Plants and animals are made up of cells. For sustaining the life of an organism cells plays an important role. These cells work in the form of biochemical reactions which carry out all the time.

Circulatory system Transport substances. Defend the body. Regulate temperature. Excretory system Remove waste products and unwanted substances. Regulate the water content of the body. Muscular ...

Sometimes it is the most unassuming animals that cause the most consternation. Xenoturbella (pictured) are simple marine flatworms with no brain, anus, gonads, excretory system or through gut ...