WHY DO CLOTHES LOOK DARK WHEN IMMERSED IN WATER?

The colour of an object is determined by the spectral composition of the light reflected by it. When a surface is dry, the reflected light rays corresponding to the colour of the surface are superposed with diffused white light arising out of random scattering resulting from the roughness and irregularities of the surface. In the case of clothes, this superposition tends to fade the reflected colour. If clothes are immersed in water, all the kinds and interspaces are filled with water. This minimizes scattering of light on the surface. So the reflected light comes out unsuppressed with the basic hue of the cloth. Hence it looks richer and darker than when dry. The effect is conspicuous clothes as the fibres are loosely packed with a lot of microscopic air spaces. This increases the surface area and consequently the scattering of light. Hence cotton clothes look light when dry and dark when wet. The effect is not so much in synthetic and silk clothes as their surfaces are smoother and they absorb very little water

HOW DO PLANTS SURVIVE DURING CERTAIN SEASONS INSPITE OF SHEDDING LEAVES?

Abscission is a physiological process whereby plants shed a part, such as leaf, flower or fruit, and retard their vegetative growth. It is a survival mechanism adopted by plants to live through adverse conditions and is promoted by a plant hormone called abscisin produced by leaves and fruits. Extreme temperatures limit the metabolic activities such as respiration, of plants. Such a reduction consequently necessitates only a low level of photosynthetic activity. The reduction in the requirement of energy can be to such a level which could be got from the photosynthetic activity of a few green cells, present in the terminal regions, after all the leaves fall. Sometimes, in winter, ice crystals begin to form in the extra-cellular spaces and the viscosity of the cell protoplasm increases. To counter this, compatible osmotica such as betaine begins to build up. This process, osmo-regulation, helps plants to overcome the stress due to frost.