functions of roots
TRANSCRIPT
Functions of Roots
1 To anchor the plant in the ground
2 To take in water and minerals
3 To bring water and minerals up to the stems (xylem)
4 To bring prepared food from the leaves to the roots (phloem)
5 To store food.
Need of Water and Minerals for plants
Photosynthesis
Water is used up in the green leaves as a raw material in the synthesis of glucose
Transpiration
A large quantity of water gets evaporated as water vapour during transpiration, for cooling in hot
weather, for producing a suction force, etc.
Transportation
Transportation of substances in water solution from the roots upward into the shoot (mineral salts) or from leaves to other parts (sugar, etc)
Mechanical stiffness
Water provides turgidity (fully distended condition), which is necessary for the stiffness of
plant tissues.
Characteristics of Roots for Absorbing water
1
2
3
Root hair increases Surface
area
Thin permeable cell walls
allow water
Large vacuole filled with Cell Sap. Has higher conc. than surrounding thus draws water inside
Phenomena which help in absorption of water
Imbibition
Imbibition is a phenomenon by which the living or dead plant cells absorb water by surface attraction
Diffusion
Free movement of water molecules from higher concentration to lower during direct contact.
Osmosis
Movement of water from region of higher concentration to lower through semipermeable
membrane
Active Transport
Passage of substance from lower to higher concentration through living membrane using
energy from cell.
Turgidity & Flaccidity
1. Turgidity - When cell accommodates maximum amount of water.
2. Flaccidity - Cell content is shrunken.
Osmosis
Movement of water from region of higher concentration to lower through semipermeable
membrane
Osmosis
Endosmosis is an inward diffusion of water through a semipermeable membrane when the surrounding solution is less concentrated. This
tends to swell up the cell.
Endosmosis
Exosmosis is outward diffusion through a semipermeable membrane when the
surrounding solution is more concentrated. This tends to cause shrinkage of cell.
Exosmosis
Tonicity
Relative concentration of the solutions that determine the direction and extent of diffusion is
called tonicity.
Isotonic
Animal Plants
The relative concentration of water molecules and the solute on either side of the cell membrane is the
same. There was no net movement of water. (No osmosis)
Hypotonic
Animal Plants
The solution outside the cell has a lower solute concentration than the fluids inside the cell.
As a result, the water molecules from outside will move into cell (endosmosis)
Hypertonic
Animal Plants
The solution outside the cell has a higher solute concentration than the fluid inside the cell.
Due to this the water molecule from inside the cell moves out (exosmosis)
What is meant by Ascent of Sap
The upward movement of water from the root to aerial parts of the plant body is called ascent of
sap.
Ascent of Sap occurs in the Tallest Trees
Trees like Sequoia sempervirens can range from 300 to 400 ft and can be of 4000 yrs old.
5 forces responsible for Ascent of Sap
Osmosis
Osmosis pushes water to root hairs
Root pressure
Root pressure pushes water to stem
Capillary Action
Capillary action results in rise up of water at base of stem
Adhesion-Cohesion
Adhesion cohesion makes column of water molecules
Transpiration
Transpiration creates transpiration pull
Overview of Ascent of Sap
Water and Mineral uptake by roots
Entry of water by Root Hair Cell
● The root hair cells have low concentration of water as compared to soil.
● Thus the water moves down the concentration gradient and enters the root hair cells
Higher water concentration Lower water
concentration
Entry of Minerals by Root Hair Cell
● Minerals are taken up in ionic form by active transport.
● Thus the energy is utilised in uptake of minerals.
● Due to active uptake the concentration of minerals increases in plants in comparison to surrounding.
Positively chargedE.g., Ca2+, H+
Transport takes place by ion exchange using proton pump
Negatively chargedE.g., NO3-
Transport takes place by symport with H+ ions
Cations Anions
Fig. Movement of Minerals
Guttation
Guttation is the loss of water in the form of water droplets from hydathodes (small pores) on the leaf
margin of a small herbaceous plant
Tracheid
EpithemGuard cell
Structure of Hydathode
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