Absorption by roots | Diffusion | Active transport | Osmosis
- It is the branch of biology which deals with the study of external structures of plants and animals.
- A plant consists of a root system (underground part) and a shoot system (above the ground parts).
- Roots are the parts of the root system; and stem, leaves, flowers, and fruits are parts of the shoot system.
- Also Read Transpiration
- Roots help in anchoring plant and absorption of water and minerals take place by Roots.
- Developed from the radicle part of a cotyledon
- It consists of a region of meristematic activity covered by a root cap, a region of elongation, and a region of maturation having root hairs.
Types of roots system
- Tap root system
- It consists of a primary root that grows deep inside the soil.
- It also bears lateral roots referred to as secondary and tertiary roots.
- Example- Dicotyledons (mustard)
- Fibrous root system
- Primary root is short-lived and is replaced by a large number of secondary roots.
- Example- Monocotyledons (wheat)
- Adventitious roots
- Roots arise from parts other than the radicle.
- Example- Banyan tree
- Prop roots – Example: banyan tree
- Stilt roots – Example: maize and sugarcane
- Pneumatophores (that helps in respiration) – Example: Rhizophora
Characteristics of Root for Absorbing Water
- Enormous surface area
- Root hairs containing cell sap at higher concentration
- Thin walled root hairs
- It is a biological process that involves the transport of dissolved material within a plant.
- It mainly occurs with the help of xylem and phloem.
- The transport of food from leaves to other parts of plant occurs by phloem. Movement of food in phloem is bidirectional.
- The conduction of water and minerals from soil to the rest of the plant occurs by xylem. Movement of water in xylem is unidirectional.
- Also read Photosynthesis
Need of Water and Minerals for Plants
Need of Water
- For photosynthesis
- For transpiration
- For transportation
- For mechanical stiffness
Need of Minerals
- Needed as nutrients for the plants
- For the synthesis of a variety of compounds and enzymes
Means of Transport
- It is the spontaneous movement of molecules from a region of high concentration to a region of low concentration.
- It is a slow process and does not require any energy expenditure.
- It does not require a semi-permeable membrane and can take place through any membrane along concentration gradient.
- Rate of diffusion is affected by
- concentration gradient
- membrane permeability
- It involves the movement of molecule from the region of higher concentration to lower concentration, mediated by a carrier (mainly protein) molecule.
- Movement of molecules across membrane occurs without expenditure of energy.
- Porins – They are large protein molecules that form pores in membranes of plastids, mitochondria, and some bacteria
- Porins allow the movement of small-sized proteins across membrane. Aquaporins are proteins, which form a water-permeable channel.
- Some protein molecules allow diffusion only if two molecules are present. Based upon the direction which is followed by both molecules, the path can be of three types.
- Symport – when both molecules cross the membrane in same direction
- Antiport – when both the molecules move in the opposite directions
- Uniport – when single molecule moves across a membrane independent of other molecule
- It involves the transport of molecules from a region of low concentration to a region of high concentration with an expenditure of energy.
- It is carried out by membrane proteins.
- Osmosis is a special type of diffusion which involves the movement of water molecules from the region of high concentration to the region of low concentration through a semi-permeable membrane.
- Semi-permeable membrane = Selectively permeable membrane.
- Types of Osmosis:
- Rate of osmosis is affected by
- pressure gradient
- concentration gradient
- Osmotic pressure is the hydrostatic pressure produced by a difference in concentration between solutions on the two sides of a semi-permeable membrane.
- Tonicity : Relative concentration of solution and its surroundings.
- Isotonic solution: Solution that has the same salt concentration as the normal cells
- Hypotonic solution: Solution that has lower salt concentration than the normal cells
- Hypertonic solution: Solution that has higher salt concentration than the normal cells
- It is the contraction of cells within plants due to the loss of water through osmosis.
- When cells are placed in hypertonic solution, a cell tends to lose water to the surrounding solution due to exosmosis. The plasma membrane shrinks and the cell is said to be plasmolysed.
- When cells are placed in hypotonic solution, cells get deplasmolysed (turgid) due to movement of
water into the cell from surrounding as a result of endosmosis.
- The opposite of plasmolysis.
- If not dead, the protoplasm absorbs water
- The cell swells up
Difference between Diffusion and Osmosis
|Movement of substances from higher concentration to lower
|Movement of selective substances thro
|It occurs in any medium
|It occurs in liquid medium.
|It helps in equalising the concentration in the available space.
|It does not equalise the concentration
|It does not depend on solute potential
|It depends on the solute potential.
- It is the positive pressure that develops in the roots of plants by active absorption of nutrients from soil.
- It pushes the water up to small heights.
- Root pressure is linked to the phenomenon of guttation.
- Guttation: It involves the loss of water in the form of liquid droplets through the vein endings of the leaves.
- Guttation occurs early in the morning and late in the evening when evaporation is low and root pressure is high.
- Water transport in tall trees occurs by transpiration pull.
- Transpiration pull is generated by transpiration. It is also called cohesion – tension – transpiration pull model of water transport.
- The ascent of xylem sap is dependent on three physical properties of water:
- Surface tension
Absorption by roots