ICSE 10 Biology Absorption by Roots Short

⚡ Quick Revision: Root Structure & Adaptation

🔹 Why Roots are Built for Absorption?

• ✔ Enormous Surface Area: Millions of root hairs increase the area for water intake.
• ✔ Concentrated Cell Sap: Root hair cells have higher solute concentration than soil water, aiding osmosis.
• ✔ Thin Walls: Cell wall is permeable and cell membrane is semi-permeable for easy movement.

Labeled Structure of a Root Hair Cell

Term Card

Root Pressure: Inward pressure exerted by cortical cells of the root that pushes sap into the xylem.

❌ Don't Confuse:

Cell Wall with Cell Membrane. Remember: The Cell Wall is freely permeable, but the Cell Membrane is selectively permeable.

⚡ Quick Revision: Imbibition, Diffusion & Osmosis

🔹 Physical Processes

• ✔ Imbibition: Adsorption of water by hydrophilic plant surfaces (e.g., seeds swelling in water).
• ✔ Diffusion: Free movement of molecules from high concentration to low concentration (until equilibrium).
• ✔ Osmosis: Movement of water molecules from a dilute to a concentrated solution through a semi-permeable membrane.

🔹 Types of Solutions

Solution Type	Concentration Relative to Cell	Effect on Cell
Hypotonic	More dilute outside	Cell swells (Endosmosis)
Hypertonic	More concentrated outside	Cell shrinks (Exosmosis)
Isotonic	Same concentration	No net change

Term Card

Active Transport: Movement of molecules against a concentration gradient using ATP (energy).

❌ Don't Confuse:

Diffusion with Osmosis. Remember: Diffusion is for any substance (gas/solid/liquid) and needs no membrane; Osmosis is for water only and must have a semi-permeable membrane.

⚡ Quick Revision: Turgidity & Plasmolysis

🔹 The Turgid State

• ✔ Turgidity: State where the cell is fully distended due to water intake (Endosmosis).
• ✔ Turgor Pressure: The outward pressure exerted by the cell sap on the cell wall.
• ✔ Wall Pressure: The inward pressure exerted by the cell wall against the turgor pressure.

🔹 Plasmolysis & Flaccidity

• ✔ Plasmolysis: Contraction of cytoplasm from the cell wall when placed in a hypertonic solution.
• ✔ Flaccid: A state between turgidity and plasmolysis where the cell is not firm.
• ✔ Deplasmolysis: The recovery of a plasmolysed cell when placed back in water.

Term Card

Wilting: The drooping of leaves due to excessive loss of water (Exosmosis) leading to loss of turgidity.

❌ Don't Confuse:

Turgor Pressure with Wall Pressure. Remember: Turgor is outward (from sap), Wall Pressure is inward (from wall). At equilibrium, both are equal.

⚡ Quick Revision: Root Pressure & Guttation

🔹 Root Pressure: The Upward Push

• ✔ Mechanism: Continuous osmotic entry of water into root hairs builds pressure in the cortical cells.
• ✔ Action: It forces water into the xylem vessels and pushes it up to a certain height in the stem.
• ✔ Demonstration: Can be seen as "bleeding" (sap oozing) from a freshly cut stem.

🔹 Guttation: Loss of Liquid Water

• ✔ Cause: Occurs when root pressure is high and transpiration is low (e.g., humid nights or early mornings).
• ✔ Structure: Water escapes through special pores called Hydathodes located on leaf margins.
• ✔ Content: Unlike transpiration, guttation water contains dissolved salts and sugars.

Term Card

Bleeding: Exudation of plant sap from the injured or cut parts of a plant due to root pressure.

❌ Don't Confuse:

Guttation with Dew. Remember: Guttation is water coming from inside the plant through hydathodes; Dew is atmospheric moisture condensing on the leaf surface.

⚡ Quick Revision: Ascent of Sap & Forces Involved

🔹 Ascent of Sap

• ✔ Definition: The upward movement of water and minerals from roots to the aerial parts of the plant through the Xylem.
• ✔ Xylem Elements: Primarily conducted through Tracheids and Vessels (non-living pipeline).

🔹 The Transpiration Pull

• ✔ Suction Force: As water evaporates from leaves, it creates a vacuum that "pulls" the entire water column upwards.
• ✔ Cohesion: The force of attraction between similar water molecules that keeps the column unbroken.
• ✔ Adhesion: Attraction between water molecules and the xylem walls that prevents the column from slipping down.

Term Card

Capillarity: The tendency of water to rise in very narrow tubes (like xylem vessels) due to surface tension.

❌ Don't Confuse:

Root Pressure with Transpiration Pull. Remember: Root pressure is a "push" from below (dominant in small plants/nights), while Transpiration Pull is a "pull" from above (dominant in tall trees/sunny days).