Plant Growth and Development (SAQs)

Botany-2 | 6. Plant Growth And Development – SAQs:
Welcome to “SAQs” in “Chapter 6: Plant Growth And Development”. This page includes the most important FAQs from previous exams. Each answer is provided in simple English, followed by a Telugu explanation, and then presented in the exam format. This method ensures you’re well-prepared to achieve great results in your final exams.

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SAQ-1 : Write a note on agricultural/horticultural applications of auxins.

Introduction

Auxins are a vital group of plant hormones that play a crucial role in the growth and development of plants. These hormones are primarily produced in the stems and root tips of plants and are involved in various processes that help plants thrive. Whether it’s helping a seedling grow stronger roots or ensuring fruits develop properly, auxins have several important applications, especially in agriculture and horticulture.

Applications of Auxins in Agriculture and Horticulture

1. Promoting Root Formation: One of the most common uses of auxins is in root formation. Imagine you have a cutting from a plant, like a rose or hibiscus, and you want to grow a new plant from it. For this, you need strong roots to form from the stem cutting. Auxins are often applied to the base of the cutting to stimulate root growth, making it easier to establish new plants. This technique is widely used in horticulture to propagate plants efficiently.
2. Stimulating Fruit Growth: Auxins also play a significant role in stimulating fruit growth. For example, in tomato farming, auxins can be used to encourage the fruits to grow larger and more robust. This is particularly beneficial for farmers who want to improve the yield and quality of their crops. By applying auxins, farmers can ensure that their tomatoes are plump and ready for market.
3. Preventing Premature Fruit Drop: Another crucial application of auxins is in preventing premature fruit drop. Have you ever seen fruits fall off a tree before they are ripe? This can be a significant problem for fruit growers. Auxins help prevent this by ensuring that the fruits stay attached to the plant until they are fully mature. This is essential for commercial fruit production, where the timing of harvest is critical for quality and profit.
4. Supporting Xylem Differentiation: Auxins are also involved in the differentiation of xylem tissue, which is responsible for transporting water throughout the plant. This process is vital for the overall health and development of the plant, as it ensures that water and nutrients are efficiently distributed. Healthy xylem tissue supports the plant’s ability to grow and thrive, making auxins an essential part of this process.
5. Use in Lawn Care: In lawn care, synthetic auxins like 2,4-D are commonly used to maintain the health and appearance of lawns. These auxins help control weeds by targeting broadleaf plants without harming the grass. This ensures that the lawn remains lush and green, which is particularly important in areas where a well-maintained lawn is valued, such as in parks or residential areas.
6. Promoting Lateral Bud Growth: Auxins also have a role in promoting lateral bud growth. After pruning, where the shoot tip is removed, auxins help stimulate the growth of lateral buds. This is especially useful in practices like tea plantations and hedge-making, where dense, bushy plants are desired. By regulating the growth of these buds, auxins help create fuller, more productive plants.

Summary

In conclusion, auxins are powerful plant hormones with a wide range of applications in agriculture and horticulture. From root initiation to stimulating fruit growth and preventing premature fruit drop, auxins are essential for enhancing crop production and quality. Understanding how to use auxins effectively can significantly improve agricultural practices, leading to healthier plants and better yields, much like how a good recipe leads to a delicious meal.

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SAQ-2 : Write the physiological responses of gibberellins in plants.

Introduction

Gibberellins are a group of plant hormones that have a profound impact on plant growth and development. These hormones, often abbreviated as GA followed by a number like GA1, GA2, or GA3, are known for their ability to influence various physiological processes in plants. Whether it’s helping a plant grow taller, aiding in fruit ripening, or improving the shape of fruits, gibberellins play a vital role in the overall health and productivity of plants.

