NCERT Solutions for Class 11 Science Biology Chapter 15 - Plant Growth And Development

Answer:

Ethylene is a gaseous plant growth regulator (PGR). This PGR is highly effective in fruit ripening.

Hence, the correct answer is option b.

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Cytokinin hormone is present in the coconut water. Cytokinin helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot formation.

Hence, the correct answer is option c.

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Cytokinin hormone helps to overcome apical dominance and this hormone also promote the mobilsation of nutrients that helps in delay of leaf senesense.

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Correct Match:
 

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Ethylene is a gaseous PGR and is also called ripening hormone. This hormone is highly effective in ripening of fruit because it enhances the rate of respiration during fruit ripening and the rise in rate of respiration is called respiratory climactic. Apples are generally wrapped in waxed paper to prevent aerobic respiration by checking the entry of O₂ .

Hence, the correct answer is option b.

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At cellular level, growth is principally a consequence of increase in the amount of protoplasm.
Growth is measured by a variety of parameters such sa:
(i) Increase in fresh weight
(ii) Dry weight
(iii) Length
(iv) area
(v) volume
(vi) cell number

Hence, the correct answer is option d.

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When two hormones act together and contribute to the same function, it is called the synergistic action of hormones.

Hence, the correct answer is option b.

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Plasticity is the ability of plants to follow different path ways in response to environment or phases of life to form different types of structures.
For example: heterophylly in cotton, coriander and larkspur.

Hence, the correct answer is option b.

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Carbohydrates in the form of sugar is stored in sugarcane stem. Spraying gibberellin on sugarcane crop increase the length of the stem and thus increasing their yield by as much as 20 tonnes per acre.

Hence, the correct answer is option c.

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ABA (Abscisic acid) acts as an antagonist to gibberellic acid because they act oppositely to each other like gibberellic acid promotes growth and ABA inhibits growth. Gibberellic acid promotes germination and ABA promotes seed dormancy and so on.

Hence, the correct answer is option c.

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Biennials and annual plants are monocarpic plants such plants normally flower once in their life span, bear seeds and die. For example: sugarbeet, cabbages, carrot.

Hence, the correct answer is option b.

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Photoperiodism is the response of plants to periods of day or night to induce flowering. The site of perception of light or dark durations are on leaves.

Hence, the correct answer is option d.

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a. A phase of growth which is maximum and fastest is   Log or exponential phase   .
b. Apical dominance as expressed in dicotyledonous plants is due to the presence of more  auxin  in the apical bud than in the lateral ones.
c. In addition to auxin, a   cytokinin   must be supplied to culture medium to obtain a good callus in plant tissue culture.
d.   Leaves  of a vegetative plants are the sites of photoperiodic perception.

Answer:

a. Gibberellins
b. Cytokinins
c. Ethyline
d. Abscisic acid
 

Answer:

Growth rate:
L₁ = L_o + rt
19 = 5 + r × 1
19 – 5 = r × 1
14 = r × 1
r = 14 cm
Relatives growth rate = $\frac{\mathrm{Final} \mathrm{size} \mathrm{of} \mathrm{plant}}{\mathrm{Initial} \mathrm{size} \mathrm{of} \mathrm{plant}}\times 100$

                                  $$\begin{gathered} \Rightarrow \frac{19}{5}\times 100 \\ \Rightarrow 3.8\times 100 \\ \Rightarrow 380\% \end{gathered}$$

Answer:

(a) Functions of gibberellin:
(i) Gibberellins promotes bolting or internodal elongation just prior flowering in beet, cabbages and many plants with rosette habit.
(ii) This hormone is also responsible for delaying senescence.

(b) The rice seedling shows uncontrolled growth in their internodal region when the plant is infected by the fungus,  as gibberellin promotes internodal elongation.

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Gibberellins promote the formation of   male  flowers on genetically   female  plants in Cannabis whereas ethylene promotes formation of    female  flowers on genetically  male  plants.

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Ethylene is a plant growth regulator that promotes female flowers in cucumbers and increasing the yield.

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a. IAA - IAA or indole acetic acid is produced by the growing apices of the stems and roots.
b. Gibberellins - This hormone is synthesised in the apical shoot buds, young leaves and root tips.
c. Cytokinin - This hormone is synthesised at the meristmatic region of the root as well as developing shoot buds and growing embryos.

