4.1.2 Cell division

Question 1

What are chromosomes made up of?

Answer 1

Chromosomes consist of DNA molecules combined with proteins. They contain genes which provide the instructions for protein synthesis.

Question 2

What is a gene?

Answer 2

A section of DNA which codes for a protein.

Question 3

How many chromosomes are found in the nucleus of human body cells?

Answer 3

46

Question 4

How many chromosomes are found in the nucleus of gametes?

Answer 4

23

Question 5

How are chromosomes arranged in the nucleus of a body cell?

Answer 5

Arranged in pairs - 46 chromosomes form 23 pairs.

Question 6

What are the three main stages of the cell cycle?

Answer 6

1. Replication of DNA and synthesis of organelles
2. Mitosis
3. Division of cell

Question 7

Why is mitosis important?

Answer 7

● Produces identical cells which all have the same genetic information.
● Produces additional cells for growth and repair.

Question 8

Describe the first stage of the cell cycle

Answer 8

Longest stage - cells grow and increase in mass, replicate DNA and synthesise more organelles (eg. mitochondria, ribosomes).

Question 9

Describe the second stage of the cell cycle

Answer 9

Each chromosome in a pair is pulled to opposite poles of the cell, then the nucleus divides.

Question 10

Describe the third stage of the cell cycle

Answer 10

The cytoplasm and cell membrane divide - two identical daughter cells are produced.

Question 11

What is a stem cell?

Answer 11

An unspecialised cell which is capable of differentiating into other cell types and of self-renewal.

Question 12

What is the function of stem cells in embryos?

Answer 12

Embryonic stem cells can replicate themselves and differentiate into many other types of cells. Embryonic stem cells may be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells.

Question 13

What is the function of stem cells in adult bone marrow?

Answer 13

Adult stem cells can differentiate into several cell types to replace dead or damaged tissues. For example, bone marrow stem cells can form many different types of blood cell.

Question 14

What is the function of stem cells in plant meristems?

Answer 14

Meristem stem cells retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant.

Question 15

What is therapeutic cloning?

Answer 15

A cloning method where an embryo is produced with the same genetic makeup as the patient. The stem cells which originate from the embryo will not be rejected by the patient’s immune system, so can be used to treat certain medical conditions.

Question 16

What are the advantages of cloning plants using meristem stem cells?

Answer 16

● Can prevent rare plants from becoming extinct.
● Can produce large numbers of plants with a
favourable characteristic.
● Can produce identical plants for research.

Question 17

What are issues are associated with the use of embryonic stem cells?

Answer 17

● Many embryonic stem cells are sourced from aborted embryos - some people have an ethical/religious objection.
● Development of stem cell therapies is slow, expensive and difficult.
● Adult stem cells infected with viruses could transfer infections to patients.
● If donor stem cells do not have a similar genetic makeup to the patient, an immune response could be triggered.