Lab 3
Cells and Cell Replication

Learning Objectives
In this lab students will:
- Learn how to use the microscope to observe cells from multicellular organisms.
- View and compare prepared human and frog blood smears.
- Identify the 4 stages of mitosis in a magnified onion root tip.
- View magnified cells of the aquatic plant Elodea before and after undergoing plasmolysis.

Cells

• As we saw in Lab 2, the Cell Theory states that all living things are made up of cells. All cells share basic common characteristics. They share these common characteristics because there is an evolutionary link between simple prokaryotic cells and more complex eukaryotic cells.
• All cells are composed of four macromolecules: proteins, lipids, carbohydrates, and nucleic acids (DNA and RNA).
• All cells are surrounded by a cell (or plasma) membrane made up of lipids and proteins.
• All cells store genetic information in the form of DNA.
• All cells contain ribosomes, the site where proteins are made.
• All cells contain a gel like cytosol.
• Although all cells share the above characteristics, there are major differences between prokaryotic cells and eukaryotic cells.
• "Prokaryote" means "before (pro) the nucleus (karyon). Prokaryotic cells lack a large organelle called the nucleus. This is the most obvious difference between prokaryotic cells and eukaryotic cells. Prokaryotic cells are also much smaller (about 10 times smaller then a typical eukaryotic cell) and have fewer internal structures (organelles).
• "Eukaryote" means true (Eu) nucleus (karyon). All eukaryotic cells have a large nucleus that stores the genetic information (DNA). Eukaryotic cells are much larger and have membrane-bound organelles. Organelles are internal structures that carry out specific functions for the cell.
• Plants, animals, fungi, and protists all have eukaryotic cells. You are a eukaryote!

This figure shows the organelles found in a typical animal cell.
• The nucleus stores the DNA and is surrounded by a double membrane called the nuclear envelope.
• Inside the nucleus is one or more darker staining regions. This is the nucleolus, the site where ribosomes are made.
• The endoplasmic reticulum (ER) is a membranous organelle that may have ribosomes associated with it (rough ER) or no ribosomes associated with it (smooth ER). • The rough ER is the site for the synthesis of proteins that will leave the cell to carry out their functions elsewhere.
• The smooth ER is where lipids are made.
• The Golgi complex is a collecting, packaging, and sorting center for the cell. Materials made by the cell and destined for use outside the cell are processed and modified in the Golgi complex.
• Lysosomes are sites where large macromolecules or worn-out organelles are broken down.
• The mitochondria are the organelles where responsible for making energy (the mighty mitochondria). When cells receive nutrients from their environment, the mitochondria convert the potential energy in the nutrients into a form that can be used by the cell to carry out its functions.
• Chloroplasts (not shown in the image because they are only found in plant cells and some protists) are organelles responsible for converting energy from the sun into chemical energy that plants, and other photosynthetic organisms can use to drive the synthesis if glucose. Chloroplasts are found in photosynthetic cells.

• In this exercise you will investigate the structures of the various multicellular eukaryotes: human cheek epithelial cells, human and frog blood cells, cells of an aquatic plant, Elodea, and actively dividing cells from an onion root tip.