Transport in Plants Test - 7

Cohesion is the action or property of like molecules sticking together, being mutually attractive.

Water, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration.

A potometer is a device used for measuring the rate of water uptake of a leafy plant shoot. The main reason for water uptake by a cut shoot is transpiration (evaporation in plants) and is effected by the transpiration stream.

Rate of transpiration is influenced by wind speed, availability of water and temperature. Rate of transpiration is highest when soil is wet and air is dry.

Opening and closing of stomata is affected by potassium ions (K⁺) concentration of starch molecules in stomatal guard cells. Nitrogen is not factor affecting stomata opening and closing.

Normally stomata are open in the day time and close during the night. The immediate cause of the opening or closing of the stomata is a change in the turgidity of the guard cells.

In CAM plants, stomata opens during night and close during day to prevents loss of water by the process of transpiration that also occurs through stomata.

Wilting is the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells. The rate of loss of water from the plant is greater than the absorption of water in the plant.

Opening and closing of stomata is caused by rise in pH of guard cells and hydrolysis of starch present in guard cells. (K⁺) ions also play important role in stomatal change

In an isobilateral (often monocotyledonous) leaf the Stomata distribution is amphistomatic i.e., stomata equally distributed on both the surfaces.

Imbibition is a special type of diffusion when water is absorbed by solids-colloids causing an enormous increase in volume.