Absorption by roots

Absorption by roots | Diffusion | Active transport | Osmosis

Morphology

• 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

• 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

1. 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)
2. Fibrous root system
   • Primary root is short-lived and is replaced by a large number of secondary roots.
   • Example- Monocotyledons (wheat)
3. Adventitious roots
   • Roots arise from parts other than the radicle.
   • Example- Banyan tree

Root modifications

• 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

Translocation

• 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

Diffusion

• 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
  • temperature
  • pressure

Facilitated diffusion

• 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

Active transport

• 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

• 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:
  • Endosmois
  • Exosmosis
• 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

Plasmolysis

• 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.

Deplasmolysis

• The opposite of plasmolysis.
• If not dead, the protoplasm absorbs water
• The cell swells up

Difference between Diffusion and Osmosis