A deep pond of water has its top layer frozen during winter. State the expected temperature of the water layer at the bottom of the pond.

How does the anomalous expansion of water help in preserving the aquatic life during cold weather?
Or
How do fish survive in frozen lakes?
Or
How are aquatic animals able to survive inside a frozen pond?

In the following food chain, $5 \mathrm{J}$ of energy is available to man. How much energy was available at the producer level?

$\mathbf{Plant}\mathbf{\to }\mathbf{Sheep}\mathbf{\to }\mathbf{Man}$

In the following food chain, plants provide 2000 J  of energy to rats. How much energy will be available to hawks from the snakes?