NCERT Exemplar Class 11 Biology Solutions Chapter 15 Plant Growth and Development

Question:1

Ethylene is used for

(a) Retarding ripening of tomatoes
(b) Hastening of ripening of fruits
(c) Slowing down the ripening of apples
(d) Both b and c

Answer:
The answer is option (b) Hastening the ripening of fruits Ethylene is a naturally composed hormone within fruits and monitors the ripening of the fruit by inducing and regulating many chemical and biochemical activities.

Question:2

Coconut water contains
(a) ABA
(b) Auxin
(c) Cytokinin
(d) Gibberellin

Answer:
The answer is the option (c) Cytokinin
Coconut water hosts an abundance of cytokinin, which helps regulate cell growth and cell division.

Question:3

The effect of apical dominance can be overcome by which of the following hormones:
(a) IAA
(b) Ethylene
(c) Gibberellin
(d) Cytokinin

Answer:

The answer is the option (d) Cytokinin
During apical dominance, cytokinin antagonises the auxin and triggers outgrowth. The presence of cytokinin can induce the movement of nutrients towards the site where it is present. In lateral buds, the cytokinin present encourages growth despite the lateral buds having apical buds.

Therefore, cytokinin is antagonistic to auxin, and thus apical dominance can be overcome through the use of
cytokinin.

Question:4

Match the Following

Options:
(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)

Answer:

The answer is the option (a) A- (iv), B - (iii), C -(v), D - (ii), E- (i)

Question:5

Apples are generally wrapped in waxed paper to

(a) Prevent sunlight from changing its colour
(b) Prevent aerobic respiration by checking the entry of O₂
(c) Prevent ethylene formation due to injury
(d) Make the apples look attractive

Answer:
The answer is option (b) Prevent aerobic respiration by checking the entry of O₂.
To avoid the ripening of the apple, in order for it to stay fresh for a much longer time, aerobic respiration is prevented because it makes the apple rot much faster.

Question: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

Answer:

The answer is option (d) All the above
The growth can be in lateral or apex regions and can cause an enlargement in height or weight; all of these changes are collectively termed growth.

Question:7

The term synergistic action of hormones refers to

(a) When two hormones act together but bring about the opposite effect
(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 bong about anyone's function

Answer:

The answer is option (b) When two hormones act together and contribute to the same function.

When two or more hormones function mutually to deliver a certain effect, their outcomes are called synergistic. These results can be additive or complementary.

Question: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

Answer:
The answer is option (b) Plant development is dependent on the environment.
Plants take distinct paths in response to environmental changes and different stages of life to develop various types of compositions. This entire ability is called plasticity.

Question:9

To increase sugar production in sugarcanes, they are sprayed with
(a) IAA
(b) Cytokinin
(c) Gibberellin
(d) Ethylene

Answer:

(c) Gibberellin
Explanation: Gibberellin increases the length of the stem and thus increases the amount of sugar in sugarcane.

Question:10

ABA acts antagonistically to

(a) Ethylene
(b) Cytokinin
(c) Gibberellic acid
(d) IAA

Answer:

The answer is the option (c) Gibberellic acid
ABA's function is to inhibit growth and to be antagonistic to it; the correct option should encourage and promote growth and gibberellin does, so it is the correct option.

Question: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

Answer:

The answer is option (b) Flower once and die.
Monocarpic plants are known to flower, set seeds and then die consequentially.

Question:12

The photoperiod in plants is perceived at

(a) Meristem
(b) Flower
(c) Floral buds
(d) Leaves

Answer:

The answer is the option (d)Leaves
Leaves are the primary producers and receive light energy and thus are key players in the photoperiod.

NCERT Exemplar Class 11 Biology Chapter 15 Solutions -Very Short Answer Question:

The detailed answers to the Very Short Answer questions are given below:

Question:1

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 the culture medium to obtain a callus in plant tissue cultures.
(d) ___________ of vegetative plants are the sites of photoperiodic perception.

Answer:
(a) exponential phase
(b) auxin
(c) cytokinin
(d) Leaves

Question: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

Answer:
(a) Gibberellic acid
(b) Cytokinin
(c) Ethylene
(d) Abscisic acid

Question: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.

