TOPIC 3 - INFECTION AND RESPONSE

Question 1

What are bacteria?

Answer 1

Very small cells that make you feel ill by producing toxins that damage your cells and tissues.
They reproduce rapidly inside your body.

Question 2

What are viruses?

Answer 2

They are not cells. They are tiny and reproduce rapidly.
They live inside your cells and replicate themselves by cropping themselves. The cell will the burst, releasing new viruses. The cell damage is that makes you feel ill.

Question 3

What are protists?

Answer 3

Protists are single-called eukaryotes.
Some are parasites. Parasites line on or inside other organisms and can cause them damage. They are often transferred to the organism by a vector, which doesn’t get the disease itself.

Question 4

What is fungi?

Answer 4

Some fungi are single-celled. Others have a body which is made up of hyphae (thread like structures). These hyphae can grow and penetrate human skin and the surface of plants, causing diseases.
The hyphae can produce spores, which can be spread to other plants and animals.

Question 5

How can pathogens be spread?

Answer 5

Water - eg cholera
Air - eg influenza (flu)
Direct contact - eg athletes foot is a fungus which makes skin itch and flake off.

Question 6

What is measles?

Answer 6

A VIRAL DISEASE
It is spread by droplets from an infected persons sneeze or cough.
People with measles develop a red skin rash, and they will show signs of a fever, eg a high temperature.
Measles can be fatal is there are complications. For example, it can lead to pneumonia (lung infection) or a brain infection called encephalitis.
Most people are vaccinated against measles when they are young.

Question 7

What is HIV?

Answer 7

A VIRUS
It is spread by sexual contact, or by exchanging bodily fluids such as blood. This may happen when people share needles while doing drugs.
Initially, HIV causes flu-like symptoms for a few weeks. Usually, the person doesn’t experience any symptoms for several years. During this time, HIV can be controlled by antiretroviral drugs which stop the virus replicating.
The virus attacks the immune cells.
If the body’s immune system is badly damaged, it can’t cope with other infections or cancers. At this stage, the virus is known as late stage HIV infection or AIDS.

Question 8

What is tobacco mosaic virus?

Answer 8

A VIRUS
It affects many species of plant
It causes a mosaic pattern on the leaves of the plants - part of the leaves become discoloured.
The discolouration means the plants can’t carry out photosynthesis as well, so the virus affects growth.

Question 9

What is rose black spot?

Answer 9

A FUNGAL DISEASE
it is a fungus that causes purple or black spots to develop on the leaves of rose plants. These leaves can then turn yellow and drop off.
This means that less photosynthesis can happen, so the plant doesn’t grow very well.
It spreads through the environment in water or by the wind.
Gardeners can treat this disease using fungicides and by stripping the plant of its affected leaves. These leaves then need to be destroyed so that the fungus can’t spread to other rose plants.

Question 10

What is Malaria?

Answer 10

A DISEASE CAUSES BY A PROTIST
Part of the malaria protists life cycle takes place inside the mosquito. The mosquitos are vectors - they pick up the malarial protist when they feed on an infected animal.
Every time the mosquito feeds on another mammal, it infects it by inserting the protist into the animal’s blood vessels.
Malaria causes repeating episodes of fever. It can be fatal.
People can be protected from mosquitos using insecticides and mosquito nets.

Question 11

What is salmonella?

Answer 11

A BACTERIAL DISEASE
Infected people can suffer from fever, stomach cramps, vomiting and diarrhoea.
These symptoms are called by toxins that the bacteria produces.
You can get salmonella by eating foods that have been infected with the salmonella bacteria eg chicken that caught the disease whilst it was alive or eating food that has been contaminated by being prepared in unhygienic conditions.
In the UK, most poultry is give a vaccination against Salmonella. This is to control the spread of the diseases.

Question 12

What is Gonorrhoea?

Answer 12

A BACTERIAL DISEASE
This is a STD.
It is caused by the gonorrhoea bacteria.
A person with this disease will get pain when they urinate. Another symptom is thick yellow or green discharge from the vagina or penis.
It used to be treated with the antibiotic penicillin, but now strains of bacteria have become resistant.
To prevent the spread, people should use barrier ,ethics of contraception such as condoms.

Question 13

How can the spread of disease be reduced?

Answer 13

Being hygienic
Destroying vectors - eg using insecticides.
Isolating infected individuals.
Vaccination.

Question 14

Explain the bodies defence system for fighting diseases.

Answer 14

Skin - acts as a barrier to pathogens. It also secrets antimicrobial substances which kill pathogens.

Hairs and mucus in your nose trap particles that could contain pathogens.

The trachea and bronchi secrete mucus to trap pathogens.

The trachea and bronchi are lined with cilia. These are hair-like structures which wafts the mucus up to the back of your throat where it can be swallowed.

