Have you ever had the flu? A cold? Chicken pox? If so, you have had a virus. A virus is a nonliving particle made of proteins, nucleic acids, and (sometimes) lipids. Viruses are considered to be nonliving because they do not have the ability to reproduce on their own. They must be inside a host cell in order to reproduce.

Viruses differ widely in terms of size and structure, as you can see in the following diagram. However, all viruses are much smaller than the cells they infect. Most viruses are so small they can be seen only with the aid of a powerful electron microscope.

Directions: Observe the structure of the viruses below. As you look from virus to virus, note which structural components all the viruses have in common. Click on "Check" to see if your response is correct. 

As you can see, all the viruses shown some type of genetic material, either DNA or RNA, and a capsid, or protein coat, surrounding the virus. The capsid has three functions:

1. It protects the virus.
2. It contains special sites on its surface that allow the virus to attach to a host cell.
3. It provides proteins that enable the virus to penetrate the host cell membrane.

Directions: Below is a picture of a virus. Label the virus by dragging the labels to the appropriate structure. Click on "Check" to see if you labeled the diagram correctly. 

Viruses are different from living cells. Two eukaryotic cells—one a plant cell and the other an animal cell—are shown below. Remember that eukaryotic cells contain membrane-bound organelles, such as a nucleus. 

Study the plant and animal cells shown. Are there any structures that these eukaryotic cells have in common with viruses?

Directions: Drag and Drop the structures into the correct position in the chart below.

Directions: Watch the Kid2Kid: Comparing Cells to Viruses video to learn more about similarities and differences between cells and viruses.

Miren el Kid2KId: Comparando Cèlulas y Virus vidèo para aprender más sobre los similarites y diferencias de cèlulas y viruses.