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.

Answers to Hands-on Pg 50-53

Aim : To study the growth pattern of maize plant (Zea mays)

Variables : Manipulated variable : Time of growth

                   Responding variable : Mass of seedlings

                   Fixed variable : Amount of water, fertilizer

Time (weeks)	Mass of 3 seedlings (g)		Mean mass of 1 seedling (g)
	Fresh	Dry	Fresh	Dry
0	0.90	0.60	0.30	0.20
1	0.60	0.45	0.20	0.15
2	0.90	0.60	0.30	0.20
3	1.20	0.90	0.40	0.30
4	2.40	1.80	0.80	0.60
5	4.20	3.15	1.40	1.05
6	6.00	5.25	2.00	1.75
7	8.85	7.50	2.95	2.50
8	11.40	10.20	3.80	3.40
9	14.10	13.20	4.70	4.40
10	15.30	14.70	5.10	4.90
11	15.90	15.00	5.30	5.00
12	16.20	15.30	5.40	5.10

Draw a graph based on the above table

Discussion :

1. Sigmoid growth curve
2. Week 5 to week 8
3. Growth rate is negative from the beginning of the activity ti week 1.  This is because the germinating seeds use food stored in the endosperm.  Week 1 to wek 4 shows slow growth rate because young leaves are starting to grow and photosynthesis has just begun.  Week 5 – 8 shows highest growth rate.  The growth rate slows down from week 8 onwards because the plant has reached maturity.

Conclusion :

The growth pattern of the maize seedling represented by a graph of the mass of maize seedlings against time is a sigmoid curve. The hypothesis is accepted.

Answers to Hands-on Pg 47-49

Aim : To observe the germination of pollen grains

Observation :

Pollen grain

Germinating pollen grain

Discussion

1. The slide with the sucrose solution.
2. To stain the male nuclei and the tube nuclei.
3. The surface of the pollen grain is coarse and has germinating pores.
4. The sucrose solution secreted by the stigma cells stimulates the growth of a pollen tube which grows into the ovule to fertilise the eg cell and polar nuclei in the embryo sac

Baby process from 0 to 9 months

Fertilization and Fetal Development