Relationship among living beings

Organisms are classified into trophic levels according to

Algae are producers in aquatic ecosystems

Which of the following is a producer?

Carnivores are primary consumers.

Decomposition is carried out by

Tertiary consumers feed on

In the food chain: acorns ---> squirrels ---> fox ----> bacteria, the fox is a

An omnivore is a primary consumer if it eats blackberries but it is a secondary consumer if it eats a rabbit

Birds make their nests in the branches of the trees where they are protected from the wind and the rain

The fleas and the lice live in the coat of the animals and they feed on their blood.