When and in what habitat did animals likely originate, and when did today's major groups of animals arise?

What happens when the cell copies its chromosomes

An organ system consists of a group of organs that performs specific functions necessary for the survival of an organism. humans have eleven different organ systems: integumentary, skeletal, muscular, nervous, endocrine, circulatory, lymphatic, respiratory, digestive, urinary, and reproductive. discuss the function of neurons, the brain and the spinal cord within the human nervous system while explaining the interrelationship of each organ.

Why do we perceive objects as retaining their brightness under different lighting levels?