Cell cycle, Mitosis and Meiosis

Question 1

List the stages of the cell cycle in order and outline what happens at each stage.

Answer 1

1. Interphase- Period of cell growth and DNA replication
2. Mitotic phase- mitosis and cytokenisis (cytoplasmic division)
3. G0- where the cell leaves the cycle either temporarily or permanently

Question 2

List the 3 stages of interphase in order

Answer 2

G1- first growth phase
S- synthesis phase
G2- Second growth phase

Question 3

Describe what happens during the G1 stage of interphase

Answer 3

G1- The first growth phase- proteins from which organelles are synthesised are produced and organelles are duplicated- cell increases in size

Question 4

Describe what happens during the S stage of interphase

Answer 4

S- synthesis phase- DNA is replicated in the nucleus

Question 5

Describe what happens during the G2 stage of interphase

Answer 5

G2- Second growth phase- the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors.

Question 6

List the 2 stages of the mitotic phase and outline what happens at each stage.

Answer 6

Mitosis- the cell divides

Cytokenisis- the cytoplasm divides and two cells are produced

Question 7

Describe the significance of G0 as a phase that cells enter when they leave the cell cycle.

Answer 7

It is the place where a cell leaves the cycle, reasons could be:

1. Differentiation
2. DNA of a cell may be damaged so it is no longer viable
3. As you age- the number of these cells in your body increases- linked to arthritis and cancer

Question 8

Outline the role of checkpoints to control the cell cycle.

Answer 8

Checkpoints are the control mechanisms of the cell cycle. They monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress to the next phase.

Question 9

State 3 examples of checkpoints in the cell cycle, where they occur and what is checked at each checkpoint.

Answer 9

1. G1 checkpoint- at the end of G1 before entry into S phase- checks- cell size, correct nutrients, growth factors and DNA damage
2. G2 checkpoint- at the end of G2 phase before the start of the mitotic phase- checks- Cell size, all DNA replicated correctly, DNA damage
3. Spindle assembly checkpoint- at the point in mitosis where all the chromosomes should be attached to spindles and have aligned- checks- chromosome attachment to spindle

Question 10

Outline the link between cell-cycle regulation and cancer.

Answer 10

Tumours are often the result of damage or spontaneous mutation of the genes that encode the proteins that are involved in regulating the cell cycle, including the checkpoint proteins.

Question 11

Define the term “mitosis”

Answer 11

A type of cell divisions where parent cell divides to produce two genetically identical daughter cells. It takes place in the mitotic phase of the cell cycle.

Question 12

Define the term “chromosome”

Answer 12

Structures of condensed and coiled DNA in the form of chromatin. Chromosomes become visible under the light microscope when cells are preparing to divide.

Question 13

Define the term “chromatid”

Answer 13

One arm of a double stranded chromosome

Question 14

Define the term “sister chromatids”

Answer 14

Sister chromatids are the two identical copies formed by the replication of a single chromosome, with both copies joined together by a centromere.

Question 15

Define the term centromere

Answer 15

The region at which two chromatids are held together

Question 16

Define the term centrioles

Answer 16

Component of the cytoskeleton of most eukaryotic cells composed of microtubules. They are involved in the development of spindle fibres in cell division.

Question 17

Define the term spindle fibres

Answer 17

Spindle fibres form a protein structure that divides the genetic material in a cell.

Question 18

Define the term homologous chromosomes

Answer 18

1. Pairs of matching chromosomes- each chromosome in the pair contains the same genes but different alleles.
2. One is maternal and one paternal
3. They are usually a similar length and contain centromere in the same position.
4. Pair up in meiosis 1 to form bivalents

Question 19

List the stages of mitosis in order.

Answer 19

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
5. (cytokenisis)

Question 20

Describe what happens in prophase

Answer 20

1. The chromosomes condense getting shorter and fatter.
2. Tiny bundles of protein called centrioles start moving to opposite ends of the cell forming a network of proteins fibres across it called the spindle.
3. The nuclear envelope breaks down and chromosomes lie free in the cytoplasm

Question 21

Describe what happens in metaphase

Answer 21

1. The chromosomes line up along the middle of the cell (metaphase plate) and become attached to the spindle by their centromere
2. At the checkpoint the cell checks that the chromosomes are attached to the spindle before mitosis can continue.

