The correct answer is option 1, loss of heat from the body. The layer of fat present below the skin acts as insulation, preventing the loss of heat from the body. Fat is a poor conductor of heat, so it helps to trap and retain the body heat, keeping us warm. This is especially important in cold climates or during exposure to low temperatures.

Option 2, loss of essential body fluids, is incorrect because fat does not play a role in preventing the loss of body fluids. This is mainly regulated by other mechanisms such as the presence of intact skin and the balance of water and electrolytes in the body.

Option 3, loss of salt from the body, is also incorrect. The preservation of salt balance is primarily governed by the kidneys and the dietary intake of salt.

Option 4, entry of harmful micro-organisms from the environment, is unrelated to the role of fat. The skin acts as a physical barrier to prevent the entry of micro-organisms, while the immune system helps to defend against harmful pathogens.