14 Most VSAQ’s of Transport in Plants Chapter in Inter 2nd Year Botany (TS/AP)

2 Marks

VSAQ-1 : What are porins? What role do they play in diffusion?

Porins are protein channels located in the outer membranes of plastids, mitochondria, and some bacteria. They play a crucial role in facilitating diffusion by forming large pores that enable the passage of small-sized molecules, including specific proteins. This creates a pathway for these molecules to move across membranes, enhancing the process of diffusion.

VSAQ-2 : Define water potential. What is the value of water potential of pure water?

Water potential (ψ_w) represents the potential energy of water molecules to move within a plant, driving processes like diffusion and osmosis. The water potential of pure water is zero, serving as a reference point for measuring water potential in plant tissues, where values become more negative as water moves away from this reference.

VSAQ-3 : Differentiate osmosis from diffusion.

  1. Osmosis is the movement of solvent (water) molecules from an area of lower concentration to an area of higher concentration through a semipermeable membrane. It takes place in liquid mediums, such as water moving through plant cells.
  2. Diffusion, on the other hand, is the movement of solute molecules from an area of higher concentration to an area of lower concentration, and it doesn’t necessitate a membrane. It primarily occurs in gases and liquids, like the diffusion of gases (CO2 and O2) during photosynthesis.

VSAQ-4 : What are apoplast and symplast?

  1. Apoplast is the path of water transport in a plant that occurs outside the cell membranes. It involves fast water movement through the cell walls and spaces between cells.
  2. Symplast, on the other hand, is the path of water transport in a plant where water moves through the cytoplasm of cells, crossing some membranes. It is slower compared to apoplast because it requires crossing cell membranes.

VSAQ-5 : How does guttation differ from transpiration?

  1. Guttation is the process where water is lost from plant leaves in the form of water droplets. It typically happens at night or early morning when humidity is high. Guttation is uncontrolled, and water is forced out due to root pressure.
  2. Transpiration, on the other hand, is the process where water is lost from plant leaves in the form of water vapor. It primarily occurs during the day when leaf stomata are open, allowing water vapor to escape. Transpiration is a controlled process where water loss is regulated by the opening and closing of stomata to maintain water balance in the plant.

VSAQ-6 : What are the physical factors responsible for the ascent of sap through xylem in plants?

Physical Factors for Ascent of Sap

  1. Cohesion:
    • Water molecules exhibit cohesion.
    • They stick together due to mutual attraction.
    • This forms a continuous column in the xylem.
  2. Adhesion:
    • Water molecules are attracted to the inner walls of the xylem.
    • This attraction helps water climb up the xylem.
  3. Transpiration Pull:
    • Water loss through transpiration in leaves.
    • Creates a negative pressure.
    • Pulls water up from the roots to replace lost water.

VSAQ-7 : Compare imbibing capacities of pea and wheat seeds.

Comparison of Imbibing Capacities of Pea and Wheat Seeds

  1. Imbibing Capacities: Proteinaceous pea seeds exhibit a higher imbibing capacity and swell more than starchy wheat seeds.
  2. Explanation: This disparity in imbibing capacities can be attributed to the fact that proteins possess a greater imbibition capacity in contrast to carbohydrates such as starch.

VSAQ-8 : With reference to transportation of food within a plant, what are source and sink?

Transportation of Food within a Plant: Source and Sink

  1. Source: A source is a specific part of the plant, such as the leaves, where food material, primarily sugars, is produced through the process of photosynthesis.
  2. Sink: On the other hand, a sink refers to another part of the plant, such as fruits or buds, where the food material produced in the source is either stored or utilized for growth and development.

VSAQ-9 : Does transpiration occur at night? Give an example.

Transpiration does not typically occur at night because most plants close their stomata during nighttime to reduce water loss. However, some plants like Bryophyllum and Cacti have a unique adaptation called Crassulacean Acid Metabolism (CAM) that allows them to transpire at night.

VSAQ-10 : Compare the pH of guard cells during the opening and closing of stomata.

During stomatal opening, the pH of guard cells increases, facilitating water uptake and making them turgid, which leads to stomatal opening. In contrast, during stomatal closing, the pH of guard cells decreases, causing water loss and rendering them flaccid, resulting in stomatal closure. These pH shifts play a critical role in regulating stomatal movements.

VSAQ-11 : In the wake of transpirational loss, why do the C_4 plants are more efficient than C_3 plants?

C4 plants are more efficient than C3 plants in reducing transpirational loss due to their unique carbon fixation mechanism. In C4 plants, the initial carbon fixation occurs in mesophyll cells, forming 4-carbon compounds. These compounds are then transported to bundle sheath cells for the Calvin cycle. This separation of carbon fixation and the Calvin cycle minimizes exposure to oxygen, reducing photorespiration and consequent water loss. As a result, C4 plants lose only half as much water as C3 plants for the same CO2 fixation, making them more water-efficient.

VSAQ-12 : What is meant by transport saturation? How does it influence facilitated diffusion?

Transport saturation occurs when all available transporters for a specific substance are at their maximum capacity. In facilitated diffusion, this happens when the substance’s concentration is high enough to fully engage all transporters. Additional increases in concentration do not further enhance the rate of facilitated diffusion, as transporters are already working at their maximum capacity.

VSAQ-13 : How does ABA bring about the closure of stomata under water stress conditions?

Abscisic acid (ABA), produced in response to water stress, induces stomatal closure in plants to reduce water loss. ABA achieves this by facilitating the efflux of K^+ ions from guard cells. As K^+ ions exit, water follows, causing guard cells to shrink and stomatal closure. This mechanism effectively prevents additional water loss from leaves, aiding water conservation during dry conditions.

VSAQ-14 : Compare transpiration and evaporation.

Transpiration involves the loss of water from living tissues in the aerial parts of plants and is an internal, physiological process that occurs relatively slowly.

Evaporation, in contrast, is the loss of water from any free surface, whether living or non-living. It is a surface-level process, happening as a physical phenomenon, and occurs relatively quickly.