BACKGROUND:
Cells are the fundamental units of living
material. The bodies of all living things are formed from cells, and without
cells there would be no life. Every large living thing is made of billions of
cells that have different sizes, shapes, and functions. Cells contain special
structures called organelles which have specific functions for maintaining the
health of cells. The types of jobs that organelles perform include taking in
food and breaking it apart into simple molecules, releasing energy from food,
building and repairing cell parts, getting rid of harmful wastes, and making
more cells.
These organelles can help identify whether
a cell comes from a plant or an animal. Only plants, for instance, have
chloroplasts and starch grains. Chloroplasts are needed for photosynthesis and
starch grains (amyloplasts) store the starch that is produced by
photosynthesis. Vacuoles in an animal cell are not as large as those in plant
cells. Learning the specific functions of the various organelles will continue
in the post lab, so it is important that the students recognize and be able to
distinguish the differences between animal and plant cells.
PROCEDURE:
- Students have compared an ideal model of
a plant cell with an ideal model of an animal cell. However, when you look at
real samples, the differences may not be as obvious as they were on the
models.
- Have the students look at a thin slice
of onion and animal cell as directed in the lab. Cut the onion skin very thin
and put a drop of food coloring and then blot it. Use some hamburger meat and
squish the cells on a glass slide. Make sure the students see that the onion
cell has a thicker wall around each of the cells. This is the only real
difference the students can see with the Swift-GH. You may want to use a
higher magnification.
- Then have the students look at the 3
unknowns (pine stem x.s. [plant], hyaline cartilage tracheo region s.x.
[animal], and bone cancellous sec. [animal]. The major difference is the cell
wall that can be seen in the pine stem.
