Stages in mitosis and meiosis

Question 1

during interphase, each chromosome is copied to form _____

Answer 1

during interphase, each chromosome is copied to form two sister chromatids
Sister chromatids remain joined at the centromere

Question 2

diagram of cell at the end of interphase

Answer 2

https://www.shutterstock.com/image-vector/interphase-cell-division-cycle-260nw-2065936799.jpg

Question 3

state the four stages in mitosis in order

Answer 3

prophase
metaphase
anaphase
telophase

Question 4

Describe what happens in prophase

Answer 4

The first stage of mitosis is called prophase.

During prophase, the chromosomes condense and become visible in the nucleus.

Each chromosome consists of two sister chromatids joined at the centromere

The nucleolus disappears and the nuclear membrane starts to break down

A pair of centrioles move to either side (or pole) of the cell)

Proteins begin to form spindle fibres, (from the centrioles) which attach to the centromere of each chromosome.

These spindle fibres start to move the chromosomes towards the centre of the cell

Question 5

Describe what happens in metaphase

Answer 5

The second stage of mitosis is called metaphase.

At metaphase, the spindle apparatus has completely formed and the chromosomes are lined up at the centre (or equator) of the cell

Question 6

Describe what happens during anaphase

Answer 6

Anaphase is the third stage of mitosis

In anaphase, the centromeres divide into two, and the spindle fibres begin to shorten.

This pulls the sister chromatids towards opposite poles of the cell

Question 7

Describe what happens during telophase

Answer 7

The last stage of mitosis is called telophase

In Telophase, the chromatids have reached the poles of the cell.

They are now referred to as chromosomes again

The spindle apparatus breaks down and the nuclear membranes reform

The chromosomes uncoil back to their chromatin state.

The nucleolus also reappears in each nucleus

At this point, the cell has now finished nuclear division by mitosis and starts cytokinesis.

Question 8

Describe what happens during cytokinesis

Answer 8

During cytokinesis, the central cell membrane is pulled inwards by the cytoskeleton.
This creates a groove or furrow (at each end of the cell) which gradually deepens.

Eventually, the membranes fuse to form two independent cells

At this stage, cell division by mitosis is finished

Question 9

draw a diagram showing mitosis

Answer 9

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/f4e50e04-dc30-4492-9d11-ba633c9a7ba9/stages-of-mitosis.png

Question 9

describe the stages of meiosis

Question 10

describe how meiosis can lead to genetic variation

Question 11

where does cell division meiosis take place
and how is this different to mitosis

Answer 11

Cell division by meiosis only takes place in sex organs

mitosis take place in virtually all cells

Question 12

explain why cell division by meiosis only takes place in sex organs

Answer 12

Cell division by meiosis only takes place in sex organs
This is because cell division by meiosis is only ever used to produce gametes (sperm and egg cells in mammals, and pollen and eggs in plants)

Question 13

In cell division by meiosis what do we start with and what do we end up with

Answer 13

In cell division by meiosis we start with a diploid cell and at the end we have four haploid gametes

Question 14

In cell division by mitosis what do we start with and what do we end up with

Answer 14

In cell division by mitosis we start with a diploid cell and at the end we have two identical diploid cells

diploid cell - cell which has pairs of chromosomes

contains chromosomes in pairs - diploid cells

Question 15

What do the products of meiosis contain

Answer 15

Products of meiosis - haploid gametes

These contain individual chromosomes and not pairs

Question 16

Explain why it is important that gametes are haploid cells

Answer 16

It is important that gametes are haploid cells

This is because during fertilisation, gametes fuse together to produce a fertilised egg or zygote.

Because gametes are haploid, the zygote has the diploid number of chromosomes

Question 17

zygotes have ______, while gametes have _____

Answer 17

zygote have diploid number of chromosomes (diploid cells), while gametes have a haploid number of chromosomes (are haploid)

Question 18

What can be said about all of the gametes made by meiosis

Answer 18

All of the gametes made by meiosis are genetically different

Question 19

describe the features of a homologous pair of chromosomes

Answer 19

Diploid cells contain chromosomes in pairs
e.g. chromosome 9 pair

One chromosome in a homologous pair comes from your mother and the other chromosome in a homologous pair comes from your father

Both chromosomes in a homologous pair have exactly the same genes, but may have different alleles since you can inherit different alleles from each parent

e.g. both copies of chromosome 9 have the gene which determines blood group

However you can inherit different alleles from each parent e.g. for blood group inherit A allele from mother and B allele from father

Question 20

Explain why the gametes produced from cell division by meiosis are all genetically different

Answer 20

Before the nucleus divides by meiosis, all the chromosomes are copied in interphase

each chromosome is copied to form two sister chromatids
Sister chromatids remain joined at the centromere.

At an early stage in meiosis, the two chromosomes in a homologous pair come together.
The chromatids of the two chromosomes wrap around each other

This process is called crossing-over

The attached pair of chromosomes are called a bivalent

The points where the chromatids are joined are called chiasmata

Parts of the chromatids can break off and exchange between the homologous chromosomes. (process of crossing-over)

The maternal and paternal chromosomes have now exchanged DNA

These are now recombinant chromosomes

Because these chromosomes have exchanged DNA, that means that they can exchange alleles

after crossing-over it
means that the recombinant chromosomes, each contain one chromatid with one allele and one chromatid with another allele ( A and B)

Since chiasmata can form at multiple points. So a large number of alleles can be exchanged.

This exchange of alleles is a major source of genetic variation in meiosis

Question 21

describe binary fission

Answer 21

Binary fission in prokaryotic cells involves:

• replication of the circular DNA and of plasmids
• division of the cytoplasm to produce two daughter cells, each
  with a single copy of the circular DNA and a variable number
  of copies of plasmids.

Question 22

where does binary fission take place

Answer 22

binary fission takes place in prokaryotic organisms

Question 23

is mitosis a controlled or uncontrolled process

Answer 23

mitosis is a controlled process

Question 24

what can uncontrolled cell division lead to

Answer 24

. Uncontrolled cell division can lead
to the formation of tumours and of cancers

malignant tumour = cancer
benign tumour = not cancerous

Question 25

how do many cancer treatments work

Answer 25

Many cancer
treatments are directed at controlling the rate of cell division.

Question 26

do viruses undergo cell division

explain your answer

Answer 26

Being non-living, viruses do not undergo cell division

Following
injection of their nucleic acid, the infected host cell replicates the
virus particles.