NCERT Exemplar Class 11 Biology Solutions Plant Growth and Development
Multiple Choke Questions
1.Ethylene is used for
(a) retarding ripening of tomatoes
(b) hastening of ripening of fruits
(c) slowing down ripening of apples
(d) both (b) and (c).
Solution. (b): Ethylene is a fruit ripening hormone. It stimulates all the biochemical changes which take place upon fruit ripening.
2.Coconut water contains
(a) ABA (b) auxin
(c) cytokinin (d) gibberellin.
Solution.(c) : Cytokinins (Letham, 1963) are plant growth hormones which are basic in nature, either aminopurine or phenyl urea derivatives, that promote cytokinesis (= cell division) either alone or in conjunction with auxin. Coconut milk is a rich source of cytokinin.
3.The affect of apical dominance can be overcome by which of the following hormone?
(a) IAA (b) Ethylene
Solution.(d): Presence of cytokinin in an area causes preferential movement of nutrients towards it. When applied to lateral buds, they help in their growth despite the presence of apical bud. Thus, they act antagonistically to auxin.
4.Match the following:
A.IAA (i) Herring sperm DNA
B.ABA (ii) Bolting
C.Ethylene(iii) Stomatal closure
D.GA (iv) Weed-free lawns
E.Cytokinins(v) Ripening of fruits
(a) A-(iv), B-(iii), C-(v), D-(ii), E-(i)
(b) A-(v), B-(iii), C-(iv), D-(ii), E-(i)
(c) A-(iv), B-(i), C-(v), D-(iii), E-(ii)
(d) A-(v), B-(iii), C-(ii), D-(i), E-(iv)
5.Apples are generally wrapped in waxed paper to
(a) prevent sunlight for changing its colour
(b) prevent aerobic respiration by checking the entry of 02
(c) prevent ethylene formation due to injury
(d) make the apples look attractive.
6.Growth can be measured in various ways. Which of these can be used as parameters to measure growth?
(a) Increase in cell number
(b) Increase in cell size
(c) Increase in length and weight
(d) All the above
Solution.(d): Growth, at a cellular level, is princi-pally a consequence of increase in the amount of protoplasm. Growth is, measured by a variety of parameters such as (i) Increase in length, e.g., stem, root, pollen tube, (ii) Increase in volume e.g., fruits, (iii) Increase in area, e.g., leaves, (iv) Increase in diameter, e.g., tree trunks, fruits, (v) Increase in fresh or dry weight. One single maize root apical meristem can give rise to more than 17,500 new cells per hour, whereas cells in a watermelon may increase in size by upto 3,50,000 times. In the formep, growth is expressed as increase in cell number; the latter expresses growth as increase in size of the cell.
7.The term synergistic action of hormones refers to
(a) when two hormones act together but bring about opposite effects
(b) when two hormones act together and contribute to the same function
(c) when one hormone affects more than one function
(d) when many hormones bring about any one function
Solution.(b) : Growth, differentiation and development processes of plants are found to be regulated by two or more phytohormones acting synergistically or antagonistically, e.g., cell division is promoted by both auxins and cytokinins acting synergetically. Cell growth is controlled by auxins, gibberellins and cytokinins. Morphogenesis is an interplay of auxins and cytokinins, where both must be present in some minimum concentration.
8.Plasticity in plant growth means that
(a) plant roots are extensible
(b) plant development is dependent on the environment
(c) stems can extend
(d) none of the above.
Solution. Different kinds of structures develop in plants in different phases of growth or in response to environment. This ability is called plasticity.
9.To increase sugar production in sugarcanes, they are sprayed with
Solution. (c) : Sugarcane stores carbohydrates in its stem. Spraying the sugarcane crop with gibberellins increases the length of stem and yield of sugarcane to as much as 20 tonnes/ acre.
10.ABA acts antagonistic to
(c) gibberellic acid
Solution.(c): Abscisic acid is an antagonist to gibberellins as shown in the table given below:
11.Monocarpic plants are those which
(a) bear flowers with one ovary
(b) flower once and die
(c) bear only one flower
(d) all of the above.
