Chapter 5 - Continuity Of Cells

Question 1

The three phases of a cell division

Answer 1

Interphase, mitosis, cytokinesis

Question 2

What is involved in interphase?

Answer 2

Two gap(growth) phases (G1 and G2) separated by a synthesis(S phase)

Question 3

What is Mitosis?

Answer 3

A nuclear division during which the chromosomal material is partitioned into daughter nuclei

Question 4

What is cytokinesis?

Answer 4

When the cell divides into two daughter cells.

Question 5

What is the stages of mitosis and their order?

Answer 5

Prophase, Metaphase, Anaphase, Telophase

Question 6

What happens during the G1 phase?

Answer 6

Synthesis of macromolecules, including proteins and nucleotides, occurs and organelles are produced so that the cell increases in size

Question 7

What happens during S phase?

Answer 7

DNA Synthesis occurs. Histones(proteins that bind to and support the DNA within the chromatids) are also produced. DNA and chromatids formed are identical.

Question 8

What happens during the G2 phase?

Answer 8

Proteins such as tubulin are synthesised - forms the microtubles of the spindle fibres, energy stores are increased, cell grows in size.

Question 9

What happens during Prophase in mitosis?

Answer 9

Chromatin condenses.
The centrioles move towards opposite poles.
The spindle begins to form.
As chromosomes condense two chromatids joined at the centromere become visible
Nuclear envelope breaks down

Question 10

What happens during Metaphse in mitosis?

Answer 10

Spindle formation is completed and attach to the centromere and moves the chromosomes along the equator of the cell(lines up along equator)

Question 11

What happens during Anaphase in mitosis?

Answer 11

The centromeres attaching the two chromatids of each chromosome split and the contraction of the spindle fibres pulls the chromatids apart.
The sister chromatids move towards opposite poles

Question 12

What happens during Telophase in mitosis?

Answer 12

Each chromatid is now a separate chromosome.
The two groups of chromosomes reach opposite poles of the cell.
A new nuclear envelope forms around each group.

Question 13

What is the process of Cytokinesis in animal cells?

Answer 13

A cleavage furrow forms as protein microfilaments pull the cell surface membrane in along the equator, the furrow deepens and when the membranes fuse the cell is cleaved in two.

Question 14

What is the process of Cytokinesis in plant cells?

Answer 14

The cell wall prevents cleavage. In the plant cell the Golgi bodies produce vesicles that collect and fuse together to form an equatorial cell plate. The vesicles secrete the material of the middle lamella on each side of which a new cellulose cell wall is laid down.

Question 15

What is the G1 checkpoint?

Answer 15

The supply of nutrients and growth factors is assessed so that the cell has grown to an appropriate size.
The DNA is checked for damage and if damage is detected the DNA is repaired.
If these requirements are met it proceeds to S phase, if not it enters G0 (the resting state)

Question 16

What is the G2 checkpoint?

Answer 16

At the end of the G2 phase.
The cell checks that DNA replication has taken place accurately and there is no DNA damage.
If it has not replicated or there is damage the cell cycle stops?

Question 17

What is the Metaphase checkpoint?

Answer 17

This check establishes whether the chromosomes have correctly attached to the spindle fibres before Anaphase proceeds.
Mitosis cannot proceed unit check is passed.

Question 18

What is the use of drugs to treat cancer?

Answer 18

Chemotherapy

Question 19

How do drugs to treat cancer work?

Answer 19

The inhibition of microtuble formation. For example Vincristine (mitotic poisons)
Antimetabolites that act as S phase inhibitors preventing DNA synthesis. For example Fluorouracil.

Question 20

What is Meiosis?

Answer 20

It is the process of reduction division, which is cell division that halves the number of chromosomes in gametes.

Question 21

Differences in mitosis and meiosis.

Answer 21

It only takes place in reproductive organs.
It involves two divisions resulting in four daughter cells.
Chromosome arrangements in the daughter cells are both different form each other and different for the parent cell.

Question 22

What is a haploid cell?

Answer 22

A cell that contains only one of each type of chromosome

Question 23

What are the stages of Meiosis1 in order?

Answer 23

Prophase1, Metaphase1, Anaphase1, Telophase 1

Question 24

What happens during Prophase in meiosis?

Answer 24

Homologous chromosomes have paired up to form Bivalents.
The chromatids appear, the chromatids in the bivalent are entwined at points called chiasmata(chiasma s).
The chromatids may break at chiasmata and rejoin with a different chromatid(crossing over)

Question 25

What happens during Metaphase in meiosis?

Answer 25

The bivalents move to the equator of the spindle | Each chromosome of the pair become attached to a spindle fibre by the centromere.

Question 26

What happens during Anaphase in meiosis?

Answer 26

Pulling by the spindle fibres causes the homologous chromosomes to move apart towards opposite poles. The homologous chromosomes are separated, each chromosome still consists of two chromatids.

Question 27

What happens during Telophase in meiosis?

Answer 27

Chromosomes reach the opposite poles of the cell. A nuclear envelope forms around each separate group of chromosomes. Each nucleus contains the haploid number of chromosomes.

Question 28

What happens during Meiosis2?

Answer 28

Normally prophase2 continues in each daughter cell immediately after meiosis1. The spindle fibres are formed at right angles to the old spindle and the outcome is the separation of each of the chromosomes into two chromatids. It is very similar to mitosis. Meiosis produces 4 unique daughter cells.

Question 29

What is independent assortment?

Answer 29

Only one chromosome from each homologous pair can enter a gamete. This is dependent on the random nature of how chromosomes line up at the equator at the start of metaphase1. With 23 pairs of chromosomes in humans, there are millions of possible combinations for any one gamete. This process of independent assortment is very important in variation.

Question 30

What is crossing over?

Answer 30

Sometimes two non sister chromatids break and exchange sections with each other. This happens during prophase1. The point where the chromosomes cross over is called chiasmata(chiasma singular).