12.5 Cell Cycle and Division

Question 1

When in the cell cycle does DNA replication occur?

Answer 1

Occurs during the interphase of the cell cycle.

Question 2

Finish the sentence: Mitosis is a _____ division.

Answer 2

Nuclear

Question 3

Briefly explain mitosis.

Answer 3

The part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with identical copies of DNA produced by the parent cell during DNA replication.

Question 4

Explain the 3 main stages of interphase.

Answer 4

G1 phase- protein synthesises, and the cell increases in size.
S phase- DNA replication by semi-conservative DNA replication
G2 phase- Cell gets ready for divisions, synthesis, and stores of ATP. New organelles synthesised (additional growth).

Question 5

Explain the behaviour of chromosomes during interphase.

Answer 5

Chromosomes are not yet visible.

Question 6

What is a gene?

Answer 6

A section of DNA which codes for a specific polypeptide/protein.

Question 7

What is a chromosome?

Answer 7

An independent DNA molecule which has been supercoiled into a condensed form.

Question 8

What is mitosis used for?

Answer 8

Increasing cell numbers and growth of an organism.
Repair of damaged tissues (not cells).
Replacement of worn out/dead cells.

Question 9

Describe the features of Prophase

Answer 9

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

Question 10

Describe the features of Metaphase

Answer 10

Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;

Question 11

Describe the features of Anaphase

Answer 11

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

Question 12

Describe the features of Telophase

Answer 12

Nuclear membrane begins to reform;
Chromosomes unwind;

Question 13

What is a homologous pair of chromosomes?

Answer 13

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

Question 14

Explain what is meant by cytokinesis.

Answer 14

Once the nuclear material has divided, the cell surface membrane pinches together.
The cytoplasm divides forming two daughter cells.

Question 15

What is the role of the spindle fibres?

Answer 15

Attach to centromeres and separate sister chromatids and pull them to opposite poles.

Question 16

What happens if mitosis goes wrong?

Answer 16

Mutations can cause uncontrolled cell division, leading to the formation of tumours and cancers.
Many cancer treatments are directed at controlling the rate of cell divisions and inhibiting this cell division.

Question 17

What are tumour suppressor genes?

Answer 17

Code for proteins that slow down the cell cycle.

Question 18

What are proto-onco genes?

Answer 18

Code for proteins that speed up the cell cycle

Question 19

What type of cell division occurs in prokaryotes (bacteria)?

Answer 19

Binary fission.

Question 20

Describe binary fission in bacteria.

Answer 20

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

Question 21

Do viruses undergo cell division?

Answer 21

Viruses do not undergo cell division as there are non-living.

Question 22

How do virus particles replicate?

Answer 22

Following injection of their nucleic acid (single or double stranded DNA/RNA), the infected host cell replicates the virus particle.

Question 23

Viruses can only replicate inside host cells. Explain why.

Answer 23

They use the host cells enzymes to replicate and transcribe viral DNA and translate viral proteins, making more virus particles, which then burst out of the cell.

Question 24

Explain how viruses replicate using host cells.

Answer 24

• The specifically complementary attachment proteins on capsid attach to (the receptors on) the cell surface membrane of the host cells.
• The virus genetic material enters the cell cytoplasm.
• The viruses DNA/RNA is inserted into the host cells own DNA. Host cell is now infected.
• Viral DNA is transcribed and translated into proteins. Cell replicates viral DNA.
• Genetic material and protein coats assembled into virions which eventually burst out of the cell, often destroying it.

Question 25

If a virus has RNA as its genetic material, what is it called?

Answer 25

Retrovirus

Question 26

What is the mitotic index?

Answer 26

Proportion of cells undergoing cell division.
Greater value= faster rate of cell division.

Question 27

Give the mitotic index equation.

Answer 27

MI= (number of cells with condensed chromosomes)/(total number of cells) x 100/time of one cell cycle

Question 28

Give the serial dilution equation.

Answer 28

M1 x V1 = M2 x V2
M1 -Desired diluted concentration
V1 -Desired volume
M2 -Original concentration
V2 -Unknown volume of stock solution

Question 29

Briefly explain the process of meiosis.

Answer 29

• Form of cell division that is used by diploid organisms to form haploid gametes.
• Increases variation- 4 genetically different daughter cells produced.
• For sexual reproduction.

Question 30

What happens in the first meiotic division?

Answer 30

Homologous chromosomes pair up and are separated.

Question 31

What happens in the second meiotic division?

Answer 31

Chromatids are separated.

Question 32

What are the two processes in which meiosis increases genetic variation between the daughter cells in meiosis 1?

Answer 32

• Crossing over between non-sister chromatids of homologous chromosomes.
• Independent segregation of homologous chromosomes during meiosis.

Question 33

Explain the process of crossing over.

Answer 33

• Homologous chromosomes pair to form bivalents.
• Chiasmata form by chromosomes entangling.
• Equal lengths of non-sister chromatids exchanged which creates new combo’s of alleles.

Question 34

Explain the process of independent segregation.

Answer 34

• Occurs during metaphase of first division.
• Homologous chromosomes attach to spindle fibres and pair up randomly along equator and can be reshuffled in any combination.
• Chromosomes separate randomly.
• Gametes may receive different combinations of maternal and paternal chromosomes.

Question 35

Give two differences between mitosis and meiosis.

Answer 35

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 36

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 36

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 37

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

Answer 37

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 38

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

Answer 38

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;