Cell Cycle & Cell Division

Question 1

Describe the features of prophase (3)

Answer 1

1. Nuclear membrane begins to breakdown
2. Centrioles move to poles of the cell
3. Chromosomes supercoil and condense and become visible

Question 2

Describe the features of metaphase (3)

Answer 2

A
1. Spindle fibres form and attach
2. To centromere of chromosomes
3. Chromosomes align at the equator of cell

Question 3

Describe the features of anaphase (3)

Answer 3

1. Spindle fibres shorten
2. Centromere splits
3. Sister chromatids are separated and pulled to opposite poles of the cell

Question 4

Describe the features of telophase (2)

Answer 4

1. Nuclear membrane begins to reform
2. Chromosomes unwind and become thinner

Question 5

Q
Describe the appearance and behaviour of chromosomes during mitosis (5)

Answer 5

A
1. During prophase, chromosomes supercoil and condense to become visible
2. Chromosomes appear as 2 identical sister chromatids joined by a centromere
3. During metaphase, chromosomes line up at the equator of the cell
4. Chromosomes attach to spindle fibres
5. By their centromere
6. During anaphase, the centromere splits
7. Sister chromatids are pulled to opposite poles of the cell making a V shape
8. During telophase, chromatids uncoil/unwind and become thinner

Question 6

Formula to work out Mitotic Index?

Answer 6

(number of cells with condensed chromosomes/total number of cells) x 100

Question 7

What is a homologous pair of chromosomes? (1)

Answer 7

A
two chromosomes that carry the same genes in the same loci

Question 8

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for his root tip was accurate. (2)

Answer 8

1. Examine large number of cells
2. To ensure representative sample
   OR
3. Repeat count
4. To ensure figures are correct
   OR
5. Method to deal with parts of cell showing at edge /count only whole cells
6. To standardise counting

Question 9

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. (5)

Answer 9

1. Homologous chromosomes pair up
2. Maternal and paternal chromosomes are arranged in any order
3. Independent segregation
4. Crossing over
5. Equal lengths of alleles are exchanged between chromosomes
6. Produces new combination of alleles
7. Chromatids separated at meiosis II

Question 10

Describe the process of crossing over and explain how it increases genetic diversity (4)

Answer 10

1. Homologous pairs of chromosomes form a bivalent
2. Chiasmata form
3. Equal lengths of alleles are exchanged
4. Producing new combinations of alleles

Question 11

Describe and explain the processes that occur during meiosis that increase genetic variation (5)

Answer 11

1. Homologous chromosomes form a bivalent
2. Independent segregation occurs
3. Maternal and paternal chromosomes are reshuffled in any combination on the equator
4. Crossing over leads to equal lengths of alleles being exchanged
5. Creates new combination of alleles

Question 12

Give two differences between mitosis and meiosis (2)

Answer 12

1. Mitosis involves one division whereas meiosis involves two divisions
2. Mitosis produces genetically identical daughter cells whereas meiosis produces genetically different daughter cells
3. Mitosis produces 2 cells whereas meiosis produces 4 cells
4. Mitosis involves diploid to diploid or haploid to haploid whereas meiosis involves diploid to haploid
5. Separation of homologous chromosomes only in meiosis
6. Crossing over only in meiosis
7. Independent segregation only in meiosis

Question 13

Describe binary fission in bacteria (3)

Answer 13

A
1. Replication of (circular) DNA
2. Replication of plasmids
3. Division of cytoplasm (to produce daughter cells)