Cell Division

Question 1

Describe the features of Prophase.

Answer 1

• Nuclear membrane begins to breakdown
• Centrioles move to poles of the cell
• Chromatin supercoils and condense in chromosomes

Question 2

Describe the features of Metaphase.

Answer 2

• Spindle fibres form and attach to the centromere of chromosomes
• Chromosomes align at the equator

Question 3

Describe the features of Anaphase.

Answer 3

• Spindle fibres shorten
• Centromere splits
• Sister chromatids are separated
• Chromatids pulled to opposite poles of the cell

Question 4

Describe the features of Telophase.

Answer 4

• Nuclear membrane begins to reform

- Chromosomes unwind

Question 5

What is a homologous pair of chromosomes?

Answer 5

Two chromosomes that carry the same genes in the same loci/location

Question 6

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

Answer 6

Description, explanation; 
1. Examine large number of fields of view/many cells; 
2. To ensure representative sample
OR 
3. Repeat count
4. To ensure figures are correct
OR
5. Method to deal with part cells shown at edge/count only whole cells
6. To standardise counting

Question 7

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

Answer 7

1. Homologous chromosomes pair up
2. Maternal and paternal chromosomes are arranged in any order
3. During independent segregation
4. Crossing over
5. (Equal) lengths of chromatids are swapped between chromosomes
6. Produces new combination of alleles
7. Chromatids separated at meiosis II/ later

Question 8

Describe the process of crossing over and explain how it increases genetic diversity.

Answer 8

1. Homologous pairs of chromosomes associate/form a bivalent;
2. Chiasma(ta) form
3. (Equal) lengths of (non-sister) chromatids/alleles are exchanged;
4. Producing new combinations of alleles

Question 9

Give two differences between mitosis and meiosis.

Answer 9

Mitosis given first

1. One division, two divisions in meiosis
2. (Daughter) cells genetically identical, daughter cells genetically different in meiosis
3. Two cells produced, (usually) four cells produced in meiosis
4. Diploid to diploid/haploid to haploid, diploid to haploid in meiosis
5. Separation of homologous chromosomes only in meiosis
6. Crossing over only in meiosis
7. Independent segregation only in meiosis

Question 10

Describe binary fission in bacteria.

Answer 10

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