Plant Water Relation

Osmosis, Plasmolysis and Imbibition

Transportation of food

The transportation of food from the leaves to other parts of the plant occurs in the vascular tissue, namely the phloem. This process of transporting food is known as translocation. The phloem also transports amino acids and other substances to storage organs of the plant (along with the growing organs) such as roots, fruits, and seeds. The phloem consists of companion cells, sieve tubes, phloem parenchyma, and fibres.

The translocation of food occurs in the sieve tubes with the help of companion cells.

Translocation in the phloem, unlike the xylem, is achieved by utilizing energy from ATP. For example, a food material such as sucrose is transported into the phloem tissue using ATP energy. As a result, the osmotic pressure in the tissue increases, causing the water to move into it. This pressure moves the material in the phloem to the tissues, which have less pressure. This is helpful in moving materials according to the requirements of the plant.

Transportation of food

The transportation of food from the leaves to other parts of the plant occurs in the vascular tissue, namely the phloem. This process of transporting food is known as translocation. The phloem also transports amino acids and other substances to storage organs of the plant (along with the growing organs) such as roots, fruits, and seeds. The phloem consists of companion cells, sieve tubes, phloem parenchyma, and fibres.

The translocation of food occurs in the sieve tubes with the help of companion cells.

Translocation in the phloem, unlike the xylem, is achieved by utilizing energy from ATP. For example, a food material such as sucrose is transported into the phloem tissue using ATP energy. As a result, the osmotic pressure in the tissue increases, causing the water to move into it. This pressure moves the material in the phloem to the tissues, which have less pressure. This is helpful in moving materials according to the requirements of the plant.

Water Potential (ψ_W)

• Greater the concentration of water in a system, greater is its kinetic energy and greater is the water potential.

• Unit → Pascal (Pa)

• Symbol denomination − ψ_w

• If two systems are in contact, then there is movement of water from the solution with greater ψ_w to lower ψ_w.

• Solute potential (ψ_s) − Magnitude of lowering of water potential when a solute is added to the water

• Pressure Potential (ψ_p) − Magnitude of increase of water potential when pressure greater than atmospheric pressure is applied to pure water or a solution

• ψ_w = ψ_s + ψ_p

• ψ_w of pure water not under any pressure is zero.
  ψ_s is always negative and ψ_p is always positive.

Water Potential (ψ_W)

• Greater the concentration of water in a system, greater is its kinetic energy and greater is the water potential.

• Unit → Pascal (Pa)

• Symbol denomination − ψ_w

• If two systems are in contact, then there is movement of water from the solution with greater ψ_w to lower ψ_w.

• Solute potential (ψ_s) − Magnitude of lowering of water potential when a solute is added to the water

• Pressure Potential (ψ_p) − Magnitude of increase of water potential when pressure greater than atmospheric pressure is applied to pure water or a solution

• ψ_w = ψ_s + ψ_p

…