Question 1:
Diagram I shows the different stages in a cell division.


(a)(i) Name the type of cell division.


(a)(ii) Arrange the stages of the cell division in the correct sequence.

(b)(i) Explain the chromosomal behaviour in stage C.

(b)(ii) State one importance of the chromosomal behaviour in (b)(i).

(c) Diagram II shows the involvement of cells produced by this type of cell division in the formation of zygote.


Explain how zygote is formed.


(d) Diagram III shows the karyotype of an offspring produced.


(i) State the number of chromosomes in the offspring.

(ii) Name the genetic disease suffered by the offspring.

(iii) Give one reason for the answer in (d)(ii).

(iv) Explain how radioactive rays can cause this genetic disease.


Answer:
(a)(i)
Meiosis I

(a)(ii)

(b)(i)
The chromosomes condense, thicken and become clear.
Homologous chromosome exchange the genetic material in a process of crossing over.

(b)(ii)
Increases genetic diversity/ causes variation.


(c)
When the nucleus of a sperm (haploid) fuses with the nucleus of an ovum (haploid) during fertilization, a zygote (diploid) is formed.

(d)(i)
45/ 44 + X

(d)(ii)
Turner’s syndrome

(d)(iii)
The absence of one X chromosome which is a sex chromosome

(d)(iv)
Radioactive radiation can cause mutation of the chromosomes, as a result of which only one X chromosome is present.

Question 1:
Figure I shows cells R and S undergoing cell division.


(a)(i) Name the structures labelled K and M.

(a)(ii) State the phase of division of cells R and S.


(b) Cell R undergoes three consecutive divisions.

(c)(i) Cell S undergoes the first nuclear division and produces two cells.
Complete the diagram to show the chromosomes in one of the cells produced.

(c)(ii) Name one organ where cell S is found.

(c)(iii) The number of chromosomes I a somatic cell of a fly is 12.
State the number of chromosomes in a daughter cell produced at the end of the type of cell division as shown by cell S.


(d) Cancer is a disease which causes uncontrolled growth of tissues.
Radiotherapy is a method to treat cancer by using radiation.
Explain how this treatment stops the growth of cancer cells.

(e) An oil palm planter wants to produce a large number of oil palms in a short time.
State the best technique to be used by the planter and one problem to be considered in using the technique.



Answer:
(a)(i)
K: Chromatid
M: Spindle fibre

(a)(ii)
Cell R: Metaphase
Cell S: Metaphase I

(b)
8 daughter cells

(c)(i)



(c)(ii)
1. Testis
2. Ovary

(c)(iii)
6 chromosomes

(d)
Radioactive rays destroy the cells, so the rate of mitosis is controlled.

(e)
- Cloning / culture tissue
- All the clones are easily attacked by diseases because all the clones have the same resistance towards diseases.