Form 3:
Growth and Development

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1. Explain why several auxiliary buds sprout when a terminal bud in a young tree is removed.

IAA /auxins produced by terminal bud; inhibits growth of lateral buds, when cut the suppression cease thus auxiliary buds sprouts.

2. Account for loss in dry weight of cotyledons in a germinating bean seed.

Food stored is used in (mobilized) up for respiration and growth.

3. What is the effect of gibberellins on shoots of plants?

- They promote cell division

- Promote fruit formation without fertilization/ parthenocarpy.

4. A student set up an experiment as shown in the diagram below

The set up was left at room temperature for a week

(a) What was the aim of the experiment?

Oxygen is necessary for germination

(b) What would be the expected results at the end of the experiment?

Germination in B, no germination in A.

5. State two advantages of metamorphosis to the life of insects

The adult and larvae exploit different food riches

Do not compete for food.

6. During germination and early growth, the dry weight of endosperm decreases while that of the embryo increases. Explain

Endosperm material was converted into new cytoplasm/ the stored food endosperm is used up to the germination seed while the embryo is growing and adding on more protoplasm.

7. In an experiment, a group of student set up four glass jars as shown in the diagram below jar A, B and C were maintained at 250C for 7 days. While Jar D was maintained at 00 c for the same period of time.

(a) What was this set up supposed to investigate?

Condition necessary for the germination of seed /to show that water, oxygen and warmth are needed for germination.

(b) Why was pyrogallic acid included in glass jar A?

To absorb all oxygen from the jar

(c) Explain why glass jar C and D were included in the experiment

To show water is needed for germination of seeds.

(d) What result would you expect in glass jar A and B at the end of the experiment?

Jar A – seeds would not germinate

Jar B – seeds would has germinated

(e) State two artificial ways of breaking seed dormancy

Scarification i.e. scratching to make impermeable seed coat permeable

Varnilasation – Cold treatment e.g. species of wheat.

8. Removal of the apical bud from the shrub is a practice that results in the development of the lateral buds which later from the branches.

(a) Give reasons for the development of the lateral braches after the removal of the apical bud

Apical bud produce auxins which inhibits the development of lateral buds.

Removal of terminal buds cause the growth and development and sprouting of lateral buds.

(b) Suggest one application of this practice

The pruning of coffee/tea.

(c) What is the importance of this practice?

More yield /production

9. In an experiment some germinating seeds were placed in large airtight flask and left for four days

(a) Suggest the expected changes in the composition of gases in the flask on the fifth day

Low oxygen and increase in CO2

(b) Give reasons for your answer in (a) above

Germinating seeds respire using O2 and release CO2 only.

(c) Name two factors that cause dormancy in seeds

-Absence of light

-impermeability of seed coat to water

-immature embryo

- lack of growth hormones presence of inhibitors.

10. (a) Distinguish between epigeal and hypogeal germination ( 1 mark)

- Epigeal germination – Epicotyle grows very fast pushing out of soil surface with the cotyleons.

-Hypogeal germination – Epicotyle grows very fast and plumule grows out forming first foliage leaves cotyledons remain underground.

11. An experiment was carried out to investigate the effect of hormones on growth of lateral buds of three pea plants

The shoots were treated as follows:

Shoot A- Apical bud was removed

Shoot B – Apical bud was removed and gibberellic acid placed on the cut shoot

Shoot C- Apical bud was left intact.

The length of the branches developing from the lateral buds were determines at regular intervals

The results obtained are as shown in the table below

(a) Using the same axes, draw graphs to show the length of branches against time  ( 8 marks)


(b) (i) What was the length of the branch in shoot B on the 7th day? ( 1 mark)

68 + 1

(ii) What would be the expected length of the branch developing from shoot A on the 11th day? ( 1 mark)


(c) Account for the results obtained in the experiment ( 6 marks)

Shoot A- Removal of apical bud promotes growth of lateral buds, due to

removal of auxins hormones which inhibit lateral bud development.

Shoot B- Gibberellic acid promotes growth of lateral branches

Shoot C- Presence of apical bud inhibit lateral bud development due to

reserve of auxins. This is called apical dominance.

(d) Why was shoot C included in the experiment? ( 1 mark)

As a control experiment to show the effect of hormones (auxins) on lateral bud development.

(e) What is the importance of gibberallic acid in agriculture? ( 1 mark)

- Promotes flowering.

- Promote lateral bud development hence increase yields.

- Break seed dormancy (promote germination)

(f) State two physiological processes that are brought about by the application of gibberellic acid on plants. ( 2 marks)

- Germination

- Flowering

- Activate hydrolytic enzymes

12. (a) State tow environmental conditions that can cause seed dormancy

- Absence of water (moisture)

- Unsuitable temperature.

- Lack of oxygen

- Lack of light

(b) Name the part of a bean seed that elongates to bring about epigeal germination  ( 1 mark)


13. (a) “True growth is not simply an increase in size” State four different ways in which true may be defined.

- Increase in dry mass

- Increase in cell number

- Irreversible increase in volume of cytoplast

- Increase in differentiation.

(b) State two external factors, which influence growth in plants and describe one effect of each.

i) Light intensity influence rate of photosynthesis.

ii) Temperature – influence metabolic rate via enzyme action.

(c) Fill in the spaces in the following table, which refers to hormones involved in growth processes.

14. Seedling from 100g of maize seed was grown in the dark for 10 days. The seedlings were then analyzed and compared with 100g of ingeminated maize. The following results were obtained.

(a) Why is dry mass used for comparison?

It indicated the amount of organic material present which is a measure of

change in mass cytoplasm.

(b) How would one ensure that the drying process had been completed

Weigh, reheat at 1100C for several hours, and cool constant Mass.

(c) Account for the decrease in the total dry mass of the seedlings

Most of mass is starch which is converted to sugars and used up in respiration

and other metabolic activities.

(d) Why did the seedling contain more cellulose than the underminated seeds?

Cellulose is synthesized during growth of new cell walls.

(e) What is the most likely source of the carbon used to form this new cellulose?

Starch → Glucose → Cellulose