CBSE Class 11 Biology VBQs Plant Growth And Development

Refer to the given structure of a hormone (A) whose various concentration effect is shown in the graph B and answer the questions.

Question. The given structure A represents
(a) NAA
(b) GA
(c) IAA
(d) ABA

Answer : C

Question. Which of the following is correct regarding action of A from the given graph B?
(a) A helps in elongation of both root and shoot but the optimum concentration for the two is different.
(b) A acts as growth inhibitor at higher concentration.
(c) Movement of A is basipetal in root but acropetal in the stem.
(d) Both (a) and (b)

Answer : D

Question. High concentration of A is present in
(a) flower
(b) stem apex
(c) node
(d) petiole.

Answer : B

Question. Which of the following effects of A or plants is the basis for their commercial application in tissue culture?
(a) Callus formation
(b) Curvature of stem
(c) Induction of root formation in stem cuttings
(d) Induction of shoot formation

Answer : C

Question. Artifical application of A to unpollinated pistils can form
(a) fruits with much flesh
(b) seedless fruits
(c) larger fruits
(d) sweet fruits

Answer : B

Very Short Answer Type Questions

Question. What is Richmond-Lang effect?

Answer.  The delay in senescence of leaves and other parts by mobilisation of nutrients is called Richmond-Lang effect.

Question. Name a plant growth regulator that is often inhibitory in function but also promotes certain functions.

Answer.  Ethylene

Question. Name the universal natural auxin.

Answer.  Universal natural auxin is IAA -Indole 3-Acetic acid.

Question. Which hormone is used to increase sugar production in sugarcanes?

Answer.  Gibberellin is used to increase sugar production in sugarcane.

Question. What is bioassay? Name any two bioassays for auxins.

Answer.  Quantitative estimation of biologically active substances by measurement of their activity on living organisms or their part is called bioassay. Avena curvature test and root growth inhibition test are the bioassays for examining auxin activity.

Short Answer Type Questions

Question. (a) What is the site of synthesis of auxin in plants?
(b) How is it transported in plant body?

Answer. (a) Auxin is synthesised in shoot apices and leaf primordia.
(b) It is transported by shoot tip to region of elongation. Its movement in plants body is polar, i.e., basipetal in stem and acropetal in root.

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

Answer. 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.

Question. 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.

Answer. (a) Auxins like IBA, NAA.
(b) Ethylene
(c) Cytokinins
(d) Cytokinins
(e) Gibberellins
(f) Abscisic acid (ABA)

Question. Suggest some ways in which inhibitors might be important to plant survival.

Answer. Inhibitors are important to the survival of higher plants in temperature zones. These plants become dormant during harsh winter period or when conditions are not capable of supporting an active plant. Seeds often will not begin to germinate until they have been exposed to cold and then brought to moderate temperature. The breaking of dormancy and the beginning of growth depend on the release from inhibition of vigorous metabolic activity.

Question. 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) Antiauxins
(c) Synthetic auxins

Answer. (a) Auxin precursors : These are the raw materials used in synthesis of auxin. e.g., tryptophan is precursor for indole- 3-acetic acid (IAA).
(b) Anti-auxins : These 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.

Question. Give one bioassay for gibberellins.

Answer. Some seeds of dwarf seedlings of garden pea (Pisum sativum) were germinated. Once their coleoptile was formed, a solution rich in GA was administered to some seedlings, while other seedlings were kept under control. After some days, it was found that in the dwarf plants kept under control, reduced internode elongation was exhibited which is characteristic of the dwarf growth habit, whereas for those plants treated with solution containing gibberellin, the stem was elongated due to elongation of the internodes. It was also found that when gibberellin was applied to the dwarf mutant of pea (or rice or bean etc.), it restores a normal tall phenotype; however, gibberellin has no appreciable effect on the genetically normal plant.

Question. In metro cities there is lack of space for gardens. Suggest a technique by which plants can be grown without need of soil and land space.

Answer. The technique which can be used is hydroponics, in which nutrient solution is used for growing plants.

Question. These days the fruits we bring from market are to be washed thoroughly and some need to be dipped in water for sometime before eating, why?

Answer. In market these days the fruits are artificially ripened using chemicals like carbide. These chemicals produce ethylene which increases the rate of ripening of the fruits. So, the fruits sure to by washed to remove these chemicals.

Question. These phytohormones were first discovered in Japan when rice plants suffered from bakane (the foolish seedling disease) caused by a fungus Gibberella fujikuroi.
(a) Name and give two functions of this phytohormone.
(b) Which property of this phytohormone caused foolish seedling disease in rice?

Answer. (a) The phytohormone is identified as gibberllin. 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. Two 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 leads to abnormal increase in stem length of rice plants causing foolish seedling disease or bakane disease.

Question. (a) Gibberellins are plants hormones with a large number of physiological functions. Some of these gibberellins are used commercially to improve production in agriculture. Mention its commercial applications.
(b) Where are gibberellins synthesised in plants and how do they get transported?

Answer. (a) The commercial uses of gibberellin are - (i) Application of gibberellins increases the number and size of several fruits, e.g., grape, tomato. Size and shape of apple fruits is also enhanced by application of GA4 and GA7 mixture. (ii) Seedless pomaceous fruits can be produced by application of gibberellins to unpollinated flowers, i.e., induce parthenocarpy. (iii) Gibberellins (e.g., GA3) increases the yield of malt from barley grains. (iv) Gibberellins can be employed for breaking seed and bud dormancy. They induce germination of positively photoblastic seeds of tobacco and lettuce in complete darkness. (v) GA7 delays senescence so that fruit can be left on the tree for longer period. Ripening of Citrus fruits can also be delayed with the help of gibberellins which is useful in storing the fruits. (vi) Gibberellins can be used in inducing offseason flowering in many long day plants as well as requiring vernalisation. (vii) Spraying of sugarcane crop with gibberellins increases length of stem and yield of sugar to as much as 20 tonnes/ acre. (b) Gibberellins are synthesised in apical shoot buds or young leaves, root tips and developing seeds. They are transported through simple diffusion as well as through conducting channels.

Question. What functions of ethylene contribute towards improved growth and increase in number of fruits?

Answer. (i) Ethylene is used in thinning of excess flowers and young fruits, which helps in improved growth of remaining fruits.
(ii) It stimulates flowering in certain group of plants and help in synchronising fruit set. (iii) It has a feminising effect on certain plants, hence number of female flowers increases. Thus, fruit formation is enhanced in plants.

Long Answer Type Questions

Question. Mention the factors which prove that phytohormones act synergisticalliy or antagonistically. 

Answer. The factors which prove the phytohormones act synergistically or antagonistically are
(i) Cell division is promoted by both auxins and cytokinins acting synergistically.
(ii) Auxin and cytokinins interact to control morphogenetic differentiation of shoot and root. When auxin is in excess, roots differentiate on the callus, while excess of cytokinins promote bud formation.
(iii) Auxins and cytokinins acts antagonistically in controlling apical dominance. Auxins causes apical dominance, while cytokinins overcome same.
(iv) Senescence is prevented by auxins and cytokinins, while it is stimulated by abscisic acid and ethylene.
(v) The activity of cambium and fruit growth seem to be promoted by auxins, gibberellins and cytokinins, the same is inhibited by abscisic acid.
(vi) The dormancy of seeds and buds is mostly due to abscisic acid, the same is broken by gibberellins.
(vii) Cytokinins cause opening of stomata, while abscisic results in their closure.