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Bacteria are the simplest, smallest forms of life

They are everywhere: in the bread you eat, the soil plants grow in, even inside you.

They prokaryotic cells = do not have an organized nucleus

They do have DNA molecules, strung together in a chromosome

they do have a cell membrane and cell wall

Almost no organelles, just ribosomes

Very small. Need a microscope to see them

The role of bacteria

Some help plants absorb nitrogen (N2) gas – from the atmosphere into the soil.

Some cause diseases like botulism.

Some bacteria live inside the stomachs of cows to help them break down cellulose. Cows, without them, can only digest grass as well as we do. Yet with the right bacteria, they can break down the plant cellulose and release the energy from it.

from the Virtual Museum of Bacteria (http://www.bacteriamuseum.org/)


What are bacteria? This exhibit is the best place to start.

Not all microorganisms are bacteria.  Microorganisms that are not bacteria are briefly described here.

What is bacteriology? The study of bacteria is explained here.

Applied bacteriology how bacteria are applied in industry.

Bacteriophages are viruses that prey on bacteria. So bacteria can be ill, too.

Bacteria and our senses describes how we can see, taste, feel and hear bacteria. Or not.

Worksheets on bacteria (MS Word format)
Archaea and Bacteria


Sample questions

MCAS: The illustration below shows the external features of a prokaryotic organism. Which of the following can be concluded about the internal cellular contents of this prokaryote?

A. The cell does not contain ribosomes.
B. The cell does not contain a nucleus.
C. The cell contains mitochondria.
D. The cell contains a vacuole.


Feb 2016 MCAS.

Which of the following statements best compares reproduction in viruses with reproduction in single-celled protists?

A. Viruses reproduce by releasing spores; single-celled protists reproduce by dividing in half.

B. Viruses require large colonies to reproduce; single-celled protists reproduce as individual cells.

C. Viruses require the cellular machinery of host cells to reproduce; single-celled protists reproduce on their own.

D. Viruses form haploid gametes when they reproduce; single-celled protists form diploid gametes when they reproduce.


Learning Standards

Massachusetts Science and Technology/Engineering Curriculum Framework

Life Science (Biology), Grades 6–8.
Classify organisms into the currently recognized kingdoms according to characteristics that they share. Be familiar with organisms from each kingdom.

Biology, High School
5.2 Describe species as reproductively distinct groups of organisms. Recognize that species are further classified into a hierarchical taxonomic system (kingdom, phylum, class, order, family, genus, species) based on morphological, behavioral, and molecular similarities.

Benchmarks for Science Literacy, American Association for the Advancement of Science

Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology… A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.

SAT Biology Subject Area Test

Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.

Teaching About Evolution and the Nature of Science, National Academy Press (1998)

Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.

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