Chapter 3

ANSWERS SCHEME : PAST YEARS QUESTIONS 2020/2021

CHAPTER 3
1.








A B
FIGURE 1

The following questions are based on FIGURE 1.

(a) Which chromosome would be present in a cell in Prophase I?
A
[1 mark]
(b) What are the important events that happen during Prophase I?
 Pairing of homologous chromosome/ Synapsis
 Cross over between non sister chromatid/ homologous chromosome
 Centriol/ centrosome move to opposite poles
 shortening and thickening of chromosome
 form spindle fiber
 (choose any THREE appropriate answers)

[3 marks]
(c) Compare the process of mitosis and meiosis.

Mitosis Meiosis
Occurs in soma cell Occurs in gonad cells (ovaries in females and
testes in males)
Conserve chromosome number (2n) Reduce the chromosome number by half (n)
By end of Prophase, no synapsis occur to form Synapsis occurs to form bivalent/ homologous
bivalent chromosome during Prophase 1
No chiasma occurs so there is no crossing over Some chiasma occurs after crossing over
Genetic contain in daughter cell is identical with Genetic contain in daughter cell is not identical
parent cell as the parent cell
At the end of cell division, two diploid daughter At the end of cell division, four haploid
cells produce daughter cell produce
Cytokinesis occurs once Cytokinesis occurs twice
Daughter cells can undergo mitosis and meiosis Daughter cell can undergo mitosis but not
meiosis
[6 marks]

(d) What are the major phases that involved in the cell cycle?
 Interphase
 Mitotic phase
[2 marks]

2. FIGURE 1 shows several stages of cell division in an organism.











FIGURE 1

(a) Choose the diagram (A-F) that best match the following description.
(i) Metaphase of mitosis : A
(ii) Anaphase II of meiosis: C
(iii) Replication of DNA: B
(iv) Anaphase of mitosis: D
(v) Arrangement of bivalents at the equator: E
[5 marks]

(b) List TWO differences in the behaviour of chromosomes in mitosis
compared to meiosis.

Mitosis Meiosis
There is no synapsis/ pairing between There is a synapsis/ pairing of homologous
homologous chromosomes chromosomes

There is no formation of chiasmata Chiasmata may be formed

There is no crossing over between Crossing over may occur between
chromosomes chromosomes.

Separation of chromatid during Separation of homologous chromosome
anaphase during anaphase I

[2 marks]

(c) The chromosome number of a chicken is 78.

(i) How many chromosomes does the chicken inherit from each parent?
39

(ii) How many chromosomes are in the chicken’s gamete?
39

(iii) How many chromosomes will be in somatic cell of the chicken?
78
[3 marks]

3. FIGURE 1 shows chromosomal behavior during two stages of cell division in an organism.













FIGURE 1
i. Name the stages shown in FIGURE 1.
P: Anaphase I
Q: Anaphase II / Anaphase
[2 marks]
ii. Describe the differences between stages P and Q.

Anaphase I Anaphase II
(a pair) homologous chromosomes being Sister chromatids being pulled apart/
pulled apart/ separate to the opposite separate to the opposite poles.
poles // sister chromatids are not
separated
Centromeres are not separated Centromeres are separated
[2 marks]
List TWO differences between mitosis and meiosis.

Properties Mitosis Meiosis
DNA replication Occurs during interphase Occurs during interphase
before mitosis begins before meiosis I begins
Number of divisions Once Twice(meiosis I, meiosis II)

Synapsis( of Does not occur Occurs during prophase I,
homologous (forming tetrads/bivalent)
chromosomes)
Number of daughter Two Four
cells
Number of chromosome Diploid/2n Haploid/n
in daughter cells
Genetic composition Identical to parent cell Not identical to parent cell
Crossing over Does not occur Occur
[2 marks]

Give TWO mechanisms on how meiosis can lead to variation. Name the stages in
meiosis where they occur.

Mechanism Stage in meiosis
Crossing over Prophase I
Independent assortment of chromosomes Metaphase I
[4 marks]

4. FIGURE 1 shows two cells, X and Y, in a flowering plant. The parent cell has 4 chromosomes.
each cell shows the position of chromosomes during the process of cell division.













FIGURE 1

a) i. Name the type of cell division that occurs in cell X and Y.
Cell X: Meiosis
Cell Y: Mitosis
[2 marks]

ii. Name the stage in cell X and Y that takes place during the cell division.
Cell X: Anaphase I
Cell Y: Anaphase
[2 marks]

b) What happen to the chromosomes in cell X and Y during the stage in (a)(ii)?
- Homologous chromosomes separate and move to the opposite poles in cell X
- Sister chromatids separate and move to the opposite poles in cell Y
[2 marks]
c) How many chromosomes in each daughter cell at the end of the cell division?
Cell X: 2
Cell Y: 4
[2 marks]
d) Give ONE example for cells X and Y.
Cell X: anther // ovary / ovule
Cell Y: root tip // shoot apex // cambium
(do not accept other somatic plant cells)


5. FIGURE 1 shows two stages in cell division

B
A






















CELL 1 CELL 2

FIGURE 1

a. Identify the stages for cell 1 and cell 2.
Cell 1: Metaphase
Cell 2: Anaphase
[2 marks]
b. Name the structures labeled A and B.
A: Spindle fibre/ (Kinetochore) microtubules/ microtubules
B: Centriole