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The growing apical bud in higher plants inhibits the growth of the lateral or axillary buds and this phenomenon is called apical dominance. Removal of shoot tips is called decapitation results in the growth of lateral buds because it decreases the level of auxin and increases the level of cytokinin in the plant. Cytokinin promotes lateral shoot growth. This method of shoot tip removal is applied in tea plantations to increase its yield.

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Photosynthesis, transpiration and flowering are three physiological processes in plants that are affected by light.

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Labelled graph:

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Yes, unicellular organisms also grow. The unicellular organisms grow by dividing the cell due to an increase in cell mass as well as an increase in cell number.

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Gibberellin hormone is responsible for internodal elongation of plants. Foolish seeding disease in rice is caused due to the internodal elongation by gibberellin hormone.

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A short day plants are types of plants that require exposure to light period less than critical light period. The flowering in such plants is initiated only when the photoperiod is below the critical period. Leaves are the site of perception for light or dark period. Some hormonal substances play an important role in flowering and these substances migrates from leaves to shoot apices to induce flowering only when the plants are exposed to the required inductive photoperiod.

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a. Meristematic cells near root tip:-
The meristematic cells near root tip have actively dividing cells. They have large nucleus, rich protoplasm and less number of vacuoles. No intercellular spaces are observed within the cells.
b. The cells in the elongation zone of the root:-
In this region, cells contain a large number of small vacuoles and they fuse to form one large central vacuole. Due to this, cells become elongated and also produce longitudinal growth in this zone.

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Yes, the growth pattern in plants is different from the growth pattern in animals. In plants, only meristmatic tissues have actively dividing cells that grow indefinitely throughout the plants life.

Answer:

a. Differentiation: The process of leading to maturation is called differentiation. In this process the cells that are derived from root apical and shoot apical meristems as well as cambium differentiate and mature in order to play essential roles. The cells undergo some major structural changes in their cell walls and protoplasm.
For example: To form a tracheary element, the cells would lose their protoplasm. They also develop a very strong, elastic, lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension.
b. De-differentiation: It is a phenomenon in which the differentiated cells that have lost their dividing capacity, regain the capacity to divide under specific conditions.
For example: Meristems formation - interfasicular cambium and cork cambium from fully differentiated parenchyma cells.
c. Redifferentiation: It is a phenomena in which the dedifferentiated cells again lose their ability to divide.
​For example: Tissues present in woody dicotyledenous plant.

Answer:

a. Auxin precursors: They are the raw materials that are needed for synthesis of auxin.
For example: Tryptophan is a precursor of auxin.
b. Anti-auxins: They are some compounds that inhibit the action of auxin.
For example: NPA (Napthylphthalamic acid).
c. Synthetic auxins: They are artificial auxins synthesised in the laboratory.
For example: 2, 4-D (2, 4 - dichlorophenoxy acetic acid), ​NAA - (naphthalene acetic acid).

Answer:

Positive role of ethylene:
(i) This hormone influences horizontal growth of seedlings swelling of axis and formation of apical hook in dicot seedlings.
(ii) It breaks seed dormancy and promotes sprouting in potato tubers.

Negative role of ethylene:
This hormone promotes senescence and abscission of plant organs especially in leaves and flowers.

Positive role of abscisic acid:
(i) It helps to reduce water loss by reducing transpiration.
(ii) It induces flowering in short day plants.
(iii) It helps plants to combat environmental stress situations.

Negative role of abscisic acid:
(i) ABA inhibits seed germination and also stimulates the closure of stomata.
(ii) It induces fruit and flower abscission.

Answer:

Plant growth regulators (PGRS) may act synergistically or antagonistically. When the two hormones comes together it is called synergistic effect. When two hormones counters the effect of each it is called antagonistic effect. Due to this it becomes difficult to assign any effect seen to any single hormone.
For example: auxin and cytokinin act synergistically to control the shoot stem-cell meristem. On the other hand, both the hormones act antagonistically to control the root meristem,

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The growing apical buds in higher plants inhibits the growth of the lateral (axillary) buds. This phenomenon is called apical dominance.
Auxins play an important role in controlling apical dominance because they are generally produced by the growing apices of the stems
and roots.
Apical dominance can be overcome by the removal of shoot tips (decapitation) which reduces the level of auxin and  results in the growth of lateral buds.

