A deep pond of water has its top layer frozen during winter. State the expected temperature of water layer just in contact with ice.

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?

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