What is the most important determinant for daylengh sensitiv

What is the most important determinant for daylengh sensitivity?

Solution

Daylength sensitivity is a physiologic reaction of the organisms by which they alter their developmental/metabolic responses. This sensitivity to relative lengths of light and dark periods is also known as Photoperiodism.

There are different mechanism by which plants (both long day and short day plants) and animals sence the daylenght. This sensitivity sets their biological clock for regulating various physiological and biochemical mechanisms.

Mostly, flowering plants determine the daylength sensitivity by using a photoreceptor protein called as phytochrome or cryptochrome. Accordingly they make seasonal changes, day night length changes. Flowering occurs on the basis of sensing the \'critical photoperiod\'

Similargy, many biological and behavioural changes in animals are dependent upon the capability to sense the daylength. eg. color of fur/ feathers, migration, hibernation, sexual behaviour etc. Mostly, photoperiod in aminals is sensed by retinal light-sensitive ganglion cells (not involved in vision). Through retinohypothalamic tract (RHT) the information is passed on to the suprachiasmatic nucleus (SCN). Thus due to this sensitive mechanism present, mammals are highly seasonal.

Thus for all living systems, that sence light, the intensity of light is senced by different photo-receptor mechanisms, and the lenght of day and night becomes most important in setting up a biological clock for their growth and development.