Chapter 15: Plant Growth and Development

Q1Written answer

Fill in the blanks 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 cultures.

d. ……… of a vegetative plants are the sites of photoperiodic perception.

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Worked solution

Ans: Exponential phase

Ans: Auxin

Ans: Cytokinin

Ans: Leaves

Q2Written answer

Plant growth substances (PGS) have innumerable practical application. 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

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Worked solution

Ans: Gibberellic acid

Ans: Cytokinin

Ans: Ethylene

Ans: Abscissic acid

Q3Written answer

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

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Worked solution

Ans. Absolute Growth rate can be calculated as follow:

\[{W_1} = {W_0}{e^{rt}}\;\]

Where, \[{W_1}\]is the ultimate size (weight, height, number etc.)

\[{W_0}\]\[ = \] initial size at the beginning of the period

\[r\]\[ = \]growth rate

\[t{\text{ }} = \]time of growth

\[e{\text{ }} = \]base of natural logarithms

Here,\[\;r\] is the relative growth rate

Given \[{W_1}{\text{ }} = \] \[19{\text{ }}cm\]

\[{W_0}{\text{ }} = \]\[5{\text{ }}cm\]

\[t{\text{ }} = {\text{ }}7\]\[days\]

\[ \Rightarrow 19 = 5 \times {\left( {2.7} \right)^{r \times 7}}\]

\[ \Rightarrow \dfrac{{19}}{5} = {\left( {2.7} \right)^{r \times 7}}\]

\[ \Rightarrow 3.8 = {\left( {2.7} \right)^{7r}}\]

\[ \Rightarrow \log 3.8 = 7r \times \log 2.7\]

\[ \Rightarrow 0.5798 = 7r \times 0.4314\]

\[ \Rightarrow r = \dfrac{{0.5798}}{{7 \times 0.4314}} = 0.1907\]

Relative growth rate can be calculated as follows:

$r = \dfrac{{final\,size}}{{initial\,size}}$

$\therefore r = \dfrac{{19}}{5} = 3.8cm$

Absolute growth rate \[ = {\text{ }}0.1907\]

Relative growth rate \[ = 3.8{\text{ }}cm\]

Q4Written answer

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?

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Worked solution

Ans: Gibberellin induces bolting, i.e. growth of internode in rosette plants. Gibberellin also induces seed germination by breaking seed dormancy.

Ans: The fungus produces a lot of Gibberellin. This promotes too much growth in internodes and the plant becomes too tall to hold its own weight.

Q5Written answer

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

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Worked solution

Ans: In Cannabis, gibberellins encourage the development of male flowers on genetically female plants, whereas ethylene encourages the development of female flowers on genetically prepared male plants.

Q6Written answer

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.

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Worked solution

Ans: Long Day Plants (LDP): Bryophyllum, Spinach, Henbane

Short Day Plants (SDP): Xanthium, Rice, Strawberry

Day Neutral Plants (DNP): Sunflower, Tomato and Maize

Q7Written answer

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?

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Worked solution

Ans: Ethylene

Q8Written answer

Where are the following hormones synthesized in plants

a. IAA

b. Gibberellins

c. Cytokinins

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Worked solution

Ans: Growing apices of plant, e.g. shoot tip, leaf primordial and developing seeds.

Ans: Apical shoot buds, young leaves, root tips and developing seeds

Ans: These are synthesized mainly in roots

Q9Written answer

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

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Worked solution

Ans: These plants' apical dominance prevents the formation of lateral branches. Removing the shoot apex encourages lateral development, resulting in bushier plants.

Q10Written answer

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

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Worked solution

Ans: Photosynthesis, transpiration, and blooming are three physiological processes in plants that are influenced through light.

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