Transport in Plants (SAQs)

Botany-2 | 1. Transport In Plants – SAQs:
Welcome to “SAQs” in “Chapter 1: Transport In Plants”. 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 approach helps you prepare effectively and aim for great results in your final exams.

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SAQ-1 : Define and explain water potential.

Introduction

Water potential is a key concept in understanding how water moves within a plant. It helps us understand where water will flow based on differences in concentration and pressure within the plant. Think of it as a way to measure how likely water is to move from one part of a plant to another.

Understanding Water Potential

Water potential, symbolized as (ψ_w), indicates the tendency of water to move within a plant. This movement can happen through processes like diffusion and osmosis. In simple terms, water potential tells us whether water will move towards an area or away from it. The unit for measuring water potential is Pascals (Pa).

In a standard environment, where conditions are stable, the water potential of pure water is set to zero. However, when we add substances or apply pressure, this value changes. For example, if you dissolve sugar in water, the water potential of the solution will drop.

Components of Water Potential

1. Solute Potential (ψ_s): When you dissolve a solute in pure water, you lower the concentration of pure water, which decreases the water potential. This decrease is called solute potential, and it is always a negative value. Imagine adding salt to a glass of water. The more salt you add, the lower the water potential becomes.
2. Pressure Potential (ψ_p): The second component is pressure potential. When water enters a plant cell due to osmosis, it causes the cell to swell. This swelling increases the pressure inside the cell, which raises the water potential. This increased pressure is known as pressure potential and it is always a positive value. For instance, when a plant cell is fully turgid, it has high pressure potential.

Calculating Total Water Potential

To find the total water potential in a plant, you add the solute potential and pressure potential.

So, the formula is: Total Water Potential (ψ_w) = Solute Potential (ψ_s) + Pressure Potential (ψ_p)

Summary

Water potential is crucial for understanding how water moves in plants. It includes solute potential, which lowers water potential, and pressure potential, which raises it. By understanding these components, we can better predict how water will move within a plant, which is essential for studying plant health and function.

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SAQ-2 : What is meant by plasmolysis? How is it practically useful to us?

Introduction

Plasmolysis is an important process that happens in plant cells when they lose water. This causes the cell contents to shrink and pull away from the cell wall. Understanding plasmolysis is not just a fascinating aspect of plant biology but also has practical applications, especially in food preservation.

Understanding Plasmolysis

Plasmolysis occurs when a plant cell is placed in a hypertonic solution—a solution with a higher concentration of solutes compared to the inside of the cell. This difference in solute concentration causes water to move out of the cell through a process called osmosis. Osmosis is the movement of water from an area of low solute concentration to an area of high solute concentration.

How Plasmolysis Happens

When the cell is surrounded by this hypertonic solution, water molecules inside the plant cell move out into the surrounding solution. As water leaves, the cell membrane shrinks, and the cell’s internal contents, known as the protoplast, pull away from the cell wall. This shrinking of the protoplast from the cell wall is what we call plasmolysis.

Practical Uses of Plasmolysis

The principle of plasmolysis is quite useful in everyday life, particularly in food preservation. For example, when pickles are preserved using salt, the high salt concentration creates a hypertonic environment. This causes water to move out of bacterial cells, leading to their death and preventing spoilage. Similarly, this concept is applied in preserving fish, meat, and prawns. The high salt concentration helps to inhibit bacterial growth and extend the shelf life of these foods.

Summary

Plasmolysis is a process where plant cells lose water, causing the cell contents to shrink and separate from the cell wall. Beyond its role in plant biology, this process is practically applied in preserving food, such as pickles, fish, meat, and prawns. By understanding and utilizing plasmolysis, we can effectively prevent spoilage and extend the freshness of various food items.

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SAQ-3 : How does ascent of sap occur in tall trees?

Introduction

The ascent of sap is a crucial process that allows water to travel from the roots up to the rest of the plant. This is especially important for tall trees, which need to transport water over long distances. Understanding how sap moves helps us appreciate how plants survive and thrive, even in challenging conditions.

Understanding Ascent of Sap

Ascent of sap refers to the upward movement of water and dissolved minerals through a special tissue called the xylem. This process occurs against gravity, which can be quite challenging, particularly for tall trees that reach great heights. The xylem acts like a network of tiny pipes that carry water from the roots up to the leaves and other parts of the plant.

