Topic 2-Cells

Question 1

Describe how HIV is replicated.
(4 marks)

Answer 1

1) Attachment proteins attach to receptors on helper T cells/ lymphocytes
2) Nucleic acid/ RNA enters the cell
3) Reverse transcriptase converts RNA to DNA
4) Viral protein/ capsid/ enzyme produced
5) Virus (particles) assemble and release from the cell

Question 2

Describe the role of one named organelle in digesting bacteria.
(3 marks)

Answer 2

1) Lysosomes
2) Fuse with vesicle
3) This releases hydrolytic enzymes
ACCEPT
Pagosome for vesicles, lysozymes for hydrolytic enzymes, ribosomes/ RER form hydrolytic enzyme and Golgi body forms lysosomes.

Question 3

Describe the role of one named organelle in the process of digesting bacteria in the cytoplasm after being ingested.
(3 Marks)

Answer 3

1. Lysosomes
2. Fuse with vesicle
3. Releases hydrolytic enzymes

Question 4

Give 2 structures found in all prokaryotic cells and all eukaryotic cells.
(2 Marks)

Answer 4

1. Cell surface membrane
2. Ribosomes
3. Cytoplasm
4. DNA

Question 5

Describe how a sample of chloroplasts could be isolated from leaves.
(4 Marks)

Answer 5

1. Break open cells/ tissue and filter
   OR grind/ blend cells/ tissues/ leaves and filter.
2. In cold, same water potential/ concentration, PH controlled solution.
3. Centrifuge/ spin and remove cell/ nuclei residue.
4. Centrifuge/ spin at higher speed, chloroplasts settle out.

Question 6

Outline the role of organelles in production, transport and release of proteins from eukaryotic cells.
(4 Marks)

Answer 6

1. DNA in nucleus is code for protein.
2. Ribosomes/ RER produce protein.
3. Mitochondria produce ATP for protein synthesis.
4. Golgi apparatus package/ modify.
   OR carbohydrate added / glycoprotein produced by Golgi apparatus.
5. Vesicle transport
   OR RER transports
6. Vesicles fuse with cell-surface membrane.

Question 7

Describe binary fission in bacteria.
(3 Marks)

Answer 7

1. Replication of the circular DNA.
2. Replication of plasmids.
3. Division of cytoplasm to produce daughter cells.

Question 8

Suggest and explain two environmental variables which could be changed to increase the growth rate of bacteria cells.
(4 Marks)

Answer 8

1. Increased concentration of glucose;
2. Increased respiration.
3. Increased concentration of oxygen;
4. Increased respiration.
5. Increased temperature;
6. Increased enzyme activity.
7. Increased concentration of phosphate;
8. Increase in DNA/RNA/ATP
9. Increased number of nucleotides;
10. Increased DNA synthesis.

Question 9

Describe the role of spindle fibres and the behaviour of chromosomes in the phases: Prophase, metaphase and anaphase.
(5 Marks)

Answer 9

1. In prophase, chromosomes condense.
2. In prophase OR metaphase, centromeres attach to spindle fibres.
3. In metaphase, chromosomes/ pairs of chromatids are at the equator/centre of the cell/spindle.
4. In anaphase, the centromeres divide.
5. In anaphase, chromatids from each pair are pulled to opposite poles/ends of the cell.
6. In prophase, metaphase and anaphase, spindle fibres shorten.

Question 10

Describe the appearance and behaviour of chromosomes during mitosis.
(5 Marks)

Answer 10

During prophase;
1. chromosomes coil/condense/become visible.
2. Chromosomes appear as 2 separate chromotids joined by a centromere.
During metaphase
3. Chromosomes line up across the equator/ centre of the cell.
4. Chromosomes attach to spindle fibres.
5. By their centromeres.
During anaphase;
6. The centromere splits/divides.
7. Sister chromatids/ chromosomes are pulled to opposite poles/ ends of the cells.
During telophase;
8. Chromatids/ chromosomes uncoil/ become longer/ thinner.

Question 11

Name and describe 5 ways in which substances can move across the cell-surface membrane into a cell.
(5 Marks)

Answer 11

1. Simple diffusion of small/ non polar molecules, down a concentration gradient.
2. Facilitated diffusion down a concentration gradient via carrier protein/ channel.
3. Osmosis of water down a water potential gradient.
4. Active transport against a concentration gradient via protein carrier using ATP.
5. Co-transport of 2 different substances using a carrier protein.

