Cell Division

Question 1

How does life continue ?

Answer 1

• All cells originate from pre-existing cells.
• For life to continue, genetic information must be transferred to the next generation.

Question 2

What is the process of asexual reproduction?

Answer 2

• New individuals are formed from just one parent.
• The offspring are genetically identical to the parent and each other.
• Involves mitosis.

Question 3

What is mitosis?

Answer 3

A type of nuclear division in somatic cells that maintains the parental diploid number of chromosomes in the daughter cells; it is the basis of bodily growth and asexual reproduction in many eukaryotic species

Question 4

what is the first stage of mitosis ?

Answer 4

Interphase

Question 5

What happens during interphase ?

Answer 5

• Centrosomes and DNA are replicated.
• DNA begins to condense.
• In a human cell this stage takes approx 22 hours.

Question 6

what is the second stage of mitosis ?

Answer 6

Early prophase

Question 7

What happens during early prophase ?

Answer 7

• Chromosomes continue to condense, making them easily visible under the light microscope.
• The nuclear membrane slowly starts to disintegrate.
• The cell completes the prophase stage in 19 minutes approx.

Question 8

What is the third stage of mitosis?

Answer 8

Late prophase

Question 9

What happens during late prophase?

Answer 9

• Chromatids visible as chromosomes shorten and thicken.
• Nucleolus disappears.
• Nuclear envelope disappears.

Question 10

What is the fourth stage of mitosis?

Answer 10

Metaphase

Question 11

What happens during metaphase?

Answer 11

• The spindles are fully developed and are made up of a mixture of microtubules and proteins.
• The paired chromosomes (chromatids) are aligned across the equator of the cell.
• The spindles extend from the poles at either end of the cell and attach themselves to the chromatids aligning them exactly in the centre of the cell separating the two poles.
• Over time each chromosome splits longitudinally into two identical chromatids.

Question 12

What is the fifth stage of mitosis?

Answer 12

Anaphase

Question 13

What happens during anaphase?

Answer 13

The chromatids abruptly separate and move towards the spindle poles. This is achieved by shortening of the microtubules, and forces are mainly exerted at the microtubules.

Question 14

What is the final stage of mitosis?

Answer 14

Telophase

Question 15

What happens during telophase?

Answer 15

• Two new nucleoli and nuclear envelopes form using fragments of the parent cell’s nuclear membrane, and the chromatin fibres from each chromosome uncoil inside them.
• Finally, the mitotic spindles disappear and mitosis is finished, chromosomes regain their threadlike form.

Question 16

What is the final product of mitosis?

Answer 16

Cytokinesis

Question 17

What happens during cytokinesis ?

Answer 17

• The cytoplasm divides between the two daughter cells in order to form two relatively complete cells.
• This stage also includes the division of the cell membrane, creating two structurally independent cells.

Question 18

What happens during cytokinesis in plants ?

Answer 18

• involves the formation of a cell plate, cellulose is deposited on the cell plate to complete the cell walls of the two new daughter cells.

Question 19

What happens during cytokinesis in animals?

Answer 19

a cleavage furrow is created.

Question 20

What is asexual reproduction in prokaryotes ?

Answer 20

Binary Fission

Question 21

What happens during binary fission ?

Answer 21

• involves division of the parent body into two, fairly equal parts to produce two identical cells.
• Has no spindle
• Fast

Question 22

What is Binary fission ?

Answer 22

• The division of a cell into two cells without mitosis, a prokaryotic cell undergoes binary fission to form two identical daughter cells, a form of asexual reproduction

Question 23

What are gametes ?

Answer 23

New individuals are formed by the joining of two sex cells

Question 24

The joining of two gametes is called ?

Answer 24

Fertilisation

Question 25

During fertilisation what is formed?

Answer 25

Zygote

Question 26

How do you increase variation in a genotype?

Answer 26

The offspring are genetically different from their parents and each other

Question 27

How are gametes formed ?

Answer 27

meiosis

Question 28

What is meiosis ?

Answer 28

the process in eukaryotic, sexually-reproducing organisms that reduces the number of chromosomes in a cell before reproduction.

Question 29

what is the process of meiosis ?

Answer 29

A type of cellular division in sexually reproducing organisms that involves two rounds of cell division, but only one round of DNA replication; during meiosis the chromosome number of a cell is halved so that the daughter cells are haploid; meiosis is the basis of gamete formation

Question 29

What happens during interphase in meiosis ?

Answer 29

- Chromosomes (DNA) replicates - Each duplicated chromosome consists of two identical sister chromatids attached at their centromeres - Centriole pairs also replicate - Nucleus and nucleolus visible

Question 29

What are tetrads ?

Answer 29

Homologous pairs that carry genes controlling the same inherited traits

Question 30

What happens during prophase 1

Answer 30

- The longest and most complex phase - Chromosomes condense - Synapsis occurs: homologous chromosomes come together to form a tetrad - Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids)

Question 30

What is a homologous chromosomes ?

Answer 30

Pair of chromosomes (maternal and paternal) that are similar in shape and size

Question 30

What is a locus?

Answer 30

position of the gene

Question 31

What is the process of crossing over ?

Answer 31

- Crossing over may occur between non-sister chromatids at the chiasmata - Crossing over: segments of non-sister chromatids break and reattach to the other chromatid - Chiasmata (chiasma) are the sites of crossing over

Question 32

What happens during metaphase 1?

Answer 32

- Tetrads align on the metaphase plate. - INDEPENDENT ASSORTMENT OCCURS: The orientation of homologous pairs to poles is random. -> Variation

Question 33

what happens during anaphase 1?

Answer 33

- Homologous chromosomes separate and move towards the poles. - Sister chromatids remain attached at their centromeres.

Question 34

what happens during Telophase 1?

Answer 34

- Each pole now has a haploid set of chromosomes. -Cytokinesis occurs and two haploid daughter cells are formed.

Question 35

What happens during prophase II ?

Answer 35

-Spindles start to form, usually at right angles to one formed in meiosis I

Question 36

What happens during metaphase II?

Answer 36

-Chromosomes arrange themselves on the equator

Question 37

What happens during Anaphase II?

Answer 37

- Chromatids pull apart and move to opposite poles

Question 38

What happens during telophase II ?

Answer 38

- Nuclei form - Cytokinesis occurs

Question 39

What is the significance of meiosis?

Answer 39

- Halving the chromosome number ensures that when gametes with the haploid number fuse to form a zygote the normal diploid number is restored.

Question 40

What is fertilisation?

Answer 40

The fusion of haploid male and female gametes during sexual reproduction to produce a diploid zygote; the random union of gametes is known as random fertilisation

Question 41

What are the two types of fertilaistion?

Answer 41

- internal fertilisation - external fertilisation

Question 42

What is internal fertilsation?

Answer 42

- When the sperm and ovum unite inside the female’s body.

Question 43

What is external fertilisation?

Answer 43

- When the sperm and ovum unite outside the female’s body.