Transport in Plants (VSAQs)
Botany-2 | 1. Transport In Plants – VSAQs:
Welcome to “VSAQs” in “Chapter 1: Transport In Plants”. This page covers the most important VSAQs from previous exams. Use these concise answers to strengthen your understanding and get ready to do well in your final exams.
VSAQ-1: What are porins? What role do they play in diffusion?
Porins are protein channels found in the outer membranes of plastids, mitochondria, and certain bacteria. Imagine them like small gates that allow molecules to pass through. These gates form large pores that facilitate the movement of small molecules, including specific proteins, across membranes. This process makes it easier for substances to move in and out of the cell or organelle, enhancing the overall process of diffusion. For example, in our cells, these channels help essential nutrients and waste products move efficiently.
VSAQ-2: Define water potential. What is the value of water potential of pure water?
Water potential (ψ_w) is a measure of the potential energy of water molecules in a plant. It drives the movement of water through the plant during processes like diffusion and osmosis. Think of it as the pressure that pushes water through plant tissues. The water potential of pure water is zero. This zero value serves as a reference point for comparing the water potential in other plant tissues, where the values become more negative as water moves away from pure water.
VSAQ-3: Differentiate osmosis from diffusion.
Osmosis is a special type of movement involving solvent (water) molecules. It occurs through a semipermeable membrane, moving from an area of lower concentration of solutes to an area of higher concentration. For example, water entering a plant cell through its membrane is an example of osmosis.
Diffusion, however, involves the movement of solute molecules, not just water. It occurs from an area of higher concentration to an area of lower concentration and does not require a membrane. An everyday example is the way a drop of perfume spreads through the air, moving from a concentrated spot to a wider area.
VSAQ-4: What are apoplast and symplast?
The apoplast is the pathway through which water moves in a plant, traveling outside the cell membranes. This route allows water to flow quickly through the cell walls and the spaces between cells. It’s like water flowing through a series of pipes.
In contrast, the symplast is a slower route where water moves through the cytoplasm of cells, crossing some membranes. This process involves the water traveling from one cell to another through small channels called plasmodesmata. It’s similar to water moving through a network of interconnected tubes within the plant cells.
VSAQ-5: How does guttation differ from transpiration?
Guttation and transpiration are two different ways plants manage water, but they occur under different conditions. Guttation happens when plants release water droplets from their leaves, usually during the night or early morning when humidity is high. This process is like when water droplets appear on the outside of a cold glass on a humid day. Guttation is driven by root pressure and is mostly uncontrolled, meaning the plant pushes out water when there’s too much pressure inside the roots.
Transpiration, on the other hand, is the process where plants lose water as vapor through tiny openings on their leaves called stomata. This mainly occurs during the day when the stomata are open, allowing water vapor to escape into the air. It’s like when you see steam rising from a hot cup of tea. Transpiration is a controlled process where the plant regulates water loss to maintain its balance, closing the stomata to conserve water when necessary.
VSAQ-6: What are the physical factors responsible for the ascent of sap through xylem in plants?
The ascent of sap in plants involves several physical factors. Cohesion is when water molecules stick together due to their mutual attraction. This creates a continuous column of water inside the xylem, the plant’s water transport system. Think of it like a chain of water droplets clinging together.
Adhesion refers to water molecules being attracted to the inner walls of the xylem vessels. This helps water climb up the xylem, much like how a sponge absorbs water by sticking to it.
Another key factor is the transpiration pull, which occurs when water evaporates from the leaves through transpiration. This loss of water creates a negative pressure that pulls more water up from the roots to replace what’s lost, similar to how a straw draws liquid up when you suck on it.
VSAQ-7: Compare imbibing capacities of pea and wheat seeds.
When comparing the imbibing capacities of pea and wheat seeds, pea seeds show a higher capacity to absorb water compared to wheat seeds. This means that pea seeds, which contain a lot of proteins, swell more when they take up water. Proteins in pea seeds can absorb more water than the carbohydrates (like starch) found in wheat seeds. It’s similar to how a sponge soaks up more water than a piece of cloth because of its structure.
