Biology

Plant Growth and Development

Question:

While experimentation, why do you think it is difficult to assign any effect seen to any single hormone?

Answer:

Regulatory links between various plant hormone metabolism include both synergistic and antagonistic interactions and have been described in a number of plant tissues. It is evident that the balance between synergistic and antagonistic relationships is the dominating principle of integral hormone action in plants. A single hormone can regulate an amazingly diverse array of cellular and developmental processes while at the same time multiple hormones often influence a single process. When used in vitro, plant hormones display a very broad and complex action spectrum which implies that exogenous application of plant hormone does pot ensure the same effect in the plant as in the culture medium. This is because, different cells, tissues respond differently to same hormone and different processes are sensitive to different levels of hormones, even in the same cell. Thus, it is difficult to assign any effect seen while experimentation to any single hormone.

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Plant Growth and Development

Q 1.

Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.

Q 2.

Gibberellins were first discovered in Japan when rice plants were suffering from bakane (the foolish seedling disease) caused by a fungus Gibberella fujikuroi.
(a) Give two functions of this phytohormone.
(b) Which property of gibberellin caused foolish seedling disease in rice?

Q 3.

Where are the following hormones synthesised in plants?
(a) IAA
(b) Gibberellins
(c) Cytokinins

Q 4.

Name a hormone which
(a) is gaseous in nature
(b) is responsible for phototropism
(c) induces femaleness in flowers of cucumber
(d) is us «d for killing weeds (dicots)
(e) induces flowering in long day plants.

Q 5.

In a slide showing different types of cells can you identify which type of the cell may be meristematic and the one which is incapable of dividing and how?

Q 6.

Gibberellins promote the formation of________ flowers on genetically________plants of Cannabis whereas ethylene promotes formation of________ flowers on genetically________plants.

Q 7.

Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?

Q 8.

Light plays an.important role in the life of all organism. Name any three physiological processes in plants which are affected by light.

Q 9.

A farmer grows cucumber plants in his field. He wants to increase the number of female flowers in them. Which plant growth regulator can be applied to achieve this?

Q 10.

Growth is one of the characteristic of all living organisms. Do unicellular organism also grow? If so, what are the parameters?

Q 11.

Does the growth pattern in plants differ from that in animals? Do all the parts of plant grow indefinitely? If not, name the regions of plant, which can grow indefinitely.

Q 12.

What would be expected to happen if:
(a)  GA3 is applied to rice seedlings
(b) dividing cells stop differentiating
(c) a rotten fruit gets mixed with unripe fruits
(d) you forget to add cytokinin to the culture medium.

Q 13.

‘Both growth and differentiation in higher plants are open’. Comment.

Q 14.

A rubber band stretches and reverts back to its original position. Bubble gum stretches, but it would not return to its original position. Is there any difference between the two processes? Discuss it with respect to plant growth (Hint: Elasticity (reversible) Plasticity (irreversible).

Q 15.

In animals there are special glands secreting hormones, whereas there are no glands in plants. Where are plant hormones formed? How are the hormones translocated to the site of activity?

Q 16.

Define parthenocarpy. Name the plant hormone used to induce parthenocarpy.

Q 17.

While eating watermelons, all of us wish it was seedless. As a plant physiologist can you suggest any method by which this can be achieved.

Q 18.

Nicotiana tabacum, a short day plant, when exposed to more than critical period of light fails to flower. Explain.

Q 19.

While experimentation, why do you think it is difficult to assign any effect seen to any single hormone?

Q 20.

What do you understand by photoperiodism and vernalisation? Describe their significance.

Q 21.

What are the structural characteristics of
(a) meristematic cells near root tip
(b) the cells in the elongation zone of the root.

Q 22.

On germination a seed first produces shoots with leaves, flowers appear later.
(a) Why do you think this happens?
(b) How is this advantageous to the plant?

Q 23.

List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/ horticultural applications of any one of them.

Q 24.

Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth, flowering and rooting. Write a line to explain the meaning of the following terms related to auxins.
(a) Auxin precursors (b) Anti-auxins
(c) Synthetic auxins

Q 25.