Answer:
The absolute Growth rate can be calculated as follows:
$W_1=W_0{e}^{rt}$
Where W₁ = final Size (weight, height, number etc.)
W₀ = initial Size at the beginning of the period
r = growth rate
t= time of growth
e = base of natural logarithms
Here, r is the relative growth rate
Given W₁ = 19 cm
W₀ = 5 cm
t =7 days
or,
Using W₁ = W₀ e^rt
$Weget19=5\times (2.7{)}^{7�r}$
Then
Then $3.8=(2.7{)}^{7�r}$
Then taking log on both sides,
$\log 3.8=7r\times \log 2.7$
Then, $0.5798=7r\times 0.4314$

$r=\frac{0.5798}{7\times 0.4314}$
Or $r=0.1907$
The relative growth rate can be calculated as follows:
$r=\frac{finalsize}{initialsize}$
$r=\frac{19}{5}$
r = 3.8 cm
Absolute growth rate$=0.1907$
Relative growth rate $3.8cm$

Question:4

Gibberellins were first discovered in Japan when rice plants were suffering from bakane (the foolish seedling disease) caused by the fungus Gibberena fujikuroi.

(a) Give two functions of this phytohormone.

(b) Which property of gibberellin caused foolish seedling disease in rice?

Answer:

(a) Two functions of the Gibberellin phytohormone are that encourage the sprouting of the seed by disruption of seed dormancy. In rosette plants, gibberellin induces the development of internodes; it encourages the process of bolting.

(b) The surplus quantity of gibberellin produced by the fungus causes foolish seedling disease in rice. The surplus of gibberellin thus induces the plants' development and hastens the growth in internodes. This thus results in the plant growing too tall and being
unable to bear its own weight.

Question:5

Gibberellins promote the formation of __________ flowers on genetically _____ plants in Cannabis, whereas ethylene promotes the formation of _________ flowers on genetically _______ plants.

Answer:
male, female, female, male

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

Question: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, Bryophyllum, Sunflower, Tomato, Maize, Strawberry

Answer:

Question: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?

Answer:

Ethylene
Ethylene encourages the development and increases the number of female flowers in monoecious species as it is known to be a growth regulator that has a feminising effect.

Question:8

Where are the following hormones synthesised in plants
(a) IAA
(b) Gibberellins
(c) Cytokinins

Answer:
(a) IAA is synthesised mainly in the shoot apices, primarily in the growing apices of plants. This includes the leaf primordial and developing seeds.

(b) Gibberellin hormone is synthesised in plants primarily in apical shoot buds, root tips as well as developing seeds.

(c) Cytokinin is synthesised in plants primarily in roots, endosperm region in the seeds as well as developing shoot buds and growing embryos.

Question:9

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

Answer:
Regular trimming makes the plants bushy as this growth is primarily based on the apical dominance of the plants. The apical dominance thus does not allow and in fact, prevents the growth of nearby lateral buds. This happens through the release of certain
auxins. If the shoot apex or the apical bud is removed, then the lateral buds can grow and sprout. This can lead to bushy growth.

Question:10

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

Answer:

The physiological processes in plants which are affected by light are: -

• Photosynthesis,
  This is the process through which the plant manufactures its own food in the presence of sunlight by utilising inorganic substances.
• Transpiration
  This is the process by which plants experience water loss in the form of vapour or dew formed on the leaves, primarily through the stomata. This process requires sunlight as the stomata are active and functioning only in the presence of sunlight.
• Photoperiodism
  This process typically decides the flowering of the plant, and the number of light hours affects this growth.

Question:11

In the figure of Sigmoid growth curve given below, label segments 1, 2 and 3.

Answer:

1. Lag phase.
2. Exponential phase and
3. Stationary phase

Question:12

Growth is one of the characteristics of all living organisms. Do unicellular organisms also grow? If so, what are the parameters?

Answer:
Growth is a process which marks the distinction between living and non-living beings. Unicellular organisms do not experience technical growth in length or volume, unlike their multicellular counterparts. In unicellular organisms, growth is synonymous and characterised by reproduction. The process of cell synthesis divides the cell into two daughter cells.

Question:13

The rice seedlings infected with the fungus Gibberella fujikuroi are called foolish seedlings. What was the reason behind it?

Answer:

The rice seedlings infected with the fungus Gibberella fujikuroi are called foolish seedlings because the rice plants which get infected with the fungus grow excessively in length in comparison to the plant species that are not infected. The height of the plant becomes disproportionate and is too much for the plant to bear, and it cannot support the weight of the plant, which leads to the plant's death ultimately. Hence, the plant causes its own death due to the infection by the fungus and is called foolish seedlings.

