functions of roots

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

Reach out to me @amrit_rj

amrit.raj@vedantu.com