Short & Long Question Answers with Solution: Plant-Growth & Development - NEET PDF Download

Short Answer Type Questions

Q1: What are the functions of  Auxins in plant growth?
Ans: Auxins are among the most significant plant hormones and are typically synthesized at the tips of both stems and roots. In all vascular plants, auxins serve essential functions, which include:

• Facilitating cell division.
• Aiding in plant propagation.
• Stimulating the flowering of plants.
• Triggering the formation of roots and stem cuttings.
• Preventing the premature shedding of fruits and leaves.

Q2: Which plant hormone is used to manipulate and stimulate the maturation of sugarcane crop?
Ans: Ethylene, the plant ripening hormone, contributes to the maturation of sugarcane crops by enhancing the accumulation of sucrose in plants.

Q3: What are Plant growth regulators?
Ans: Plant growth regulators, sometimes known as phytohormones or plant hormones, constitute a category of organic compounds that operate by regulating and altering the physiological mechanisms governing plant growth, development, and mobility.

Q4: Where are plant hormones formed? How are the hormones passed to the specific site of activity?
Ans: Plant hormones are synthesized by various plant tissues, including root tips, shoot tips, leaves, meristematic tissues, and apical buds, among others. The presence of vascular tissues like phloem and xylem aids in the transport of these hormones to their sites of action.

Q5: Why is it difficult to designate any effect to a single hormone during experimentation?
Ans: Numerous hormones can exhibit both antagonistic and synergistic interactions with one another, making their effects complex and challenging to understand.

Q6: Is there a difference in the growth pattern of plants and animals? Do all parts of the plant grow endlessly? List the regions of the plant that can grow endlessly, if no.
Ans: Yes, there are differences in plant and animal growth. Plant growth differs because plants have the capacity to undergo continuous growth throughout their lifespan. This ability is attributed to the existence of meristems in specific parts of the plant body. Meristematic cells within these meristems can divide and proliferate continuously. The plant's body is primarily composed of cells that have lost the ability to divide. This growth pattern, where cells are consistently added to the plant's body through meristematic activity, is known as open growth form.
In contrast, animal growth is typically limited by genetic and environmental factors. Animals do not possess meristems or the same type of continuous growth observed in plants. Animal growth is more constrained and generally follows a predetermined pattern, reaching a relatively fixed size and structure as they mature.

Q7: Write the structural features of
(a) Meristematic cells near the root tip
(b) The cells in the elongation zone of the root
Ans: (a) These cells are identified by the following characteristics:

• Prominent nucleus, which is easily noticeable.
• Abundance of protoplasm within the cell.
• Thin cell walls primarily composed of cellulose and having a basic nature.
• A relatively small number of vacuoles.
• A high number of mitochondria within the cell.
• Numerous plasmodesmata, which are channels that connect adjacent plant cells for communication and transport.

(b) Cells in the elongation zone are distinguished by the following features:

• Increased dimensions, signifying their role in the growth and elongation of plant organs.
• Greater vacuolation, which contributes to the expansion of cell size.
• Accumulation of new cellulosic cell walls, aiding in the structural support and elongation of plant tissues.

Long Answer Type Questions

Q1: Winter varieties, when planted in spring, do not produce flowers or mature grains within the span of a flowering season. Explain?
Ans: In certain plant species, the process of flowering is influenced either qualitatively or quantitatively, and it relies on a combination of internal and environmental factors. One such environmental factor is exposure to lower temperatures, a phenomenon known as vernalization. Vernalization serves to slow down the plant's reproductive development rate, allowing it more time to reach maturity by impeding its growth and development during the typical maturation season. Vernalization induces flowering in plants through a prolonged period of cold temperatures.
For instance, some plants like wheat and barley exhibit two distinct varieties: spring and winter. Spring varieties are sown in the spring season and produce grains as they approach the end of the growing season. Conversely, winter varieties planted in the spring fail to flower or yield mature grains during the same season. These winter varieties are sown in the autumn, germinate over the winter months, and develop into small seedlings. They then resume their growth in the spring and are typically harvested in mid-summer.

Q2: Winter varieties, when planted in spring, do not produce flowers or mature grains within the span of a flowering season. Explain.
Ans: In certain plants, the process of flowering depends on exposure to lower temperatures, a phenomenon known as vernalization, which can influence flowering either qualitatively or quantitatively. Vernalization works by slowing down the rate of advanced reproductive development during the maturation season, providing the plants with ample time to reach maturity. This is achieved through a period of sustained low temperatures, which promotes flowering.
For instance, some plant species like wheat and barley exhibit two distinct varieties: spring and winter varieties. Spring varieties are typically sown in the spring and proceed to flower, producing grains towards the end of the growing season. In contrast, when winter varieties are planted in the spring, they do not flower or yield mature grains within the same flowering season. This is why they are specifically sown in the autumn. During the winter, they germinate and emerge as small seedlings. Their growth resumes in the spring, and they are typically harvested in mid-summer.

Q3: Is there a difference in the growth pattern of plants and animals? Do all parts of the plant grow endlessly? List the regions of the plant that can grow endlessly.
Ans: Yes, there are distinctions in the growth patterns of plants and animals.
In plants, growth follows an indeterminate pattern. This means that plants can undergo continuous growth throughout their entire lifespan due to the presence of meristematic tissues located in specific parts of the plant, including the apical (at the tips), intercalary (in between), and lateral (on the sides) regions. These meristematic cells have the perpetual ability to divide and support local growth. In contrast, most cells in the rest of the plant body lose their capacity to divide. This growth model, where cells are continually added to the plant body through meristems, is referred to as open growth.
In animals, growth generally occurs within a finite timeframe, after which their bodies cease to grow.
It's important to note that not all parts of a plant exhibit indefinite growth. The shoot apex and root apex, which contain apical meristematic tissues, continue to grow and contribute to the plant's vertical elongation.