Solution.(b): Monocarpic plants are those plants that flower once during their life time, set seeds and then die, e.g., bamboos.
12. The photoperiod in plants is perceived at
(a) meristem (b) flower
(c) floral buds (d) leaves.
Solution.(d) : It has been experimentally demonstrated that photoperiodic stimulus is perceived by leaves. This conclusion is based on the following observations â€”
(i) A plant from which all the leaves have been removed fails to flower even after getting the required inductive cycles.
(ii)In Xunthium (a short day plant) flowering occurred if one-eighth of a leaf was exposed to short days.
Short Answer Type Questions
1.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.
Solution. (a) exponential phase
2. 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.
Solution. (a) Gibberellin
(d) Abscisic acid
3.A primary root grows from 5 cm to 19 cm in a week. Calculate the growth rate and relative growth rate over the period.
Solution.Growth is dependent on three factors – initial size (Wâ€ž), rate of growth (r) and time interval (f) for which the rate of growth is retained.
Relative growth rate
Thus/absolute growth rate is 0.1919 while relative growth rate is 3.8 cm.
4. 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?
Solution.(a) Gibberellins are weakly acidic growth hormones having gibbane ring structure which cause cell elongation of intact plants in general and increased internodal length of genetically dwarf plants in particular. Functions of gibberellins are as follows:
(i) Bolting : Gibberellin induce subapical meristem to develop faster. This causes elongation of reduced stem or bolting in case of rosette plants.
(ii)Seed germination : During seed
germination, especially of cereals, gibberellins stimulate the production of some messenger RNAs and hydrolytic enzymes like amylases, lipases, ribonucleases and proteases; which solubilise the reserve food of the seed. This food is then transferred to embryo axis for its growth.
(b) Gibberellins help in cell growth of stem, leaves and other aerial parts. Therefore, they increase the size of stem, leaves, flowers and fruits. This property of gibberellin lead to abnormal increase in stem length of rice plants causing foolish seedling disease or bakane disease.
5. Gibberellins promote the formation of________ flowers on genetically________plants of Cannabis whereas ethylene promotes formation of________ flowers on genetically________plants.
Solution. Gibberellins promote the formation of mdle flowers on genetically female plants of Cannabis whereas ethylene promotes formation of female flowers on genetically male plants.
6.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.
Solution. Long day plants are henbane (Hyoscyamus niger), spinach Short day plants are Xanthium, rice, strawberry, Bryophyllum. (It is a short day plant but requires long photoperiods for floral initiation and short photoperiods for blossoming). Day neutral plants are sunflower, maize, tomato.
7.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?
Solution. Ethylene, is a plant growth regulator that has a feminising effect on sex expression. Ethylene promotes formation of female flowers in monoecious plants like cucumber.
8.Where are the following hormones synthesised in plants?
Solution.(a) Shoot apices, leaf primordia and developing seeds.
(b) Apical shoot buds, root tips and developing seeds.
(c) Roots, endosperm region of seeds, growing embryos, developing shoot buds, etc.
9.In botanical gardens and tea gardens, gardeners trim the plants regularly so that they remain bushy. Does this practice have any scientific explanation?
Solution. The phenomenon of regularly trimming the plants resulting in bushy growth is based on apical dominance i.e., apical bud does not allow the nearby lateral buds to grow (by releasing auxins). When the apical bud is removed, the lateral buds sprout. This produces dense bushy growth. The phenomenon is widely used in tea plucking and hedge making.
10. Light plays an.important role in the life of all organism. Name any three physiological processes in plants which are affected by light.
Solution.Physiological processes in plants that are affected by light are:
(i) Photosynthesis : It is the process of manufacturing of food from inorganic substances in presence of sunlight.
(ii)Transpiration: It is loss of water in vapour form, from the stomata. In majority of plants, stomata open in light.
(iii)Photoperiodism : Duration of light hours affect the growth and development of plants, especially flowering.
11.In the figure of sigmoid growth curve given below, label segments 1,2 and 3.
12.Growth is one of the characteristic of all living organisms. Do unicellular organism also grow? If so, what are the parameters?