Role of Transpiration

One of the key factors in the ascent of sap is transpiration. This is the process where water evaporates from the surface of the leaves. Imagine standing under a tree on a hot day; you might notice a slight mist coming from the leaves. This is water vapor being released into the air. As water evaporates, it creates a suction force that pulls more water up from the roots, almost like drinking through a straw.

Key Physical Properties

The movement of sap in the xylem is influenced by three important physical properties:

1. Cohesion: This is the attraction between water molecules. Water molecules stick to each other due to hydrogen bonds, helping to maintain a continuous column of water in the xylem vessels. Think of it like a line of people holding hands to form a chain.
2. Adhesion: This refers to the attraction between water molecules and the walls of the xylem vessels. Water sticks to the sides of the vessels, which helps to keep the water column intact. It’s like how water clings to the sides of a glass when you pour it in.
3. Transpiration Pull: The main force driving the upward movement of water is the transpiration pull. As water is lost from the leaves, a negative pressure or tension is created in the xylem vessels, pulling more water up from the roots. This pull is strong enough to lift water to the top of even the tallest trees.

Influence of These Properties

These properties—cohesion, adhesion, and transpiration pull—give water the strength it needs to defy gravity. They allow it to rise through narrow xylem tubes and reach the highest branches and leaves of the tree. Without these properties, the sap could not make its way up through the plant.

The Role of Xylem

The xylem is essential not just for transporting water but also for supplying the nutrients absorbed from the soil. During photosynthesis, the plant produces its food and needs a constant supply of water to carry out this process. The xylem vessels from the roots to the leaves ensure that this water and nutrients are delivered where they are needed.

Summary

The ascent of sap is vital for the growth and survival of plants, particularly tall trees. It involves the movement of water from the roots to the leaves through the xylem, driven by transpiration and supported by the physical properties of water. By understanding these processes, we see how plants manage to thrive and grow even in the tallest and most challenging environments.

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SAQ-4 : “Transpiration is a necessary evil”. Explain

Introduction

Transpiration is the process where plants lose water through evaporation from their surfaces, mainly the leaves. The term “necessary evil” is often used to describe transpiration because, while it provides many important benefits, it also has some drawbacks that can be challenging for plants.

Benefits of Transpiration

One of the most important roles of transpiration is the transpiration pull. This is like a suction force that helps move water up from the roots through the plant’s vascular system. Imagine drinking through a straw: as you suck, the liquid rises up. Similarly, as water evaporates from the leaves, it pulls more water up from the roots, ensuring the plant gets the water it needs.

Transpiration also supplies water necessary for photosynthesis. Photosynthesis is the process by which plants convert sunlight into energy. Just like how you need ingredients to bake a cake, plants need water to make food. Without enough water from transpiration, the plant can’t produce the energy it needs to grow.

Another crucial benefit is the transportation of minerals. Water carrying dissolved nutrients travels through the plant, ensuring that essential minerals reach all parts of the plant, much like how a delivery truck brings supplies to different parts of a city.

Additionally, transpiration helps cool the plant. When water evaporates from the leaf surfaces, it has a cooling effect, much like how sweating cools down your body on a hot day. This cooling is important for maintaining the plant’s optimal temperature.

Transpiration also helps keep plant cells turgid or firm. Think of turgid cells like inflated balloons—just as the air keeps a balloon firm, the water inside the cells maintains the plant’s structure and shape.

Drawbacks of Transpiration

Despite these benefits, excessive transpiration can have some downsides. For instance, if too much water is lost, the plant cells can become flaccid, or soft, which can weaken the plant and affect its stability. It’s similar to how a balloon loses its shape if you let out too much air.

High rates of transpiration can also lead to water stress. In dry conditions, this can be problematic because the plant may not have enough water to support its growth, leading to slower growth rates. It’s like running a car without enough fuel—it will eventually slow down.

Another issue is the significant water loss that occurs with transpiration. In drought conditions, losing too much water can be detrimental and may lead to dehydration, affecting the plant’s survival.

Finally, excessive transpiration can limit the water available for photosynthesis. If too much water is lost, there might not be enough left to produce the plant’s food, indirectly impacting its growth and health.

