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NCERT Class 11 Biology Chapter 15 Plant Growth and Development
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Plant Growth and Development
Chapter: 15
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
Ans. Growth is irreversible and permanent increase in the weight and volume of an organism.
Differentiation — It is process by which totipotent cell undergo changes as per function they have to do.
Dedifferentiation — It is process by which differentiated cell regain the capacity to divide.
Redifferentiation — It is process by which product cells of dedifferentiation undergo differentiation and maturation into specific cell types.
Development refers to the various changes from growth, differentiation and maturation which occur in the life cycle of an organism.
Determinate growth – is limited growth or growth which stops after a time period.
Meristem is tissue consisting of unspecialized immature cells having the capacity of continuous cell divisions and adding new cells.
Growth rate -is increased growth per unit time.
Q.2. Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
Ans. Any one parameter is not good enough to demonstrate growth throughout the life of a flowering plant because increase in the growth may occur in number, length, weight or volume.
Q.3. Describe briefly:
(a) Arithmetic growth.
Ans. Arithmetic growth: It is a linear growth curve mathematically expressed as Lₜ = L₀ + r t.
(b) Geometric growth.
Ans. Geometric growth: It is sigmoid growth curve mathematically expressed as Wₜ = Wₒ eʳᵗ.
(c) Sigmoid growth curve.
Ans. Sigmoid growth curve: Growth curve is graphic representation of total growth against time. It is S shaped or sigmoid curve. It consist of four parts-
(i) Lag phase (Slow growth).
(ii) Log or exponential phase (rapid growth).
(iii) Diminishing growth phase.
(iv) Stationery (growth is steady or stop).
(d) Absolute and relative growth rates.
Ans. Absolute and relative growth rates Absolute growth rate is the measurement and comparison of total growth per unit time.
Relative growth rate is the growth of a particular system per unit time, expressed on a common basis.
Q.4. List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural / horticulture applications of any one of them.
Ans. Five main groups of plant growth regulators are:
(i) Indole derivatives – IAA / indole acetic acid.
(ii) Adenine derivative – cytokinin (aminopurine)
(iii) Carotenoids derivate – abscisic acid.
(iv) Terpenes – Gibberellins.
(v) Gases – ethylene.
Gibberellin was first isolated from fungal pathogen Gibberella fujikuroi which causes Bakane disease [foolish seedling] disease of rice seedlings.
(vi) GA’S are acidic growth hormone.
(vii) They are synthesized in apical shoot buds (young leaves), root tips and developing seeds.
Functions-
(i) Cell elongation Stem and leaf growth by increase in length of axis.
(ii) Fruit growth — increases the number and size of fruits.
(iii) Bolting [ internode elongation prior to flowering] in rosette plants e.g. cabbages and radish.
(iv) Seed germination Gibberellins produce enzymes which solubilize the reserve food of seed.
(v) Flowering in long day plants.
(vi) Delay senescence / ripening of fruits.
(vii) Spraying sugarcane crop with gibberellins increases length of stem and yield of sugarcane.
(viii) Early maturity in Juvenile conifers.
(ix) Gibberellin is used to speed up malting process in brewing.
Q.5. What do you understand by photoperiodism and vernalisation? Describe their significance.
Ans. PHOTOPERIODISM:
(a) It is the flowering response of plants to periods of day/night.
(b) Site of perception of light/dark duration are leaves.
(c) Phytochrome-
(i) This is cytoplasmic chromoprotein in leaves that perceives the photoperiodic stimulus.
(ii) Phytochrome regulates photoperiodism, germination and vegetative growth.
VERNALIZATION:
(a) It is shortening of Juvenile or vegetative phase and hastening the flowering by exposure to low temperature.
(b) Stimulus of Vernalization is perceived by meristematic cells like root apex, shoot tips, embryo tips.
(c) It is seen in:
(i) Annual plants like wheat, barley, rye.
(ii) Biennial plants [these are monocarpic plants that flower and then die in second season] e.g. sugar beet, cabbage, carrot etc.
(d) Vernalization can be replaced by Gibberellins.
Q.6. Why is Abscisic acid also known as stress hormone?
Ans. Abscisic acid is called stress hormones hormone because It increases resistance to cold, drought and other types of stress.
Q.7. Both growth and differentiation in higher plants are open’. Comment.
Ans. Plant growth is open or they growth throughout their life due to meristems where cells have capacity to divide. Differentiation in plants is open because cells from same meristem have different structures at maturity.
Q.8. ‘Both a short day plant and a long day plant can flower simultaneously in a given place’. Explain.
Ans. Both a short day plant and a long day plant can flower simultaneously in a given place by using Cytokinins and gibberellins respectively.
Q.9. Which one of the plant growth regulators would you use if you are asked to:
(a) Induce rooting in a twig.
Ans. Auxins.
(b) Quickly ripen a fruit.
Ans. Ethylene.
(c) Delay leaf senescence.
Ans. &.
(d) Induce growth in axillary buds.
Ans. Cytokinins.
(e) ‘Bolt’ a rosette plant.
Ans. Gibberellic acid.
(f) Induce immediate stomatal closure in leaves.
Ans. Abscisic acid.
Q.10. Would a defoliated plant respond to photoperiodic cycle? Why?
Ans. A defoliated plant will not respond to the photoperiodic cycle because phytochrome is present in the leaves.
Q.11. What would be expected to happen if:
(a) GA3 is applied to rice seedlings.
Ans. Internodal elongation and increase in height.
(b) Dividing cells stop differentiating.
Ans. Callus formation.
(c) A rotten fruit gets mixed with unripe fruits.
Ans. Ethylene produced by rotten fruits will hasten the ripening of the unripe fruits.
(d) You forget to add cytokinin to the culture medium.
Ans. Cell division will not occur.
