Pre-test		Post-test
Q&A	Assignment Discovery: Cells	Q&A

Instruction 1-1

Basic Cell Characteristics | Nucleus, Mitochondria, Chloroplasts | Mitosis and Organism Development

Eukaryotic vs. Prokaryotic Cells
http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/euproreview/eupro.html

There are big differences between eukaryotic and prokaryotic cells, but they do have some things in common:

• Both have DNA as their genetic material.
• Both are encased in membranes. The membranes of Prokaryotic cells and of some eukaryotic cells are surrounded by a strong cell wall.
• Both have a similar basic metabolism (the word metabolism refers to the formation and break down of chemicals in the body).

The major difference is that eukaryotes have a nucleus and prokaryotes do not.

Also, eukaryotic cells contain a wide variety of organelles (tiny "organs" or structures inside the cell) that perform various functions. Some of the most important organelles are mitochondria, chloroplasts, lysosomes and ribosomes -- which we'll tell you about in our next section of this lesson.

But first, here is the basic structure of an eukaryotic cell:

• The membrane (the outside or coating)
• The nucleus (the place where the DNA is stored and from where instructions are sent to the rest of the cell for the production of proteins. The nucleus has its own membrane)
• The cytoplasm or cytosol, which contains everything between the membrane and the nucleus (including organelles)

Eukaryotic cells are, on average, ten times as large as prokaryotic cells. Their DNA is more complex and is formed into chromosomes. And their organelles enable them to do more complex jobs.



3.5 Billion Years Ago

Many scientists think that prokaryotic cells arose about 3.5 billion years ago -- and that they were the first life forms on Earth; they believe this because they have found fossils of prokaryotic cells that are 3.5 billion years old. After about 2 billion years, aggregates of prokaryotic cells evolved into eukaryotic cells.

Today, the only prokaryotes we know of are bacteria (like the bacteria that give you strep throat and the bacteria in our digestive systems that help us to digest our food) and cyanobacteria (blue-green algae). To learn more about prokaryotic cells, go to http://www.biology4kids.com/files/micro_prokaryote.html

All other organisms are formed of cells that are eukaryotes. Different eukaryotes have different characteristics. Let’s begin by looking at the structure of plant cells.

 

Plant Cells vs. Animal Cells
http://sun.menloschool.org/~cweaver/cells/

As we said, most plants are made up of eukaryotic cells. But eukaryotic plant cells are different from eukaryotic animal cells. And the biggest difference is the cell membrane.

In animals (like us) the membrane is the actual outside of the cell. But plants have something extra -- a cell wall that goes all the way around the outside of the membrane, shown with the brown shading in the diagram above.

Remember, the main difference between plant cells and animals cells is this -- plant cells have a cell wall and animal cells don't. This cell wall is made of cellulose.

Cellulose is important in human nutrition since it provides fiber (roughage), which keeps your digestive system going. That's why it's important to eat a diet rich in plant material like fruits, whole grains and vegetables.

 

Experiments for Home and Classroom

In this classroom activity, students are invited to learn about the parts of a cell by role-playing the parts of giant one. Click:
http://sln.fi.edu/biosci/activity/bio-3.html

Plants provide needed fiber in our diet. In this "Plant Parts Salad" activity, students are invited to delve a little more deeply into the role of various plant parts in our diet. Click:   http://www.hhmi.org/coolscience/vegquiz/index.html