1.1.3 - Cell Division (New Cells) Part 12, 13 & 14

Question 1

1. Mitosis occupies an amount of the cell cycle. Give an estimate in percentages of how much mitosis occupies of the cell cycle.
2. List the other stages that take up the remaining percentage.

Answer 1

5 - 20%

Mitosis occupies only a small percentage of the cell cycle whilst other stages in the interphase such as G1 (biosynthesis), S (synthesis of new DNA) and G2 (growth).

Question 2

Describe the behaviour of: chromosomes, nuclear envelope, cell membrane and centrioles during the S-phase of interphase.

Answer 2

• Chromosomes - there are 92 long, tetraploid chromosomes,
• Nuclear envelope - still intact.
• Cell membrane - One surface
• Centrioles - They are together; not opposite each other. There are also no spindle fibres.

Question 3

What phase is this cell at? Give reasons for your answer.

Answer 3

(Early) Prophase - We can tell this because:

• Chromosomes - are condensed and visible.
• Nuclear envelope - beginning to break down.
• Centrioles - begin to migrate.
• Spindle fibres - start forming.

Question 4

Describe how metaphase differs from anaphase.

Answer 4

During metaphase, the chromosomes are aligned on the equator, however during anaphase, the spindle fibres retract and the centromeres divide, pulling the chromosomes apart.

Question 5

Describe what late prophase looks like and how does this differ from early prophase.

Answer 5

• Chromosomes - condensed.
• Nuclear envelope - in early prophase, this has begun to break down. In late prophase, the nuclear envelope has completely disappeared.
• Centrioles - in early prophase, the centrioles have started to migrate. In late prophase, the centrioles are already opposite each other.
• Spindle fibres - unilke in early prophase where we see the beginnings of the spindle fibres form, in the late prophase, the spindle fibres will have attached themselves to the centromeres.

Question 6

What is this phase? Explain your answer.

Answer 6

This cell is at telophase. This is because:

• Nuclear envelope - is starting to form.
• Chromosomes - starting to unwind.
• Nucleolus is starting to form.
• Membrane is beginning to split.

Question 7

Define the term ‘homologous pair of chromosomes’.

Answer 7

Homologous pair - refers to the two chromosomes (one from the mother and one from the father) that carry the same genes.

Question 8

Why is mitosis significant in the growth of multicellular organisms?

Answer 8

Multicellular organisms grow by producing extra cells which must be genetically identical to the parent cell in oder to perform the same function.

Question 9

How does mitosis help repair tissues in the body?

Answer 9

Damaged cells in the tissue have to be replaced by the new cells. Mitosis means that the new cells have made genetically identical and therefore can replace the damaged cell by carrying out the same functions.

Question 10

Name the process that takes place when single-celled organisms undergo mitosis.

Answer 10

Asexual reproduction.

Question 11

A different process of cell division happens in yeast. State the name of this process and describe what happens during this process.

Answer 11

Budding:

• Cytokinesis happens by producing a small ‘bud’ that nips off the cell.
• They are different in sizes.
• Organelles are produced in the large parent cell and are then transported to the ‘bud’.

Question 12

True or false: Cells produced as a result of meiosis are genetically identical.

Answer 12

False: Meiosis produces cells that are non-identical to each other.