WHAT IS A CELL?

WHAT IS A CELL LESSON

Directions:

Print the What is a Cell reading comprehension passage and questions (see below).

Students should read the passage silently, then answer the questions.  Teachers may also use the text as part of a classroom lesson plan.

Lesson Excerpt

A cell is the smallest basic unit of a living thing. Humans are made up of billions of cells that work together to create tissue, muscles, organs, and complex systems that allow us to live life healthy lives. Without cells our body would not exist. Without cells, no species in the world would be alive today.

In 1839 Theodor Schwann and Matthias Jakob Schleiden formulated (created) what is called the cell theory. The cell theory states that all living things are made up of one or more cells. An organism, which is another word for a living thing, that is made up of one cell is unicellular. Different forms of bacteria such as the amoeba are unicellular. An organism that is made up of more then one cell is multi-cellular. Humans, other mammals, birds, reptiles, plants, and many other organisms are multi-cellular.

The cell theory also states that new cells are produced by cells that have already formed. Additionally, Schwann and Schleiden believed that cells contain the information that is passed on to new generations of cells. This includes information on heredity that will pass on to the offspring of the original organism. So, your parents' cells passed on information which was used to make your cells when you were a developing embryo and fetus.

The final part of the cell theory states that any function that is vital to life within an organism occurs in the cells. Today, we know this is true since we've been able to examine cells at microscopic levels. This is something that was virtually unheard of when the cell theory was being developed. (continued...)