Physiological Responses of Gibberellins in Plants

1. Stem Elongation and Fruit Ripening: One of the most well-known effects of gibberellins is their role in stem elongation. Imagine you have a sunflower in your garden, and you notice it growing taller and reaching towards the sky. This growth is often driven by gibberellins, which stimulate the cells in the stem to divide and elongate, allowing the plant to grow taller. Similarly, gibberellins are also crucial for fruit ripening. For example, in fruits like grapes, gibberellins help ensure that the fruits mature properly, reaching their full size and sweetness.
2. Seed Production: Gibberellins also play a significant role in seed production, especially in plants like conifers. These hormones can accelerate the maturity of these plants, allowing them to produce seeds earlier than they would naturally. This early seed production is particularly beneficial for plant reproduction and propagation, helping ensure the continuation of the species.
3. Use in the Brewing Industry: In an interesting application outside of traditional agriculture, gibberellins, particularly GA3, are used in the brewing industry. They are used to speed up the malting process by inducing the production of enzymes that break down starches into sugars. This process is essential for producing malt, a key ingredient in brewing beer, making gibberellins an important tool for brewers.
4. Improvement in Fruit Shape and Size: Gibberellins also contribute to improving the shape and size of certain fruits. For instance, when gibberellins are applied to apples, they can cause the apples to elongate and improve in shape. This not only makes the fruits more appealing to consumers but also increases their marketability, leading to better sales for farmers.
5. Delaying Senescence: Another important physiological response of gibberellins is their ability to delay senescence, or the aging process in plants. By slowing down the aging of plant organs like leaves and fruits, gibberellins help extend the functional lifespan of these parts. This means that the leaves stay green and healthy for longer, and fruits remain fresh and edible for an extended period, which is particularly beneficial for both farmers and consumers.
6. Increase in Yield: In sugarcane farming, the application of gibberellins has been shown to significantly increase yield. When gibberellins are applied to sugarcane stems, they stimulate the stems to grow longer, leading to a higher production of sugarcane per acre. In some cases, this can result in an increase of up to 20 tonnes per acre, which is a substantial boost for farmers looking to maximize their crop output.

Summary

In conclusion, gibberellins are powerful plant hormones that have a wide range of physiological effects on plants. From stem elongation and fruit ripening to seed production, improving fruit shape and size, delaying senescence, and increasing crop yield, these hormones are essential for optimizing plant growth and productivity. Understanding how to effectively use gibberellins can provide significant benefits in both agriculture and the brewing industry, helping to improve crop production and processing efficiency.

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SAQ-3 : Write any four physiological effects of cytokinins in plants.

Introduction

Cytokinins are essential plant growth hormones that play a crucial role in plant growth and development. These hormones are like tiny messengers that help plants grow, especially in areas where cells are actively dividing, such as the root tips, shoot buds, and young fruits. Cytokinins are particularly important because they promote cell division, which is the foundation for plant growth.

Physiological Effects of Cytokinins in Plants

1. Promotion of Cell Division: One of the most important roles of cytokinins is to stimulate cell division. Imagine you have a small plant in your garden, and you want it to grow taller and stronger. Cytokinins help by encouraging the cells in the root tips and shoot tips to divide and multiply. This process is like building blocks that stack up to make the plant grow bigger and healthier. Without cytokinins, the plant wouldn’t be able to produce new cells as effectively, which would slow down its growth.
2. Formation of New Leaves and Chloroplasts: Another critical effect of cytokinins is their role in the formation of new leaves and chloroplasts. Leaves are essential for a plant because they are the sites of photosynthesis, where the plant makes its food using sunlight. Cytokinins help in the creation of new leaves, ensuring that the plant has plenty of ‘solar panels’ to capture sunlight. Additionally, within these leaves, cytokinins assist in developing chloroplasts, which are the tiny green structures where photosynthesis actually happens. This ensures that the plant can efficiently produce the energy it needs to grow and thrive.
3. Stimulating Lateral Shoot Growth: Cytokinins also have a significant impact on the growth of lateral shoots. Lateral shoots are the side branches that make a plant look fuller and bushier. For example, in a well-maintained garden, you might notice how some plants have a dense, bushy appearance. This is often due to the action of cytokinins, which encourage the growth of these side branches. By promoting adventitious shoots (shoots that develop from unexpected places like roots or stems), cytokinins help the plant spread out and fill in empty spaces, making it more robust and visually appealing.
4. Enhancing Nutrient Metabolism and Delaying Senescence: Cytokinins also play a vital role in nutrient metabolism. They help the plant utilize nutrients more efficiently, ensuring that every part of the plant gets the food it needs to grow strong and healthy. Moreover, cytokinins are known for their ability to delay senescence, which is the aging process in leaves. Imagine you have a beautiful green plant, and you want to keep its leaves from turning yellow and falling off too soon. Cytokinins help by keeping the leaves young and functional for a longer time, allowing the plant to continue photosynthesizing and staying healthy.
5. Overcoming Apical Dominance: Another fascinating effect of cytokinins is their ability to overcome apical dominance. Apical dominance is when the main shoot of the plant suppresses the growth of side branches. This is why some plants grow tall and straight without many branches. However, cytokinins can counteract this effect, allowing the plant to grow more lateral branches. This results in a bushier and more branched plant, which can be especially desirable in certain types of gardening and agriculture, like in tea plantations where a fuller plant is preferred.