Question 12

The movement of sodium ions out of the cell allows the absorption of glucose into the cell lining of the ileum.
Explain how.
(2 Marks)

Answer 12

1. Maintains/generates a concentration gradient for sodium ions from ileum to cell.
2. Sodium ions moving in by facilitated diffusion brings glucose with it
   OR sodium ions move in by co transport, and bring glucose in with it.

Question 13

Describe and explain two features you would expect to find in a cell specialised for absorption.
(2 Marks)

Answer 13

1. Folded membrane/microvilli so large surface area for absorption.
2. Large number of co-transport/carrier/channel proteins so fast rate of absorption
   OR for active transport OR for facilitated diffusion.
3. Large number of mitochondria to make more ATP by respiration.
   OR for aerobic respiration OR to release more energy for active transport.
4. Membrane bound/ digestive enzymes so keeps concentration gradient for faster absorption.

Question 14

Describe how the movement of of substances across cell membranes is affected by membrane structure.
(5 Marks)

Answer 14

1. Phospholipid bilayer allows the movement/diffusion of non polar/ lipid soluble substances.
2. Phospholipid bilayer prevents the movement/diffusion of polar/ lipid insoluble substances
   OR Membrane proteins allow polar substances to move across the membrane/bilayer.
3. carrier proteins allow active transport.
4. channel/ carrier proteins allow facilliated diffusion/ co-transport.
5. The number of channels/ carriers will determine the amount of movement.
6. The shape/charge of carriers/ channels control which substances move.
7. The membrane surface area will determine how much diffusion/ movement.
8. Cholesterol can affect fluidity/ rigidity and permeability.

Question 15

Compare and contrast the process in which water and inorganic ions enter the cell.
(2 Marks)

Answer 15

Comparisons
1. Both move down a concentration gradient.
2. Both move through protein channels in the membrane
Contrast
3. Ions can move against a concentration gradient using active transport.

Question 16

High absorption of salt from the diet can lead to higher than normal concentrations of salt in the blood plasma entering capillaries. This can lead to a buildup of tissue fluid.
Explain how.
(2 Marks)

Answer 16

1. Higher salt concentration leads to lower water potential in the tissue fluid.
2. So less water is returned to the capillaries by osmosis (at venue end).
   OR
3. Higher salt results in higher blood pressure/ volume.
4. So more fluid is pushed out (at atriole end) of the capillary.

Question 17

Use your knowledge of phagocytosis to describe how a monoclonal antibody would enter and kill a tumour cell.
(3 Marks)

Answer 17

1. The cell engulfs/ingests the antibody.
   OR cell membrane surrounds the antibody.
2. Lysosomes fuse with the vesicle/ phagosome.
3. Lysosome bread down/ digests the antibody which releases the drug.

Question 18

Describe how HIV is replicated once inside of T-Helper cells.
(4 Marks)

Answer 18

1. RNA is converted into DNA using reverse transcriptase.
2. DNA is inserted into the T-Helper cells DNA/ nucleus.
3. DNA is transcribed into HIV mRNA.
4. HIV mRNA is translated into new viral proteins for assembly into viral particles.

Question 19

Give two other types of cell, other than pathogens, that can simulate an immune response.
(2 Marks)

Answer 19

1. Cells from other organisms/ transplants.
2. Abnormal/ cancer/ tumour cells.
3. Cells infected by a virus

Question 20

What is the role of a disulphide bridge when forming the quaternary structure of an antibody?
(1 Mark)

Answer 20

Joins 2 different polypeptides.

Question 21

Explains how HIV affects the production of antibodies when AIDS develops in a person.
(3 Marks)

Answer 21

1. Less/ no antibody produced.
2. Because HIV destroys T-Helper cells.
3. So no/ fewer B cells are activated.
   OR no/fewer B cells for plasma cells.

Question 22

Suggest and explain how a virus is able to infect many different species.
(2 Marks)

Answer 22

1. Mutation in the viral DNA/RNA/ genetic material.
2. Altered the tertiary structure of the viral attachment protein.

Question 23

Determining the genome of the virus could allow scientists to develop a vaccine.
Explain how.
(2 marks)

Answer 23

1. The scientist could identify proteins that derive from the genetic code.
2. They could then identify potential antibodies to use in the vaccine.