Question 22

Describe what happens in anaphase

Answer 22

1. The centromeres divide, separating each pair of sister chromatids.
2. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first.

Question 23

Describe what happens in telophase

Answer 23

1. The chromatids reach the opposite poles on the spindle.
2. They uncoil and become long and thin again- chromosomes again
3. A nuclear envelope forms around each group of chromosomes, so there are now two nuclei

Question 24

Describe what happens during cytokenisis

Answer 24

1. The cytoplasm divides- in animal cells, a cleavage furrow forms and the cell-surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle.
2. There are now two daughter cells that are genetically identical to the original cell and to each other.
3. Cytokenisis begins in anaphase and ends in telophase. But is separate to the process of mitosis.

Question 25

Explain the role of the centrioles and spindle fibres in mitosis.

Answer 25

Centrioles form a spindle fibres in prophase.

Spindle fibres move the chromosomes to form a plane in the centre of the cell and then pull the chromatids apart.

Question 26

Describe cytokenisis in plant cells

Answer 26

Plant-

1. Have cell walls so can’t form cleavage furrows.
2. Vesicles from the Golgi apparatus begin to assemble in the same place where the metaphase plate was formed.
3. The vesicles fuse with each other and the cell surface membrane dividing the cell into two.
4. New sections of cell wall then form along new sections of membrane.

Question 27

Identify the stages of mitosis (and the cell cycle) in photomicrographs or diagrams of cells.

Answer 27

Use an online quiz.

Question 28

Explain the reasons for doing each step in a method to produce a root tip squash to view plant cells in different stages of the cell cycle.

Answer 28

1. Treat the very tips of the roots with HCl
2. Then breaking them open and spreading the cells thinly on a microscope slide using a mounted needle.
3. A few drops of stain are then added to the spread out cells before they are physically squashed beneath a coverslip.

Question 29

Calculate the mitotic index of a sample of dividing cells.

Answer 29

mitotic index= number of cells with condensed chromosomes/ total number of cells * 100

Question 30

Explain how to calculate the length of time each stage in the cell cycle takes given a sample of cells undergoing mitotic cell division and the total duration of the cell cycle.

Answer 30

1. find number of cells in that stage
2. Divide it by the total number of cells and multiply by 100 to get a percentage.
3. Find the amount of time in one stage by multiplying percentage by the total time spent

Question 31

Describe the purpose of mitotic cell division.

Answer 31

Mitosis ensures that both daughter cells produces when a parent cell divides are genetically identical. It is needed in growth, replacement and repair of tissues as well as asexual reproduction.

Question 32

List 4 roles of mitotic cell division.

Answer 32

1. Grow new cells to repair damage
2. grow new cells
3. Grow new cells to replace sheded skin cells
4. Asexual reproduction

Question 33

Define the term “diploid”

Answer 33

Normal chromosome number- two chromosomes of each type- one inherited from each parent

Question 34

Define the term “haploid”

Answer 34

Half the normal chromosome number- one chromosome of each type.

Question 35

Define the term “gamete”

Answer 35

Haploid sex cells produced by meiosis in organisms that reproduce sexually.

Question 36

Define the term zygote

Answer 36

The initial diploid cell formed when two gametes are joined by means of sexual reproduction. Earliest stage of embryonic development.

Question 37

Define the term meiosis

Answer 37

A type of cell division where the nucleus divides twice resulting in halving the number of chromosomes to create four genetically different haploid cells.

Question 38

Define the term reduction division

Answer 38

Cell division resulting in the production of haploid cells from a diploid cell- meiosis.

Question 39

Explain the role of meiosis in life cycles.

Answer 39

Meiosis forms gametes which contains half of the chromosome number of the parent cell- haploid.
Cells formed by meiosis are geneticallly different because each new cell ends up with a different combination of chromosomes.

Question 40

State 2 ways in which meiosis produces variation.

Answer 40

1. Crossing over of chromatids during prophase 1.

2. Independent assortment of chromosomes

Question 41

Suggest the importance of the creation of different allele combinations in populations.

Answer 41

It produces genetic variation so it allows species to adapt to changes in their environment. It makes gametes by halving the number of chromosomes. This means that species can adapt.

Question 42

Define the term bivalent

Answer 42

The name for two homologous chromosomes that have paired up in prophase 1 of meiosis.

