Cell Division

Question 1

Mitosis is important in the life of an organism. Explain why [3]

Answer 1

1. Growth / increase in cell number;
2. Replace cells / repair tissue / organs /body;
3. Genetically identical cells;
4. Asexual reproduction / cloning;

Question 2

Describe the behaviour of chromosomes during mitosis and explain
how this results in the production of two genetically identical cells. [6]

Answer 2

1) chromosomes shorten/thicken/supercoiling;

2) chromosomes (each) two identical chromatids/strands/copies
(due to replication);

3) chromosomes/chromatids move to equator/middle of the spindle/cell;
4) attach to individual spindle fibres;
5) spindle fibres contract / centromeres divide / repel;
6) (sister) chromatids/chromosomes (separate) move to opposite poles/ends of the spindle;

7) each pole/end receives all genetic information/
identical copies of each chromosome;

8) nuclear envelope forms around each group of
chromosomes/ chromatids/at each pole;

9) Chromosomes unwind/uncoil

Question 3

Describe and explain the appearance of one

of the chromosomes in the cell [3]

Answer 3

Chromosome is formed of two chromatids;

(Because) DNA replication (has occurred);

(Sister) chromatids held together by centromere;

Question 4

Describe how bacterial cells replicate

Answer 4

The circular DNA and plasmids in the cell replicate

the two copies of the DNA attach to different points on the cell’s membrane

The bacterial cell grows so that the attached DNA move further away from each
other

the plasmids divide randomly between the two sides of the cell (moving by
diffusion)

The cell membrane pinches inwards in the middle of the cell, so the cytoplasm
divides

New cell wall forms so the cell is divided into two

Question 5

Describe how viruses replicate

Answer 5

Virus attaches to a host cell

Virus injects its genetic material into the host cell

The host cell transcribes and translates the viral genes

These proteins form new virus particles

The virus particles burst out of the host cell, so the host cell is destroyed

Question 6

Why does each virus only infect a specific

type of cell? [3]

Answer 6

Outside of virus has antigens/proteins;

With complementary shape to receptor/protein in membrane of
(target) cells;

(Receptor/protein) found only on membrane of that specific type of
cells;