Cell cycle and immune system

Question 1

Explain the advantage of cells lining human intestine completing cell cycle in short time

Answer 1

1. Replace cells quickly

Question 2

Describe two events that occur during interphase which prepare a cell for mitosis

Answer 2

1. DNA replication
2. Synthesis of proteins

Question 3

What is the importance of meiosis?

Answer 3

1. Halves the number of chromosomes
2. Full number restores at fertilisation

Question 4

Describe the role of spindle during mitosis

Answer 4

1. Attachment to centromeres
2. Separation of chromatids

Question 5

Explain how the behaviour of chromosomes causes change in the amounts of DNA during mitosis

Answer 5

1. Chromosomes double in mass during replication (increase)
2. Homologous chromosomes separate (decrease)
3. Sister chromatids separate (2nd decrease)

Question 6

Why do you not twist coverslips when investigating mitosis on root onion tip

Answer 6

1. Could break chromosomes

Question 7

How do you know if a cell is in anaphase from a picture

Answer 7

1. Chromosomes are at poles of spindle
2. V shape shows that chromatids have pulled apart at their centromeres

Question 8

Suggest and explain how 2 environmental variables that could increase the growth rate of bacteria

Answer 8

1. Increased concentration of glucose – increased respiration
2. Increased temperature – increased enzyme activity

Question 9

Suggest why farmed trout producing diploid cells when normal trout produce haploid cells will have sterile offspring

Answer 9

1. Too many chromosomes
2. Chromosomes do not pair

Question 10

Explain why investigating cell division in an onion root you only used the first 5mm from the tip of an onion root

Answer 10

1. Where mitosis occurs

Question 11

Why do you press down firmly on the cover slip

Answer 11

1. Thin layer of cells
2. So light passes through

Question 12

Why do you not push the cover slip sideways

Answer 12

1. Avoid breaking chromosomes

Question 13

Describe and explain what should be done when counting cells to make sure that the mitotic index obtained for a root tip is accurate

Answer 13

1. Repeat count
2. To ensure figures are correct

Question 14

Why would a chemical that prevents the formation of spindle stop the growth of roots

Answer 14

1. Stops anaphase
2. Prevents separation of sister chromatids

Question 15

When a scientist placed cells in a solution that had a slightly higher water potential than the cytoplasm, why did it cause the chromosomes to move further apart

Answer 15

1. Water moves into the cells by osmosis
2. Cell gets bigger

Question 16

Suggest two ways the structure of the chromosome could differ along its length to result in more stain binding in some areas

Answer 16

1. Differences in condensation
2. Differences in interactions with histones

Question 17

Describe 2 aseptic techniques you could use to transfer a sample of broth culture onto an agar plate

Answer 17

1. Keep lid on petri dish to prevent unwanted bacteria contaminating dish
2. Wear mask/gloves to prevent contamination from bacteria on hands/mouth

Question 18

Explain why antibodies only attach to specific proteins

Answer 18

1. Antibody has tertiary structure complementary to binding site of protein

Question 19

Why is a control strip important

Answer 19

1. Prevent false negatives
2. Shows it has word as antibody moves up strip

Question 20

Why will a solution remain colourless is indirect ELISA test if person is not infected with the disease testing for

Answer 20

1. Antibody not present
2. So enzyme will not bind

Question 21

Suggest 2 purposes of having a control well when doing indirect ELISA test

Answer 21

1. Show that enzyme is producing the colour change
2. Washing the well is effective

Question 22

People with AIDS die because they are unable to produce an immune response to pathogens. Explain why this leads to death

Answer 22

1. Infected by pathogens
2. Pathogen reproduces
3. Damage to cells/organs
4. Releases toxins

Question 23

Suggest why vaccinations for HIV may not be considered safe for public during testing

Answer 23

1. Inactive viruses may become active
2. People may test positive for disease HIV
3. This may affect there life

Question 24

Give 2 ways in which pathogens can cause disease when they enter the body of their host

Answer 24

1. Release toxins
2. Damage to cells

Question 25

What is a vaccine

Answer 25

1. Sample of dead/inactive pathogen injected 2. Stimulate immune system to produce memory cells

Question 26

Explain why it is important to wash the well in indirect ELISA test

Answer 26

1. To remove any unbound antibodies 2. Otherwise could have false positive

Question 27

Explain why there is no colour change if antibodies being tested for are not present

