2.6 Cell division

Question 1

How do prokaryotes and eukaryotes replicate/reproduce?

Answer 1

-Prokaryotes replicate via binary fission whereas eukaryotes do it via mitosis

Question 2

What is the significance of mitosis?

Answer 2

-Growth of multicellular organisms: allows the unicellular zygote to grow into a multicellular organism
-Replacement of cells: as cells are constantly dying they need to be continuously replaced by genetically identical cells
-Asexual reproduction: allows plants to grow off from the parent and detach

Question 3

When is chromatin condensed and decondensed? and why?

Answer 3

-Chromatin is decondensed for most of its life, its long thin strings which allow it to be accessed easily by replication machinery
-Chromatin condenses when the cell divides and separates into chromosomes

Question 4

Describe the stages of interphase?

Answer 4

-Gap 1: Cell grows, increases size, doubles organelles, undergoes biosynthesis (e.g making enzymes needed)
-S phase: chromosomes replicate
-Gap 2-cells continues to grow in size, energy stores increase and special chemicals check cell is ready for mitosis

Question 5

What is interphase: gap 0 and why does it occur?

Answer 5

-When a cell leaves the cell cycle
-Differentiated cells cannot divide so undergo Gap 0
-Damaged DNA-cell can’t function so cell undergoes apoptosis (programmed cell death)
-Senescence: cells can only divide a limited amount of times

Question 6

When do checkpoints happen in interphase to check there isn’t any mistakes?

Answer 6

-Gap 1,Gap 2 and during spindle assembly

Question 7

What are the stages of mitosis in order?

Answer 7

-Prophase, Metaphase, Anaphase, Telophase and then cytokinesis

Question 8

What happens during Prophase?(Mitosis)

Answer 8

-Chromatin condense and become visible
-Two centrioles migrate to opposite poles of the cell and microtubules develop spindle shaped structures across the cell
-Nuclear envelope breaks down

Question 9

What happens during metaphase?(Mitosis)

Answer 9

-Microtubules attach to the centromere
-Chromosomes are pulled to the equator or metaphase plate, lined up, and are held there.

Question 10

What happens during Anaphase?(Mitosis)

Answer 10

-Centromere of chromatids split and chromatid splits into chromosomes and each pair is pulled to opposite sides as the spindle fibres shorten

Question 11

What happens during Telophase?(Mitosis)

Answer 11

-The two sets of chromosomes at each pole have a nuclear envelope form around them
-Spindle fibers disintegrate

Question 12

What happens during cytokinesis?(Mitosis)

Answer 12

-Animal cells: a cleavage furrow forms around the middle of the cell and is pulled in by the cytoskeleton
-Plant cells: cell wall prevents a cleavage furrow so vesicles from the golgi apparatus form along the equator and fuse with each other into a cell membrane splitting the cell into two.

Question 13

What is the difference between mitosis and meiosis?

Answer 13

-Mitosis is for growth and repair, asexual reproduction whereas meiosis produces gametes for sexual reproduction
-Mitosis produces diploid cells whereas meiosis produces haploid cells which are genetically indifferent from diploid cells

Question 14

What are the stages of meiosis in order?

Answer 14

Prophase 1, Metaphase 1, Anaphase 1, Telophase 1, Cytokinesis, Prophase 2, Metaphase 2, Anaphase 2, Telophase 2 and cytokenesis

Question 15

What is the differences in stages between mitosis and meiosis?

Answer 15

Prophase- the same but in meiosis (Prophase 1) homologous chromosomes form pairs called bivalents
Metaphase- the same but in metaphase 1 and 2 there is an independent assortment of chromosomes
Anaphase- anaphase 1 chromatids stay joined together and anaphase 2 chromosomes are pulled apart
Telophase- the same

Question 16

What is crossing over?

Answer 16

-In meiosis a homologous pair of chromosomes cross over at a point called the chiasma to increase genetic variation