SB2. Cells and Controls - Mitosis and Stem cells

Question 1

SB2a - How are tumours formed?

Answer 1

• When cells mutate, they can become cancer cells.
• This means that they will divide even when they don’t require to divide. (uncontrolled cell division)

Question 2

SB2a - How many types of chromosomes are in a human cell and what is it called when these are alone or paired up?

Answer 2

• 23 types of chromosomes.
• When they are paired up to have 46 chromosomes this is a diploid cell and a haploid cell only has 23 chromosomes.
• Gametes are haploid cells while all other cells in a human are diploid.

Question 3

SB2a - Describe stages of mitosis

Answer 3

Mitosis

• Interphase
  
  • Copies of the chromosomes are formed in the nucleus
• Prophase
  
  • The nucleus starts to break up and spindle fibres appear.
• Metaphase
  
  • The chromosomes are lined up on the spindle fibre across the middle of the cell
• Anaphase
  
  • The chromosome copies are separated and moved to either side of the cell
• Telophase
  
  • A membrane forms around each set of chromosomes to from a nuclei
• Cytokeniesis
  
  • Cell surface membrane forms separating the two cells (In plants, a cell wall is also formed)

Question 4

SB2a - What are the products of mitosis called?

Answer 4

Daughter Cells

Question 5

SB2a - What type of organisms do not require mitosis to occur?

Answer 5

Unicellular organisms

Question 6

SB2a - Why does asexual reproduction require mitosis?

Answer 6

• As asexual reproduction only needs one parent, the offspring will have the same DNA as the parent.
• As the offspring are clones and their chromosomes are identical, their cells are formed by mitosis.

Question 7

SB2a - Why is mitosis important in organisms?

Answer 7

• Asexual Reproduction
• Growth
• Repairing damage
• Cell Replacement

Question 8

SB2b - Define growth.

Answer 8

The increase in size as a result of an increase in size of or numbers (due to cell division) of cells.

Question 9

SB2d - How can stem cells be used to treat leukemia?

Answer 9

• A patient’s bone marrow is destroyed using radiation
• Adult stem cells are inserted into the patient
• The stem cells will differentiate specialise and divide to form new blood cells and bone marrow

Question 10

SB2d - What are the problems with using stem cells in medicine? (6)

Answer 10

• If stem cells continue to divide, it can cause a cancerous tumour to form
• Stem cells of one person can be rejected by the immune system of another
• Embryonic stem cells pose an ethical issue
• Potential long-term side effects are unknown
• Stem cells could be contaminated during the operation, so when transferred into the patient it only makes them sicker

Question 11

SB2d - What is an embryonic stem cell?

Answer 11

A cell in an early stage embryo that is not specialised and can differentiate to form any type of specialised cell.

Question 12

SB2d - What the ethical risks of using stem cells? (2)

Answer 12

1. Embryos that were used to provide stem cells are destroyed which is seen as unethical and a waste of potential human life
2. May lead to the reproductive cloning of humans

Question 13

SB2d - Where can adult stem cells be found and how are they different to embryonic stem cells?

Answer 13

Adult stem cells can be found in most tissues including bone marrow but can only differentiate to cells in the tissue around them .

Question 14

SB2d - Why don’t plants have adult stem cells?

Answer 14

Their cells remain able to differentiate freely throughout their lives.

Question 15

SB2d - What are the benefits of using stem cells in medicine ? (4)

Answer 15

1. Treating damage or disease
2. Treating otherwise untreatable diseases
3. Growing organs for transplants
4. Used in scientific research

Question 16

What are chromosomes made from?

Answer 16

A single molecule of DNA. Each section of this molecule (called a gene) - codes for the production of a particular protein

Question 17

SB2c - What are the meristems?

Answer 17

• A group of cells near the end of each shoot that allow plants to continue growing throughout their lives.
• They divide rapidly and the cells are elongated and differentiated.

Question 18

SB2c - What are the zones of differentiation elongation and cell division?

Answer 18

• D: Where cells are specialised
• E: Where cells are elongated (vertically extended)
• CD: Where rapid mitosis occurs (Meristems)