responses used by plants

● Thorns and hairs to deter animals
● Leaves that droop/curl on contact
● Mimicry to trick animals