NCERT Exemplar Class 11 Biology Chapter 15 Solutions-Long Answer Type Questions:

The detailed answers to the Long Answer questions are given below:

Question:1

Some varieties of wheat are known as spring Wheat While Others are called winter wheat. The former variety is sown and planted in spring, and it 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.

Answer:

Some plants require special extrinsic conditions in order to commence the flowering stage, and one of the requirements can be a low temperature. Thus, the plants remain vegetative during the summer season and wait till they receive a low temperature to begin bearing flowers. Waiting for lower temperatures helps prevent precocious early active reproductive development. This helps the plant to gain proper maturity and develop within the vegetative state before advancing to the reproductive stage. This is called the vernalisation. Some plants have separate spring and winter varieties. For example, spring wheat is planted in the spring season and comes to flower and fruit right at the end of the season, but if the winter varieties are sown in the same season, then it will not bear flowers and fruits as compared to the spring variety.

Instead, the winter is planted in the autumn, and during the winter they form the seedlings. The seedlings resume their growth in the spring season and bear flowers during the summer. The winter wheat requires specific low temperatures to begin sprouting and maturing.

Question:2

It is known that some varieties of wheat are sown in autumn but are harvested around mid-summer.
(a) What could be the probable reason for this?
(b) What term is used for this promotion of flowering under low temperatures?
(c) Which plant hormone can replace the cold treatment?

Answer:
(a) These plants usually germinate and grow as seedlings throughout winter. They only resume growth when it is summer and are finally harvested around the upcoming midsummer. This is because these plants require low temperatures to bear flowers and
fruits and are able to finish their vegetative phase of growth over the period of winter and summer.
(b) This process mentioned here is called vernalisation.
(c) Gibberellin hormone can replace cold treatment effectively.

Question:3

Name a hormone which
(a) is gaseous in nature
(b) is responsible for phototropism
(c) induces femaleness in flowers of cucumber
(d) is used for killing weeds (dicots)
(e) induces flowering in long-day plants

Answer:
(a) Ethylene hormone is gaseous in nature.
(b) Auxin is responsible for phototropism.
(c) Ethylene hormone induces female characters in the flowers of cucumbers.
(d) Synthetic auxin (2,4-D) is used to kill weeds
(e) Gibberellin hormone induces flowering in long-day plants

NCERT Exemplar Class 11 Biology Chapter 15 Solutions- Short Answer Type Questions:

The detailed answers to the Short Answer questions are given below:

Question:1

Nicotiana tabacum, a Short-Day plant, when exposed to more than critical light fails to flower. Explain.

Answer:

Nicotiana tabacum is a short-day plant, and these plants require much less exposure to light than the required amount in normal plants. They demand a continuous critical dark period, which if interrupted, can affect the flowering of the plant. These plants require a photoperiod less than the generally required one and play a key role in flowering. This is due to the fact that flowering is regulated by a hormone which is present in the leaves and requires the dark photoperiod to migrate to the required places in the shoot apices.

Question:2

What are the structural characteristics of

(a) Meristematic cells near the root tip

(b) The cells in the elongation zone of the root

Answer:
(a) Meristematic cells are located in the zone, which is the growing point of the root, and in an active state of cell division. The cells are closely arranged and thin-walled and have dense protoplasm. They are essential for the growth of roots.

(b) In this zone, the cells are newly formed and lose the ability to divide, which is why they elongate and rapidly increase the length of the root. They have a large number of small vacuoles. These vacuoles fuse to form one large central vacuole. This is what
causes the cells to elongate and longitudinally grow in this region.

Question:3

Does the growth pattern in plants differ from that in animals? Do all the parts of the plant grow indefinitely? If not, name the regions of the plant, which can grow indefinitely.

Answer:

Animals and plants have different growth patterns and habits. Animals experience growth of definite, determinate form, which means they experience limited growth or stop growth after attaining maturity. Plants, on the other hand, can experience growth of definite or indefinite and indeterminate form. They can stop growing after attaining maturity of developing leaves and flowers or parts like the stem, and their branches can continue to grow. Plants experience continuous growth since they contain meristematic areas with potential for cell division, whereas animals have cell division only to replace and repair and not for the purpose of growth.