It is known that some varieties of wheat are sown in autumn but are harvested around next mid summer.
(a) What could be the probable reason for this?
(b) What term is used for this promotion of flowering under low temperature?
(c) Which plant hormone can replace the cold treatment?

Q 26.

Would a defoliated plant respond to photo- periodic cycle? Why?

Q 27.

In botanical gardens and tea gardens, gardeners trim the plants regularly so that they remain bushy. Does this practice have any scientific explanation?

Q 28.

Fill in the places with appropriate word/ words.
(a) A phase of growth which is maximum and fastest is________
(b) Apical dominance as expressed in dicotyledonous plants is due to the presence of more________ in the apical bud than in the lateral ones.
(c) In addition to auxin, a ________must be supplied to culture medium to obtain a good callus in plant tissue culture.
(d)________of a vegetative plant are the sites of photoperiodic perception.

Q 29.

Classify the following plants into Long-Day Plants (LDP), Short Day Plants (SDP) and Day Neutral Plants (DNP) Xanthium, Henbane (Hyoscyamus niger), Spinach, Rice, Strawberry, Bryophyllum, Sunflower, Tomato, Maize.

Q 30.

Fill in the blanks:
(a) Maximum growth is observed in________phase.
(b) Apical dominance is due to________
(c)________ initiate rooting.
(d) Pigment involved in photoperception in  flowering plants is________

Q 31.

What is the mechanism underlying the phenomenon by which the terminal/apical bud suppresses the growth of lateral buds? Suggest measures to overcome this phenomenon.

Q 32.

Which one of the plant growth regulators would you use if you are asked to
(a) induce rooting in a twig
(b) quickly ripen a fruit
(c) delay leaf senescence
(d) induce growth in axillary buds
(e) ‘bolt’ a rosette plant
(f) induce immediate stomatal closure in leaves.

Q 33.

The role of ethylene and abscisic acid is both positive and negative. Justify the statement.

Q 34.

Explain in 2-3 lines each of the following terms with the help of examples taken from different plant tissues.
(a) Differentiation (b) Dedifferentiation
(c) Redifferentiation

Q 35.

Label the diagram.
(a) This is which part of a dicotyledonous plant?
(b) If we remove part 1 from the plant, what will happen?
ncert-exemplar-class-11-biology-solutions-plant-growth-and-development-6

Q 36.

‘Both a short day plant and a long day plant can produce flower simultaneously in a given place’. Explain.

Q 37.

Some varieties of wheat are known as spring wheat while others are called winter wheat. Former variety is sown, and planted in spring and is harvested by the end of the same season. However, winter varieties, if planted in spring, fail to flower or produce mature grains within a span of a flowering season. Explain, why?

Q 38.

Both animals and plants grow. Why do we say that growth and differentiation in plants is open and not so in animals? Does this statement hold true for sponges also?

Q 39.

Many discoveries in science have been accidental. This is true for plant hormones also. Can you justify this statement by giving an example? Also what term is used for such accidental findings?

Q 40.

A gardener finds some broad-leaved dicot weeds growing in his lawns. What can be done to get rid of the weeds efficiently?

Q 41.

Why is abscisic acid also known as stress hormone?

Q 42.

In the figure of sigmoid growth curve given below, label segments 1,2 and 3.

ncert-exemplar-class-11-biology-solutions-plant-growth-and-development-4

Q 43.

Plant growth substances (PGS) have innumerable practical applications. Name the PGS you should use to
(a) Increase yield of sugarcane.
(b) Promote lateral shoot growth.
(c) Cause sprouting of potato tuber.
(d) Inhibit seed germination.

Q 44.

A primary root grows from 5 cm to 19 cm in a week. Calculate the growth rate and relative growth rate over the period.

Q 45.

The rice seedlings infected with fungus Gibberella fujikuroi are called foolish seedlings? What was the reason behind it?

Q 46.

Describe briefly
(a) Arithmetic growth
(b) Geometric growth
(c) Sigmoid growth curve
(d) Absolute and relative growth rates

Q 47.

To get a carpet like grass, lawns are mowed regularly. Is there any scientific explanation for this?

Q 48.

ABA acts antagonistic to
(a) ethylene
(b) cytokinin
(c) gibberellic acid
(d) IAA.