Sample answer to Question 1 Paper 3 (Pg 196 Bioscore)

a)

Pattern of thumbprints	No of students with the same pattern of thumbprint
Whorl	12
Loop	10
Composite	22
Arch	6

b) i)

1. The number of students with the pattern of thumbprint composite is 22.

2. The number of students with the pattern of thumbprint arch is 6.

(ii)

1. The number students with the pattern of thumbprint composite is high because

     it is a dominant trait.

2.  The number of students with the pattern of thumbprint arch is low because it

     is a recessive trait.

Variable	Method to handle the variable
Manipulated variable Pattern of thumbprints	Use different types of thumbprints which are composite, loop, whorl and arch
Responding variable Number of students with the same pattern of thumbprints	Count and record the number of student with each pattern of thumbprint by using thumbprint set.
Controlled variable Type of fingers	Fix the type of finger  to be same

(d) When the pattern of thumbprint is composite, the number of students is the highest.

(e)i)

Pattern of thumbprints	No of students with the same pattern of thumbprint
Whorl	12
Loop	10
Composite	22
Arch	6

(ii) Draw a bar chart

(f) The type of variation found in thumbprint is discontinuous variation because the is no range/intermediate values between the different thumbprint pattern and falls in a distinct/discrete category.

(g) Bell shape/normal distribution.

Height is a continuous variation and it has intermediate values and is influenced by genetic and environment factors.

Answers to Hands-on Pg 65-69

Objective Questions

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

Structured Questions

Section A

1. (a) (ii) Tall plants with coloured flowers

(b) (i) Dihybrid cross

(ii) TtCc

(d)(i)

Gametes	TC	Tc	tC	tc
tc	TtCc	Ttcc	ttCc	ttcc

(ii) A plant which is heterozygous for tallness and coloured flowers has the genotype TtCc. The plant produces four types of gametes, TC, Tc, tC and tc. When the plant is crossed with another plant which is homozygous recessive, the gametes combine at random to produce plants with TtCc, Ttcc, ttCc and ttcc as their genotypes.

(e) To obtain consistent results as pure-breeding plants are able to produce offspring which have received identical genes from the parents. When self-fertilised, they are able to produce offspring having exactly the genes they have inherited.

2. (a) (i) Genes are carried on the sex chromosomes and passed down to the next generation.

(ii) Usually are carried on the X chromosome and it mostly affects the males

(b) Bakri’s mother must be a carrier with the genotype X^HX^h in which ‘h’ is the recessive gene for haemophilia. Bakri inherits X^h from his mother and the Y chromosome from his father.

(c) One of them inherits X^H from her father and X^H from her mother. The other one inherits X^H from her father and X^h from her mother. Both are normal but genotypically, one of them is a carrier.

(d) Males are determined by the presence of the X and Y chromosomes. Sex-linked genes are absent in the Y chromosomes. Therefore, the presence of one sex-linked gene in the X chromosome will affect the male as compared to the female who

needs genes to be present in both X chromosomes for her to be affected.

(e)

Gametes	Xh	Y
XH	XHXh	XHY
Xh	Xh Xh	XhY

(f) 100%

Answers to Hands-on Pg 63-64

Aim : To illustrate Mendel’s first law using coloured buttons

Colours of buttons	Number of pairs	Trait represented by buttons
Red and red	24	Tall
Red and white	53	Tall
White and white	23	Dwarf

Discussions:

1. Red
2. Gamete
3. Tall plant. Red button represent the gene for tallness which is dominant. Therefore when it is paired with a white button which is recessive, then a tall plant is produced.  A dominant gene expresses itself even when it is in the heterozygous condition.
4. The ratio of tall : dwarf is 3:1.  This is because an organism’s characteristic is determined by a pair of genes which will separate and be carried in a gamete and the dominant gene will express itself.

Conclusion :

Mendel’s first law is illustrated by separating the buttons before pairing them again which shows that a characteristic in an organism is represented by a pair of genes. The genes will separate and each gene is carried by a gamete.

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.