Summary

In conclusion, cytokinins are vital plant hormones that influence several key aspects of plant growth and development. They play a crucial role in promoting cell division, aiding in the formation of new leaves and chloroplasts, stimulating lateral shoot growth, enhancing nutrient metabolism, delaying leaf senescence, and overcoming apical dominance. Understanding these effects is essential for anyone involved in plant care, whether in gardening, agriculture, or horticulture, as it helps optimize plant health and productivity.

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SAQ-4 : What are the physiological processes that are regulated by ethylene in plants.

Introduction

Ethylene is a simple, gaseous plant hormone with a surprisingly significant impact on plant growth, development, and how plants respond to their environment. Despite its simplicity, ethylene influences everything from how a seed sprouts to how fruits ripen and leaves fall. It’s like the conductor of a plant’s orchestra, making sure everything happens at the right time.

Physiological Processes Regulated by Ethylene

1. Regulating Seedling Growth: One of the first things ethylene does is help seedlings grow properly. When a seed starts to grow under the soil, it needs to push through the surface to reach the sunlight. Ethylene promotes horizontal growth in seedlings, which is when the seedling bends sideways as it tries to break through the soil. It also causes the swelling of the seedling’s central axis, making it stronger and helping form an apical hook in dicot seedlings. This hook is a curved structure that protects the delicate tip of the plant as it pushes through the soil, just like how we might shield our head when crawling under something.
2. Promoting Senescence and Abscission: As plants grow, they also need to manage their resources efficiently. Ethylene plays a crucial role in promoting senescence (which is the aging process) and abscission (the natural shedding of leaves and flowers). When a leaf or flower is no longer useful to the plant, ethylene helps the plant decide to let it go. This process ensures that the plant doesn’t waste energy on parts that are no longer beneficial, much like how we might prune a tree to keep it healthy and thriving.
3. Role in Fruit Ripening: Ethylene is perhaps most famous for its role in fruit ripening. If you’ve ever left bananas in a closed bag to ripen faster, you’ve seen ethylene at work. This hormone speeds up the ripening process, making fruits more edible and enhancing their nutritional value. By controlling how fast fruits ripen, ethylene ensures that fruits are ready to be eaten at just the right time, benefiting both the plant and the animals that rely on its fruits.
4. Increasing Respiration Rate: Another important function of ethylene is to increase the plant’s respiration rate during a phase known as the respiratory climacteric. This is a critical period where the plant produces a lot of energy, similar to how we might need extra energy when we’re busy or under stress. This boost in respiration is vital for the plant’s survival and growth, especially during times of high energy demand like fruit ripening.
5. Breaking Dormancy: In addition to its role in growth and ripening, ethylene also helps in breaking dormancy. Dormancy is like a plant’s way of taking a nap, conserving energy until the conditions are just right for growth. Ethylene acts as an alarm clock, waking up seeds and buds and triggering their growth. For instance, it helps in the germination of peanut seeds and the sprouting of potato tubers, getting them ready to start the next phase of the plant life cycle.
6. Promoting Growth in Aquatic Plants: Ethylene is also important in aquatic plants, where it promotes rapid petiole (the stalk that attaches the leaf to the stem) and internode elongation. This helps the plant adapt to its watery environment, allowing it to stretch and reach for the surface where it can access more light and air.
7. Stimulating Root Growth: Lastly, ethylene has a role in stimulating root growth. It enhances the formation of roots and root hairs, which are tiny extensions that increase the root’s surface area. This makes the plant more efficient at absorbing water and nutrients from the soil, ensuring that it has all the resources it needs to grow strong and healthy.

