Question

*In cold regions, aquatic animals can survive at a temperature of 4°C. Because,*

1️⃣ Ice floating in water is an insulator.
2️⃣ The heat of water under ice cannot go into the atmosphere.
3️⃣ The Anomalous behaviour of water.
4️⃣ All of the above options.​

Answer 1

Answer:

When the temperature of the surface layers falls to 4 °C, the water body acquires maximum density and sinks down. The water that sinks down displaces water below, and the lower layers of water simultaneously rise up. This also gets cooled to 4 °C and again sinks down.

Answer 2

The aquatic animals in colder regions can survive a temperature as low as 4°C because of the anomalous behaviour of water, and, the insulating property of ice floating above the surface of the water bodies.

What is meant by the density of a substance/fluid?

Density is actually the ratio of the mass of a substance to its volume.

$Density= \frac{Mass}{Volume}$

Since, volume is a temperature-dependent parameter, so is its density.

Volume ∝ Temperature, and, Density ∝ $\frac{1}{Volume}$

∴ Density ∝ $\frac{1}{Temperature}$

Thus,

• As we decrease the temperature, the volume of the fluid decreases, and the density increases.
• As we increase the temperature, the volume of the fluid increases, and the density decreases.

What is the anomalous behaviour of water?

As per the usual behaviour of fluids on their density, as we go on decreasing the temperature, the density increases and vice-versa.

But water does not follow this trend.
In the case of water:

• The density of water at first increases as we lower the temperature up to 4°C.
• From 4°C to 0°C, water does not expand, instead, it contracts.
  This means that the density of water increases thereafter.

Thus, water has its greatest density at 4°C.

This behaviour of water is known as the anomalous behaviour of water.

How is the anomalous behaviour of water useful for the survival of aquatic life in the colder regions?

• In colder regions, as the temperature falls down to the freezing point, the above water layer contracts, becomes heavy, and sinks down. The lower warmer water layers replaces this colder layer and comes above.

• This sets in a circulation and this process continues until water reaches its maximum density at 4°C.
• If the temperature falls further below, the upper layers remain on top due to its less density, and freezes. This refrains the lower layer from freezing, thus, helping the aquatic life to survive.

Thermal conductivity of ice:

Ice is a poor conductor of heat. Ice functions as an insulator.
This means that ice does not permit the exchange of heat between the water and the surrounding atmosphere, which is colder than the inner water layers.

Thus, the anomalous behaviour of water along with the insulating property of ice helps in the survival of aquatic life in the colder areas. Based on the above explanation, All the options are correct.

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