Cells are the basic unit of living systems,
but obviously there's a lot more to an organism than just cells. Cells are the
building blocks that are used to create larger groups of cells which perform
more specific tasks.
The second level of organization is the
tissue. A tissue is a group of similar cells that work together to perform a
specific job. Remember that there are specialized cells in multicellular
organisms, for example, nerve, muscle, and blood cells. Tissues function to
perform many tasks that are too complicated for a single cell to perform.
Tissues are used for support, movement, secretion, protection, growth, and
reproduction. Specialized cells form specialized tissues such as blood tissue.
A group of tissues working together to
perform a specific function is called an organ. Organs are the third level of
organization. Examples of organs include the skin, heart, eye, stomach, and
lungs. The complexity of organs is a characteristic that is used to separate
groups of organisms.
The skin is a large organ with many
different cells. As part of this lab, students are to look at their skin cells
at different locations on their bodies and then compare the same areas on
their partners. The skin is the largest organ of the body and is very complex.
It wraps the adult body in about 20 square feet of tissue and weighs some
seven pounds. The skin has 3 layers, however, students will only be dealing
with the epidermis, or the outer layer. The outer skin is composed of dead
cells that are always being worn off. We shed our skins continuously, not all
at once but little by little, which goes on mostly unnoticed.
Have students look at
the prepared slides of the different groups. See if they can predict whether
something is a whole organism, appendage, cell, tissue or organ. An appendage
is an auxiliary part of the main body. Appendages can contain part of an
organ, depending on the type of organism. Students will also see examples of
the whole organisms and synthetic substances. List the answers