B3d - cell division

Question 1

Describe advantages of being multicellular(3)

Answer 1

Allows organisms to be larger

Allows organisms to be more complex

Allows different cells to take on different jobs(cell differentiation)

Question 2

Why does becoming multicellular require the development of specialised organ systems(3)

Answer 2

Communication between cells in the body

Supplying the cells with nutrients

Controlling exchanges with the environment such as heat and gases

Question 3

Describe the term mitosis(2)

Answer 3

A process that produces new cells for growth

The cells made are genetically identical

Question 4

Why must DNA replication take place before
cells divide(2)

Answer 4

Body cells in mammals have two copies of each chromosome( they are diploid cells)

DNA replication must take place before cells divide so each cell produced still has two copies of each chromosome

Question 5

Describe the process of DNA replication(2)

Answer 5

1. The two strands of the DNA molecule which forms the double helix unzips to form single strands
2. New double strands are formed by DNA bases freely floating in the nucleus lining up in complementary base pairings

Question 6

Describe the process of mitosis(4)

Answer 6

1. The chromosomes line up along the centre of the cell
2. Then the chromosomes divide
3. The copies move to opposite poles of the cell
4. Cytoplasm divides, resulting in two new cells containing exactly the same genetic material

Question 7

Describe gametes(2)

Answer 7

Haploids(only contain one chromosome from each pair)

Formed by meiosis

Question 8

How is the structure of a sperm cell adapted

to its function(2)

Answer 8

Many mitochondria to provide energy for swimming to the egg(between the nucleus and the tail)

An acrosome that releases enzymes to digest the egg membrane(at the tip of its head)

Question 9

How does fertilisation result in genetic variation(2)

Answer 9

Male and female gametes combine to form a diploid cell, which is called a zygote(fertilised egg)

The zygote will have inherited chromosomes from two parents, so it will show features of both parents, but won’t be exactly like either of them

Question 10

Describe the process of meiosis(4)

Answer 10

1. DNA replicates just like it does before mitosis
2. Chromosomes arrange themselves into pairs so that both chromosomes in a pair contain information about the same features
3. First division - one chromosome from each pair moves to opposite poles of the cell
4. Second division - chromosomes divide and move to opposite poles of the cell(just like mitosis)

Question 11

Describe the term meiosis(3)

Answer 11

Forms gametes(sex cells) in the ovaries and testes

Forms 4 genetically different cells
-chromosomes gets shuffled up during meiosis and each gamete only gets half of them, at random