Cell division

Question 1

What is mitosis?

Answer 1

It is a form of nuclear division that produces daughter nuclei containing the same number of chromosomes as the parent nucleus. The daughter nuclei are genetically identical.

Question 2

What is growth?

Answer 2

It is a permanent increase in size. It is accompanied by cell division and differentiation to form tissues and organs .

Question 3

What are chromosomes made of?

Answer 3

Deoxyribonucleic acid(DNA).

Question 4

What does DNA store?

Answer 4

It stores all the information that a cell needs in order to grow and to carry out vital activities.

Question 5

How is DNA stored?

Answer 5

as genes.(sections of dna)

Question 6

Why is mitosis important?

Answer 6

1.For growth
New cells produced are genetically identical to existing cells
2. To repair worn-out body parts and wound healing .Ensures that damaged cells in organism are replaced by new cells identical to
original cells.
3. For asexual reproduction(production of genetically identical offspring)Applies to single cellular organisms like bacteria (binary fission), or vegetative reproduction in flowering plants.

Question 7

Why is it important to have genetically identical cells and fine control of replication?

Answer 7

To maintain genetic stability within populations of cells.

Question 8

What is the cell cycle

Answer 8

1. Interphase (DNA replication,
   centriole replication; not part
   of mitosis)
2. Mitosis (prophase,
   metaphase, anaphase,
   telophase)
3. Cytokinesis (cytoplasm is
   divided into two; not part of
   mitosis)

Question 9

What kind of cells undergo mitosis?

Answer 9

somatic cells(non-reproductive cells)

Question 10

What are the stages of mitosis?

Answer 10

Prophase
Metaphase
Anaphase
Telophase

Question 11

What happens during interphase?(mitosis)

Answer 11

Chromatin threads
replicate producing
two identical sister
chromatids attached at
the centromere, Cells still carry out
activities – absorbing
nutrients and building
up protoplasm. Nuclear envelope
and nucleolus still intact.

Question 12

what happens during prophase?(mitosis)

Answer 12

Chromatin condenses into chromosomes
Nuclear envelope and nucleolus
disappears. Centrioles begin migrating to opposite poles. A spindle forms with the spindle fibres extending from one pole of the cell to the other. Asters form around centrioles. Asters are made of microtubules.

Question 13

what happens during metaphase?(mitosis)

Answer 13

Chromosomes line up along the equatorial plane of the spindle. The centromere of each chromosome is attached on both sides to a spindle fibre. (its basically like in the middle of a spindle fibre, attached to a spindle fibre on both sides).

Question 14

What happens during anaphase?(mitosis)

Answer 14

spindle fibres shorten and pull the
sister chromatids apart to opposite poles of
the cell. Each separated sister chromatid is now considered a daughter chromosome.

Question 15

What happens during telophase?(mitosis)

Answer 15

spindle fibres break down. nuclear envelope reforms around chromosomes at each pole of the cell. A nucleolus reforms in each nucleus and the chromosomes uncoil to become thin chromatin threads.

Question 16

what happens during cytokinesis?

Answer 16

In animal cells, furrow appear in the cytoplasm between the two nuclei. The furrows deepen and two identical daughter cells are finally produced. In plant cells, a cell plate is formed between the two daughter nuclei, dividing the cell into two. The cell plate is formed by the fusion of small fluid-filled vesicles produced by the golgi apparatus.

Question 17

What are gametes?

Answer 17

They are reproductive cells that contain half the number of chromosomes as the normal body cells(eg sperm and ovum)

Question 18

What causes the gametes to contain half the numbers of chromosomes as the normal body cells?

Answer 18

In the sex organs, the cells undergo meiosis. This is called reduction division, because each of the daughter cells produced contains half the number of chromosomes as the parent cell.

Question 19

What are haploid cells?

Answer 19

cells that contain half the no.
of chromosomes as
parent cells, have one set(either male or female) of unpaired chromosomes found in gametes
(reproductive cells), produced by meiosis
(reductive division)

Question 20

What are diploid cells?

Answer 20

cells that contain the full no.
of chromosomes have 2 sets of paired
chromosomes (1 set
from each parent) produced by mitosis
or through fusion of gametes to give a
zygote.

Question 21

what are homologous chromosomes?

