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Plant growth refers to the expansion of a plant's shape, size, weight, and volume. Growth is a necessary process that causes permanent and irreversible changes in any plant or component of it. While animal growth is spread, plant growth is localized and uneven (nail in the plant stem occupies a similar height till several years of growth). The primary stage of plant growth is seed germination. Growth is an aspect of development, but development is not growth. During growth, weight grew, with the exception of potato and seed germination, when weight decreased.
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Very Short Answers [1 Mark]
Ques. Determine which organism is capable of performing the photosynthesis process?
- Plants and some bacteria only
- Plants and algae only
- Plants only
- Plants, some bacteria and algae
Ans. The answer is Plants, some bacteria and algae. Photosynthesis is the process of conversion of light energy into chemical energy by green plants and other organisms.
Ques. Mention the 4 growth regulators of plants?
Ans.
- Auxins
- Gibberellins
- Cytokinin
- Abscisic acid
Ques. What is the definition of cell enlargement?
Ans. Enlargement is defined as the process by which the size of cells, tissues, and organs grows due to the production of protoplasm, water absorption, the development of vacuoles, and the thickening and permanent addition of cell walls.
Ques. Name the 3 stages of cellular growth.
Ans.
- Cell division
- Cell enlargement
- Cell maturation
Ques. What is the difference between growth inhibitors and growth promoters?
Ans. Flowering, seed production, cell division, and other processes are aided by growth promoters. Growth inhibitors, on the other hand, stop plants from growing and cause them to go dormant.
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Ques. What are the factors that influence plant growth?
Ans. Plant development is influenced by a number of factors that are:
- Light
- Temperature
- Plant Growth Regulators
- Soil Nutrients
- Water
Short Answers [2 Marks]
Ques. Why is Abscisic acid also regarded as a stress hormone?
Ans. Abscisic acid enhances plant tolerance to a variety of stresses by causing the epidermis' stomata to close. As a result, it's sometimes referred to as the stress hormone. It promotes seed dormancy and ensures seed germination in favorable conditions. It aids seed desiccation resistance. It also stimulates leaf, fruit, and flower abscission and aids in the induction of dormancy in plants towards the end of the growing season.
Ques. What is the definition of Vernalization?
Ans. The term vernalizations refers to the process of blossoming that occurs after a period of cold treatment. Plants which need the cold treatment frequently behave as biennials in blooming plants. In the first season, they germinate and grow vegetatively, and in the second season, they produce blooms. Various grafting experiments have proven that the developing point is the place that receives the cold shock. It is in charge of the creation of a hormone-like molecule. If plants are exposed to high temperatures again, the impact of vernalization can be reversed.
Ques. Describe the biological significance of growth. What are the key differences between plant and animal growth?
Ans. The aggregate of several processes that combine to generate an irreversible increase in weight, mass, or volume is referred to as growth. Growth is always accompanied by differentiation, which can be described by quantitative changes in the cell's structure and functions. Plant growth varies from animal growth since its pattern of growth is infinite and rather undefined.
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Ques. Comment your opinion: 'In higher plants, both differentiation and growth are open.'
Ans. The existence of meristems at specific sites on the body of higher plants allows them to maintain their potential to grow indefinitely throughout their lives. These meristems give rise to cells with the ability to divide and reproduce on their own. This is why higher plants' growth is unrestricted. After a few rounds of cell division, a small percentage of these cells undergo differentiation. As a result, differentiation is also possible.
Ques. What would happen to parenchyma tissue culture if
- Cytokinin and Auxin were present in equal amounts?
- There was more cytokinin than auxin
- There was more auxin than cytokinin.
Ans.
- Cells that divide but do not differentiate
- Shoot buds emerge from the callus
- Roots emerge.
Ques. What is heterophylly, and how does it work?
Ans. Plants use a variety of pathways to produce various structures in response to their environment and life stage. It's referred to as plasticity. Cotton heterophylly, coriander heterophylly, and larkspur heterophylly are among examples. The leaves of young plants differ from those of older plants in form. Buttercup leaves generated in the air and those produced in the water differ in shape, indicating heterophyllus development as a result of the environment. Plant plasticity can be shown in the occurrence of heterophylly.
Ques. Explain how phytohormones play a role in seed germination.
Ans. Apart from seed germination, it is a regulatory pigment that controls various light-dependent developmental processes in plants. Pr and Pfr are two interconvertible types of phytohormones. Pr becomes Pfr when it absorbs red light, and Pfr becomes Pr either quickly or slowly in darkness when it absorbs far red light. Pfr promotes germination, which necessitates the use of red light. Pr development is aided by darkness (far-red), which induces dormancy and prevents germination.
Ques. Why isn't any single parameter sufficient to illustrate flowering plant growth over time?
Ans. At the cellular level the growth of plants is mainly due to an increase in protoplasm levels. Protoplasm growth is measured using the weights of the dry tissue sample, the weights of the raw tissue sample, and changes in length, volume, area, and cell number over the growth phase. As a result, no one metric can fully capture a blooming plant's growth over the course of its life.
