2 Cells

Question 1

Name the process by which prokaryotic cells divide. (1)

Answer 1

Binary fission.

Question 2

Name two structures present in plant cells that are not present in animal cells. (1)

Answer 2

Any two of the four answers to get the mark
- Chloroplasts
- Cell wall
- Cell vacuole
- Starch grains

Question 3

Cell fractionation Explain why the solution was ice-cold, buffered and isotonic. (3)

Answer 3

Ice-cold - Slows enzyme activity to prevent digestion of organelles.
Buffered - Maintains pH so that enzymes are not denatured.
Isotonic - Prevents osmosis so no shrinkage of organelles.

Question 4

Cell fractionation Explain why the biologist used a blender and then filtered the mixture. (2)

Answer 4

The blender homogenises the cells. It is then filtered to remove larger debris.

Question 5

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

Answer 5

The DNA in the nucleus codes for specific proteins.
The ribosomes produce the proteins.
Mitochondria produce ATP used for protein synthesis.
The Golgi apparatus modifies and packages the proteins.

Question 6

Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope. (1)

Answer 6

Higher resolution.

Question 7

What is the function of the mitochondrion? (1)

Answer 7

Aerobic respiration.

Question 8

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

Answer 8

Movement of sodium out of the cell generates a concentration gradient for Na.
The Na moves into the cell lining the ileum by co-transport, bringing the glucose molecules with it.

Question 9

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

Answer 9

Microvilli increases surface area for absorption.
Large number of carrier proteins which increase the rate of absorption.

Question 10

Give two similarities in the movement of substances by diffusion and by osmosis. (2)

Answer 10

Diffusion and osmosis both move substances down a concentration, from high concentration to low concentration.
Both diffusion and osmosis are passive processes which do not use energy from respiration.

Question 11

Explain the advantages of lipid droplet and micelle formation. (3)

Answer 11

The droplets increase surface area for enzyme action so hydrolysis happens faster.
Micelles carry fatty acids and glycerol through the membrane to the intestinal epithelial cell.

Question 12

Explain how high absorption of salt leads to a build up of tissue fluid. (2)

Answer 12

Higher salt absorption results in lower water potential of the tissue fluid, so less water returns to the capillary by osmosis.

Question 13

Give three properties of water that are important in biology. (3)

Answer 13

Water is a solvent.

Water has a relatively high specific heat capacity.

Water has cohesion.

Question 14

Name the fixed position occupied by a gene on a DNA molecule. (1)

Answer 14

Locus/Loci

Question 15

Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer. (3)

Answer 15

The base sequence of the gene is in triplets. This determines the sequence of amino acids in the polypeptide.

Question 16

Mitosis is important in the life of an organism. Give two reasons why. (2)

Answer 16

Replaces damaged or dead cells.

Increase in cell number.

Question 17

In which phase of the cell cycle does DNA replication take place? (1)

Answer 17

Interphase.

Question 18

Describe the role of the spindle during mitosis. (2)

Answer 18

The spindle separates the chromosomes of a parent cell into two daughter cells.

Question 19

Meiosis also occurs during the life cycle of organisms. What is the importance of meiosis? (2)

Answer 19

The chromosome number is halved by meiosis, which then ensures that during the new cell has a full number of chromosomes a fertilisation.

Question 20

Describe how a phagocyte destroys a pathogen present in the blood. (3)

Answer 20

The phagocyte engulfs the pathogen, which forms a phagosome. This fuses with a lysosome which then releases hydrolitic enzymes which hydrolyse the pathogen.

Question 21

Give two types of cell, other than a pathogen, that can stimulate an immune response. (2)

Answer 21

Abnormal cells

Antigen presenting cells

Question 22

What is the role of the disulfide bridge in forming the quaternary structure of an antibody? (1)

Answer 22

The disulfide bridges join the different polypeptide chains together.

Question 23

Determining the genome of viruses could help scientists develop a vaccine. Explain how. (2)

Answer 23

The scientists can identify the proteome. They could then identify the potential antigens to use in the vaccine.

Question 24

What is a monoclonal antibody? (1)

Answer 24

Antibodies produced from cloned plasma cells.

Question 25

Describe how HIV is replicated. (4)

Answer 25

Attachment proteins attach to receptors on the helper T cell.
RNA enters the cell where it is converted into DNA by reverse transcriptase. A viral protein is produced, and then the virus is assembled and released from the cell.

Question 26

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells. (4)

Answer 26

The RNA is converted into DNA by reverse transcriptase. This DNA is inserted into the T helper cell’s nucleus. The DNA is transcribed into HIV mRNA, where it is then translated into HIV proteins for assembly and release into viral particles.