Answer 27

1. No antibody to bind 2. 2nd antibody wont bind

Question 28

Explain why number of HIV viruses in blood rise during first few months of infection

Answer 28

1. HIV is invading cells making new viruses 2. New viruses are released into bloodstream

Question 29

Explain how the destruction of T ells by HIV leads to death of infected person

Answer 29

1. T cells cannot stimulate b cells 2. Person unable to fight off opportunistic infections

Question 30

Some of the antigens found on the surface of tumour cells are also found on the surface of healthy human cells, why would a drug targeting tumour cells cause side effects

Answer 30

1. Drug binds to healthy cells 2. Causes death/damage to healthy cells

Question 31

why would a drug need to be tested on healthy people before the sick people it is treating

Answer 31

to check for side effects

Question 32

Describe how HIV is replicated once inside helper T cells

Answer 32

1. Reverse transcriptase uses viral RNA to create complementary strand of DNA 2. DNA is inserted into helper T cells DNA 3. DNA transcribed into RNA 4. Translated into viral proteins

Question 33

Give 2 types of cell, other than pathogens that can stimulate an immune response

Answer 33

1. Abnormal cells 2. Cells from other organisms

Question 34

Suggest and explain how viruses that only infect one species of frog become able to infect other species of frog

Answer 34

1. Mutation in viral DNA 2. Altered viral attachment protein

Question 35

How could determining the genome of a virus allow scientists to develop a vaccine

Answer 35

1. Could identify the proteome 2. Could identify potential antigens to use in vaccine

Question 36

Describe the role of antibodies in producing a positive result in an ELISA test

Answer 36

1. First antibody binds to antigen 2. Add second antibody with enzyme attached 3. Antibody binds to antigen 4. Add substrate complementary to active site of enzyme and a colour change should occur demonstrating a positive result

Question 37

Describe and explain the role of antibodies in stimulating phagocytosis

Answer 37

1. Act as markers 2. Clump pathogens together in agglutination

Question 38

Describe how phagocytosis of a virus leads to presentation of its antigens

Answer 38

1. phagosome fuses with lysosome 2. Virus destroyed by lysozymes 3. Antigen are displayed on cell membrane

Question 39

What is an antigen?

Answer 39

1. Foreign protein that stimulates an immune response

Question 40

What is an antibody?

Answer 40

1. A protein specific to an antigen 2. Produced by B cells

Question 41

When a vaccine is given to a person, it leads to the production of antibodies against a disease causing organism. Describe how

Answer 41

1. Vaccine contains antigens from pathogen 2. Macrophage presents antigen on surface 3. T cell with complementary receptor protein binds to antigen 4. T cell stimulates B cell 5. B cell secretes large amounts of antibody 6. B cell divides to form clones all secreting antibody

Question 42

Describe the difference between active and passive immunity

Answer 42

1. Active immunity produces memory B cells whereas passive does not 2. Active immunity provides long term cause antibody is produced in response to antigen 3. passive doesn’t provide long term immunity because antibody is broken down 4. Passive involves antibody introduced into body from outside source 5. Passive provides immediate protection whereas active immunity takes a longer time

Question 43

Describe the appearance and behaviour of chromosome during prophase and during anaphase of mitosis

Answer 43

1. Replicated chromosomes shorten and thicken 2. Becomes visible Anaphase 3. Sister chromatids are pulled apart by the shortening of spindle fibres to opposite poles of the cell 4. Centromeres divide

Question 44

explain why antibody A only attaches to the protein found in SARS - CoV-2

Answer 44

1. antibody has specific tertiary structure 2. only complementary to the shape of the binding site found in SARS -CoV-2

Question 45

why is there a control line on Covid and pregannacy tests?

Answer 45

1. prevents false negatives 2. shows that unbound antibodies have moved up the test strip

Question 46

explain what is meant by herd immunity and suggest the advantages of it

Answer 46

1. herd immunity is when a large proportion of the population is vaccinated 2. reduces the infection rate of population 3. can lead to eradication of disease 4. protects vulnerable people who cannot have vaccine eg babies 5. prevents future pandemics