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Suggested answers to Practical Workbook

for SBA

Ch 11 Cell cycle and division

Practical 11.1 Examination of different stages of the cell cycle

Questions (p. 11-2)

1

CellCell

growth(Prophase)

Mitosis (Nuclear division)Cytoplasmic

divisionStage 1 Stage 2

(Metaphase)Stage 3

(Anaphase)Stage 4

(Telophase)

A ✓

B ✓

C ✓

D ✓

E ✓

F ✓

G ✓

H ✓

I ✓

J ✓

2 Interphase: Individual chromosomes cannot be distinguished.

Prophase: Chromosomes become visible, each is seen to consist of two chromatids held together at the centromere. The nuclear membrane disintegrates.

Metaphase: The chromosomes line up in the middle of the cell.

Anaphase: The two chromatids of each chromosome separate and move to the opposite poles of the cell. The cytoplasm starts to divide.

Telophase: New nuclear membranes form around each set of chromosomes. The chromosomes uncoil to become chromatin again.

3 The cells near the tips divide actively by mitotic cell division.

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Practical 11.2 Investigation of the relative time required for each

stage of the cell cycle

Results (p. 11-6)

1

2

StageNumber of cells in the stage Relative time spent in the stage

(min)Area 1 (A1) Area 2 (A2) Area 3 (A3)

Interphase 23 25 24 551

Prophase 3 2 3 61

Metaphase 2 2 1 38

Anaphase 1 1 1 23

Telophase 1 2 1 30

Cytoplasmicdivision

1 0 1 15

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Total number of cells in each area T1 = 31 T2 = 32 T3 = 31

3

Questions (p. 11-8)

1 To expose more cells for observation.

2 a To intensify the stain.

b To avoid the slide being overheated and broken.

3 The number of cells in each phase is directly proportional to the time required by the cells in that phase.

4 a (Answer varies with results.)

b (Answer varies with results.)

5 a The results are different. This is because different students and groups used slightly different criteria to categorize the phases (i.e. personal judgment and subjectivity) or different groups collected their data from different samples.

b No. The findings are based on an assumption without testing. If the assumption is wrong, the findings will also be incorrect.

c Subjectivity; Tentativeness; Observation vs. Inference; Creativity; Empirically based.

Conclusion (p. 11-9)

Interphase takes the longest time in the cell cycle. Phases in mitosis are relatively short.

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Practical 11.3 Examination of meiotic cell division

Questions (p. 11-13)

1 4.

2 8.

3 abdce

a) Homologous chromosomes line up at the middle of the cell. → b) Separation of homologous chromosomes. → d) Formation of two daughter cells each with chromosome number halved. → c) Arrangement of chromosomes at the middle of the cell. → e) Formation of four haploid daughter cells.

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Ch 12 Reproduction in flowering plants

Practical 12.1 Examination of binary fission in bacteria

Results (p. 12-2)

Questions (p. 12-2)

1 2

2 Mitotic cell division.

3 a Binary fission is a type of asexual reproduction.

b Binary fission does not involve gametes.

The offspring are genetically identical to each other and to the parent.

4 bac

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Practical 12.2 Examination and cultivation of a vegetative

propagating organ

Results (p. 12-5)

1

2 The iodine solution turns dark blue in colour.

3 a (Results vary with Ss.)

b (Results vary with Ss.)

Questions (p. 12-6)

1 Vegetative propagation is the process by which the vegetative parts of the flowering plants develop into new plants.

2 Starch is stored in the tuber.

3 The buds of the tuber.

4 The swollen end of an underground stem.

5 The potato tuber becomes smaller because food stored in the tuber is used up for the development of a new plant.

6 1 In spring, the buds use the food stored in the tuber to produce adventitious roots and shoots.

2 In summer, some food made in the leaves is sent to the underground shoots and stored. The ends of underground shoots swell and form new tubers.

3 In winter, the aerial shoots die and the new tubers remain dormant.

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4 In the next growing season, each bud in the tubers may grow into a new plant.

