There are several ways by which a skeletal system <span>help aid the body when its sick. Firstly, it helps in producing red blood cells in the body. It also helps in maintaining the level of calcium in the body. It also produces the stem cells that increases the immunity of the body. I hope that the answer has come to your help.</span>
I would say energy myself, and this is because energy plays a key role in all of these. With trophic levels energy is being transferred amongst the levels. Food chain's is a map of how the energy is passed along the chain. Food web is a web of how energy is transferred, and this is why I would say energy is a keyword.
The Ovaries produce hormones, that trigger menstruation. They also release one egg each month for possible fertilization.