The question asks about the state of a fully turgid cell, specifically regarding its turgor pressure (TP) and osmotic potential. Turgor pressure is the hydrostatic pressure exerted by the cell's contents against its cell wall. Osmotic potential (also called solute potential) is related to the concentration of solutes in a solution. Water potential (\(\Psi\)) is the sum of pressure potential (\(\Psi_p\), which is turgor pressure) and solute potential (\(\Psi_s\), which is osmotic potential).
The formula for water potential is:
\[ \Psi = \Psi_p + \Psi_s \]B) Maximum turgor pressure and zero osmotic potential difference with outside
A fully turgid cell has absorbed the maximum amount of water, leading to the highest possible turgor pressure. In a hypotonic environment (like pure water), the cell will continue to absorb water until its internal water potential equals the external water potential (which is zero for pure water). This means that the turgor pressure (\(\Psi_p\)) will become numerically equal to the negative of the osmotic potential (\(-\Psi_s\)), making the overall water potential inside the cell zero. Thus, there is no net
The question asks for the best explanation for the upward movement of water in tall trees against gravity. This phenomenon, known as the ascent of sap, is a critical process in plant physiology. We need to evaluate the given options based on their scientific validity and their ability to explain water transport over long distances in tall trees.
C) Cohesion-tension (transpiration pull) theory — This theory provides the most comprehensive and widely accepted explanation for the ascent of sap in tall trees. Transpiration from the leaves creates a negative pressure or tension in the xylem. Due to the strong cohesive forces between water molecules (hydrogen bonds) and adhesive forces between water and xylem walls, a continuous column of water is pulled upwards from the roots to the leaves, effectively overcoming gravity over great heights.
Guttation is a process where plants exude water droplets from specialized pores called hydathodes, typically at leaf margins. This phenomenon occurs under specific environmental conditions that affect water uptake and transpiration rates.
Correct Option: D) Root pressure is high and transpiration is very low (usually at night/early morning)
This option accurately describes the conditions necessary for guttation. High root pressure pushes water up the xylem, and low transpiration means this water cannot be released as vapor, leading to its exudation as liquid droplets through hydathodes.
The question asks about the primary route for transpiration in plants. Transpiration is the process of water loss from plants in the form of water vapor, mainly from their aerial parts. We need to identify which plant structure is responsible for the majority of this water loss.
B) Stomata (stomatal transpiration) — Stomata are specialized pores on the leaf surface that regulate gas exchange and are the primary sites for water vapor release during transpiration, accounting for the vast majority of water loss from plants.
The question asks about the primary mechanism regulating the opening and closing of stomata. Stomata are pores on the leaf surface crucial for gas exchange and transpiration. Their regulation is a key physiological process in plants.
A) Changes in turgor pressure of guard cells — This is the direct and primary mechanism by which stomata open and close. When guard cells become turgid, the stomata open; when they become flaccid, the stomata close.
The question asks about the mechanism of sugar translocation in phloem according to the pressure-flow hypothesis (Munch's hypothesis). We need to identify the primary driving force for this movement.
B) A turgor pressure gradient — high pressure at source (loading area) to low pressure at sink (unloading area) — This accurately describes the driving force for translocation according to the pressure-flow hypothesis. The active loading of sugars at the source and unloading at the sink create an osmotic potential difference, leading to water movement and thus a turgor pressure gradient that facilitates bulk flow.