Summary

In conclusion, ethylene is a powerful plant hormone that regulates a wide range of physiological processes. From guiding seedlings as they break through the soil, to ripening fruits, and even shedding old leaves, ethylene is essential for maintaining the delicate balance of growth and development in plants. Understanding how ethylene works helps us improve agricultural practices, ensuring that plants grow efficiently and produce high-quality fruits and vegetables.

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SAQ-5 : Write short notes on seed dormancy.

Introduction

Seed dormancy is an essential phase in a plant’s life cycle where a seed temporarily delays or completely halts germination. This period of inactivity is not without purpose; it’s a survival strategy that allows seeds to withstand unfavorable conditions until the environment is just right for growth. Understanding seed dormancy helps us appreciate how plants manage their life cycles, especially in challenging climates like those we experience in places like Telangana and Andhra Pradesh.

Factors Influencing Seed Dormancy

1. Dormancy Due to External Factors: One of the main reasons for seed dormancy comes from external factors like the hard seed coat. Imagine trying to drink water through a thick, sealed cover—this is similar to how a hard seed coat can block water and oxygen from reaching the seed. Without these essential elements, the seed remains dormant, waiting for the right moment when the seed coat becomes soft or breaks open, allowing germination to begin. This natural barrier protects the seed from sprouting too early, especially in unpredictable weather conditions.
2. Internal Factors Leading to Dormancy: Apart from external barriers, seeds can also remain dormant due to internal factors. Some seeds contain inhibitory chemicals that prevent them from sprouting. For instance, the seeds of a tomato plant have a compound called lycopene, which can inhibit germination. These internal chemicals act like a built-in timer, ensuring that seeds only sprout when conditions are ideal for growth. This mechanism is particularly important for plants growing in areas with extreme climates, where sprouting at the wrong time could lead to the seedling’s failure.
3. Effects of Temperature on Seed Dormancy: Temperature is another crucial element that affects seed dormancy. Some seeds, like those of the Polygonum plant, require exposure to low temperatures in moist conditions before they can germinate. This process can take weeks or even months. It’s as if the seed is waiting for a signal from the environment, ensuring that it only sprouts when the cold season has passed, and warmer, more favorable conditions are on the way. This adaptation is especially useful in regions with distinct seasons, where timing is everything for a plant’s survival.
4. Overcoming Seed Dormancy: To overcome seed dormancy, especially in horticulture, techniques like stratification are used. This involves placing seeds in a cold, moist environment—similar to mimicking winter conditions—using materials like moist sand or peat. By exposing seeds to these conditions, dormancy is broken, and the seeds are ready to germinate when planted. Stratification is commonly practiced in agriculture to synchronize germination and ensure that crops grow uniformly. For instance, in nurseries, this technique is often used to get all the seeds to sprout at the same time, leading to a more manageable and predictable growing season.

Summary

In conclusion, seed dormancy is a critical phase that ensures seeds only germinate under optimal conditions, influenced by both external factors like a hard seed coat and internal factors like chemical inhibitors. Temperature also plays a significant role, with some seeds requiring cold conditions before they can sprout. By using techniques like stratification, we can effectively manage and overcome seed dormancy, leading to better plant growth and agricultural success. Understanding this process is essential for anyone involved in farming or gardening, particularly in regions with varying climates like Telangana and Andhra Pradesh.

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SAQ-6 : Which one of the plant growth regulators would you use if you are asked to.