Answer:

Plant hormones are produced in different tissues and are translocated at the site of activity by the vascular bundle tissues such as xylem and phloem.
For example: These hormones are produced at the shoot tip, root tip, meristmatic tissues, apical buds and soon.

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The given statement "The discovering of plant hormones have been accidental" is true. This can be explained with the help of an example:
Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass that responded to unilateral illumination by phototropism (growing towards the light source). After a chain of experiments, it was concluded that the tip of coleoptile was the site of transmittable influence that is responsible for bending of the entire coleoptile.
F. W. Went isolated auxin hormone from the tips of coleoptiles of oat seedlings.

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Mowing lid tode capitation that involves the removal of shoot tips to promote the growth of lateral buds and inhibits apical dominance.

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The meristematic cells having following characteristics:
(a) Such cells possess thin cell wall.
(b) They have dense cytoplasm.
(c) Such cells show cell division.
(d) They have small or no vacuoles.
(e) They have no intercellular space.

Absence of above mentioned characteristics is observed in cells which are incapable of dividing.

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Rubber band have the property of elasticity and due to this they are stretched and revert to its original position. While bubble gum have the property of plasticity and due to that they would not return to its original position. It is an irreversible situation. Plants also have the ability of plasticity. In this phenomenon, they follow several pathways in response to environment or phases of life to form different kinds of structures.
For example: heterophylly in cotton, larkspur and coriander.

Answer:

Label 1 is shoot apical meristem and label 2 and 3 are leaf primordia.
a. It is the shoot apex meristem of a dicotylednous plant.
b. If part 1 is removed it will inhibit apical bud and promote the growth of lateral bud.

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In plants the growth is indeterminate as the cells can divide and enlarge continuously during their life time. Due to the presence of meristmatic tissue, plant cells divide continuously and they grow as well as replace old organs. While in animals, growth is determinate as the cells grow at some certain period, after that they mature and stop growing externally.
Sponges are the animals that have cellular level of organisation and shows the features of open ended growth. However, they can not grow after attaining a certain size.

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The process of development of fruit without fertilisation is called parthenocarpy. Such fruits does not contain seeds.
Parthenocarpy can be induced artificially by the application of auxin and gibberellin hormones in tomatoes, grapes, papaya etc.

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Parthenocarpy is the process of development of fruit without fertilisation. Fruits produced by this process are seedless. To produce seedless watermelon, auxin and gibberellin hormones are sprayed on the watermelon.

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Synthetic auxins such as 2, 4 - D is widely used to kill dicotyledonous weeds and it does not affect the mature monocotyledonous plants. This hormone is used to prepare weed free lawn by gardeners.

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a. After seed germination the plant enters into the vegetative growth phase. In this growth phase, leaves perceive light stimulus and a flowering hormone called florigen is synthesized that induces flowering.
b. The vegetative phase in plants prepare them for reproductive phase by making it capable of bearing reproductive structures such as flowers, fruits, etc. This phase also helps in survival of plant.

Answer:

a. Maximum growth is observed in  exponential  phase.
b. Apical dominance is due to  auxin . 
c.  Auxin hormone initiate rooting.
d. Pigment involved in Photoperception in flowering plants is  phytochrome .

Answer:

Flowering in some plants is dependent on exposure to low temperature and this phenomenon is termed as vernalisation. For example - wheat, rye and barley. These food grains have two varieties - winter and spring varieties.
If winter varieties of wheat is planted in spring season, it would fail to flower or produce mature grain within a span of flowering season. So, they are planted in autumn and they germinate and over winter, they come out as small seedlings. They resume growth in the spring and are harvested around mid-summer.

Answer:

a. If the winter varieties of wheat is planted in spring season, it would fail to flower and produce mature grains. So, they are planted in autumn and germinate. Over winter, they come out as small seedlings. They resume growth in the spring season and then are harvested around mid summer. This occurs because these wheat varieties complete their vegetative phase of growth during winter and summer season.
b. A phenomenon called vernalization in which flowering in some plants is dependent on exposure to low temperature.
c. Gibberellin hormone is used to replace the cold treatment in such plants. This hormone in many long day plant may induce flowering early by reducing their vegetative growth period.

Answer:

a. Ethylene
b. Auxin
c. Ethylene
d. Auxin
e. Gibberellin