[2 marks]

c. State the chromosomal behavior for cell 1 and cell 2.
Cell 1: Chromosomes/ sister chromatid align at the metaphase plate
Cell 2: Sister chromatids separate and move to the opposite poles
[2 marks]

d. How many chromosomes in each daughter cell at the end of the cell division for
cell 1 and cell 2?
Cell 1: 2
Cell 2: 3
[2 marks]

e. State TWO importance of mitosis in multicellular organism.
- To increase cell numbers in tissues and organ / growth
- To repair worn out/ damaged cells/ cell replacement/ regeneration
- To facilitate asexual reproduction/ produce identical cell
- Genetic stability
[2 marks]


6. FIGURE 1 shows the cell cycle.













FIGURE 1

(a) i. Identify phases A, B and C.
Phase A : G1 / first growth / first gap
Phase B : S / synthesis
Phase C : G2 / second growth / second gap
[3 marks]
ii. State what happens during phase C.
- increase in organelles/ mitochondrion/ Golgi bodies/ endoplasmic
reticulum (any organelle)
- energy stores
- formation of microtubules/ spindle fibre
- increase in nucleus size
- increase volume of cytoplasm

- complete preparation for the cell division
- cell grow more
- protein synthesis for formation spindle fibre
[2 marks]

iii. Name the process of the cell cycle that causes the cytoplasm to divide.
Cytokinesis
[1 mark]
(b) Name TWO parts in plant where the cells actively dividing by mitosis.
 Root tips
 Shoot apex/ shoot bud // buds
 Cambium
[2 marks]
(c) State TWO importance of mitosis.
 To repair damage cell/ to replace the worn out cell
 To produce genetically identical daughter cell with parent cell // genetic
stability
 To maintain chromosome number
 Growth
 Asexual // regeneration
[2 marks]


7. 1. FIGURE 1 shows the behaviourism of chromosomes during one stage in a cell
division.





















FIGURE 1

(a) Name A, B and C.
A: Centromere
B: Chiasma / Chiasmata
C: Homologous Chromosome / Bivalent / Tetrad [3 marks]

(b) State the type and the stage of cell division in FIGURE 1.

Type of cell division: Meiosis
Stage of cell division: Prophase I [2 marks]

(c) Explain what happens to the chromosomes in FIGURE 1.
 Each replicated chromosome comprises of two (sister) chromatids
pairing up with its homologous chromosome
 Crossing over occurs between two non-sister chromatids
 The segments at the chiasma break off and recombine
 Exchange of genetic materials occurs and this will contribute to genetic variation
[3 marks]

(d) Give TWO importance of the process that occurs at structure B.
 Genetic variation
 Genetic recombinant [2 marks]



8. FIGURE 5 shows mitosis in plant cell.
















FIGURE 5

(a) Name the stage of mitosis in FIGURE 5.
Prophase [1 mark]


(b) If plant cell in FIGURE 5 undergo meiosis process, draw labeled diagram that shows stage of
anaphase II.


Spindle fibre

Chromosome

Centromere

Cell wall

# Correct diagram with:
1. Plant cell/cell wall
2. 4 sister chromatids
3. The same nu. of chromosomes with the original diagram
4. No. centrioles
[3 marks]
(c) Name TWO precise locations where mitosis occurs in plants.
Root tip // shoot tip / apex / bud // (vascular) cambium // (cork) cambium // bud
[2 marks]
(d) Hoe does cytokinesis in plant cell differs from animal cell?
Plant cell: Golgi body produces vesicle to form cell plate
Animal cell: Formation of cleavage furrow
[2 marks]



9. FIGURE 4 shows chromosomal behavior at different stages of cell division.









FIGURE 4

(a) State the stage where the chromosomal behaviors are seen.
[2 marks]
P: Prophase I
Q: Prophase/ Telophase / Interphase / G 1

(b) Explain briefly how chromosomal behavior differs between prophase I
[2 marks]

Prophase I Prophase
Synapsis of homologous chromosome No synapsis of homologous chromosome

Chiasma form between two non-sister No chiasma formed
chromatids or between the chromatids of
homologous chromosomes

Crossing over occurs No crossing over

(c) Give THREE importance of meiosis.
[3 marks]
Formation of haploid gametes
Genetic variation
Maintain the chromosomal number from generation to generation

(d) Draw and label a diagram to show the stage of anaphase II in animal cell with a
diploid chromosome number, 2n=2.
[3 marks]












Correct diagram
Label ( any 2)

10. FIGURE 3 shows the stages of cell cycle.












FIGURE 3

(a) Name the stages labeled P, Q, R and S.
[4 marks]
P : M/mitosis/mitotic
Q : G1/ Gap 1/G1
R : S (phase)
S : G2/ Gap 2/ G2

(b) What happen to the chromosomes and cells during stage P?
[2 marks]
Chromosomes thickened during prophase// chromosomes aligned on the
metaphase plate during metaphase // sister chromatid separate during
anaphase // chromosome reach opposite pole during telophase

Cell division/cytokinesis/cytoplasm division

(c) In which phase do stages Q, R and S exist?
[1 mark]
Interphase

(d) State THREE processes that occur during stage Q.
[3 marks]
Cell increase in size/ volume of cytoplasm increase
Double/ increase the number of organelles/ mitochondria/ribosomes/ any
other organelles
Increase amount of protein // accumulate materials for DNA synthesis /
replication.
(protein synthesis/ synthesis of protein – NOT ACCEPTED