B2- Cell Division

Question 1

What are chromosomes made up of?

Answer 1

DNA molecules combined with proteins. They contain genes that provide instructions for protein synthesis.

Question 2

What is a gene?

Answer 2

Section of DNA that codes for a protein.

Question 3

How many chromosomes are found in the nucleus of a human cell?

Answer 3

46 (23 pairs)

Question 4

How many chromosomes are found in the nucleus of a gamete (sex cell)?

Answer 4

23 (because it is a haploid cell)

Question 5

What is the arrangement of chromosomes in the cells?

Answer 5

Pairs (23 pairs)

Question 6

Three main stages of cell division

Answer 6

• Replication of DNA and sub-cellular organelles
• Mitosis
• Division of cell

Question 7

Importance of Mitosis (2)

Answer 7

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

Question 8

First stage of Mitosis:

Answer 8

Longest Stage - where cells grow and increase in mass, replicate DNA and synthesise more organelles (mitochondria, ribosomes etc.)

Question 9

Second stage of Mitosis:

Answer 9

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

Question 10

Third stage of Mitosis:

Answer 10

Cytoplasm and Cell membrane divide creating two identical daughter cells.

Question 11

What is a stem cell?

Answer 11

An unspecialised cell that is capable of differentiating into different types of cells and 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 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 different cell types to replaced dead or damaged tissues. (i.e. 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 cell.

Question 15

Definition - Therapeutic Cloning

Answer 15

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

Question 16

Advantages of meristem stem cell cloning for plants (3)

Answer 16

• Prevent rare plant species from extinction.
• Can produce large numbers of plants with a favourable characteristic.
• Can produce identical plants for research.

Question 17

What are the issues related to the use of stem cells? (4)

Answer 17

• Many embryonic stem cells are retrieved from aborted embryos - some people have religious/ethical objections.
• 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 similar genetic makeup to the patient, an immune response could be triggered.