Question 24

Describe how the B-Lymphocytes would respond to a vaccine against a virus.
DO NOT use cellular response in the answer.
(3 Marks)

Answer 24

1. B cell binds to the viral complementary antigen/ receptor.
2. B cell clones
   OR B cell divides by mitosis
3. Plasma cells release monoclonal antibodies against the virus.
4. Plasma cells produce memory cells.

Question 25

What is a monoclonal antibody? (1 mark)

Answer 25

Antibodies with the same tertiary structure. OR Antibodies produced from identical plasma cells.

Question 26

Describe the role of antibodies in producing a positive result on an ELISA test. (4 Marks)

Answer 26

1. First antibody binds to the antigen. 2. Second antibody with attached enzyme is added. 3. Second antibody attaches/ binds to the antigen. 4. Substrate/ solution is added and colour changes

Question 27

Describe and explain antibodies role in stimulating phagocytosis. DO NOT include details about the process of phagocytosis. (2 Marks)

Answer 27

1. Bind to antigen 2.Antibodies cause clumping/ agglutination. OR attract phagocytes.

Question 28

Explain how treatment against a snake's venom would work and why it is essential to use passive immunity rather than active immunity. (2 Marks)

Answer 28

1. The antibodies form the treatment would bind to the toxin/ antigen and cause its destruction. 2. Active immunity would be too slow

Question 29

During vaccination, each animal is injected with a small amount, then a larger amount two weeks later. Use your knowledge of the humoral immune response to explain this vaccination programme. (3 Marks)

Answer 29

1. B cells specific to the vaccine produce by mitosis. 2. B cells produce plasma cells and memory cells. 3. The second dose produces antibodies in the secondary immune response in a higher concentration and quicker.

Question 30

Describe how phagocytosis of a virus leads to presentation of its antigens. (3 Marks)

Answer 30

1. Phagosome/vesicle fuses with lysosome. 2. Virus is destroyed by lysosomes/ hydrolytic enzymes. 3. Antigens from the virus is displayed on the cell membrane.

Question 31

Describe how presentation of a virus antigen leads to the secretion of an antibody against the virus antigen. (3 Marks)

Answer 31

1. T-Helper cells bind to the antigens on the antigen presenting cell. 2. This T-Helper cell stimulates a specific B cell. 3. Bell clones OR Bell divides by mitosis. 4. To form plasma cells with antibodies.

Question 32

What is an antigen? (2 Marks)

Answer 32

1. a foreign protein 2. that stimulates an immune response/ production of antibodies.

Question 33

What is an antibody? (2 Marks)

Answer 33

1. A protein/ immunoglobulin specific to an antigen 2. Produced by B cells OR secreted by plasma cells

Question 34

Describe the difference between active and passive immunity. (5 Marks)

Answer 34

1. Active involves memory cells whereas passive does not. 2. Active involves the production of antibodies for memory cells/ plasma cells. 3. Passive involves antibodies introduced into the body from the outside. 4. Active is long term, as the antibody is produced in response to the antigen. 5. Passive is short term, because antibody given is broken down. 6. Passive is fast working, whereas active can take time to develop.

Question 35

What is a monoclonal antibody? (1 mark)

Answer 35

Antibodies with the same teritary structure OR antibodies produced from identical/ cloned plasma cells.

Question 36

The vaccine for shingles is available on the NHS to everyone over 70. The vaccine contains a protein from the varicella virus. Describe how the immune system would create antibodies after being exposed to the shingles vaccine. (5 marks)

Answer 36

1) Phagocyte will engulf antigen. 2) Forms antigen presenting cell. 3) T helper cell activated by antigen presenting cell. 4) T helper cell activates B cell 5) With complementary receptor. 6) B cell divides by mitosis 7) Plasma cell secretes antibodies.

Question 37

Explain what is meant baby herd immunity and suggest the advantages of it. (5 marks)

Answer 37

1) Herd immunity is when the majority of a population is vaccinated. 2) Prevents transmission of pathogen in the community. 3) Reduces infection rate in population. 4) Can lead to eradication of disease. 5) Protects vulnerable populations/ named examples. 6) Prevents future pandemics