Infection and Response

Question 1

Communicable diseases

Answer 1

Disease caused by pathogens that can be spread through contact with contaminated surfaces, bodily fluids, blood products, insect bites or air and water. Examples include cholera, HIV and malaria.

Question 2

Pathogens

Answer 2

Pathogens are microorganisms that can cause infectious diseases.

Question 3

Viruses

Answer 3

Viruses are tiny, non-living (do not have cells) particles that can reproduce rapidly within the body.
To survive and replicate, they invade host cells (animals or plant cells).
The virus particle inserts its own DNA into the host cell’s DNA, which is then copied and used to make more viruses.
Once the new virus particles have been synthesised (made), they cause the cell to burst.
This releases the new viruses to invade more cells.

Question 4

Measles

Answer 4

Measles is a highly contagious and a potentially serious viral infectious disease that can be fatal if complications arise.

Symptoms include fever and red skin rash.
The virus is spread by the inhalation of droplets from coughs or sneezes.
There is no treatment for measles but there is a vaccine for prevention.

Question 5

HIV

Answer 5

Human immunodeficiency virus can eventually lead to AIDS (acquired immunodeficiency syndrome.

HIV starts with a flu-like illness. If untreated it can travel to the lymph nodes and attack cells of the immune system. It can stay hidden for a long time until the immune system is so badly damaged that it can no longer deal with other infections. This late stage HIV is known as aids.

The virus can be spread by direct sexual contact, the exchange of bodily fluids or from mother to child at birth or in breast milk.

There is no cure for HIV, although the use of antiretroviral drugs used early in the infection can now effectively control the disease to slow or halt the progress to AIDS.

Question 6

TMV

Answer 6

Tobacco mosaic virus is a widespread plant pathogen that infects about 150 species of plants including tomato and cucumber.

The symptoms are distinctive mosaic pattern of discolouration of the leaves as the virus infects the chloroplasts. The plant will not grow as much due to the lack of photosynthesis.

The virus is spread by plants including tomato direct contact with an infected plant. The virus can stay in the soil for about 50 years.

There is no treatment for TMV and the best method of control is good field hygiene to prevent the spread of the virus.

Question 7

Disease

Answer 7

A disease is an illness or disorder of the body or mind that leads to poor health.

Question 8

Bacteria

Answer 8

Bacterial pathogens are cells that can infect plants and animals, causing disease. Not all bacteria is harmful - both skin and large intestine are home to hundreds of different bacterial species.

Bacterial pathogens produce toxins that cause damage to cells and tissue directly. In certain conditions bacteria can reproduce rapidly.

Question 9

Salmonella

Answer 9

Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions. It is found in the gut of many animals.

The symptoms of a salmonella infection start between 8 - 72 hours of eating infected food. The bacteria secrete toxins that cause the body to react with; fever, abdominal cramps, vomiting and diarrhoea. These symptoms are the body trying to remove the infection from the gut. Generally the infection does not last very long but is more common in children.

Contaminated food that has not been cooked properly is the main cause of salmonella food poisoning.

It can be prevented with proper hygiene and cooking food thoroughly.

Question 10

Gonorrhoea

Answer 10

Gonorrhoea is a sexually transmitted disease STD.

In the early stages symptoms include a thick, yellow or green discharge from the vagina or penis and pain when urinating. Some infectious people can be asymptomatic. If left untreated, it can cause infertility, ectopic pregnancy and pelvic pain. Babies born to women with the disease can get eye infections and be born blind.

It is spread by unprotected sexual contact.

Barrier methods of contraception such as a condom can prevent it spreading. It can be treated with antibiotics, but now many strains are becoming resistant to the most used antibiotics penicillin. Tracing of all sexual partners is essential so that all individuals can be tested and treated.

Question 11

Fungi

Answer 11

Fungi are unicellular or multicellular organisms that each have bodies made up of hyphae (thread-like structures). The hyphae are able to grow and penetrate tissues, such as human skin or the surface of plants. The hyphae produce spores that can spread to other plants and animals

Question 12

Rose black spot

Answer 12

Rose black spot is a fungal disease of plants where purple or black spots develop on the leaves, which often turn yellow and drop early. It affects the growth of plants as photosynthesis is reduced. It is spread in the environment by water or wind. They can be treated by using fungicides or removing and destroy the affected leaves.

