Plants tend to stay in one spot, letting the sunlight fall on them, making do with whatever water and nutrients are available where they are. They create their own food from carbon dioxide and water, using the sun's energy for photosynthesis. Because they stay in one place, individuals of the same species vary in structure. They grow leaves and branches in a pattern that makes the most of the location in which they grow. Plants do "move" by growing, and by turning their leaves toward the light. However, most plants travel to new places only in the seed stage.

Animals live by eating plants and/or other animals. They move from place to place, searching for food. Being able to change location is a very important characteristic of animals.

Animals may crawl, wriggle, move on legs, fly, swim, or use jet propulsion (octipi). Their movements often also allow them to capture prey or avoid predators. Because movement uses energy, and because speed of movement can be a factor in survival, animal species tend to evolve to improve speed and energy efficiency. One result of this is that members of a species tend to have a normal body form that all the members illustrate.

Consider: have you ever seen a five legged dog? A six eyed cat? No, these variations would use more energy without enhancing speed or other characteristics that improve the animal's ability to survive.

However, some animals do root themselves in one spot. These animals are sessile and are found mostly in the oceans. Examples of sessile animals are barnicles, oysters, sponges, sea anemonies, and corals. These animals anchor themselves where there is a good current of water that will bring a stream of food to them. Often they have shells or some sort of armor to protect their soft bodies from predators. These life forms do travel when they are young, floating in the ocean currents until they find a suitable habitat and then anchoring themselves to that place. This works because there are lots of food particles and tiny organisms floating in the water. On land food is not carried so generously in the air, though perhaps a species could evolve that would anchor itself near a food source. Examples of this could be an animal that lives near ripe fruit which attracts clouds of fruit flies, or an animal that lives near an ant hill and preys on ants. However, the problems of what to do when the food source disappears, how to find a mate and reproduce, and how to get young animals to new places would have to be solved.

Could there be animals with chlorophyl?   A few animals live in a symbiotic relationship with algae.   Tropical corals have algae growing within their cells, and the Plants and animals adopted their different life styles when they consisted of only one cell. One cell species, the euglena, seems to combine having chloroplasts with animal-like behavior. I doubt that photosynthesis would provide enough energy for animals to use in their life processes. However, it is possible that on other planets there might be animals with chloroplasts in their skins that could get some of their necessary energy by basking in the sunshine.