Absorption by roots 

  • 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.

  • Roots

    • It helps in anchoring plant and absorbing water and minerals.
    • 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.

  • 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
      • a. concentration gradient
      • b. membrane permeability
      • c. temperature
      • d. 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 a 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

(i) pressure gradient
(ii) 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
    • Important terms : Flaccidity, Turgidity, Plasmolysis, Deplasmolysis,Wall Pressure.

  • 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 a hypotonic solution, cells get deplasmolysed (turgid) due to the movement of water into the cell from the 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 

Diffusion

Osmosis

1. Movement of substances from higher concentration to lower concentration.

1. Movement of selective substances through membrane.

2. It occurs in any medium

2. It occurs in liquid medium.

3. It helps in equalizing the concentration in the available space.

3. It does not equalize the concentration

4. It does not depend on solute potential

4. It depends on the solute potential.

 

  • Imbibition: It is a special type of diffusion that involves water absorption through colloids causing tremendous increase in volume. For example: absorption of water by seeds and dry wood

Water movement

  • Root pressure
    • It is the positive pressure that develops in the roots of plants by active absorption of nutrients from the 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.
  • Transpiration Pull
    • 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:
      • Cohesion
      • Surface tension
      • Adhesion

 






Frequently asked questions

Q: What is absorption by roots?
A: Absorption by roots refers to the process by which plant roots take in water and dissolved nutrients from the soil. It is an essential function of the roots and plays a crucial role in the overall growth and development of plants.

Q: How do roots absorb water and nutrients?
A: Roots absorb water and nutrients through tiny, hair-like structures called root hairs. These root hairs greatly increase the surface area of the roots, allowing for efficient absorption. Water enters the root hairs through osmosis, while nutrients are absorbed through active transport or facilitated diffusion.

Q: Which nutrients are absorbed by roots?
A: Roots absorb various nutrients essential for plant growth, including macronutrients such as nitrogen (N), phosphorus (P), and potassium (K), as well as micronutrients like iron (Fe), zinc (Zn), and manganese (Mn). These nutrients are present in the soil solution and are taken up by the roots through specialized transport mechanisms.

Q: What factors affect the absorption of water and nutrients by roots?
A: Several factors influence the absorption of water and nutrients by roots. These include soil moisture content, temperature, pH level, root health, root-to-soil contact, and the availability of nutrients in the soil. Factors like waterlogging, high salinity, or extreme soil pH levels can negatively impact absorption.

Q: How does the root system architecture affect absorption?
A: The structure and arrangement of the root system can affect the absorption process. Plants with a well-developed and extensive root system have a larger surface area for absorption, allowing for greater water and nutrient uptake. Additionally, the presence of root hairs and mycorrhizal associations can enhance nutrient absorption.

Q: Can roots absorb water and nutrients from any type of soil?
A: Roots can absorb water and nutrients from various types of soils, but the ability to do so depends on the soil's physical and chemical properties. Sandy soils, for example, drain quickly and may require more frequent watering to ensure sufficient moisture uptake. Clay soils, on the other hand, can retain water but may have reduced nutrient availability. Ideal soil conditions provide a balance of good drainage and water retention, along with adequate nutrient content.

Q: Are there specific mechanisms in roots for adjusting water and nutrient uptake?
A: Yes, plants have mechanisms to adjust water and nutrient uptake according to their needs. The opening and closing of tiny pores called stomata in leaves help regulate water loss and uptake. Additionally, plants can adjust nutrient uptake through selective ion transport mechanisms in the roots, allowing them to take up more of certain nutrients when they are deficient.

Q: Can excess water or nutrients be harmful to roots?
A: Yes, excessive water or nutrient levels can be detrimental to roots. Overwatering can lead to waterlogging, which deprives roots of oxygen and can cause root rot. Similarly, excessive nutrient concentrations can disrupt the osmotic balance and lead to toxicity. It is important to maintain appropriate soil moisture levels and provide balanced nutrient supply to avoid such issues.

Q: How can plants enhance nutrient absorption in nutrient-poor soils?
A: In nutrient-poor soils, plants may adapt by forming beneficial relationships with mycorrhizal fungi. These fungi form symbiotic associations with plant roots, extending their reach into the soil and enhancing nutrient uptake. Some plants also release organic compounds that mobilize nutrients in the soil or engage in other adaptive strategies to improve nutrient acquisition.

I hope these FAQs provide helpful information about absorption by roots!