Symptoms include purple or black spots on the leaves which can turn yellow and drop off. The reduction in photosynthesis means the plant has less energy to make flowers.

It is spread when spores from the fungus are carried in the wind or water.

The plant can be treated with fungicide chemicals. The leaves can be removed and burned to prevent the spread of infection. Breeding of varieties of plants that have resistance to the disease.

Question 13

Protists

Answer 13

Protists are single-celled eukaryotic organisms (they have a nucleus). Lots of protists are parasites. This means that they live on or inside other organisms. They are often transferred to the host organism by a vector, such as an insect or mosquito.

Question 14

Malaria

Answer 14

The pathogens that cause malaria are protists from the plasmodium family and can infect red blood cells in humans.

Malaria is spread by the female anopheles mosquito (a vector).
If a mosquito is carrying malaria, then it transfers the infection into a person’s bloodstream when it bites them.
Malaria leads to recurring and severe fevers, which can cause death.

If diagnosed early malaria can be treated with a combination of drugs however the protists that cause malaria have become resistant to most of the drugs. The spread can be reduced by controlling the mosquitos population - using insecticide, mosquito nets and prevent them from breading.

Question 15

Non specific defence

Answer 15

The human body has non specific defences that are designed to prevent any pathogen from entering the body and causing harm.

Question 16

Skin

Answer 16

Skin is a waterproof barrier that pathogens cannot pass through.
Good bacteria live permanently on our skin, covering the surface and preventing pathogens from growing on our skin.

Question 17

Stomach acid

Answer 17

Glands in the stomach wall produce hydrochloric acid, which destroys any pathogens that enter the stomach.

Question 18

Tears

Answer 18

Tears contain enzymes that destroy any pathogens that make contact with our eye.

Question 19

Mucus

Answer 19

Mucus is produced in the respiratory system and traps the particles and bacteria entering our airways.

Question 20

Immune system

Answer 20

Once a pathogen has entered the body they role of the immune system is to prevent the infectious organism from reproducing and to destroy it.
White blood cells help to defend against pathogens by phagocytosis, production of antibodies and antitoxins.

Question 21

Phagocytosis

Answer 21

A white blood cell finds the pathogen and engulfs it by changing shape.
The white blood cell ingests (absorbs) and digests the pathogen, destroying it.

Question 22

Production of antibodies

Answer 22

Lymphocytes produce antibodies.
Antibodies are y shaped proteins - each individual has the potential to make millions of different types of antibodies, each with a slightly different shape.

White blood cells recognise foreign antigens (proteins) on the surface of pathogens and produce protein molecules called antibodies.
Antibodies are specific to particular pathogens.

It may take a few days to make the antibodies that are specific to a pathogen and this may give the pathogen enough time to make you feel unwell.

Question 23

Production of antitoxins

Answer 23

Some bacteria produce toxins that can damage cells and tissues.
The immune system responds to this by producing antitoxins, which neutralise the toxins released by the bacteria and prevent them from causing harm.

Question 24

Vaccinations

Answer 24

Vaccination will prevent illness in an individual by providing artificial immunity
Vaccination involves exposing an individual to the antigens of a pathogen in some form, triggering an immune response which results in the formation of memory cells which can make antibodies against it
If a vaccinated individual is infected with the pathogen, they can destroy it before they become infectious

Question 25

How do vaccines work

Answer 25

Vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies
If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.

Question 26

Immunity

Answer 26

There are two types of immunity:
Active immunity that comes from the body creating antibodies to a disease either by exposure to the disease (natural) or by vaccination (artificial)
Passive immunity that comes from antibodies given to you from another organism, for example in breast milk

Question 27

Antibiotics

Answer 27

Medicines that treat the cause of the disease. Antibiotics such as penicillin are medicines that help to cure bacterial diseases by killing infective bacteria inside the body. Only certain antibiotics will work on certain diseases, so a doctor will prescribe different antibiotics depending on the type of infection. They work by stopping bacteria cellular processes such as the production of the cell wall.

