Viruses and Bacteria Review and Assessment

Contributor: Felicia Sabur. Lesson ID: 11650

If you have completed this series on Viruses and Bacteria, you are probably sick of them, but hopefully not sick from them! Take a final review of their characteristics and importance to your health!


Life Science

learning style
personality style
Grade Level
High School (9-12)
Lesson Type
Quick Query

Lesson Plan - Get It!

Audio: Image - Button Play
Image - Lession Started Image - Button Start

Bacteria and viruses are the two most common microbes. They are very different from each other. Do you remember which one needs a host cell to reproduce? Which one is bigger, a virus or a bacterium? There are more things to review, so read on!

Bacteria and viruses both cause many common diseases; however, they are very different from each other.

During the last nine lessons, you have dug deeply into the world of these microbes, and now it's time to review and assess how much you have learned. As you read through the lesson, feel free to go back to any lesson in the unit to re-watch the videos on any concepts you feel confused about.

Before you continue, if you missed, or need to review, the previous Related Lessons in this Viruses and Bacteria series, now's the time to check them out in the right-hand sidebar.

You can use this chart for a brief overview of the differences between bacteria and viruses:

  Viruses Bacteria
  • Non-living
  • Living
  • Needs a host cell to replace it's self
  • Reproduce by asexual and sexual reproduction
  • Treated with vaccines
  • Treated with antibiotics
  • Very short survival time outside of the living host
  • Long survival time outside of a living organism and can continue to reproduce
  • Smallest type of microbe
  • Much larger than viruses
  • No nucleus
  • Prokaryotes
  • Contains DNA material
  • Contains DNA material


Looking at the picture below, you can compare the sizes of viruses to bacteria and to a human red blood cell. Viruses are the smallest microbes, and they can even infect bacteria cells. The virus shape that attacks bacteria is called bacteriophage.

comparison of various biological assemblies

Image [cropped] by Guillaume Paumier, via Wikimedia Commons, is licensed under the CC BY-SA 2.5 license.

Viral shapes versus bacterial shapes

Bacteria have six basic shapes, while viruses have four basic shapes.

  • What type of bacteria is the 3D model you made in Lesson Seven of this series?
  • What shape was the 3D virus you made in Lesson Two?

Image - Video

Bacteria are classified by shape and how they group together. If coccus-shaped bacteria are grouped by pairs, then they would be called diplococcus. If coccus-shaped bacteria are grouped in clusters, then they would be called staphylococcus. If coccus-shaped bacteria are grouped in long chains, then they would be called streptococcus.

Image - Video


If you would like to review bacterial shapes some more, watch Biology Professor's Bacteria Classification by Shape, from Lesson Six:

Image - Video


Viral and bacterial structure

If you would like to review viral shapes and structures some more, watch Patrick Haney's Viral Structure, from Lesson Two:

Image - Video


Viruses come in various shapes, and the shape of a virus is dependent on the proteins that make up its capsid. All viruses, regardless of shape, have two main parts:

  1. Capsid outer protein shell, which can be made of multiple layers
  2. Nucleic acid core contains DNA or RNA with coded instructions for replication

Enveloped viruses also take the cell membrane from its host cell as its outer covering.

virus examples

Image by CNX OpenStax, via Wikimedia Commons, is licensed under the CC BY 4.0 license.

Bacteria come in many shapes, but the structure is the same. The genetic material is contained in the nucleoid in the middle of the cell, surrounded by the cytoplasm, that also contains the ribosomes and plasmid. All of those are encased inside two to three layers that consist of the plasma membrane, cell wall, and capsule. It is important to note that some bacterial cells do not have a capsule.

average prokaryote cell

Image by Mariana Ruiz Villarreal, via Wikimedia Commons, has been released into the public domain.

Viral and bacterial reproduction

Viral reproduction

Viruses reproduce by invading a living host cell. Viruses that only replicate by the lytic cycle are called virulent, and viruses that reproduce using both cycles are called temperate. The lytic and lysogenic cycles have two steps in common: they both go through the attachment and entry steps. What happens after that is where they differ. The lytic cycle takes over the cell and only replicates itself. The lysogenic cycle integrates its DNA into the host cell's genetic material.

For a brief overview of both cycles together you can watchViral replication: lytic vs lysogenic | Cells | MCAT | Khan Academy:

Image - Video

lysogenic and lytic cycles

Image by Suly12, via Wikimedia Commons, is licensed under the CC BY-SA 3.0 license.

Bacterial reproduction

Bacteria reproduce by asexual and sexual reproduction. Asexual reproduction is when there is only one parent involved and the offspring is identical to the parent. The bacterium makes an exact copy of itself. Bacteria reproduce asexually by binary fission, which is the process of one cell dividing in half to form two identical cells. There are five stages of this process.

binary fission

Image by CNX OpenStax, via Wikimedia Commons, is licensed under the CC BY 4.0 license.

Sexual reproduction is when there are two parents involved and they combine their genetic material to form an offspring that differs from both parents. However, sexual reproduction in bacteria does not actually result in additional offspring. Instead of more offspring, it results in more genetic diversity that is then passed on to new bacteria when they divide by binary fission. Genetic material diversity can be achieved by the three ways listed below:

Bacterial conjugation When a plasmid is shared from one bacterium to another, no new bacterium is created, but it introduces some genetic diversity into the population.

Bacterial transformation When bacteria pick up a plasmid from the environment, no new bacterium is created, but it introduces some genetic diversity into the population.

Bacterial transduction When a virus moves bacterial DNA from a bacterium to another via viral replication cycles, no new bacterium is created, but it introduces some genetic diversity into the population.

If you would like to review bacterial reproduction some more, watch Jaya Gupta's Bacterial Reproduction & Exchanges of Genetic Material, from Lesson Eight:

Image - Video


In the Got It? section, you will be taking the assessment for the Viruses and Bacteria series. If you are having trouble with some of the vocabulary, make flashcards to help you study. Go back through the lessons and re-watch the videos on any concepts you feel confused about. Use your 3D models to help you review viral and bacterial structures. And of course, use your workbook as a study guide. If you need to print a new Viruses and Bacteria Unit Workbook, you can download and print a copy from Downloadable Resources in the right-hand sidebar.

Continue on to the Got It? section to take the interactive assessment.

Image - Button Next