Solution.Growth is one of the major characteristic to distinguish living beings from non ¬living things. It is defined as permanent or irreversible increase in dry weight, size, mass volume of cell, organ and organism.
In unicellular organisms, growth is synchronous with reproduction. A single cell synthesises protoplasm, increase in size and – divides into two daughter cells.
13. The rice seedlings infected with fungus Gibberella fujikuroi are called foolish seedlings? What was the reason behind it?
Solution.The rice seedlings infected with fungus Gibberella fujikuroi are called foolish seedlings because infected plants grow excessively taller than rest of the non infected rice plants in the field, fall over and be unharvestable.
Short Answer Type Questions
1.Nicotiana tabacum, a short day plant, when exposed to more than critical period of light fails to flower. Explain.
Solution. Nicotiana tabacum is a short day plant, i. e., it requires a continuous critical dark period, which may be exceeded. If the plant is exposed to even a flash of light before achieving critical dark period, flowering is prevented. These plants require photoperiods below a critical length and they do not flower under long day conditions, i.e., when exposed to more than critical period of light.
2.What are the structural characteristics of
(a) meristematic cells near root tip
(b) the cells in the elongation zone of the root.
Solution. (a) Meristematic zone is the growing point of root and is subterminal. It is made up of compactly or closely arranged small thin walled isodiametric and meristematic cells which have dense protoplasm. They undergo repeated divisions and produce new cells for the root cap and basal region of the root. Therefore, it is essential for the growth of root.
(b) The cells is elongation zone are newly formed cells which lose the power of division. They elongate rapidly and increase the length of root. The cells of this region can absorb, water and minerals from the soil.
3.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.
Solution.Growth in plants is different from growth in animals because animals show definite or limited growth and stop growing after attaining maturity whereas in plants, some parts show definite or limited growth, i.e., stop growing after attaining maturity, e.g., leaves, flowers and fruits, whereas some parts show indefinite growth, e.g., stems and their branches etc. In other words, in plants growth continues throughout life as they have meristematic areas where cell division occurs regularly whereas in animals growth occurs to a certain age after which cells divide only to replace worn out and lost cells.
4.Explain in 2-3 lines each of the following terms with the help of examples taken from different plant tissues.
(a) Differentiation (b) Dedifferentiation
Solution. (a) Differentiation : During growth, meristematic cell divides by mitotic division to form daughter cells. The cells from root and shoot apical meristem, cambium or other meristems tend to differentiate into mature cells to perform specific functions. This act leading to maturation is known as differentiation. E.g., cell tends to loose their protoplasm, in order to form tracheary element. These cells also develop a very strong, elastic, lignocellulosic secondary cell wall in order to transport water to long distance even under extreme conditions.
(b) Dedifferentiation : The living differentiated cells also show another interesting phenomenon during which they regain the capacity to divide mitotically under certain conditions. The dedifferentiated cell can act as meristem, e.g., formation of interfasicular cambium and cork cambium from fully differentiated parenchyma cells.
(c) Redifferentiation : The products of dedifferentiated cells or tissue when lose the capacity to divide but mature to perform specific functions, it is known as redifferentiation, e.g., secondary cortex and cork.
5. 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
Solution.(a) Auxin precursors : These are the raw materials used in synthesis of auxin. E.g., tryptophan is precursor for indole-3-acetic acid (I A A).
(b) Anti-auxins : There are the compounds which inhibit the action of auxin. E.g., TIBA (2, 3, 5 triiodobenzoic acid) acts as anti-auxin by blocking the transport of auxin.
(c) Synthetic auxin : Auxins which are manufactured synthetically and do not occur naturally in plants. E.g., 2 : 4 D, NAA etc.
6.The role of ethylene and abscisic acid is both positive and negative. Justify the statement.
Solution.Ethylene and abscisic acid have both positive and negative effects. Ethylene is a gaseous hormone which promotes apical dominance, breaks dormancy of seeds, buds, helps in root initiation and aids in ripening of climacteric fruits. These are some positive roles of ethylene. Contrary to this, ethylene also hastens the senescence of leaves and flowers and causes abscission of leaves, flowers and fruits.