Question:4

Explain in 2-3 lines each of the following terms with the help of examples taken from different plant tissues:
(a) Differentiation
(b) De-differentiation
(c) Redifferentiation

Answer:

(a) To facilitate growth, the meristematic cells through mitotic division, divide into daughter cells. The cells ranging from the root to the shoot apical meristem are separated into different categories as they have matured and can perform specific functions. This phenomenon is called differentiation. During this phase, the cells experience critical structural modifications in the protoplasm and cell wall.

(b) Under certain conditions, the differentiated living cells can divide mitotically after recovering the ability to divide. This phenomenon is called de-differentiation. Sometimes, the de-differentiated cell may become the meristem; for example, fully differentiated parenchyma cells form the meristems and interfascicular cambium and cork cambium.

(c) The cells formed by de-differentiated cells can lose their capacity to reproduce and thus mature to perform specific functions. This is known as redifferentiation. For example, the secondary cortex and cork are prime examples as well as the cambium which de-differentiates to form the cortex.

Question:5

Auxins are growth hormones capable of promoting cell elongation. They have been 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

Answer:
(a) Auxin precursors are the raw substances utilised in the process of initial making and synthesis of auxins. For example- IAA's auxin precursor is tryptophan.
(b) Anti-auxins are compound substances which restrict the action of auxins. For example, TIBA and p-chlorophenoxy isobutyric acid (PCIB).
(c) Synthetic auxins are auxins which are artificially synthesised and do not occur naturally in plants. For example, 2:4-D, NAA.

Question:6

The role of ethylene and abscisic acid is both positive and negative. Justify this statement.

Answer:

Both ethylene and abscisic acid have positive and negative effects.
Positive Effects of Ethylene:

• Ethylene acts as a hormone which induces apical dominance and encourages horizontal growth
• It interrupts the dormancy of seeds and buds
• Ethylene aids in the initiation of the root
• Ethylene also helps in the ripening of certain fruits

Negative Effects of Ethylene:

• Ethylene causes the abscission of leaves because it hastens the senescence of leaves
• Ethylene delays longitudinal development in the plant
• Ethylene extends the dormancy of lateral buds

Positive Effects of Abscisic Acid:

• Helps reduce water loss in the form of transpiration
• Induces flowering in short-day plants
• In certain plants such as Rosen, abscisic acid encourages parthenocarpic development as well as the rooting of stem-cutting
• Helps plants form resistance to environmental stress
• Promotes root initiation in certain plants

Negative Effects of Abscisic Acid:

• Encourages the abscission of flowers and fruits and induces leaf senescence.
• Inhibits and slows down the cambial activity
• Retards the effect and functioning of growth hormones.
• Promotes dormancy in seeds and

Question:7

While experimenting, why do you think it is difficult to assign any effect seen to any single hormone?

Answer:

Plant hormones mostly work together, complementary to each other. Plant hormones can have both synergistic and antagonistic interactions which affect the plant tissues. A single hormone can have multiple effects, while multiple hormones can target and aim to achieve just one effect. Therefore it can be exceedingly difficult to identify one single hormone according to its particular effect on plant metabolism and system. Moreover, plant hormones function in the presence of a lot of extrinsic factors which are needed for the reaction. Thus, it is difficult to assign any effect seen to any single hormone.

Question: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.

Answer:
This phenomenon by which the terminal/apical bud suppresses the growth of the lateral buds is called apical dominance. On removal of the apical bud, the lateral buds are allowed to sprout, which produces bushy growth. The apical bud restricts the growth of the lateral buds through the release of certain auxins. Thus the auxin causing apical dominance can be countered with cytokinin. This attracts nutrients and helps the lateral buds to grow by acting as an antagonistic.

Question: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?

Answer:
Plant hormones are produced by individual cells in the regions where they are essential to the plants. To take an example, auxin is synthesised in the cells where there are growing apices. The vascular system of plants is where plant hormones are translocated through. Other examples include the Abscisic acid produced in many parts of plants, which is transported through diffusion and transport channels.

Question:10

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?

Answer:

Various plant hormones and other scientific research have been led by accidental means. Gibberellin was discovered accidentally, and Charles Darwin and his son Francis Darwin accidentally came across the auxin. They noticed that coleoptiles of canary grass reacted to unilateral illumination through growth in the direction of light. After some time, F W Went separated auxin from coleoptiles of oat seedlings.

The term used for accidental discovery is 'serendipity'

Question:11

To get carpet-like grass lawns are mowed regularly. Is there any scientific for this?

