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
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
A few animals live
in a symbiotic
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.
Photograph from a Corel CD-ROM : for viewing only, not for
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