cell cycle and 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

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

Answer 6

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 7

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

Answer 7

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 8

Give two differences between mitosis and meiosis.

Answer 8

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 9

Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis.

Answer 9

DNA replication (during late interphase);
Two divisions;
Separation of homologous chromosomes (in first division); 4. Separation of (sister) chromatids (in second division);
Produces 4 (haploid) cells/nuclei;

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

What is a tumour? [2]

Answer 11

1- Mass of cells/tissue OR Abnormal cells/tissue;
2- Uncontrolled mitosis/cell division;

Question 12

Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).

Answer 12

1- Glycerol joined to two fatty acid tails Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
2- Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
3- Arrange to form a phospholipid bilayer; (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)