Antibiotics will not work against viruses, as viruses reproduce inside cells. It is difficult to develop drugs that kill viruses without damaging the body’s tissues.

Question 28

Antibiotic resistance

Answer 28

Since the discovery of antibiotics, it has saved millions of lives however antibiotics have been overused and antibiotics resistance has developed in many different types of bacterial diseases.

Bacteria like all organisms have random mutations in their DNA. One of these mutations gives them resistance to antibiotics. A strain of staphylococcus aureus has developed resistance to a powerful antibiotic methicillin. This is known as MRSA (methicillin resistance staphylococcus aureus. MRSA can infect wounds and is difficult to treat without antibiotics.

Question 29

Preventing resistant bacteria

Answer 29

Doctors need to avoid overuse of antibiotics, prescribing them only when needed.
Antibiotics shouldn’t be used in non-serious infection that the immune system will clear up.
Antibiotics shouldn’t be used for viral infections.
Patients need to finish the whole course of antibiotics so that all the bacteria are killed and none are left behind to mutate to resistant strains.

Question 30

Painkillers

Answer 30

Medicines that treat the symptoms of the disease. For example ibuprofen can reduce pain and inflammation but does not kill the pathogens.

Question 31

Discovering new drugs

Answer 31

Traditionally drugs were extracted from plants and microorganisms. New drugs are being developed all the time by scientists at universities and drug companies around the world.

Lots of the medicine that we use today are based on chemicals extracted from plants.
The heart drug digitalis originated from foxgloves.
The painkiller aspirin originates from willow.
Penicillin was discovered by Alexander Fleming from the penicillium mould.

Most new drugs are synthesised by chemists however the starting point may still be a chemical extracted from a plant.

Question 32

Discovery of penicillin

Answer 32

Penicillin was first discovered by Alexander Fleming in 1928. He left some Petri dishes that had been contaminated with mould and found bacteria would not grow near the mould.
He discovered that the mould (penicillium notatum) was releasing a chemical (penicillin) that killed the bacteria surrounding it.

Question 33

Testing new drugs

Answer 33

All new drugs need to be tested and trialed before they can be used in patients. They are tested for:

Toxicity - any harmful side effects
Efficacy - does the drug work
Dose - lowest dosage that can be used and still have an effect.

Question 34

Developing new drugs

Answer 34

Preclinical testing is done in a laboratory using cells, tissues and live animals.
Clinical trials use healthy volunteers and patients. Very low doses of the drug are given at the start of the clinical trials.
If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.
In double blind trials, some patients are given a placebo.

Question 35

Preclinical testing

Answer 35

The drug is tested on cells in the lab
Computer models may also be used to simulate the metabolic pathways that may be taken by the drug
Efficacy and toxicity are tested at this stage

Question 36

Whole organism testing

Answer 36

The drug is tested on animals to see the effect in a whole organism - all new medicines in the UK have to have tests on 2 different animals by law
Efficacy toxicity and dosage are tested at this stage.

Question 37

Clinical trials

Answer 37

The drug is tested on human volunteers first, generally with a very low dose then increased. This is to make sure it is safe in a body that is working normally.

The next stage is to test on patients with the condition.
The patients are often split into two groups; one given the drug the other given a placebo. This is called a double-blind study - neither the doctor nor the patient knows if the patient is getting the placebo or the active drug.

Once the drug is found to be safe then the lowest effective dose is tested at this stage.

Question 38

monoclonal antibodies

Answer 38

Monoclonal antibodies are produced from clones (genetically identical copies) of cells (often white blood cells). They are all identical and are complementary to one type of antigen (proteins found on the surface of pathogens).
Monoclonal antibodies are specific to one binding site (area) on one protein antigen (on the surface of cells).
This means that monoclonal antibodies target specific chemicals or cells in the body.

