BACKGROUND:

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.

PROCEDURE:

1. 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

Photomicrograph of bird kidney, showing the different types of tissues making up this organ.

ANSWERS:

2. Students will discover that the shapes of the cells change from one part of the body to the other. Remember that the skin is our body’s largest organ. Have the students place the Swift GH microscope directly on the skin so students can record what they see. The key point is just to observe that there are differences. Have them compare the palm of their hand, fingertips, back of hand and leg. Just have them draw in the appropriate area on the lab sheet what they see. If they compare with their neighbors, they will notice that the skin cells from different parts of the same body do change, but that the shape is similar from different people.