Cell Cycle and Mitosis

Question 1

Describe the features of Prophase

Answer 1

1. Nuclear membrane begins to breakdown;
2. Centrioles move to poles of the cell;
3. Chromatin supercoils and condense into chromosomes;

Question 2

Describe the features of Metaphase

Answer 2

1. Spidle fibres form;
2. Spindle fibres attach;
3. To the centromere of chromosomes;
4. Chromosomes align at the equator;

Question 3

Describe the features of Anaphase

Answer 3

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

Question 4

Describe the features of Telophase

Answer 4

1. Nuclear membrane begins to reform;
2. Chromosomes uncoil / unwind into chromatin;

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;

• To ensure representative sample;
  OR
• Repeat count;
  To ensure figures are correct;
  OR
• Method to deal with part cells shown at edge /count only whole cells;
  To standardise counting;

Question 7

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. [6]

Answer 7

1. Homologous chromosomes pair up;
2. maternal and paternal chromosomes are arranged in any order;
3. Independent segregation;
4. Crossing over;
5. (Equal) Portions 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);

Question 11

Explain how the chromosome number is halved during meiosis.

Answer 11

1. Homologous chromosomes (pair);
2. One of each (pair) goes to each (daughter) cell / to opposite poles;

Question 12

Name two ways in which meiosis produces genetic variation.

Answer 12

1. Independent segregation (of homologous chromosomes);
2. Crossing over / formation of chiasmata.

Question 13

Describe virus replication

Answer 13

1. Protein molecules on capsid attach to host cell surface membrane.
2. Virus genetic material enters cell cytoplasm
3. Viral nucleic acid is inserted into the host cells own nuclear DNA
4. Host cell is now infected.
5. Viral DNA is transcribed and translated into proteins
6. Host cell replicates the viral DNA
7. Genetic material and proteins are assembled into virions
8. Virion burst out of cell.