Long Answers [3 Marks]
Ques. What do you think would happen if:
- Rice seedlings are treated with GA3.
- Cells that divide stop differentiating.
- Unripe fruits are intermingled with rotting fruits.
- You leave cytokinin out of the culture media.
Ans.
- When rice seedlings are given GA3, the internode lengthens and the rice seedlings' height increases.
- If dividing cells stopped differentiating, plant parts such as stems and leaves will not form.
- When rotten fruits are combined with unripe fruits, the ethylene generated by the rotten fruits accelerates the ripening of the unripe fruits.
- If cytokinin is not supplied to the culture media, growth, cell division, and differentiation will be slowed.
Ques. Write the difference between short day plants and long day plants
Ans. The difference between short day plants and long day plants are tabulated below.
| Short day plants | Long day plants |
|---|---|
| When the day length is less than a certain length, these plants begin to blossom. | When the day length reaches a crucial length, these plants begin to blossom. |
| Flowering requires a lengthy continuous and uninterrupted dark phase, i.e., darkness above a certain level, hence the name "long-night plants." | Flowering is dependent on the light period, which means they require darkness below the crucial time. As a result, they're known as short-night plants. |
| Flowering is induced by the presence of gibberellins under non-inductive photoperiods. | Under non-inductive photoperiods, gibberellin supply does not trigger flowering. |
Ques. Discuss the following statement: 'Growth is measurable.'
Ans. Growth (at the cellular level) is primarily caused by an increase in protoplasm levels. Because we can't directly measure growth, it's measured by some quantity that's more or less proportionate to it, so growth is assessed by a range of metrics like fresh weight, dry weight, length, area, volume, and cell number, among others. In a single hour, a single maize root apical meristem can generate around 17,500 new calls. A water melon's cells can grow up to 3,50,000 times their original size. As a result, growth can be expressed as a rise in cell number or in cell size. A pollen tube's growth is measured in terms of length. A dorsiventral leaf or dicot leaf's surface area increases as it grows.
Very Long Answers [5 Marks]
Ques. What is photoperiodism, and how does it affect you? How do you classify angiosperms according to their flowering response?
Ans. Photoperiodism is an answer to this question. Photoperiodism is the phenomena of plants blooming in response to the length of the daily period of light or the relative day and night length.
On the basis of photoperiodism, angiosperms are divided into the three categories below.
- Short-day plants (SDP): These plants require a shorter day length than flowers, such as chrysanthemum, Nicotiana, and soybean.
- Long-day plants (LDP): These plants, such as wheat, maize, and radish, require a longer day length than the critical period to flow.
- Day Neutral Plants (DNP): The duration of the day has no effect on the flowering response of their plants. Photo neutral plants, such as cotton, pea, tomato, and sunflower, are also known as indifferent plants.
Ques. Describe briefly:
- Arithmetic growth
- Geometric growth
- Sigmoid growth curve
- Absolute and relative growth rates
Ans.
- In arithmetic growth, only a daughter cell divides while the other matures and differentiates. A root elongating at a steady rate is the most basic representation of mathematical growth.
It can be stated numerically as follows:
Lt = LO + rt
Lt = length of time ‘t’
LO = length at time ‘zero’
r = growth rate/elongation per unit time / growth rate
- In geometric growth, the initial rate of expansion is sluggish (lag phase), but it then accelerates exponentially (log or exponential phase). Following mitotic cell division, both child cells retain the ability to split and continue to do so. Due to a lack of nutrients, growth slows, and the plant enters a stagnant phase. In geometric growth, the number grows in a multiplicative pattern. When we plot the growth parameter versus time in geometric growth, we get a typical sigmoid or S-curve.
The following is an example of exponential growth:
W1 = W0 ert
W1 = final size
W0 = initial size of the period
r=growth rate
t=time growth
e=base of natural logarithms
'r' stands for relative growth as well as the efficiency index, which is a measure of a plant's ability to manufacture new plant compounds. As a result, W1's final size is determined by W0's beginning size.
- It's an S-shaped graph made by charting growth against time, with four primary components, a sluggish lag phase, exponential or rapid phase, stage of reducing growth, and stationary phase.
- Absolute and relative growth rates - the absolute growth rate is the rate of change per unit of time. The growth rate per unit time per unit beginning growth is known as the relative growth rate.
Ques. What are the most significant aspects of growth? Briefly describe.
Ans. Cell division and cell differentiation are two processes that plants use to grow. Cell division is most common in the apical portions of the shoot and root. Plant growth is controlled by meristematic cells found at the shoot and root apices. These cells can also be found in the vascular bundles of dicot plants' roots and stems. They aid in the thickening of the stem and root as a result of secondary growth. The rate of plant growth is modest in the beginning and then accelerates later on. Because of the scarcity of nutrients, growth slows. The efficiency index is another name for the pace of growth.
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