Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Characteristics of Roots for Absorption: Roots possess a massive surface area through root hairs, which have cell walls that are thin and permeable. The cell sap in the vacuole is of a higher concentration than the surrounding soil water, facilitating movement.
Imbibition: This is the phenomenon by which living or dead plant cells absorb water by surface attraction. Hydrophilic substances like cellulose and proteins assist in the uptake of .
Diffusion: The movement of molecules from a region of their higher concentration to a region of their lower concentration when in direct contact. This allows and exchange.
Osmosis: The movement of water molecules from a dilute solution (higher concentration) to a concentrated solution (lower concentration) through a semi-permeable membrane. Endosmosis is the inward flow, while Exosmosis is the outward flow.
Turgidity and Flaccidity: A cell is Turgid when it is fully distended with water (). Flaccidity occurs when the cell loses water. Plasmolysis is the contraction of the cytoplasm from the cell wall when placed in a hypertonic solution.
Active Transport: The passage of a substance (typically mineral ions like , , ) from its lower to higher concentration using energy from the cell in the form of .
Root Pressure: The pressure built up in the xylem of roots due to the inward movement of water, which helps in the Ascent of Sap up to a certain height in the stem.
📐Formulae
💡Examples
Problem 1:
What happens to a plant cell when placed in a hypertonic solution (e.g., strong salt solution)?
Solution:
The cell undergoes Exosmosis. Water moves out of the cell vacuole into the surrounding medium.
Explanation:
Because the external concentration of solutes is higher, water potential is lower outside. The protoplasm shrinks away from the cell wall, leading to a state called Plasmolysis.
Problem 2:
Why do raisins swell up when kept in pure ?
Solution:
Raisins swell due to Endosmosis.
Explanation:
The sugar concentration inside the raisin is much higher than the pure water outside. Water moves across the semi-permeable skin of the raisin into the interior until the cell becomes turgid.
Problem 3:
Explain the significance of the equation in a turgid plant cell.
Solution:
It represents the state of equilibrium where the inward Wall Pressure () equals the outward Turgor Pressure ().
Explanation:
As water enters the cell, the central vacuole expands and pushes against the cell wall (). The rigid cell wall exerts an equal and opposite pressure () to prevent the cell from bursting. This pressure provides mechanical strength to non-woody plants.