Answer to Hands - on Pg 54-56

Objective Questions

1	B	11	D
2	D	12	C
3	B	13	D
4	B	14	D
5	C	15	A
6	D	16	B
7	B	17	C
8	B	18	B
9	C	19	A
10	B

1. (a) P : 2n           Q : n              R : n

(b) W : Mitosis

X : Meiosis I

Y : Meiosis II

(c) Spermatogonium →Primary spermatocyte→Secondary spermatocyte →Spermatid →

Spermatozoa

(d) (i) Mitochondrion

(ii) To produce energy through cellular respiration for the sperms to swim to the ovum

(iii) To propel the sperm forward when swimming towards the ovum

(e) Artificial insemination in which sperms from a donor can be obtained from a sperm bank and injected into the uterus of a woman during ovulation.

2. (a) (i) Root cap

(ii) Protects the root tip

(b) (i) Zone of cell division

(ii) Draw on your own

(c)(i) Draw on your own

(ii) Cell in zone Q absorbs water through osmosis. The vacuole expands and pushes

the cytoplasm against the cell wall. The cell elongates.

(d) Xylem and phloem

(e) Draw on your own

3. (a) Growth curve of a rat: Sigmoid curve

Growth curve of a cockroach: Series of steps

(b) (i) Early phase

(ii) Mainly cell division through mitosis where growth rate is slow

(c)(ii) In the exponential phase, growth speeds up exponentially. The number of cells increases and cells increase in size quickly. In the maturity phase, growth slows down as it reaches maturity.

(d) (i) X is a stage of ecdysis.

(ii) The cockroach takes in air to expand its body. The old exoskeleton is shed to expose the new and soft exoskeleton beneath it. Growth of organs and tissues takes place quickly before the new exoskeleton hardens.