Cells
Living things are made up of smaller units, like blocks or bricks that make a building.  These building blocks of living things are called cells.  A cell is the basic unit of structure and function in a living thing.  All living things are made up of cells.  Some, such as bacteria, are made of only one cell.  Others. like you, are made up of many millions of cells.  Most cells are too small to be seen without a microscope.  But each celll is a tiny living unit.  Most celss carry out all the activities needed to stay alive.
Animal Cells
Plant Cells
Cell Parts

         Cells are made up of many smaller parts.  Some parts are common to all cells. All cells have a cell membrane.  The thin wall of the cell membrane encloses a celll and gives a cell shape.  It also is a sort of gatekeeper.  In controls what enters and leaves a cell. All cells also have cytoplasm, a jellylike substance that fills most of the space in a cell.  Other cell parts float in the cytoplasm.  Cytoplasm is made mostly of water.Most cells have a nucleus, located near the center of a cell.  The nucleus controls all cell activities.  It is like the brain of a cell. Other cell structures are scattered throughout the cell. 
          All cells are not identical, just as all living things are not identical.  Cells differ in size and shape.  Different kinds of cells also have different parts.  The outermost part of an animal cell is the cell membrane.  Plant cells have a cell membrane, but it is not the outermost part of the cell.  Plant cells have a stiff wall surrounding the cell membrane.  The cell wall is a structure that keeps the cell rigid and provides support to the entire plant.  Plant cells also have chloroplasts scattered throughout their cytoplasm.  Chloroplasts contain chlorophyll --- the green part of a plant that makes the food.

Compare Plant and Animal Cells

Life Science Safari

Cell Oranelle Table

Comparing Plant and Animal Cells
Science Net
Venn Diagram

Play Cell Jeopardy

One-Celled Microorganisms

          All plants and animals are made up of many cellls.  Many other living things are made up of only one
cell.  These living things.  often called microorganisms, are so small they can be seen only with a
microscope.  These tiny creatures live all around you - in air, water, soil and even inside other living
things.  Like plant cells, the cell of a single-celled microorganism is made up of smaller parts.  These cell
parts carry out all the life processes that keep the cell alive.

The cell of a paramecium has
structures that allow it to move
about and catch food.

There are many kinds of algae such as these.  They
all have chloroplasts and make their own food.  The
cells of algae are surrounded by cell walls.

This Euglena has parts that allow it to move and catch
food as an animal does.  It also has chloroplasts, so it
can make its ownd food, as a plant does.

An amoeba uses its cytoplasm to help it capture food
and move about.  This causes the amoeby to
constantly change shape.

 
Many-Celled Microorganisms

          Some microorganisms are made up of many cells.  These cellls work
together to carry out the processes that keep the organism alive.  The cellls of a many-celled microorganism are not all alike.  Some cells are specialized, or have features to carry out a specific job.  For example, some cells have structures to move and to get food. Other cells have features to digest food.

Volvox are singe-celled
microorganisms that live in colonies. 
When they live in colonies, individual
Volvox cells specialize to caryy out the
processes that keep the colony alive. 
Some cells work to move the colony. 
Others work to get food.

Rotifers are microscopic wormlike animals that make
their homes in pond water, oceans, and moist soil. 
Although they feel on one-celled life, they are
many-celled.  A rotifers cells are speciallized to carry
out different talks.  For example, cells surrounding
themouth of a rtifer have cilia.  These hairlike parts
move back and forth causing a current that draws
food into the mouth of the rotifer.  Once food is taken
into a rotifer, it is broken into smaller pieces by tiny
jawlike structures.  The food particles thn move to the
stomach and pass through the intestines.