Infection and response

Question 1

Give two ways to prevent high levels of mosquito bites.

Answer 1

• Insecticides
• Use mosquito nets

Question 2

Explain why TMV causes plants to be smaller than healthy plants.

Answer 2

Discolouration means less chlorophyll so less photosynthesis. Less glucose made so less amino acids made and therefore less proteins made which are needed for growth. Glucose is also needed for respiration, less glucose means less energy released for growth.

Question 3

Suggest a way of measuring growth of plants.

Answer 3

Use a balance to measure mass

Question 4

Describe how a monoclonal antibody for HIV can be produced.

Answer 4

• Inject a mouse with a small amount of HIV antigen to stimulate b-lymphocytes to produce antibodies
• Collect b-lymphocytes and fuse with a tumour cell to form a hybridoma
• Clone hybridoma specific to HIV which will divide rapidly to produce many monoclonal antibodies
• Collect and purify

Question 5

Explain how MAbs prevent infection.

Answer 5

Complementary to specific protein antigen. Attach to antigen of a pathogen so pathogen can no longer bind to healthy cells and so pathogen doesn’t grow and spread.

Question 6

Explain why antibiotics won’t kill viral diseases.

Answer 6

Only kill bacteria as viral diseases reproduce INSIDE living cells so it is difficult to create antibiotics that don’t also damage living cells.

Question 7

Describe how the human body prevents pathogens from entering.

Answer 7

• Skin a physical barrier that secretes sebum that repels pathogens
• Scabs act as a barrier formed by platelets
• Breathing system has trachea and bronchi lined with cilia and mucus that trap and waft pathogens to the stomach
• Stomach has HCl that kills pathogens in food/swallowed in mucus

Question 8

Describe how the human body defends itself from pathogens inside the body.

Answer 8

• WBCs/immune system
• WBCs produce antibodies and can be stored in memory cells that bind to specific antigens and kill pathogen
• WBCs produce antitoxins that neutralise toxins
• WBCs can engulf pathogens by phagocytosis

Question 9

Explain why AIDs takes longer to recover from other infections.

Answer 9

Immune system is weakened so fewer WBCs so pathogen can’t be killed.

Question 10

What are three reasons for drug trials?

Answer 10

• To test for toxicity/ side effects
• To find the right dosage
• Efficacy

Question 11

Explain how vaccinations can prevent an illness.

Answer 11

Inject a small amount of dead/inactive pathogen to body. Stimulates WBCs to produce antibodies specific to pathogen. Stored in memory cell so if pathogen reenters antibodies rapidly reproduce to destroy and kill the pathogen before person gets any symptoms

Question 12

Explain how plants defend themselves against microorganisms.

Answer 12

• Cell walls (strengthened by cellulose) act as a physical barrier that is difficult to penetrate preventing microorganisms entering
• Antibacterial chemicals to kill pathogens
• Waxy cuticle which is difficult to penetrate

Question 13

Why is a placebo used during clinical trials?

Answer 13

Acting as a control, preventing patients thinking they feel better and false claims

Question 14

What is the purpose of a double-blind trial?

Answer 14

Prevent false claims and patients believing they feel better as neither doctor or patients know who has the drug/placebo

Question 15

Explain what testing must be done during clinical trials.

Answer 15

• Initially on healthy volunteers with an initial low dose to monitor safety and side effects
• Then on patients in a double-blind trial with two equal large groups where one group is given a placebo with no one knowing who has the real drug then gradually increase to find optimum dosage

Question 16

What are general points to consider during a double blind trial?

Answer 16

• Large sample sizes
• Having equal groups so that test is repeatable and representative
• Control medicine dosage and age

Question 17

Explain why nitrate ions are needed in plants.

Answer 17

Needed for protein synthesis. They combine with glucose to make amino acids which make proteins needed for growth.

Question 18

What is the purpose of mechanical plant defences?

Answer 18

To deter and trick herbivores so less of the plant is damaged

Question 19

What is the purpose of chemical plant defences?

Answer 19

To deter herbivores - may harm/kill bacteria and insects so less of the plant is damaged

Question 20

Explain the purpose of physical plant defences

Answer 20

Prevent invasion of microorganisms as tough and difficult to penetrate so less of the plant is damaged

Question 21

What is the problem with a magnesium deficiency?

Answer 21

Site of chlorophyll synthesis. Less chlorophyll(chlorosis) so less photosynthesis as less (sun)light is absorbed. Less glucose to make amino acids which make proteins so less proteins which are needed for growth.

Question 22

How are clinical trials carried out?

Answer 22

1) healthy volunteers initially at a low dose to test for toxicity and harmful side effects
2) patient volunteers in a double blind trials (doctor and patient don’t know who has the drug and who has placebo) to find optimum dosage and test for efficacy
Use large groups with equal sizes

Question 23

Explain how monoclonal antibodies work to treat cancer.

Answer 23

Attach MAb to toxic drug. Antibodies are complementary to protein antigens so the drug binds to cancer cells and stops them from dividing without killing healthy cells.

Question 24

Why may a report be biased?

Answer 24

For financial gain

Question 25

How does vaccinating animals cause a response and prevent an outbreak of bacterial disease in humans?

Answer 25

(injecting small amount of dead/inactive pathogen) stimulates white blood cells to produce antibodies which are complementary to specific antigens. Antibodies are stored in memory cells so if pathogen reenters they rapidly are produced in large numbers to kill the pathogen. This means fewer food will be digested that has the disease and so fewer toxins are produced in humans.

Question 26

Describe how to make monoclonal antibodies from a hybridoma

Answer 26

Cell is cloned to produce many cells which all make the same antibody. Collect and purify the antibody.

Question 27

Give one advantage of having a vaccine

Answer 27

Less chance of spreading disease (herd immunity)

Question 28

Explain why measles can’t be cured with antibiotics

Answer 28

Antibiotics only kill bacteria, not viruses (and measles is a viral disease). Virus lives and reproduces inside living cells, so killing the virus would kill the healthy cell its inside of so difficult to produce.

Question 29

Suggest why certain animals mimic others

Answer 29

Trick animals (predators) so they avoid eating them

Question 30

Explain the issue for plants for damaged root hair cells

Answer 30

• Less water absorbed so lower rate of photosynthesis meaning less glucose so less amino acids so less proteins that are needed for growth
• Less glucose also means less respiration and so less energy released for growth
• Less mineral ions absorbed: less nitrate ions so less proteins made for growth, less magnesium ions so less chlorophyll produced -> chlorosis