Question 39

Producing monoclonal antibodies

Answer 39

The lymphocytes are combined with a particular type of tumour cell to make a hybridoma cell
Tumour cells can divide repeatedly which is why they are used
The hybridoma cell can both divide and produce the antibody
Single hybridoma cells are cloned, resulting in many divisions, making high quantities of identical cells that all produce the same antibody
A large amount of the antibody can be collected and purified ready for use

Question 40

Uses of monoclonal antibodies

Answer 40

They can be used for:

Pregnancy tests
Diagnose of disease
Measuring and monitoring
Research
Treating disease

Question 41

Pregnancy tests of monoclonal antibodies

Answer 41

Pregnant women produce a hormone called Human chorionic gonadotropin (HCG).
Monoclonal antibodies can be used in pregnancy tests to bind (attach) to the HCG hormone’s antigens.
If the urine contains HCG, the antibodies bind and this shows that the person is pregnant.
If the urine does not contain HCG, then the antibodies will not bind to the HCG, showing a negative result.

Question 42

Diagnose of disease of monoclonal antibodies

Answer 42

The monoclonal antibodies are specific to antigens found on the surface of pathogens, blood clots or cancer cells. They also contain markers that help the doctors to find the location of them. It is used in the test for prostate cancer.

Question 43

Measuring and monitoring of monoclonal antibodies

Answer 43

Since monoclonal antibodies are specific to one antigen, they can be designed (created) to identify (find) specific chemicals in the blood.
For example, they can:
Identify particular molecules in a tissue or cell by binding to them with a fluorescent dye. Areas in the body with lots of these molecules can be highlighted using the dye.
Identify the levels of hormones in the blood.
Be used to test blood samples for pathogens, such as HIV.

Question 44

Research of monoclonal antibodies

Answer 44

Monoclonal antibodies with a fluorescent dye attached can be used by scientists to detect specific molecules in a cell or tissue.

Question 45

Treating diseases using monoclonal antibodies.

Answer 45

Monoclonal antibodies can be produced to bind (attach) to target cells in the body, e.g. cancer cells.
We can attach anti-cancer drugs to the monoclonal antibodies. When they bind to the cancer cells, they can deliver the drugs directly to the tumours.
This is an effective cancer treatment because the antibodies cannot bind to or damage any normal human body cells (because normal cells will not have the complementary antigens).

Question 46

Advantages of monoclonal antibodies

Answer 46

They only bind to specific molecules on diseased or damaged cells - they do not affect healthy cells.

Highly specific so can be produced to treat a range of conditions.

Hoped to be a cheaper procedure and tried and tested method of treating conditions.

Question 47

Disadvantages of monoclonal antibodies

Answer 47

Caused more side effects than first expected. The use of mice antibodies caused complications. Now humanised antibodies are being developed.

It is an expensive procedure at the moment.

Producing specific monoclonal antibodies is difficult.

Question 48

Aphids

Answer 48

Aphids have long sharp mouthpieces that pierce the surface of the stem and into the phloem so that they can feed on the sugar filled sap
They can infest a plant in large numbers and remove large quantities of the phloem sap. This can weaken the plant
Aphids can also act as a vector for the transfer of diseases
Biological pest control (using ladybirds, a natural predator of the aphid) to feed on them or using chemical pesticides are the best ways to control infestation with aphids

Question 49

Detecting plant diseases

Answer 49

Stunted growth - rose black spot, TMV and mineral deficiency.
Spots on leaves - rose black spots
Rotting - rose black spot and potato blight
Visible pests - aphids and caterpillars
Discolouration of the leaves - TMV and magnesium deficiency
Growth - crown gall bacteria infection.
Malformed stems and leaves - aphids

Question 50

Mineral deficiency

Answer 50

Nitrates - used for production of amino acids for protein. Symptoms include stunted growth, upper leaves pale green and lower leaves yellow.

Magnesium - used for synthesis of chlorophyll needed for photosynthesis. Symptoms include yellow leaves (chlorosis) and stunted growth.

Potassium - used for production of fruits and flowers. Symptoms include poor growth of fruits and flowers, yellow leaves and dead spots.

