Answer:
1. The ecosystem is consist of biotic and abiotic factor which directly or indirectly depends on each other for their survival.
Direct interaction: it is defined as the interaction between abiotic and biotic factor directly, for example all the living organism (biotic) drink water (abiotic) which is a direct interaction.
Indirect interaction: It is defined as the impact of one species or organism on another which is mediated by a third factor. for example plants take nutrients from soil (abiotic) and then plants are consumed by herbivores.
2. Autotrophs and heterotrophs are two types of organism divided on the basis of mode of nutrition.
Autotrophs are the organism which prepare their own food and do not depend on other. example : plants prepare their own food in the presence of sunlight by utilizing carbon dioxide and water (photosynthesis).
Heterotrophs are the organism which depend on other for food. example - human beings depends on plants and animals for their food.
3. Nitrogen is present in atmosphere but plants and animals can not utilize that nitrogen directly. Hence, the atmospheric nitrogen undergo nitrogen cycle to get utlized.
At first the atmospheric nitrogen is fixed with the help of soil bacteria such as cyanobacteriaand converted into ammonia (NH3) and nitate (NO3) which can be directly utilize by plants and animals. Ammonia can further undergo nitrification and gives nitrites (NO2) and nitrates (NO3). Denitrification of nitrate (NO3) than convert it again into atmospheric nitrogen(N2). And the cycle goes on.
