B2.1 Supplying the Cell - Cell cycle & Mitosis

Question 1

Define Mitosis

Answer 1

A type of nuclear cell division that is used by cells for growth, repair, and healing and asexual reproduction. A stage within the cell cycle.

Question 2

What is the cell cycle?

Answer 2

• The process of cell growth and division for growth and repair of body cells
• It has three main stages interphase, mitosis and cytokinesis,
• Results in two identical daughter cells.

Question 3

Why is interphase important?

Answer 3

• It it the stage of growth (G1) and replication (S)
• Before a cell can divide it needs to grow and duplicate all of its cellular contents

Question 4

What are homologous chromosomes?

Answer 4

• A pair of chromosomes, one from the mother, and one from the father, which are very similar to one another and have the same size and shape.
• Most importantly, they carry the same type of genetic information: that is, they have the same genes in the same locations

Question 5

What do the terms ‘diploid’ and ‘haploid’ mean?

Answer 5

• Diploid = full set of chromosomes, 23 pairs/46 strands in humans
• Haploid = half of the full set of chromosomes, 23 strands in humans

Question 6

What is the name given to the two identical copies of each chromosome?

Answer 6

Sister chromatids

Question 7

What is the name of the attatchment between sister chromatids?

Answer 7

Centromere.

Question 8

What is the name given to the way in which DNA replicates?

Answer 8

Semi-conservative

Question 9

What is meant by semi-conservative replication?

Answer 9

After replication each strand has one original strand, and one new ‘complementary’ strand

Question 10

List the key stages in DNA replication.

Answer 10

• Double helix untwists
• Hydrogen bonds between bases broken, DNA ‘unzips’
• Bases exposed on each of the two strands
• Free nucleotides form hydrogen bonds with the exposed base (A-T, C-T)
• Covalent bonds form between nucleotides to form ‘backbone’

Question 11

What happens during the cell cycle after DNA replication but before mitosis?

Answer 11

The replicated DNA is checked for errors and corrections made to avoid mutations being pass on to new cells

Question 12

Explain what happens in each of the key stages of mitosis

Answer 12

• Prophase - Chromosomes align in the middle of the cell
• Metaphase - Spindle fibres pull the arms of each chromosome to opposite ends of the cell.
• Anaphase - Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells – the nucleus has divided.
• Telophase - Cytoplasm and cell membrane divide to produce two identical daughter cells, each containing the same chromosomes.

Question 13

What is cytokinesis?

Answer 13

The formation of the two new nuclear membrane, and pinching in of the cell membrane to separate and enclose the two new nuclei, to separate the two new cells.

Question 14

Explain why the chromosome number must stay the same when cells divide by mitosis?

Answer 14

The chromosome number must stay the same when cells divide by mitosis to ensure the cells produced are normal body cells, identical to their parent cell.

Question 15

When do the sister chromatids condense>

Answer 15

During prophase the sister chromatids condense to form x-shaped chromosomes linked by a centromere.

Question 16

What is the longest stage of the cell cycle called?

Answer 16

Interphase

Question 17

During what stage does the G1, S, and G2 phases happen?

Answer 17

Interphase

Question 18

Where in a plant does mitosis take place?

Answer 18

The tips of roots and shoots

Question 19

How can mitosis be easily observed in a school laboratory?

Answer 19

Be preparing a ‘root squash’.

Question 20

What is a root tip squash?

Answer 20

A method of preparing root tip meristem cells to observe them using a light microscope at different stages of the cell cycle