Answer 21

Have same size, shape, centromere position, staining pattern, sequence of genes. One homologue originates from male parent and another from female parent.During meiosis, homologous chromosomes separate. Gametes have only one set of unpaired
chromosomes. In diploid cells, there are 2 chromosomes for each chromosome number
Each of these pairs is called a homologous pair.

Question 22

Why is there a need to half the chromosome number before fertilisation?

Answer 22

To ensure that the diploid number is maintained from one generation to the next.

Question 23

how does meiosis and fertilisation lead to genetic variation?

Answer 23

1. Crossing over of chromatids in prophase, produces new combinations of genes in gametes
2. Independent assortment and segregation of
   chromosomes in metaphase I, Random positioning of each homologous pair of
   chromosomes at equator
3. Random combination of gametes during
   fertilisation, Fusion of any 2 gametes.

Question 24

What happens during interphase(meiosis)?

Answer 24

Chromatin threads replicate, producing two identical sister chromatids attached at the centromere. The pair of centrioles also divide

Question 25

What does the two different phases of meiosis hope to achieve?

Answer 25

Meiosis I (functions to separate
homologous chromosomes) Meiosis II (functions to separate sister chromatids)

Question 26

Do somatic cells have a haploid number or diploid number?

Answer 26

A human somatic cell has two sets of chromosomes, and is said to have a diploid (2n)
chromosome number.

Question 27

What happens during prophase I ?

Answer 27

chromatin condense and shorten to
become chromosomes. homologous chromosomes(one from the male parent, one from the female parent) pair up, this is known as synapsis. Chromatids of homologous chromosomes may cross and twist around one another. The point where they cross over one another is called a chiasma. crossing over occurs due to the strength of their coiling, where exchange of corresponding sections of DNA occur between non-sister chromatids in homologous chromosomes. Crossing over produces new combinations of alleles along the chromosomes. This increases genetic variation of the gametes. As chromosomes shorten further, homologous chromosomes appear to repel each other. Asters form around the centrioles which move apart to opposite poles of the cell. Spindle fibres form and Nuclear envelope disintegrates, and nucleolus disappears.

Question 28

What happens during metaphase I?

Answer 28

pairs of homologous chromosomes
arrange themselves along the
equatorial plane of the spindle. The two chromosomes of each pair face opposite poles of the cell. Each chromosome is attached to a spindle fibre. independent assortment is due to random orientation of each
homologous chromosome along the
equator. Maternal and paternal chromosomes could be segregated into either daughter
cell in different combinations.

Question 29

What happens during anaphase I?

Answer 29

homologous chromosomes separate
and are pulled to opposite poles of
the cell. spindle fibres shorten as this
happens

Question 30

What happens during telophase I?

Answer 30

nuclear envelope reforms around
chromosomes at each pole. spindle fibres break down. chromosomes uncoil and decondense to become chromatin after reaching opposite poles of the cell.

Question 31

What happens during cytokinesis I?

Answer 31

cytoplasm cleaves into two,
producing two daughter cells. Each daughter cell has a haploid (n) number of chromosomes. Centrioles divide.

Question 32

what happens during prophase II?

Answer 32

nuclear envelope breaks down. chromatin shorten and condense to
become chromosomes, spindle fibres form

Question 33

what happens during metaphase II?

Answer 33

chromosomes are aligned along the
equatorial plane of the spindle. the equatorial plane in metaphase II is perpendicular to the equatorial plane in metaphase I. (equatorial plane in metaphase II is horizontal and equatorial plane in metaphase I is vertical)

Question 34

What happens during anaphase II?

Answer 34

sister chromatids separate and are pulled to
opposite poles of the cell

Question 35

what happens during telophase II?

Answer 35

spindle fibres break down, nuclear envelope reforms, chromosomes decondense to
chromatin

Question 36

what happens during cytokinesis II?

Answer 36

cleavage of cytoplasm results in four
daughter cells, each daughter cell contains a
haploid (n) number of chromosomes

Question 37

why is meiosis important?

Answer 37

-meiosis produces haploid gametes(which maintains normal diploid number when male gamete fuses with female gamete)
-variation in gametes produced
occurs due to crossing over and independent assortment of chromosomes
Independant assortment: one chromosome from each pair can combine with either chromosome from another pair,, resulting in 4 different gametes being produced from two chromosomes.
variation increases the chance of survival of an organism.