Summary

Transpiration is indeed a “necessary evil.” It provides essential benefits such as aiding water transport, supporting photosynthesis, cooling the plant, and maintaining its structure. However, it also comes with challenges like causing cell flaccidity, potentially slowing growth, leading to high water loss, and limiting photosynthesis under certain conditions. Plants must carefully balance transpiration to make the most of its benefits while managing its drawbacks.

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SAQ-5 : Transpiration and photosynthesis a compromise. Explain.

Introduction

Photosynthesis and transpiration are two essential processes in plants that are closely linked. Understanding how plants manage these processes often reveals a compromise or trade-off, particularly involving the stomata—tiny openings on the leaf surfaces.

Compromise between Transpiration and Photosynthesis

To perform photosynthesis, plants need to convert sunlight into energy, a process that requires carbon dioxide from the air and water from the soil. The carbon dioxide enters the leaves through the stomata, which are like small windows on the leaf surface. This is essential for making food and energy for the plant.

On the other hand, transpiration is the process where plants lose water to the atmosphere. This happens through the stomata during the exchange of gases needed for photosynthesis. As water vapor escapes from the leaves, it creates a transpirational pull that helps draw more water and nutrients up from the roots. Think of it like a straw: as you sip, the liquid rises up to replace what’s been consumed.

The Compromise

Here’s where the compromise comes in: plants must balance between getting enough carbon dioxide for photosynthesis and not losing too much water through transpiration. In dry conditions, if plants keep their stomata open to take in carbon dioxide, they risk losing too much water. To conserve water, they might close their stomata, but this also means less carbon dioxide enters, which can slow down photosynthesis.

Adaptations

Plants have developed various adaptations to handle this compromise. For instance, some plants open their stomata at night when it’s cooler and more humid, which reduces water loss. This strategy is common in plants living in arid environments, such as cacti and succulents, which have evolved to survive with minimal water.

Summary

The relationship between photosynthesis and transpiration is a delicate balance. Plants need to open their stomata to absorb carbon dioxide for photosynthesis, which also leads to water loss. To manage this balance, plants have developed various strategies and adaptations to ensure they can perform essential processes while conserving water.

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SAQ-6 : Explain the structure and mechanism of opening and closing of stomata.

Introduction

Stomata are tiny pores found mostly on the surfaces of plant leaves, and they play a vital role in controlling gas exchange and water loss. Each stoma is bordered by two special cells known as guard cells, which manage the opening and closing of the stomata.

Structure

Guard cells come in different shapes depending on the type of plant. In dicots (plants like roses and sunflowers), these cells are shaped like kidney beans, while in monocots (such as grasses and lilies), they are more like dumbbells. These cells are unique because they contain chloroplasts, which are usually found in plant cells that perform photosynthesis. The inner wall of each guard cell is thicker than the outer wall, a feature that is crucial for their ability to open and close the stomata.

Mechanism of Opening and Closing

The opening and closing of stomata are influenced by the Levitt’s K+ Ion Pump Theory, which focuses on the role of potassium ions (K+) and changes in osmotic potential.

During the day, when photosynthesis occurs, potassium ions (K+) move into the guard cells from surrounding cells. This influx of potassium decreases the water potential inside the guard cells, causing water to flow in by osmosis. As a result, the guard cells become turgid (firm and swollen), which makes the stomatal pore open. This is similar to a balloon inflating as it fills with air, making the pore wider.

In contrast, at night or under stress conditions, potassium ions are actively pumped out of the guard cells. This causes water to leave the guard cells, making them flaccid (soft and wilted), and leading to the closing of the stomatal pore. This process is similar to a balloon deflating, which makes the pore narrower.

Abscisic Acid (ABA) plays a role in water-stressed conditions. ABA is a plant hormone that triggers the efflux of potassium ions from guard cells, leading to stomatal closure to conserve water.

Summary

The structure and mechanism of stomatal function involve a sophisticated system of guard cells managing the balance between gas exchange and water conservation. During the day, guard cells become turgid, opening the stomata to allow gas exchange. At night or under stress, they become flaccid, closing the stomata to prevent water loss. In some plants, like those adapted to dry environments, special adaptations such as Crassulacean Acid Metabolism (CAM) photosynthesis help regulate stomatal activity more efficiently by opening the stomata during cooler, humid nights and closing them during hot, dry days. days.