VSAQ-8: With reference to transportation of food within a plant, what are source and sink?
In the transportation of food within a plant, source and sink are key concepts. A source is where food is produced. For example, the leaves of a plant act as a source because they make food (mainly sugars) through photosynthesis.
A sink is where this food is used or stored. For instance, fruits and buds are sinks because they either store the food or use it for growth. Think of the leaves as a kitchen where food is cooked and the fruits or buds as a dining table where the food is consumed.
VSAQ-9: Does transpiration occur at night? Give an example.
Transpiration generally does not occur at night because most plants close their stomata to prevent water loss. However, some plants, like Bryophyllum and Cacti, have adapted to transpire at night through a process called Crassulacean Acid Metabolism (CAM). This adaptation helps them manage water more efficiently in dry conditions, similar to how you might use a humidifier at night to keep the air moist.
VSAQ-10: Compare the pH of guard cells during the opening and closing of stomata.
The pH of guard cells plays a crucial role in regulating stomatal movements. When guard cells are opening the stomata, their pH increases. This increase in pH helps them absorb water, making them turgid (firm), which causes the stomata to open. It’s like blowing air into a balloon to make it expand.
Conversely, when the stomata are closing, the pH of the guard cells decreases. This decrease causes them to lose water and become flaccid (soft), leading to the closing of the stomata. This is similar to letting the air out of a balloon, making it shrink. These pH changes are essential for managing how plants lose water and exchange gases.
VSAQ-11: In the wake of transpirational loss, why are C₄ plants more efficient than C₃ plants?
C₄ plants are more efficient than C₃ plants in dealing with water loss due to their specialized method of carbon fixation. In these plants, carbon dioxide (CO₂) is initially fixed in the mesophyll cells, forming 4-carbon compounds. These compounds are then transported to bundle sheath cells, where the Calvin cycle takes place. This separation helps keep the CO₂ away from oxygen, which reduces photorespiration. Since photorespiration can waste water and energy, avoiding it helps the plant conserve water. Because of this efficient process, C₄ plants use only about half as much water as C₃ plants for fixing the same amount of CO₂. It’s like having a special air filter in your home that helps you save on energy and keep things cooler.
VSAQ-12: What is meant by transport saturation? How does it influence facilitated diffusion?
Transport saturation happens when all the transporters available for a substance are working at their full capacity. In the process of facilitated diffusion, this means that when the concentration of the substance is high enough to engage every transporter, the rate of movement cannot increase further. For example, if a conveyor belt in a factory is already running at full speed, adding more items won’t speed up the process. Similarly, once all transporters are busy, increasing the concentration of the substance doesn’t make it move faster through the membrane.
VSAQ-13: How does ABA bring about the closure of stomata under water stress conditions?
Abscisic acid (ABA) is a plant hormone that helps control stomatal closure during times of water stress. When a plant is under stress from lack of water, ABA triggers a series of actions in the guard cells surrounding the stomata. ABA helps move potassium ions (K⁺) out of the guard cells. As these ions leave, water follows by moving out of the cells, causing them to shrink. This shrinking closes the stomata, reducing water loss. It’s similar to closing a faucet to stop the flow of water when it’s needed elsewhere.
VSAQ-14: Compare transpiration and evaporation.
Transpiration and evaporation both involve the loss of water, but they happen in different ways. Transpiration is the process where water is lost from the living tissues of plants, mainly from their leaves. It’s a slower, internal process regulated by the plant’s needs and its environment. For instance, when a plant releases water vapor through its leaves, it’s actively managing its water balance.
Evaporation, on the other hand, is the loss of water from any surface, whether it’s living or non-living. It happens more quickly and is simply a physical process. An example of evaporation is the way water from a puddle on the ground disappears as the sun heats it up, regardless of whether the puddle is near a plant or not.