Final answer:
A fluffy jacket keeps you warm by trapping a layer of dead air against your body, which acts as an insulator. Helpful bacteria on the skin protect against harmful bacteria, and body fluids contain lysozyme enzymes that kill pathogens.
Step-by-step explanation:
A fluffy jacket keeps you warm by trapping a layer of dead air against your body. The correct answer is A) Air. The layer of air acts as an insulator, similar to the way animals use their fur or blubber to retain heat. Air, being a poor conductor of heat, prevents the loss of body warmth to the environment. This is why insulating garments are effective in cold conditions.
Our skin also plays a vital role in protecting our body against various environmental challenges. For instance, it protects against pathogens such as fungi and bacteria. Helpful bacteria that live on our skin compete with harmful bacteria, preventing them from causing infections. Furthermore, the skin's outermost layer, the epidermis, prevents dehydration, similar to how insulation prevents heat loss.
In addition, the human body has various mechanisms to defend against pathogens, like the lysozyme enzymes found in body fluids such as mucus and tears that can kill bacteria. It is interesting to note that various elements on Earth, like soil, have been found to yield compounds with antimicrobial activity, showing that nature has its way of regulating microbial populations.
Therefore answer is D) Bacteria.