Q4: Several variations of wheat are cultivated in autumn and harvested in the next midsummer.
(a) Give reason
(b) What is the flowering in lower temperatures referred to as?
(c) Name the plant hormone that can substitute for the cold treatment.
Ans: (a) When winter varieties are sown in the spring, they do not undergo flowering or produce fully mature grains within the flowering season. As a result, they are typically planted during the autumn season. Over the winter period, these varieties germinate and emerge as small seedlings, recommencing their growth in the spring, and are subsequently harvested in mid-summer.
(b) Vernalization.
(c) Gibberellin.

Q5: What do you understand about photoperiodism and vernalisation? Describe their significance.
Ans: Photoperiodism is the plant's response to the duration of daylight and darkness. Plants primarily react to the amount of daylight they receive. Based on their sensitivity to the length of light exposure, different plants can be categorized as short-day plants, long-day plants, or day-neutral plants. Photoperiodism serves as a trigger for various responses in addition to flowering induction. It's important to note that the light stimulus in photoperiodism is perceived specifically by green leaves. The process of photoperiodism is primarily controlled by a hypothetical hormone called florigen. It's worth mentioning that unfavorable photoperiods can counteract the effects of photoperiodism.
Vernalization, on the other hand, is the process of inducing flowering in plants by exposing them to cold temperatures. In the case of winter varieties of plants such as wheat and some biennials like carrots and cabbage, exposure to cold temperatures is essential for triggering flowering. Typically, winter crop varieties like rye and wheat are planted in the autumn. They remain in the seedling stage during the winter months and then bloom in the summer. However, if these varieties are sown in the spring, flowering does not occur.
The hormone known as florigen, although hypothetical, is believed to play a crucial role in initiating flowering and is thought to be produced in the leaves. Florigen then travels to the shoot apices and transforms them into flowering apices.
Vernalization, while important for priming the plant to respond to flowering stimuli, does not directly induce flowering itself. The cold treatment stimulus is received by leaves, embryos, and meristems. Vernalization's effects can be reversed through exposure to high temperatures.

Q6: List a hormone that:
(a) Is in nature, gaseous.
(b) Is in charge of phototropism.
(c) Influences femaleness in cucumber flowers.
(d) Is utilized to kill weeds(dicots).
(e) In long-day plants, induces flowering.
Ans: (a) Ethylene(C₂H₄)
(b) Auxin.
(c) Ethylene(C₂H₄).
(d) Auxin.
(e) Gibberellin.

Q7: Why is abscisic acid called a stress hormone?
Ans: Abscisic acid is commonly referred to as a stress hormone in plants due to its role in triggering various plant responses aimed at countering adverse environmental conditions. This hormone plays a crucial role in helping plants survive unfavorable environmental circumstances. For instance, it contributes to seed dormancy, ensuring that seeds only germinate under favorable conditions. Additionally, it prompts the closure of stomata in response to drought conditions, which is critical for water conservation. Abscisic acid also plays a significant role in inducing dormancy as plants approach the end of the growing season, aiding in the shedding of fruits, leaves, and flowers. Notably, when leaves experience water deficiency and become dry, the concentration of ABA (abscisic acid) increases, leading to stomatal closure, earning it the designation of the stress hormone.

Q8: While experimentation, why do you think it is difficult to assign any effect seen to any single hormone?
Ans: Plant hormones often interact in combination, and some may exhibit antagonistic effects while others may have synergistic effects. It is challenging to attribute a specific effect in a plant part to a single hormone, as phytohormones are synthesized individually by plant cells. These phytohormones, including auxin, gibberellins (GA), abscisic acid (ABA), ethylene, and cytokinin, lack a separate system for their transport within plants. As a result, their effects on plants tend to overlap and intertwine.
Many of the effects attributed to auxin and GA can be duplicated by other plant hormones. Similarly, ethylene and ABA often collaborate to fulfill various functions in plants. Additionally, the effects of phytohormones can differ when studied in vitro (outside the plant) compared to in vivo (inside the plant).
Furthermore, the actions of these plant hormones are influenced by various external factors, and they often work in coordination with these factors. This complexity makes it challenging to attribute a specific observed effect to any single hormone.

Q9: Explain the following with examples from various plant tissues
(a) Differentiation
(b) De-differentiation
(c) Redifferentiation
Ans: (a) Differentiation: Differentiation is the process where meristematic cells, which have the potential to divide, become specialized for specific functions and, in doing so, lose their ability to divide further. This transformation is permanent and leads to changes in the size, structure, composition, and function of cells, tissues, or organs. For example, in plants, meristematic tissues give rise to new cells that eventually mature and differentiate into specific tissues or different plant organs. This process involves significant structural changes in the protoplasm and cell wall of the cells.
(b) De-differentiation: De-differentiation is the phenomenon in which already specialized living cells regain the capacity to divide. This ability is triggered under specific conditions, leading to the reversal of cell specialization and allowing cells to divide again. For instance, in dicot stems, cortical cells can de-differentiate and transform into meristematic cells, giving rise to cambium layers such as interfascicular cambium and fascicular cambium. These meristems originate from fully developed parenchyma cells through the de-differentiation process.
(c) Re-differentiation: Re-differentiation occurs when de-differentiated cells mature and regain their specialized functions. In this process, cells that have de-differentiated undergo further transformation to perform specific functions once again. An example of re-differentiation is the cambium cells, which are formed through de-differentiation, subsequently maturing to perform specialized functions. In the case of secondary growth in woody dicot plants, secondary cortex cells re-differentiate to form secondary xylem, phloem elements, and phelloderm. The transformation of cambium cells into cortex represents an instance of re-differentiation.