Explain how light may affect the activities of organisms.

In this question you should outline how the activities, (both physical and physiological) of both plants and animals are affected by light.

• Light is an important abiotic factor which affects both plants and animals greatly.

Plants

• Photoperiodism: The duration of day light, called the photoperiod determines the time of flowering and growth in plants. It also controls leaf fall, bud dormancy and appearance of leaves.
• Light is essential for synthesis of plants pigments such as chlorophyll in plant leaves.
• Plants usually show bending growth movements in response to unidirectional exposure to light (phototropism)
• Some plants show folding of leaves during the night (e.g. oxalis) while some fold their leaves during the mid-day
• Morning glory fold flowers in absence of light.
• Light intensity is a stimulus for the opening or closing of stomata in plants.
• Light breaks dormancy and induces germination
• Too much light inhibits growth in some plants
• Too much light bleaches chlorophyll causing yellowing of leaves.

Animals

• Stimulates synthesis of vitamin D
• Aids vision of prey and predators
• UV component of light causes sun burns
• Photoperiod affect breeding behaviour of insects, certain birds and animals.
• It also influences migration of animals such as birds, eels and salmons.
• Seasonal changes in color in certain birds and mammals are related to variation in day length. Certain aquatic animals lose their color when shielded from light.
• The photoperiod also regulates the circadian rhythm, an inherent response of animals of light conditions. The appearance of light induces certain behaviour in animals while its disappearance attenuates it according to animal’s inherent biological clock. For example, going to sleep at night the waking up in the morning.
• Light affects daily movement of animals. Some animals avoid light and hide during day. They only become active at night (nocturnal)
• Light increases enzymatic and general metabolic activity of animals