Question 51

Identifying plant diseases

Answer 51

Diseases in the garden can be identified by comparing symptoms to those described in gardening manuals or online

Crop plants or forest trees, experts may visit the field/woodland to take samples which can then be taken to a lab to undergo DNA analysis. This would help to identify the specific pathogen causing the problem

Plant scientists, foresters, farmers and market gardeners can use testing kits which contain monoclonal antibodies to identify the presence of pathogens quickly and easily

Question 52

Fertilisers

Answer 52

Plants like all organisms need the correct amount of nutrients to function properly.
If plants are deficient in a mineral these can be replaced by fertilisers added to the soil.
These fertilisers are often shown as NPK ratios depending on the need of the plant that is being grown.

Question 53

Physical defences of plants

Answer 53

The cellulose cell wall not only provides support for the plant but also protection from microorganisms
The waxy cuticle of the leaf is a barrier to microbes from entering the plant. The only place that they can enter in the leaf is through the stomata
Bark provides a tough layer around the stem of the plant to prevent pathogens from entering
As deciduous trees lose leaves in the winter the infection can be taken with them

Question 54

Chemical defences of plants

Answer 54

Many plants produce chemicals that have antimicrobial properties.
Some plants produce poisons to deter herbivores from eating them. Animals will quickly learn to avoid eating plants that make them feel unwell. Examples include foxglove and yew.

Question 55

Mechanical deference of plants

Answer 55

Thorns make it unpleasant or painful for large herbivores to eat such as cactus and rose.
Drooping or curling when touched can dislodge insects and frighten of larger species such as mimosa.
Mimicry so that plants can look as though they have a disease and trick animals to not eating them. For example passion flowers.

Question 56

Preventing infection

Answer 56

By being hygienic, we can destroy pathogens or wash them away so that they are not spread.
Using antibacterial products to clean surfaces, washing our hands and sneezing into a handkerchief are all hygienic measures to prevent the spread of infection.
By isolating infected individuals, we prevent contact with other organisms. This stops the infection from spreading.
Some protist diseases are carried by vectors.
A vector is an organism that carries pathogens without being infected.
For example, we can protect against mosquitos carrying malaria using mosquito nets.
Vaccination can make people immune to (resistant to) infection.
The more individuals that are vaccinated, the less likely the disease is to spread.

Question 57

Spreading of disease

Answer 57

Some pathogens live on the surface of other organisms, such as the skin. If infected skin touches a surface, some of the pathogens can transfer from the infected skin to the surface. The pathogen then spreads to other people who also touch that surface. Athlete’s foot is spread in this way.
Some pathogens contaminate water supplies. Organisms drinking this contaminated water can be infected by pathogens.
Cholera is a disease spread in this way.
Some pathogens are released into the air inside droplets when an organism coughs or sneezes. These droplets can then be inhaled (breathed in) by other organisms.
The flu and common colds are spread in this way.

Question 58

How do pathogens cause infection

Answer 58

Pathogens cause illness to their hosts through a variety of ways. The most obvious means is through direct damage of tissues or cells during replication, generally through the production of toxins, which allows the pathogen to reach new tissues or exit the cells inside which it replicated.

Question 59

Primary response

Answer 59

During a primary infection levels of antibodies slowly increase, peak at around ten days and then gradually decrease. This is what happens when someone is vaccinated with a dead or inactive pathogen or when someone catches a disease for the very first time. It is called the primary immune response.

Question 60

Secondary response

Answer 60

A second exposure to the antigen that was in the vaccine, or to the same pathogen that made the person ill before, causes the white blood cells to respond much more quickly and in larger quantities this time. This is the secondary immune response. The antibodies are produced so quickly by the memory cells that the pathogen is killed off before it can make the person ill. This is called being immune to a disease or having immunity.

Question 61

Aseptic techniques

Answer 61

disinfect hands / work surface
sterilise Petri dish or culture medium (before use)
pass inoculating loop / forceps through a flame (before use)
work near a flame
work in a fume cupboard
tilt lid (of Petri dish) when placing discs on agar (to minimise contact with air / breath)
secure lid of Petri dish with adhesive tape