Abscisic acid promotes flowering in short day plants, induces parthenocarpic development in rose and rooting of stem-cutting (e.g., bean). On the other hand, it also induces dormancy of seeds and buds, promotes abscission of flowers and fruits and stimulates leaf senescence. Hence, ethylene and abscisic acid have both positive and negative roles.
7.While experimentation, why do you think it is difficult to assign any effect seen to any single hormone?
Solution. 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.
8.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.
Solution.Apical dominance is the phenomenon by which presence of apical bud does not allow the nearby lateral buds to grow. When the apical bud is removed, the lateral buds sprout. This produces dense bushy growth. The phenomenon is widely used in tea plucking and hedge making. Apical bud inhibits the growth of lateral buds by releasing auxins. Apical dominance caused due to auxin can be counteracted by application of cytokinin. Presence of cytokinin in an area causes preferential movement of nutrients towards it. When applied to lateral buds, they help in their growth despite the presence of apical bud. Thus they act antagonistically to auxin.
9.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?
Solution. In plants, auxins are synthesised in different regions E.g., auxin is synthesised in shoot apices, leaf primordia and developing seeds and is transported to stem and root from cell to cell by diffusion. Transport of gibberellins synthesised in shoot buds, root tips and developing seeds occurs through simple diffusion and through conducting channels. Cytokinin synthesised in roots move upwardly through xylem. Abscisic acid produced in many parts of plants, mainly inside the chloroplasts of green cells is transported through diffusion and transport channel.
lO.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?
Solution. Discovery of plant hormone gibberellin was accidental. It happened by chance in rice fields. A few plants of rice were observed, which were thin, pale green, unusually taller than the normal ones. Scientific investigation revealed that these were infected with a fungus, known as Gibberella fujikuroi. This fungus releases a plant hormone gibberellic acid in excess concentrations which makes the plant to grow unusually tall. This compound was later known as gibberellin, a hormone present in plants and fungi. The term used for accidental finding is ‘serendipity’ which means ‘fortunate happenstance’, or ‘pleasant surprise’. This term was coined by Horace Walpole in 1754.
11.To get a carpet like grass, lawns are mowed regularly. Is there any scientific explanation for this?
Solution.Regular mowing (cutting at apex) of la wn grass removes the apical portion of the plant which causes the lateral branches to grow faster. As the apical buds inhibits growth of lateral buds by releasing auxin, (phenomenon called apical dominance). Because of mowing of the grass, it becomes bushy and growth is faster. So,-to maintain evenness of the grass (carpet-like) in the lawn, this practice is followed regularly to overcome the problem of apical dominance.
12.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?
Solution. the meristematic cells can be identified on the basis of the following characteristics:
(i) Cells have thin cellulose walls and dense cytoplasm with large nucleus.
(ii)Plasmodesmatal connections are more numerous among meristematic cells.
(iii)ell division, i.e., mitosis and its various stages are distinctly visible.
(iv)Chromosomes of cells replicate and divide into two homologous chromatids.
All these features contribute to open ended growth where structure is never complete in meristematic regions.
On the other hand, cells incapable of dividing show features such as:
(i) Cells have large vacuoles.
(ii)Attain particular shape, size and thickening.
(iii)Undergo structural and physiological differentiation.
13. 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).
Solution. In an experiment with oat coleoptile, hormone auxin stimulates bending of shoot tip towards the source of light. This is called plasticity and is irreversible. Plasticity is the ability of plant to acclimatise with the prevailing environmental conditions. Attaching weight to coleoptile segment causes it to bend, stretching it. After the weight is removed, the shoot returns to its original position. This is called elasticity and is a reversible phenomenon.
14. Label the diagram.
(a) This is which part of a dicotyledonous plant?
(b) If we remove part 1 from the plant, what will happen?
The diagram shows shoot apex of a dicotyledonous plant.
(b) Part 1 is showing inner cellular mass of shoot apex known as corpus. Cells of corpus are large and divide in different planes. Cells derived from corpus form procambium and ground meristem.
15.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?
