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;
. 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

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

. Homologous chromosomes pair up;
. maternal and paternal chromosomes are arranged in any order;
. Independent segregation;
. Crossing over;
. (Equal) Portions of chromatids are swapped between chromosomes;
. Produces new combination of alleles;
. Chromatids separated at meiosis II/ later;

Question 8

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

Answer 8

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

Question 9

Give two differences between mitosis and meiosis.

Answer 9

Mitosis given first
. One division, two divisions in meiosis;
. (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
. Two cells produced, (usually) four cells produced in meiosis;
. Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
. Separation of homologous chromosomes only in meiosis;
. Crossing over only in meiosis;
. Independent segregation only in meiosis;

Question 10

Describe binary fission in bacteria.

Answer 10

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