Exchange of nutrients occurs in the digestive system. Exchange of oxygen occurs in lungs
The correct answer of the given question above would be the third option: THE EVOLUTION OF POPULATIONS OVER TIME. What is represented by the base of a phylogenic tree is the evolution of populations over time. It is also known as the evolutionary tree. This tree shows the evolutionary relationships among species.
Answer: Option B
Explanation: The first line of defense acts a barrier and does not allows the foreign materials to enter inside the body. It includes chemical and physical barriers that are always ready to protect the body from infection.
Example: Skin and mucous membrane.
Skin is largest organ and it acts as a barrier between pathogens and human body. It acts a waterproof material and the pathogens cannot get inside through skin unless the skin is broken.
Mucous membranes also acts as first line of defense and breaks the cell wall of many bacteria entering through the openings of the body.
So, skin and mucous membrane are the first line of defense.