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Practical 12.3 Dissection and examination of a flower

Results (p. 12-11)

1

Floral part Colour Number

Sepal Greenish yellow 5

Petal Yellow 5

Stamen Brown 10

Carpel Greenish yellow 1

2

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3

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4L.S. of ovary

T.S. of ovary

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Questions (p. 12-13)

1

Name Function

Stigma Receives pollen grains

Ovary Contains ovules which carry female gametes

Flower stalk Attaches the flower to the main stem of the plant

Style Supports the stigma

Anther Produces pollen grains which carry male gametes

Filament Supports the anther

Petal Protects the inner parts of the flower and attracts insects

Sepal Protects the inner parts of the flower when it is a bud

2 a carpel

stamen

b corolla

calyx

3 The ovary develops into the fruit.

4 The flowers are bisexual because they have both stamens and carpels in the same flower.

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Practical 12.4 Examination of an insect-pollinated flower and a

wind-pollinated flower

Results (p. 12-17)

1

Part of theflower

Feature Gladiolus flower Grass flower

PetalSize Large Small

Colour(Result depends on the specimen.)

Brown

Anther

Way of attachment to the filament

Firmly attached Loosely attached

PositionEnclosed inside the flower

Hang outside the flower

Pollen grainQuantity Small in number Large in number

Texture Rough and sticky Smooth and dry

Stigma

Size Relatively smaller Relatively larger

PositionEnclosed inside the flower

Hang outside the flower

Texture Sticky Feathery

Nectary Present / Absent Present Absent

2Gladiolus flower Grass flower

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Questions (p. 12-18)

1 Gladiolus is an insect-pollinated flower and grass is a wind-pollinated flower.

2

Gladiolus flower Grass flower

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Anther enclosed inside the flower. / Large brightly coloured and scented petal attracts insects and provides a platform for them. / Sticky stigma curls down to pick up pollen grains from the insect. / Nectary secretes nectar to attract insects. / Rough and sticky pollen grains attach to the insect. (Any three)

Feathery stigmas hang outside the flower to catch pollen grains in the air. / Anther hangs outside the flower to release pollen grains to the air. / Filament is thin and flexible. / A large number of light and smooth pollen grains produced. (Any three)

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Ch 13 Reproduction in humans

Practical 13.1 Examination of the mammalian reproductive

systems

Questions (p. 13-3)

A Male reproductive system1

Structure Name Function

A Seminal vesicle Secrete seminal fluid which activates and nourishes the sperm provides a medium for the sperm to swim neutralizes the acidity in the female

reproductive tract

B Prostate gland

C Cowper’s gland

D PenisEjects semen to the female ’ s vagina during sexual intercourse

E UrethraDischarges semen and urine out of the body at different times

F Testis Produces sperm and male sex hormones

G Epididymis Stores sperm temporarily

H Vas deferensTransports sperm from the epididymis to the urethra during ejaculation

I Scrotum Holds the testes

2 Sperm tubules.

3 Erectile tissues.

4 The temperature inside I is about 3°C lower than the core of the body. This provides the optimal temperature for sperm development.

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5 FGHE

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B Female reproductive system1

Structure Name Function

J Ovary Produces ova and female sex hormones

K Oviduct Transports the ovum to the uterus

L Uterus

Provides protection and a stable internal environment for the development of the embryo and foetus

The wall contracts to push out the foetus during labour

M Vagina

Holds the penis during sexual intercourse Provides an acidic environment to reduce bacterial

growth Acts as the birth canal for the foetus during labour

2 Cilia. They sweep the ovum along the oviduct to the uterus.

3 JKLM

Practical 13.2 Examination of the mammalian sperm and ova

Results (p. 13-7)

1

Sperm Ovum

Size Smaller Much larger

Shape Tadpole-like Spherical

Movement Active / Yes Inactive / No

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2Sperm Ova

Questions (p. 13-7)

1 Ova are much larger than sperm because ova contain a larger amount of cytoplasm with food reserves for the early development of the embryo.

2 After the sperm have been ejaculated into the vagina, the sperm are able to swim through the cervix, up the uterus and enter the oviducts towards the ovum for fertilization.

3 Each sperm has a tail for swimming.

4 The ovum is carried along the oviduct by the beating action of cilia and the contraction of muscular wall of the oviduct.

Practical 13.3 Examination of different stages of foetal

development

Results (p. 13-10)

Number of weeks Appearance of the embryo / foetus

8 Small, with its head on the right and body on the left

16Bigger in size, with a clear distinction between the head and the abdomen

24 Getting even bigger, spine visible

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Questions (p. 13-11)

1 Nervous system.

2 At week 10.

3 The hands of the foetus in Photo A are normal.

The hands of the foetus in Photo B are mitten.

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