Cell division

Question 1

What are the advantages of being multicellular organisms like humans?

Answer 1

It allows an organism to become larger and more complex. It also allows different cells to take on different jobs. This is called cell differentiation.

Question 2

However, when an organism becomes multicellular, it needs to have systems that can:

Answer 2

• Allow communication between all cells in the body
• Supply all the cells with enough nutrients
• Control exchanges with the environment such as heat and gases

Question 3

What is mitosis?

Answer 3

The process that produces new cells for growth.

Question 4

Mitosis and cell division

Answer 4

The cells that are made by mitosis are genetically identical. Before cells divide, DNA replication must take place. This is so that each cell produced still has two copies of each chromosome.

Question 5

Why are mammal cell diploid?

Answer 5

Body cells in mammals have two copies of each chromosome.

Question 6

Before mitosis happens, DNA is replicated. This involves:

Answer 6

• The two strands of the DNA molecule ‘unzipping’ to form single strands.
• New double strands forming by DNA bases lining up in complementary pairings.
• Then mitosis occurs. The chromosomes line-up along the centre of the cell and divide. The copies then move to opposite poles of the cell.

Question 7

What is meiosis?

Answer 7

The type of cell division that produces gametes.

Question 8

Why are gametes haploid?

Answer 8

Gametes are haploid cells because they contain only one chromosome from each pair. This means that the zygote gets one copy of the gene from one parent and another copy from the other parent. This produces genetic variation.

Question 9

What happens in the two divisions during meiosis?

Answer 9

• First, the single strands are copied to make X-shaped chromosomes and chromosomes with the same genes pair up.
• Then:
• In the first division, one chromosome from each pair moves to opposite poles of the cell.
• In the second division, the copies of each chromosome come apart and move to opposite poles of the cell.

Question 10

The structure of a sperm cell is adapted to its function. It has:

Answer 10

• Many mitochondria to provide the energy for swimming to the egg.
• An acrosome that releases enzymes to digest the egg membrane.