B1c

Question 1

What are infectious diseases caused by?

Answer 1

Pathogens, disease-causing microorganisms.

Question 2

What is one example of a disease caused by each type of pathogen?

Answer 2

Fungi - athlete’s foot
Bacteria - cholera
Virus - flu
Protozoa - malaria

Question 3

What are the meanings of parasite and host, with reference to malaria?

Answer 3

Malaria is caused by a protozoan. It’s carried by mosquitos, which are insects that feed on the blood of animals, including humans. The protozoan is a parasite - an organism that lives off another organism (called a host) and often causes it harm.

Question 4

How do vectors spread disease?

Answer 4

The mosquitos are vectors, meaning they carry the disease without getting it themselves. They pick up the malarial parasite when they feed on an infected animal. Every time the mosquito feeds on another animal it infects it by inserting the parasite into the animal’s blood vessels.

Question 5

How does the knowledge of the life cycle of a disease and the way in which vectors spread disease help control infections?

Answer 5

• The areas of water where mosquitos lay their eggs can be drained or sprayed with insecticides.
• Fish can be introduced into the water to eat mosquito larvae.
• People can be protected from mosquitoes using insecticides and mosquito nets.

Question 6

How is the human body defended against pathogens?

Answer 6

• Skin provides a barrier.
• Blood clotting prevents entry of pathogens.
• Pathogens are trapped by mucus in airways.
• Hydrochloric acid in the stomach kills pathogens.

Question 7

What is the difference between infectious and non-infectious diseases?

Answer 7

Infectious diseases are caused by pathogens and can spread. Non-infectious diseases can not spread and are often inherited e.g. red-green colour blindness.

Question 8

What changes in lifestyle and diet may reduce the risk of some cancers?

Answer 8

• Not smoking reduces your chances of getting lung cancer.

- Eating less processed meat and more fibre may reduce your risk of getting colon cancer.

Question 9

What is the difference between benign and malignant tumours?

Answer 9

Benign - this is where the tumour grows until there’s no more room and the cells stay where they are. This type isn’t normally dangerous.
Malignant - this is where the tumour grows and can spread to other sites in the body. Malignant tumours are dangerous and can be fatal.

Question 10

What does immunisation, vaccination, give protection from?

Answer 10

Certain pathogens.

Question 11

How are pathogens that enter the body destroyed by the immune system (white blood cells)?

Answer 11

1) White blood cells can engulf foreign cells and digest them.
2) Producing antibodies.
- Every pathogen has unique molecules on the surface of its cells - no two pathogens have the same one. These molecules are called antigens.
- When your white blood cells come across a foreign antigen they’ll start to produce proteins called antibodies, which lock on to and kill the new invading cells. The antibodies produced are specific to that pathogen - they won’t lock onto other pathogens.
- Antibodies are then produced rapidly and flow all around the body to kill all similar bacteria or viruses.
- Some white blood cells stay around in the blood after the pathogen has been fought off - these are called memory cells. If the person is infected with the same pathogen again these cells will remember it and immediately make antibodies to kill it - the person is naturally immune to that pathogen.

Question 12

What are the symptoms of an infected disease caused by?

Answer 12

Cell damage or by toxins produced by the pathogens.

Question 13

What is the difference between passive and active immunity?

Answer 13

Active immunity - immune system makes its own antibodies after being stimulated by a pathogen. It includes becoming naturally immune and artificially immune - immunisation. Active immunity is usually permanent.
Passive immunity is where you use antibodies made by another organism. Passive immunity is only temporary.

Question 14

What is the difference between antibiotics and antivirals?

Answer 14

Antibiotics are drugs that kill bacteria without killing your own body cells. They’re very useful for clearing up bacterial infections that your body is having trouble with, however they don’t kill viruses. Antivirals can be used to treat viral infections. Antivirals are drugs that stop viruses from reproducing.

Question 15

What is the process of immunisation?

Answer 15

Immunisation involves injecting dead or inactive pathogens into the body. These carry antigens, so even though they’re harmless they still trigger an immune response - your white blood cells produce antibodies to attack them.
Some of these white blood cells will remain in the blood as memory cells so if live pathogens of the same type ever appear, the antibodies to kill them will be produced immediately.

Question 16

What are the benefits and risks associated with immunisation?

Answer 16

Immunisation stops you from getting ill. If most people are immunised the disease won’t be able to spread as easily.
But there can be short-term side effects, e.g. swelling and redness at the site of injection and feeling a bit under the weather for a week or two afterwards.
You can’t have some vaccines if you’re already ill, especially if you’re immune system is weakened.
Some people think that immunisation can cause other disorders, e.g. one study suggested a link between the MMR vaccine and autism. Scientists now know it’s perfectly safe, but for a few years many parents weren’t willing to take the risk.

Question 17

Why are new medical treatments and drugs tested before use?

Answer 17

To make sure they’re safe and they work.

Question 18

How are new treatments tested using animals, human tissue and computer models and what objections are there to some forms of testing?

Answer 18

Computer models are often used first of all - these simulate a human’s response to a drug, so you don’t need to test on live animals at this stage. They can identify promising drugs to be tested in the next stage, but it’s not as accurate as actually seeing the effect on a live organism.
The drugs are then developed further by testing on human tissues. However, you can’t use human tissue to test drugs that affect whole/ multiple body systems, e.g. testing a drug for blood pressure must be done on a whole animal.
The last step is to develop and test the drug using animals. The law in Britain states that any new drug must be tested on two different live animals, but others believe this is the safest way to make sure a drug isn’t dangerous before it’s given to humans.

Question 19

Why are blind and double blind trials used in testing new drugs against placebos or the best existing treatment?

Answer 19

After the drug has been tested on animals it’s tested on humans:

1) This is done by a study called a clinical trial.
2) There are two groups of patients. One is given the new drug, the other is given a placebo (a ‘sugar pill’ that looks like the real drug but doesn’t do anything). This is done so scientists 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).
3) Scientists sometimes test new drugs against the best existing treatment rather than a placebo. This tells them how well the new drug compares to what we already know.
4) Clinical trials are blind - the patient in the study doesn’t know whether they’re getting the drug or the placebo. They’re often double blind - neither the patient nor the scientist know until all the results have been gathered.

Question 20

What is the need for careful use of antibiotics to prevent the increase of resistant strains such as MRSA?

Answer 20

Some bacteria are naturally resistant to certain antibiotics. Misuse of antibiotics, e.g. doctors overprescribing them or patients not finishing a course, has increased the rate of development of resistant strains. So nowadays, you won’t get antibiotics for a mild infection, only for something more serious. MRSA is the best known example of an antibiotic-resistant strain.