Introduction

Plant growth regulators, also known as plant hormones, play a crucial role in guiding the growth and development of plants. These hormones are like the plant’s internal tools, each with a specialized function that helps the plant thrive. From encouraging root growth to helping fruits ripen, these regulators are essential for various agricultural practices. Understanding how to use them effectively can make a significant difference, especially in regions like Telangana and Andhra Pradesh, where agriculture is a vital part of life.

Specific Applications of Plant Growth Regulators

1. Inducing Rooting in a Twig: When you need to induce rooting in a twig, auxins are the ideal choice. Specifically, Indole-3-butyric acid (IBA) is widely used for this purpose. Auxins are well-known for their ability to stimulate root formation, making them indispensable in plant propagation. Think of a gardener trying to grow a new plant from a cutting. By applying auxins, the gardener ensures that the cutting develops roots quickly, leading to a healthy new plant. This technique is especially useful when propagating plants like jasmine or roses, common in home gardens across Hyderabad.
2. Quickly Ripening a Fruit: For those looking to speed up fruit ripening, ethylene is the go-to plant hormone. Ethylene is a gaseous hormone that plays a key role in regulating the ripening process of fruits. Imagine a farmer wanting to sell mangoes at the market. By using ethylene, the farmer can ensure the fruits ripen uniformly, making them ready for sale at the perfect time. This hormone is also commonly used in fruit markets to ripen bananas and other fruits quickly.
3. Delaying Leaf Senescence: If you want to delay the aging process of leaves, cytokinins are the plant hormones to use. Cytokinins are involved in nutrient metabolism, which helps in delaying leaf senescence. For instance, a farmer growing leafy vegetables like spinach might want to keep the leaves fresh for longer. By applying cytokinins, the leaves remain green and healthy, ensuring a better yield and longer shelf life. This is particularly beneficial in regions with fluctuating temperatures, where leaf aging can be a challenge.
4. Inducing Growth in Axillary Buds: To promote the growth of axillary buds—the small buds found at the junction of the stem and leaf—cytokinins are again the preferred choice. They encourage the growth of lateral branches, leading to a bushier plant. Imagine a gardener aiming for a fuller, more robust marigold plant. By applying cytokinins, the plant develops more branches and flowers, enhancing its ornamental value.
5. ‘Bolting’ a Rosette Plant: When it comes to inducing rapid growth, known as bolting, in a rosette plant, gibberellins are the plant hormones to use. Gibberellins are famous for promoting stem elongation, leading to the rapid vertical growth that characterizes bolting. This is particularly useful in crops like cabbage or lettuce, where bolting is necessary for seed production.
6. Inducing Immediate Stomatal Closure in Leaves: For situations where you need to quickly close the stomata—tiny openings on the leaves—abscisic acid (ABA) is the hormone to use. ABA is crucial in stress responses like drought, causing the stomata to close and helping the plant conserve water. Imagine a farmer dealing with a sudden dry spell. By using ABA, the plants can better survive the drought by reducing water loss through the leaves.
7. Overcoming Apical Dominance: To overcome apical dominance, where the main stem suppresses the growth of lateral buds, cytokinins are effective. Cytokinins counteract the effects of auxins, allowing the lateral buds to grow and creating a more balanced plant structure. This is useful in hedge maintenance, where a gardener wants to ensure even growth across the entire plant.
8. Killing Dicotyledonous Weeds: When dealing with unwanted broadleaf weeds, the synthetic auxin 2,4-D is highly effective. This chemical selectively kills dicotyledonous weeds by causing uncontrolled growth, without harming monocotyledonous crops like wheat or rice. Farmers often use 2,4-D in their fields to keep weeds under control, ensuring their crops can grow without competition.

Summary

In summary, plant growth regulators are essential tools in agriculture and horticulture, offering precise control over various aspects of plant development. Whether you need to induce rooting, ripen fruits, delay leaf aging, or manage weed growth, understanding the specific roles of these hormones can greatly enhance your farming practices. By applying these regulators correctly, you can improve plant health, boost crop yields, and ensure better management of your plants, whether in a small garden or a large agricultural field in Andhra Pradesh or Telangana.