Question

How is aquatic life benefitted by the fact that water has maximum density at ${{4}^{0}}\text{C}$?

Answer 1

Hint: The density of water is maximum at ${{4}^{0}}\text{C}$, and below that temperature the density decreases. This phenomenon is called the anomalous expansion of water. At lower temperatures it results in only the top layer of water being frozen.

Complete Step by step Solution:
- The anomalous expansion of water is an abnormal property of water whereby the water starts to expand instead of contracting as the temperature drops from ${{4}^{0}}\text{C}$ to ${{0}^{0}}\text{C}$. The density is maximum at ${{4}^{0}}\text{C}$ and drops as the temperature drops further below. Due to this anomalous behaviour of water, the density of ice is lighter than that of water and so ice floats on water.
- When the temperature starts to fall then the upper colder layer of water moves down and thus a convection is set up in the pond till the temperature of ${{4}^{0}}\text{C}$ is reached in the entire pond. When the temperature falls further below, the density of the water being lower than the water below, the ice that starts to form on the top water layer in the pond floats on top and hence the inner layer of water stays protected from being frozen.
- Hence, the fishes survive and this is how aquatic life is benefitted by the anomalous expansion of water.

Notes: When on one hand, the anomalous expansion is good for aquatic life, there are situations when this behaviour has proven to be dangerous too. In the winter seasons, the water starts to expand and starts to exert pressure on the walls of the pipes carrying them, thereby damaging them.