Biology: Topic 3

Question 1

Interphase

Answer 1

New cell organelles are synthesised and DNA replication occurs.

Question 2

Prophase

Answer 2

Chromosomes condense becoming visible as chromatids. Centromeres move to each end (pole) of the cell and form spindles.

Question 3

Visible Chromosomes

Answer 3

Each chromosome is made up of two identical chromatids joined at one point called the centromere.

Question 4

Metaphase

Answer 4

The nuclear envelope breaks down and the chromosomes line up at the cell equator. Spindle fibres attach to the centromeres of each chromosome.

Question 5

Anaphase

Answer 5

Spindles shorten, pulling one chromatid from each chromosome to each pole.

Question 6

Telophase

Answer 6

The chromatids unravel and the nuclear envelope reforms.

Question 7

Cytoplasmic division/Cell division

Answer 7

Protein filaments cause the cell surface membrane constricts at the equator of the cell until the cell separates into two separate cells.

Question 8

Interphase: G1

Answer 8

Cell grows and carries out i’s usual functions.

Question 9

Interphase: S

Answer 9

DNA replication and synthesis of cell organelles occurs.

Question 10

Interphase: G2

Answer 10

Cell continues to grow and synthesise proteins in preparation for mitosis.

Question 11

Fertilisation

Answer 11

1. Sperm reach the ovum
2. Acrosome reaction
3. The sperm fuses with the ovum membrane.
4. The sperm nucleus enters the ovum.
5. Cortical reaction
6. Nuclei of the ovum and sperm fuse.

Question 12

Acrosome reaction

Answer 12

Triggered by chemicals released from the cells surrounding the ovum. The acrosome fuses with the sperm cell membrane, releasing digestive enzymes which break down the follicle cells and zona pellucida.

Question 13

Cortical reaction

Answer 13

Enzymes released from lysosomes in the ovum cause the zona pellucida to harden and prevent other sperm cells from entering the ovum.