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

Spidle fibres form;
Spindle fibres 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

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 5

Description; Explanation;
E.g, 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 6

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.
Describe the process of crossing over and explain how it increases genetic diversity

Answer 6

. 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;

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 7

Give two differences between mitosis and meiosis.

Answer 7

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 8

Describe binary fission in bacteria.

Answer 8

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

Question 9

HIV replication

Answer 9

the protein molecules on the capsid attaches to the cell surface membrane on the host cell
the virus genetic material enters the cells cytoplasm
the viruses nucleic acid is inserted into the host cells nuclear DNA
the host cell is now infected
the viral DNA is transcribed and translated into proteins
the cell replicates the viral DNA