The stomach irises hydrochloric acid. This kills pathogens that make it that far from the mouth.

Question 15

What is phagocytosis?

Answer 15

White blood cells engulf foreign objects and digest them.

Question 16

How do white blood cells produce antibodies?

Answer 16

Every invading pathogen has unique molecules (called antigens) on its surface.
When some types of white blood cell come across a foreign antigen they will start to produce proteins called antibodies to lock onto the invading cells so that they can be found and destroyed.
The antibodies produced are specific to that type of antigen.
Antibodies are then produced rapidly and carried around the body to find all similar bacteria or viruses.
If the person is infected with the same pathogen again the white blood cells will rapidly produce the antibodies to kill it - the person is naturally immune to that pathogen and won’t get ill.
The white blood cells that produce antibodies are also known as B-lymphocytes.

Question 17

What are vaccinations?

Answer 17

Vaccinations involve injecting small amounts of dead or inactive pathogens. These carry antigens, which causes your body to produce antibodies to attack them - even though the pathogen is harmless. If the live pathogens of the same type appear after that, the white blood cells rapidly mass-produce antibodies to kill off the pathogen.

Question 18

What are the pros of vaccination?

Answer 18

They help control lots of communicable diseases that were once common.
Epidemics (big outbreaks of disease) could be prevented if large percentages of the population were vaccinated.
Prevention is better than a cure.

Question 19

What are the cons of vaccination?

Answer 19

They don’t always give you immunity.

Sometimes people might have a bad reaction to a vaccine. Eg swelling. But bad reactions are very rare.

Question 20

What are painkillers?

Answer 20

Drugs that relieve pain. However, they don’t tackle the cause of the disease or kill the pathogens, they just help to reduce the symptoms.

Question 21

What are antibiotics?

Answer 21

They kill (or prevent growth of) the bacteria causing the problem without killing your own body cells. Different antibiotics kill different types of bacteria, so it is important to be grated with the right one. 
THEY DON’T DESTROY VIRUSES. Viruses reproduce using your body cells which makes it difficult to develop drugs that destroy the virus without killing the body’s cells.

Question 22

What is antibiotic resistance?

Answer 22

Bacteria can mutate - sometime mutations cause them to be resistant to an antibiotic.
This means that when you treat the infection, only the non-resistant strains of bacteria will be killed.
The individual resistant bacteria will survive and reproduce, and the population of the resistant strain will increase. This is an example of natural selection.
The resistant strain could cause serious infection that can’t be treated by antibiotics.
To slow down the rate of development of resistant strains, it is important for doctors to avoiding over-prescribing antibiotics. It is important to finish the whole course of antibiotics and not to just stop when you feel better.

Question 23

What is aspirin?

Answer 23

A painkiller used to lower fever. It was developed from a chemical found in willow.

Question 24

What is digitalis?

Answer 24

Used to treat heart conditions. It was developed from a chemical found in foxgloves.

Question 25

How did Alexander Fleming discover penicillin?

Answer 25

He was clearing out some Petri dishes containing bacteria. He notices that one of the dishes also had mould on it and the area around the mould was free of bacteria. He found that the mould (called penicillium notatum) on the Petri dish was producing a substance that killed the bacteria. This substance was penicillin.

Question 26

What is the first stage of drug testing?

Answer 26

In preclinical testing, drugs are tested on human cells and tissues. However, you can’t use human cells and tissues to test drugs that affect whole or multiple organ systems eg testing a drug for blood pressure must be done on a whole animal because it has an intact circulatory system.

Question 27

What is the second stage of drug testing?

Answer 27

Test the drug on live animals.
This is to test for efficacy (whether the drug works and produces the effect you are looking for).
Also, to find out it’s toxicity (how harmful it is)
Also, to find the best dosage (the concentration that should be given, and how often it should be given).
The law in Britain states that any new drug must be tested on two different live mammals. Some people think this is cruel. However, others be,Eve it is the safest way before guiding the drug to humans.
Some people believe that animals are so different from humans that it is pointless to test on them.

Question 28

What is the third stage of drug testing?

Answer 28

If the drug passes the test on animals it is the. Tested on human volunteers in a clinical trial.
First, the drug is tested on healthy volunteers. This is to make sure their are no harmful side effects when the body is wooing normally. At the start, a very low dosage is given which is gradually increased.
If these rebukes are food, the drug can be tested on patients who are randomly put into two groups. One if given the new drug, the others are given the placebo (a substance like the drug that doesn’t do anything). This is so the doctor can see the actual difference the drug makes - it allows for the placebo effect (when the patient expects the treatment to work and so feels better, even though the treatment isn’t doing anything).
Clinical trials are blind - the patient doesn’t know whether they are getting the drug or the placebo. They are often double blind, neither the doctor or patient knows until the results are gathered. This is so the doctor monitoring and analysis g doesn’t subconsciously influence the patient with their knowledge.
The results of the drug testing and drug trials aren’t published until they have been through peer review. This helps to prevent false claims being made.

