MODEL SUBJECTIVE QUESTIONS:
- What is growth? Discuss its different aspects.
- What is meristem? Gives its types.
- Give roles of Auxins in plant growth.
- Give role of gibberellins in growth.
- Give role of cytokinins in growth.
- Give role of abscisic acid in growth.
- Give role ethene in growth.
- Describe different tissue culture techniques.
- What is meant by open growth?
Ans: The plants have a growth pattern called open growth. The plant adds new organs such as branches, leaves and roots throughout the life. PIant enlarges its body from the tips of roots and shoots.
- What is A pical Meristems? What its role in plant?
Ans: The merit:terns present at the tips of roots and shoot are called apical meristems. They are primarily concerned with the extension of plant body. The perpetual growth zones are present at the apices of roots and stems. They increase the number of cells at the tips of roots and stem. Thus they play important role in primary growth. ”
- What is Intercalary Meristems? What its role in plant growth?
Ans: The meristem situated at the bases of internodes is called intercalary meristem. These are the parts of apical meristem. They get separated from apex meristem by permanent tissues. They play important role in the production of leaves and flower. These are of temporary nature.
- What is Lateral Meristems?
Ans: The cylinders of dividing cells present in the vascular and cork tissue of the plants are called lateral meristems.
- Differentiate between determinate and indeterminate • growth.
Ans: Determinate: Their growth is determinate i.e. they grow to certain size and then stop. For example leaves, flowers and fruits Indeterminate: Their growth is indeterminate i.e. they grow by meristems that continually replenish themselves during remaining youthful-age. For example. vegetative root and stem.
- Differentiate between primary and secondary growth.
Ans: Primary Growth: In this growth. primary tissues are added by the apical meristem. It increases the length of the plant. Secondary Growth: In this growth. secondar) tissues are added by the interealary or vascular cambium. It increases the thickness of plant.
- What are planthormones? Name them.
Ans: The special substances produced by the plants which influence the growth and plant responses are called plant hormones. Plant hormones are auxin, gibberellins, cytokinins, abscisic acid and ethene.
- Name some synthetic auxins.
Ans: Indole butyric acid (IBA). Naphthalene acetic acid (NAA), 2,4- dichlorophenoxyacetic acid (2,4-D). Para chlorophenoxy acetic acid.
- What is the role of auxins in apical dominance?
Ans: The terminal bud produces auxins. It inhibits the growth of lateral bud. Therefore, the main stein continues to grow. If the tip is cut off, the influence of the apex on the lateral buds is lost. Now lateral buds emerge and form branches.
- What is role of auxins in sex expression?
Ans: Auxins change the sex ratio in someeplants. The flowers of some plants like cucumber and ridge gourd -are unisexual. But both male and female flowers are borne on the same plant (Monoecious). These plants ‘produce a large number of male flowers. But it produces only a few female flowers.
- What is parthenocarpy? What is role of auxins in it?
Ans: The phenomenon in n.vhich ovary changes into fruit without fertilization is called parthenocarpy. The production of auxin increases in ovary after pollination.
- What is abscission? What is role of auxins in it?
Ans: The falling of leaves, flowers and fruits is called abscission. The green lamina of young leaves produce auxin. This auxin prevents the abscission of leaves. The old leaves cannot produce sufficient auxin. So they fall. If auxin is applied on such leaves, abscission is prevented.
- What is role of auxins in phototropism?
Ans: A stem is exposed to light from one side. One half of the stern receives the light. The other half is shaded. Auxin produced at the tip. It is transported downward. The lighted half of the stern gets about 35% of auxin. But the shaded side receives about 65 % of auxin. As a result, the shaded half of the stem grows more than the lighted half. It bends the stem towards light.
- What is seed dormancy? How it can be broken?
Ans: The physiological inability of a seed to grow is called seed dormancy. Dormant seeds do not germinate even under favourable conditions of water, air and normal temperature.Gibberellic acid breaks the dormancy in some seeds.
- What are Rosette long day plants? Give role of gibberellins
Ans: Rosette plants like Hyoscyanms and Samolus remain vegetative under short days. But they produce flowers in long days. The application of gibberellin makes the plants to flower even under short days.
- What is differentiation? Give role of hormones in it.
Ans: Differentiation of different tissues like root, shoot from callous is called morphogenesis. The ratio of cytokinins to auxin controls the morphogenesis.
- How does ABA inhibit growth?
Ans: ABA is growth inhibitor hormone. It inhibits the growth of root, stem, leaf and coleoptile. Even its very low concentration is effective. Gibberellin reverses the effect of ABA. Thus plant resumes normal growth. Therefore, abscisic acid and gibberellic acid have opposite effects on plants.
- How does ethylene play role in fruit ripening?
Ans: Ripening. of fruits: It is the most important effect of ethylene.The banana and apple are kept in storage tbr ripening. The rate of respiration of the fruit increases. It is called climacteric respiration. Such fruits arc called climacteric fruits.
- What are clonal plants?
Ans: The shoots are genetically identical to the adult plants. Thus the plants developed from them are called clonal plants. All the clonal plants have the same traits.
20.. Give three applications of tissue culture.
Ans: It is used to reproduce plants which do not reproduce by normal methods. It is used to express the recessive traits. It is used to study the effect of different hormones on plant.