B2 Cell cycle and stem cells

Question 1

What is DNA?

Answer 1

Genetic material that exists as a double helix

Question 2

What is a cell?

Answer 2

Tiny building blocks that make up all living things

Question 3

What is the nucleus?

Answer 3

A subcellular structure that contains the material of inheritance.

Question 4

What is a chromosome and how many do you have?

Answer 4

A strand of DNA that carries the genes.
Each cell in the body has 46 chromosomes in 23 pairs, except the sex cells (gametes) which only contain 50% of this.

Question 5

What is a gene?

Answer 5

A short length of DNA that determines a characteristic of an organism.

Question 6

What is the cell cycle?

Answer 6

The process in which cells divide.

Question 7

What are the 3 stages of the cell cycle?

Answer 7

1. Chromosomes and sub-cellular structures replicate.
2. Chromosomes are pulled to each side of the cell and the nucleus divides (mitosis).
3. Cell membrane pinches together and the cell divides forming 2 identical daughter cells.

Question 8

How does the speed of the cell cycle vary?

Answer 8

In some parts of the body (skin and hair), the cell cycle is fast, however in other parts it is slower. Some cells do not reproduce at all - nerve cells remain damaged.
The cell cycle happens fastest in children.

Question 9

What is cell differentiation?

Answer 9

When cells acquire different subcellular structures in order to carry out their function.

Question 10

What is specialisation?

Answer 10

Once differentiation has happened and the cell is ready to perform its function

Question 11

What is the difference between stem cells and specialised cells?

Answer 11

Stem cells can form any type of cell whereas specialised cells have undergone differentiation so are fixed.

Question 12

What is special about embryonic stem cells?

Answer 12

• They can undergo mitosis continuously
• They can differentiate to become any type of specialised cell

Embryonic stem cells differentiate quickly to become specialised cells, normally after 4-5 days.

Question 13

What is special about adult stem cells?

Answer 13

• Found in bone marrow, blood, skin, fat and liver
  → They can only differentiate to become a small number of specialised cells (e.g. red blood cell, white blood cell, platelet)
  → Can’t generate new tissue but are used for repairing damaged tissues such as blood and skin.
• May be able to be used to help cure paralysis.

Question 14

What is special about plant stem cells?

Answer 14

• Undifferentiated cells are found in the roots and stems, these areas are called meristems and mitosis occurs there almost continuously.
• Plant cells don’t differentiate until they are in the final position in the plant, and even then changes can be made.
• Taking cuttings from plants can be used to create clones of as plant. For example, every banana you eat is produced by a cloned plant.

Question 15

What are the pros and cons of embryonic stem cell research?

Answer 15

Pros
* Can treat a wide range of diseases/problems
* Painless procedure
* Better to use cells rather than waste them
Cons
* Possible harm/death to embryo
* Long term effects unknown
* Embryo cannot give consent

Question 16

What are the pros and cons of adult bone marrow stem cell research?

Answer 16

Pros
* Well tried/reliable technique
* No ethical issues - adult gives permission
* Quick recovery
* Does not kill donor
Cons
* Hazards involved in operation
* People may not want to be donors as it is painful
* Few cell types can be formed
* Few diseases can be treated