Maximum contribution of $O_2$ is from

Which of the following represents a tertiary consumer and a secondary consumer,respectively?

In a food chain of a grassland ecosystem,the top consumers are

Give scientific reasons: Coral reefs are not found in the regions from West Bengal to Andhra Pradesh,but are found in Tamil Nadu and on the east coast of India.

How much carbon is dissolved in the oceans (in $; \%$)?

The given food web contains some missing organisms $A, B, C$ and $D$. Identify these organisms and select the correct answer.