B2 - Cell Division

Question 1

How do bacteria multiply

Answer 1

• Binary fission - one bacterial cell splits into two

Question 2

How often can bacteria divide

Answer 2

• Up to once every 20 minutes
• This is with optimum conditions

Question 3

How many chromosomes does a body cell have

Answer 3

• 46 (23 pairs)
• Gametes only have 23

Question 4

Stages of the cell cycle

Answer 4

1. DNA/ Chromosomes are doubled to form 2 sets. Organelles are also doubled and the cell expands
2. Mitosis - one set of chromosomes is pulled to each end of the cell and the nucleus divides
3. The cytoplasm and cell membrane split to form two genetically identical daughter cells. Each cell has an identical set of chromosomes to each other

Question 5

Functions of mitosis

Answer 5

1. Essential for growth and development
2. Takes place during repair
3. Happens during asexual reporudction

Question 6

What are stem cells

Answer 6

Uspecialised cells that are capable of differentiating into any type of cell

Question 7

Where can stem cells be found in humans

Answer 7

Embryos and bone marrow

Question 8

Where are stem cells found in plants

Answer 8

• In the meristems (shoots and roots)
• Mitosis is constantly taking place here and cells elongate and differentiate

Question 9

What is special about plant cells and plant stem cells

Answer 9

• They can differentiate at any point in the life of the plant
• They can dedifferentiate and differentiate again depending on where they are in the plant

Question 10

How are plants cloned

Answer 10

• Tissue samples from leaf are taken (chopped up)
• Placed in agar and growth medium (auxin)
• Cells differentiate and divide into plantletes
• Plantletes are then placed into compost

Question 11

Reasons for plant cloning

Answer 11

• To clone a rare plant to stop it going extinct
• To produce lots of a plant
• Agriculture - high crop yield with favoured characteristics

Question 12

Types of stem cells in humans

Answer 12

1. Embryonic stem cells - pluripotent so can differentiate into any type of cell
2. Adult stem cells - multipotent so can differentiate into a few types of cells but not all. E,g, bone marrow + blood cells

Question 13

Ethical problems with embryonic stem cells

Answer 13

• Ethically wrong to use a human as a source of cells
• Violations of human rights as embryo can’t give permission
• Religious objections - shouldn’t intefere with sexual reporduction and creation

Question 14

Procedural problems with embryonic stem cells

Answer 14

• Risk of stem cells causing cancer as they divide rapidly
• Difficult to get stem cells to differentiate into cells needed
• Process is slow and expensive

Question 15

What can adult stem cells be used for

Answer 15

• Replace/ fix nerve cells and therefore fix paralysis
• Could also fix diabetes in the future

Question 16

Problems with adult stem cells

Answer 16

• Viruses could be in donor cells that could then get into the patient
• The donor has to be compatible otherwise there is a risk of rejection as the immune system attacks the cells

Question 17

What is Therapeutic cloning

Answer 17

• Cells removed from patient
• Cells are used to create an embryo that has the same genes as the patient
• Embryonic stem cells are then removed and then differentiate to replace cells that don’t work
• They can be transplanted without a risk of rejection as the cells are seen as self