1.2 Cell Division

Question 1

Where are chromosomes found?

Answer 1

Chromosomes are found in the nucleus.

Question 2

What are chromosomes?

Answer 2

Thread-like structures that consist of single DNA molecules combined with proteins.

Question 3

What is DNA?

Answer 3

A molecule that contains genetic information (genes) and instructions for protein synthesis.

Question 4

What is a gene?

Answer 4

A section of DNA which codes [provide the instructions] for [protein synthesis] a protein.

Question 5

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

Answer 5

46

Question 6

How many chromosomes are found in the nucleus of gametes?

Answer 6

23

Question 7

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

Answer 7

Arranged in pairs - 46 chromosomes form 23 pairs.

Question 8

What are the three main stages of the cell cycle?

Answer 8

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

Question 9

Why is mitosis important? (2)

Answer 9

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

Question 10

Describe the first stage of the cell cycle. (2)

Answer 10

Longest stage:
1. Cells grow and increase in mass
2. DNA replicates to form pairs of each chromosomes and copies (synthesises) its organelles (eg. mitochondria, ribosomes).

Question 11

Describe the second stage of the cell cycle. (2)

Answer 11

Mitosis:
1. Each chromosome in a pair is pulled to opposite poles of the cell.
2. Nucleus divides.

Question 12

Describe the third stage of the cell cycle. (2)

Answer 12

Cytokinesis:
1. The cytoplasm and cell membrane divide.
2. This forms two identical daughter cells.

Question 13

What is a stem cell? (2)

Answer 13

An unspecialised cell which is able to differentiate into other cell types and of self-renewal.

Question 14

What is the function of stem cells in embryos? (2)

Answer 14

Embryonic stem cells can replicate themselves and be cloned, and they can differentiate into any type of cells (pluripotent).

Question 15

How can embryonic stem cell be medically used; examples? (2)

Answer 15

They may be able to treat conditions by dividing to replace damaged cells, such as paralysis and diabetes.

Question 16

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

Answer 16

Adult stem cells can only differentiate into a few predetermined cell types (multi-potent).

Question 17

How can they be medically used; examples? (2)

Answer 17

They can be medically used to replace dead or damaged tissues. For example, bone marrow stem cells can form different types of blood cells.

Question 18

What is the function of stem cells in plant meristems?

Answer 18

Meristem stem cells have the ability to differentiate into any type of plant cell, required by the plant, throughout their lifespan.

Question 19

What is therapeutic cloning?

Answer 19

A cloning method where an embryo is produced with the same genetic makeup as the patient.

Question 20

How is therapeutic cloning beneficial? (2)

Answer 20

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 21

What are the advantages of cloning plants using meristem stem cells? (3)

Answer 21

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

Question 22

What issues are associated with the use of stem cells? (4)

Answer 22

• Many embryonic stem cells are sourced from aborted embryos - raises 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.