Answer:

Ans. Mowing regularly means the trimming of the apical parts of the plant, which thus causes the sprouting and faster growth of lateral branches. Thus apical dominance is prevented and restricts the longitudinal growth of the plant. Since the apices are removed, the auxins released due to the apical buds inhibit the lateral buds from getting mobilised and encourage the growth of lateral branches. This helps in maintaining carpet-like lawns.

Question: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?

Answer:

The presence of the following characteristics would indicate meristematic cells in the slides showing different types of cells:

(a) Thin cellulose wall
(b) Dense cytoplasm with a large nucleus
(c) Cells displaying cell division, like mitosis and other various stages.
(d) Smaller-sized vacuoles or even negligible vacuoles.

If the above features are absent, then it can be determined that the cells are incapable of division.

Question:13

A rubber band stretches and reverts to its original position. Bubble gum stretches, but it does 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)]

Answer:

Referring to an experiment with oat coleoptile, the auxin hormone induces the shoot tip tending in the direction of the light source. This process is irreversible and is known as plasticity. It is the plant's ability to adjust to the surrounding environmental
conditions. While, if weight is attached to the coleoptile segment, the weight causes bending and thus stretches the plant. If the weight is removed, the shoot of the plant returns to the original position meaning that this change is reversible. This is known as elasticity.

Question:14

Label the diagram

(a) This is which part of a dicotyledonous plant?

(b) If we remove part I from the plant, what will happen?

Answer:

(a) This diagram displays the shoot apex of the dicotyledonous plant.


(b) Removal of the shoot apex will prevent apical dominance. This will, in turn, help in the growth of lateral branches.

Question:15

Both animals and plants grow. Why do we say that growth and differentiation in plants are open and not so in animals? Does this statement hold true for sponges also?

Answer:
The growth of a plant can be said to be indeterminate. This is because a part of a plant can grow infinitely, i.e. always growing and forming new organs to replace the older ones. This is not the case for animals. Animal growth is limited and stops after a certain age when they mature. This is why one can say that the growth and differentiation in plants and animals are different.

The sponges can be said to be an exception in the animal kingdom. This is because they are the animals which show a cellular level of organisation. They depict the characteristics of open-ended growth but cannot be called one since they cannot grow beyond a certain size.

Question:16

Define parthenocarpy. Name the plant hormone used to induce parthenocarpy.

Answer:

Parthenocarpy is the process of formation and development of fruits that occurs without the use of any kind of fertilisation. The fruit produced by this process does not contain seeds. Fruits such as pear, banana, pineapple, and some varieties of papaya are parthenocarpic fruits. In order to induce parthenocarpy, auxins, cytokinin and gibberellins are utilised.

Question:17

While eating watermelons, all of us wish it were seedless. As a plant physiologist can you suggest any method by which this can be achieved?

Answer:

To have seedless watermelons, there needs to be a cross-hybridisation that occurs between a tetraploid female parent and a diploid male. This results in a triploid plant which has three sets of chromosomes. This particular genome thus produces the watermelon to not contain seeds.

Question:18

A gardener finds more broad-leaved dicot weeds growing in his lawns. What can be done to get rid of the weeds efficiently?

Answer:
The weed can be effectively eliminated by using weedicides. One can use the 2:4- D and 2:4: 5-T which do not affect mature monocotyledons. This is a synthetic auxin and is widely used by farmers but is to be used with caution and restraint so as to not hamper the crops.

Question:19

On 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?

Answer:

(a) On germination of the seed, shoots with leaves are produced at first as the plant is gradually entering the vegetative growth phase of the plant. The leaves begin to manufacture food, and the photoperiod follows to determine the flowering of the plant.
The leaves are produced to regulate the process of photosynthesis and produce food, which could be utilised in sexual reproduction. This marks the beginning of the important flowering process as well.

(b) The vegetative phase marks immense growth and aids the plant to gain maturity. Then the process of reproduction commences, and flowering also occurs. The vegetative phase is necessary to prepare the plant for the upcoming process and for it to develop the necessary structures for it. Thug, the vegetative phase of growth is necessary for the survival of the plant species. The flowering phase depends on this phase to provide for nourishment.

Question:20

Fill in the blanks.
(a) Maximum growth is observed in ________ phase.
(b) Apical dominance is due to __________ .
(c) ________ initiate rooting.
(d) Pigment involved in photoreception in flowering plants is _________ .

Answer:
(a) Exponential
(b) Auxin
(c) Cytokinin
(d) Phytochrome