Solution. Plant growth is different from animal growth as growth in plants is unlimited and indefinite. Root and shoot tips in the plants are open ended, i.e., always growing and forming new organs to replace the older and senescent ones due to presence of meristem cells which are capable to grow and divide. Thus, the plant growth continues throughout the life. On the contrary, animal growth is limited as growth/stops as soon as they mature. Sponges are those animals which show cellular level of organisation. These animals posses totipotent cells which are capable of giving rise to all other cells in sponges. A small part detached from a sponge can regenerate into a whole new sponge. However, growth in sponges cannot be called open or indefinite as they cannot grow beyond a certain size. Practically, they do not show open ended growth.
16.Define parthenocarpy. Name the plant hormone used to induce parthenocarpy.
Solution. Parthenocarpy is the formation of fruit without fertilisation. The fruit produced by parthenocarpy does not bear seeds. E.g., pineapple, banana, apple, pear etc. Parthenocarpy can be induced by application of auxin, gibberellin, cytokinin and abscisic acid.
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.
Solution.Seedless watermelons are actually obtained through cross hybridisation between a diploid and a tetraploid parent. These are triploid, i.e., have three sets of chromosomes. This genome makes watermelon plant sterile and they do not produce seeds. Triploid genome is obtained by mating diploid male with tetraploid female. The traditional melons are made tetraploid by treating them with colchicine. Triploid plants are grown alongside with diploid lines to produce pollen to carry out pollination, resulting in seedless watermelon.
18.A gardener finds some broad-leaved dicot weeds growing in his lawns. What can be done to get rid of the weeds efficiently?
Solution. Weeds can be eradicated by using weedicides. Weedicides are chemicals which kill weeds growing in the fields. Application of 2 : 4-D and 2:4: 5-T removes broad leaved weeds in cereal crops and lawns because they do not affect mature monocotyledons while dalapon (2-2 dichloropropionic acid) kills grasses in broad leaved crops. Weedicides should be used very carefully and only occasionally as they have wide spectrum and long lasting action.
19.0n 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?
Solution.(a) On germination, a seed first produces shoots with leaves i.e., a plant enters its vegetative growth phase. The leaves receive light stimulus and manufacture food for the whole plant by the process of photosynthesis and the plant grows vegetatively. After achieving some vegetative growth the critical photoperiod regulates flowering in a plant. Photoperiodic, stimulus is picked up by phytochrome in fully developed leaves and photoperiodic induction occurs when the plant has achieved certain minimum vegetative growth,, e.g., 8 leaves in Xanthium strumarium. Leaves receiving the stimulus produce a chemical which induces flowering that has been named as florigen.
(b) Reproductive phase follows vegetative growth phase in plants. This is an adaptation or rather necessity as vegetative growth period prepares the plant to bear reproductive structures like flower, fruits and seeds. Moreover, reproductive or gametophytic phase in flowering plants is totally dependent on vegetative phase for nourishment as it does not bear any structure to carryout photosynthesis or absorb mineral nutrition directly from soil.
20. FHI 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________
Solution. (a) exponential
Long Answer Type Questions
1.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?
Solution. Many plants do not come to flower before they experience a low temperature. These plants remain vegetative during the warm season. When they receive low temperature during winter, they grow further and then bear flowers and fruits. Requirement of low temperature prevents precocious reproductive development in autumn. It
allows the plant to reach vegetative maturity before reproduction can occur. The condition occurs in winter varieties of some annual food plants (e.g., wheat, barley, rye), some biennial (e.g., cabbage, sugarbeet, carrot) and perennial plants (e.g., Chrysanthemum). The annual winter plants also possess spring varieties. The spring varieties are planted in spring. They come to flower and bear fruits prior to end of growing season. If the winter varieties are sown similarly, they fail to flower and produce fruits before the end of growing season. They are planted in autumn, form seedlings in which form they pass winter. The seedlings resume growth in spring. They bear flowers and fruits in summer.
2.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?
Solution. (a) Winter varieties are planted in autumn, form seedlings in which form they cover winter. The seedlings resume growth in spring. They bear flowers and fruits in summer. It requires low temperature to bear flowers and fruits. Requirement of low temperature prevents precocious development in autumn.
3.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.
Solution. (a) Ethylene