Biology 3 Marks Question

→ This is the interaction in which one species benefits and the other is neither harmed nor benefited.
→ An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
→ The cattle egret and grazing cattle in close association, a sight you are most likely to catch if you live in farmed rural areas, is a classic example of commensalism.
→ The egrets always forage close to where the cattle are grazing because the cattle, as they move, stir up and flush out insects from the vegetation that otherwise might be difficult for the egrets to find and catch.
→ Another example of commensalism is the interaction between sea anemone that has stinging tentacles and the clown fish that lives among them. The fish gets protection from predators which stay away from the stinging tentacles. The anemone does not appear to derive any benefit by hosting the clown fish.

Defenses of prey species to lessen impact of predation :
→ Camouflage (cryptic colouration) of some insects & frogs.
→ Some are poisonous and so avoided by the predators.
→ Monarch butterfly is highly distasteful to its predator bird. It is due to a special chemical in
its body.
→ It is acquired during its caterpillar stage by feeding on a poisonous weed.
→ Thorns (Acacia, Cactus etc.) are the most common morphological means of defense of plants.
→ Many plants produce chemicals that make the herbivore sick, inhibit feeding or digestion, disrupt its reproduction or kill it. E.g. Calotropis produce highly poisonous cardiac glycosides.
→ Therefore cattle or goats do not eat it.
→ Nicotine, caffeine, quinine, strychnine, opium, etc. are defenses against grazers and browsers.

→ The population size is measured by its density.
→ At given time, the organisms in the population is counted per given unit area.
→ For this the unit of measurement is decided such as unit per acre or unit per hectares. For small organisms, small units are considered.
→ In our country, every 10 years population is measured.
→ In a specific habitat, the population density is fluctuating. For instance in rainy season density is high whereas in dry season it is less.
→ The population density depends on the necessity of an organism.