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Living Things
Every
individual living thing is made of smaller parts.
The smaller parts have different functions, but all
of the parts work together to enable the individual
to live and survive in its environment. The smaller
parts are made of even smaller parts, which are made
of smaller parts, and smaller parts, until you reach
the smallest part of all: the cell. The cell is the
basic building block of all living things.
Some
tiny organisms, called protists, are made of only
one cell. Since the single cell must work alone, it
has to do everything to make sure that the organism
survives. Protists can not be seen with the human
eye. To observe tiny organisms in their microworlds,
you can use a microscope.
Multi-celled
organisms are more complex. Different parts have different
functions, each part sharing the work and cooperating
to make sure that the organism survives.
In
a plant, for example, the cells working together in
the roots make sure that the plant gets the water
and nutrients from the soil that the plant needs to
survive. The cells working together in the leaves
make sure that the plant exchanges oxygen for the
carbon dioxide that the plant needs to survive. The
roots and the leaves work together as a system for
the plant to survive.
The
parts of an animal also work together to make sure that
the animal is able to survive in its environment. An
animal's anatomy must be adapted for its survival. Monkeys
have strong arms and legs and hand-like feet so that
they can climb trees easily to get food. Chameleons
are well-known for their ability to change skin color
to blend in with their environment, hiding from their
enemies. The anatomy of the chameleon also features
two eyes that can move independently, enabling the side
of the body facing an enemy to remain perfectly still
while the other side keeps watch.
Different parts have different functions, but all of
the parts work together to help the animal survive.
Some parts are responsible for allowing the animal to
reproduce. The reproductive organs on an animal also
determine its gender. Often, male and female animal
anatomy varies. Were the earthworms male or female?
Actually, neither. Earthworms are hermaphrodites, which
means that they have both male and female reproductive
organs. Their eggs and sperm are released in a protective
mucus sheath which slips over the worm's head and is
deposited in the soil.
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