Question 29

What are monoclonal antibodies?

Answer 29

Monoclonal antibodies are identical antibodies.
Antibodies are produced by B-lymphocytes - a type of white blood cell.
Monoclonal antibodies are produced from lots of clones of a single white blood cell. This means that all the antibodies are identical and will only target one specific protein antigeñ. However, lymphocytes don’t divide easily. On the other hand, tumour cells don’t produce antibodies but divide lots - so they can be grown really easily.
It is possible to fuse a mouse B-lymphocyte with a tumour cell to create a cell called a hybridoma.
Hybridoma cells can be cloned to get lots of identical cells. These cells all produce the same antibodies (monoclonal antibodies). These antibodies can be collected and purified.
You can make monoclonal antibodies that bind to anything you want eg an antigen that’s only found on the surface of one type of cell. They are really useful because they will only bind to this molecule. This means that you can use them to target a specific cell or chemical in the body.

Question 30

How are monoclonal antibodies used in pregnancy tests?

Answer 30

A hormone called HCG is found in the urine of women only when they are pregnant. Pregnancy testing sticks detect this hormone.
The fit of the stick you wee on has some antibodies to the hormone, with blue needs attached.
The test strip (the bit that turns blue if you are pregnant) has some more antibodies stuck onto it (so that they can’t move).
If you are pregnant, the hormone binds to the antibodies on the blue beads. The urine moves up the stick, carrying the hormone and the beads. The beads and the hormone bind to the antibodies on the strip. So the blue needs get stuck on the strip, turning it blue.

Question 31

How can monoclonal antibodies be used to treat diseases?

Answer 31

Different cells in the body have different antigens on their surface. So you can make monoclonal antibodies that will bind to specific cells in the body.
Cancer cells have antigens on their cell membranes that aren’t found on normal body cells. They are called tumour markers. You can make monoclonal antibodies that will bind to these tumour markers. An anti-cancer drug can be attached to these monoclonal antibodies. This might be a radioactive substance, a toxic drug or a chemical which stops cancer cells growing and dividing.
The antibodies are given to a patient through a drip.
The drug will kill the cancer cells but doesn’t kill any normal body cells near the tumour.

Question 32

How can monoclonal antibodies be used to find specific molecules in cells or tissues?

Answer 32

They are made and they will bind to the specific molecule you are looking for.
The antibodies are then bound to a florescent dye.
If the molecules are present in the sample being analysed, the monoclonal antibodies will attach to them, and they can then be detected using the dye.

Question 33

What are some problems associated with monoclonal antibodies?

Answer 33

They cause some side effects - more than originally expected. Eg fever, vomiting and low blood pressure.
This means they are not as widely used as scientists originally thought they might be.

Question 34

Why do plants need nitrates?

Answer 34

To make proteins and therefore for growth. A lack of nitrates could cause stunted growth.

Question 35

Why do plants needs magnesium ions?

Answer 35

Ended for making chlorophyll, which is needed for photosynthesis. Plants without enough magnesium suffer from chlorosis and have yellow leaves.

Question 36

What are the common signs that a plant has a disease?

Answer 36

Stunted growth 
Spots on the leaves 
Patches of decay 
Abnormal births eg lumps 
Malformed stems or leaves 
Discolouration.

Question 37

What are the plants physical defences against disease?

Answer 37

Most of their stems have a waxy cuticle which provides a barrier to stop pathogens entering
Plant cells are surrounded by cell walls made from cellulose. These form a physical barrier for pathogens that make it past the waxy cuticle.
Plants have layers of dead cells around their stems, for example the outer part of the bark of trees. These act as a barrier to stop pathogens entering.

Question 38

What are the plants chemical defences against disease?

Answer 38

Some can produce antibacterial chemicals which kill bacteria - eg the mint plant and witch hazel.
Other plants can produce poisons which can deter herbivores (organisms that eat plants) eg tobacco plants, foxgloves and deadly nightshade.

Question 39

What are the plants mechanical defences against disease?

Answer 39

Some plants have thorns and hairs. These schools animals from touching and eating them.
Other plants have leaves that droop and curl when something touches them. This means they orient themselves from being eaten by knocking insects off them and moving away from things.
Some plants can cleverly mimic other organisms. Eg the Passion flower has bright yellow spots on its leaves like butterfly eggs. This stops other butterflies laying their eggs there. Several species of plant on the ‘ice plant family’ in Southern Africa look like stones and pebbles. This tricks other organisms into not eating them.