i) Cell Division & Cell cycle

Question 1

why do cells replicate

Answer 1

Growth and development

Maintenance and repair

Reproduction

Question 2

what is asexual replication?

Answer 2

Asexual reproduction is when a living thing makes a copy of itself without needing a partner

Question 3

Binary fission steps

Answer 3

• The circular main chromosome is
  uncoiled and the DNA is replicated.
  Plasmids also replicate.
• The cell elongates (grows longer) as
  it prepares to separate into two
  new cells.
• The duplicated circular main
  chromosomes migrate to opposite ends.
• Cell undergoes CYTOKINESIS by pinching inwards and creating a SEPTUM
• a new cell wall and membrane is formed down the centre of the cell

Question 4

how do plasmids replicate?

Answer 4

Plasmids replicate independently of the main circular chromosome and could be unevenly separated into the two new cells.

Question 5

eukaryotic cell cycle steps

Answer 5

Interphase (cell growth & chromosome replication)

Mitosis ( separation of chromosomes)

Cytokinesis (division of the cytoplasm)

Question 6

Interphase

Answer 6

• G1 phase
• S phase
• G2 phase

Question 7

Gap 1 (G1) phase

Answer 7

Cell synthesizes more proteins to grow in
size

Replication of organelles

Question 8

Synthesis (s) phase

Answer 8

The cell copies its DNA.

Every chromosome is duplicated.

This gives the new cell a full set of DNA after division

Question 9

Gap 2 (G2) phase

Answer 9

Final stage of interphase

Cell continues to grow and prepare
for mitosis

Synthesizes more proteins

Question 10

Gap 0 (G0) phase

Answer 10

Some cells are quiescent – they are
dormant/resting but may re-enter the
cell cycle

Some cells are terminally differentiated
– remain there always.

(nerve cells , some muscle cells)

Question 11

mitosis

Answer 11

• prophase
• metaphase
• anaphase
• telophase

involves the seperation of the replicated chromosomes

Question 12

prophase

Answer 12

Chromatin (loose DNA ) in the nucleus condenses into

chromosomes so that they are visible.

Centrioles migrate to oppose ends of the cell and spindle

fibres begin to form.

Nuclear membrane and nucleolus disappear.

Question 13

metaphase

Answer 13

The spindle fibres are fully formed.

Centromere of each chromosome attaches to a
spindle fibre.

The chromosomes line up across the equator of the
cell.

Question 14

anaphase

Answer 14

The spindle fibres contract.

Centromere splits pulling the sister chromatids to
opposite ends of the cell.

Question 15

Telophase

Answer 15

Chromosomes collect together
at the poles of the cell.

Nuclear membrane reforms,
producing two identical
DAUGHTER CELLS.

Question 16

7. Cytokinesis

Answer 16

After mitosis, the cytoplasm and the organelles are evenly
distributed into the two daughter cells.

Question 17

cytokinesis in animals

Answer 17

a cleavage furrow develops and pinches the plasma

membrane into two cells.

Question 18

cytokinesis in plants

Answer 18

a cell plate ( later becomes a cell wall) forms at the

equator to separate the two new cells.

Question 19

Regulation of the cell cycle

Answer 19

There are 3 checkpoints in the cell cycle where the
cell is checked for errors.

G1/S

G2/M

Metaphase

If errors are found, the cell is either repaired or
undergoes apoptosis

Question 20

G1/S regulation step

Answer 20

Check to see if cell has grown to the right size

Checked to see if the cell has synthesized
protein for DNA replication

Checks if there are enough nutrients and
oxygen

Question 21

G2/M regulation

Answer 21

Ensures that DNA has replicated correctly.

Checks if the cell has enough resources for
mitosis.

Question 22

Metaphase regulation

Answer 22

The cell checks the formation of the spindle
fibres

Checks that the chromosomes are attached
and aligned before anaphase.