B2. Cell division and Stem Cells

Question 1

Why do cells divide by mitosis?

Answer 1

• To allow growth
• To repair body tissues
• To replace old/dead/worn out cells

Question 2

What are the 3 stages of the cell cycle?

Answer 2

1. Interphase
2. Mitosis
3. Cytokinesis

Question 3

What happens during interphase?

Answer 3

• The cell grows in size.
• DNA replicates
• Organelles replicate.

Question 4

What happens during mitosis?

Answer 4

• The replicated chromosomes line up along the centre of the cell.
• Spindle fibres contract and the chromosomes get pulled to opposite poles.
• Nucleus divides.

Question 5

What happens during cytokinesis?

Answer 5

• Cell membrane and cytoplasm divide.

- 2 genetically identical daughter cells are formed.

Question 6

What are the products of mitosis?

Answer 6

2 genetically identical daughter cells

Question 7

What is a stem cell?

Answer 7

A cell that has not yet become specialised cell.

Question 8

Give 2 properties of a stem cell?

Answer 8

• Can replicate many times

* Has the potential to become specialised (i.e. different types of cell).

Question 9

What are the 2 types of stem cell?

Answer 9

• Embryonic stem cells (from embryos)

* Adult stem cells (from adult tissues)

Question 10

What are embryonic stem cells?

Answer 10

Embryonic stem cells are stem cells found in embryos, and can differentiate into almost every cell type under the right conditions in a lab.

Question 11

What are adult stem cells?

Answer 11

Adult stem cells are stem cells found in adult tissues (such as bone marrow, brain, muscle, liver stem cells). They can differentiate only into cells from the type of tissue where they are found. e.g. liver stem cells can only become liver cells.

Question 12

Where are stem cells found in plants?

Answer 12

• They are found in the meristems of a plant.
• Found in root and shoot tips
• They can differentiate into any type of plant, and have this ability throughout the life of the plant.

Question 13

What are the advantages of using embryonic stem cells to treat diseases?

Answer 13

• Have the potential to develop into any type of cell/tissue.
• Cells can become any cell type.
• Used to treat human diseases.
• Painless

Question 14

What are the advantages of using adult stem cells to treat diseases?

Answer 14

• Plentiful supply
• No ethical issues (in collection) as the person can give consent.
• Safer method as it is well tried/tested.

Question 15

What are the disadvantages of using embryonic stem cells to treat diseases?

Answer 15

• Unethical – embryos cannot give permission.

- Possible harm/death to embryo.

Question 16

What are the disadvantages of using adult stem cells to treat diseases?

Answer 16

• Painful to extract
• Fewer diseases can be treated
• Can only form the type of cells as the tissue they were taken from.
• Possibility of infection during extraction of stem cells.

Question 17

Name a disease that stem cells have been used to treat.

Answer 17

• Paralysis
• Diabetes
• Eyesight in the blind

Question 18

What is therapeutic cloning?

Answer 18

Therapeutic cloning involves an embryo being produced with the SAME GENES as the patient.

Question 19

Describe the stages of therapeutic cloning.

Answer 19

1. The nucleus from a human skin cell (donor) is removed & kept.
2. Nucleus from a human egg cell is removed and discarded.
3. Skin cell nucleus is inserted into the empty egg cell.
4. Egg cell is given an electric shock to stimulate it inot dividing.
5. This develops into an embryo.
6. The cells from this embryo are stem cells & are used to treat diseases.

Question 20

How do you answer an ‘evaluate’ type question in the exam?

Answer 20

In the exam they often ask questions where they ask you to ‘evaluate’ stem cells or stem cell treatments. If you see the word evaluate your answer needs to include:
• Comparison 1
• Comparison 2
• Comparison 3 (use the data if provided)
• Use the word WHEREAS to link 2 comparisons e.g. Ms Lee is a Biology teacher WHEREAS Mr Araim is a Physics teacher.
• A balanced conclusion using data if it is given. i.e. must state _________ is ‘better because….’