Question 43

Define the term crossing over

Answer 43

The exchange of part of a chromosome between chromatids of homologous pairs- occurs at chiasmata

Question 44

Define the term chiasma (chiasmata)

Answer 44

The points where two homologous chromosomes have become twisted around each other and break in order to exchange a section of the chromatid.

Question 45

Define the term recombinant chromatid

Answer 45

A chromatid that has undergone crossing over so that it now possesses some alleles from the maternal chromosome and some from the paternal chromosome.

Question 46

Define the term random independant assortment

Answer 46

The fact that which daughter cell a chromosome ends up in after meiosis 1 or a chromatid after meiosis 2 is random and independent of the fate of chromosomes from other homologous pairs.

Question 47

Draw, label and annotate a diagram summary diagram of meiosis simplified to a single homologous pair (without any crossing over).

Answer 47

Draw it and look it up

Question 48

State the stages of meiosis in order.

Answer 48

1. Prophase 1
2. Metaphase 1
3. Anaphase 1
4. Telophase 1
5. Prophase 2
6. Metaphase2
7. Anaphase 2
   8 Telophase 2

Question 49

Describe what happens during the prophase 1 stage of meiosis

Answer 49

1. The nuclear envelope disintegrates, the nucleolus disappears and the spindle formation begins.
2. The chromosomes condense and homologous chromosomes pair up forming bivalents.
3. Chromosomes are large molecules of DNA and moving through them the cytoplasm as they are brought together results in the chromatids entangling- crossing over.

Question 50

Describe what happens during the Metaphase 1 stage of meiosis

Answer 50

1. The homologous pairs line up across the metaphase plate and attach to the spindle fibres by their centromeres.
2. The orientation of each homologous pair is random and independent of any other homologous pair- independent assortment which can result in many different combinations of alleles facing the poles.

Question 51

Describe what happens during the Anaphase 1 stage of meiosis

Answer 51

1. The spindles contract, pulling the pairs apart- one chromosome goes to each pole. the chromatids stay attached to each other.
2. Sections of DNA on chromatids which became entangled during crossing over now break off and rejoin- some resulting in the exchange of DNA. Forms recombinant DNA.

Question 52

Describe what happens during the Telophase 1 stage of meiosis

Answer 52

1. The nuclear envelope forms around each group of chromosomes
2. Cytokenisis- the division of the cytoplasm occurs and two haploid daughter cells are produced

Question 53

Describe what happens during the Prophase 2 stage of meiosis

Answer 53

1. The chromosomes which still consist of two chromatids condense and become visible.
2. The nuclear envelope breaks down and spindle formation begins.

Question 54

Describe what happens during the Metaphase 2 stage of meiosis

Answer 54

1. The individual chromosomes assemble on the metaphase plate as in mitosis.
2. Due to crossing over the chromatids are no longer identical so there is independent assortment again and more genetic variation produced.

Question 55

Describe what happens during the Anaphase 2 stage of meiosis

Answer 55

1. Results in the chromatids of the individual chromosomes being pulled to opposite poles after division of centromeres.

Question 56

Describe what happens during the Telpphase 2 stage of meiosis

Answer 56

1. The chromatids assemble at the poles as in mitosis.
2. The chromosomes uncoil and form chromatin again
3. The nuclear envelope reforms and the nucleolus becomes visible.
4. Cytokenisis results in the division of the cells forming 4 daughter cells- haploid and genetically different.

Question 57

Identify the stage of meiosis a cell is in from diagrams and photos of cells.

Answer 57

Look at diagrams and test.

Question 58

Describe crossing over

Answer 58

Homologous pairs of chromosomes come together and pair up in Prophase 1.
The chromatids twist around each other and bits of chromatids swap over.
The chromatids still contain the same genes but now have a different combination of alleles.

Question 59

Describe random assortment of chromosomes

Answer 59

When homologous pairs line up in metaphase 1 and are separated in anaphase 1, it’s completely random which chromosome from each pair ends up in which daughter cell.

Question 60

Draw a table to compare meiosis I, meiosis II and mitosis.

Answer 60

1. What lines up in the middle of the cell- M1-bivalents, M2- chromosomes, M-Chromosomes
2. Crossing over? Only in M1
3. Daughter cell number- M1-2, M2-4, M-2
4. Homologous pairs- Only in M1
5. DNA duplicated- In M1 and M during interphase
6. Diploid or haploid- M1- Hap, M2- Hap, M- Dip
7. Independent assortment- In M1 and M2