Answer:
1. The human body is a mesh of organ systems that are constantly working together to maintain homeostasis and ensure the success of the human and the species as a whole.
2. The structures found in the head, chest, and abdomen are all organs. They are all parts of systems, the brain is part of the nervous system, the mouth, stomach, and intestines make up the digestive tract, and the heart, lungs, and blood vessels make up the respiratory and circulatory systems.
3. 'External' simply means 'outer', and the internal structures are the inner pieces and parts that keep organisms alive, help them grow, and help them reproduce.
4. Arm=Leg, Elbow=Knee, Wrist=Ankle, Hand=Foot.
5. *
*I can't see the actual question part of number 5.