Distinguish among viruses, viroids, and prions.

Module 7 Overview

Origin and Classification of Life

The origin of life has been of great debate for centuries.  This module will outline the various ideas of how life and Earth itself developed.  You will learn the evidence for multiple theories on the origin of life and the evolution of these theories based on new scientific findings.

This module will also focus upon one of the most important achievements of the science of biology: the classification of organisms and the creation of an internationally agreed upon system of nomenclature.  Understanding how organisms are classified provides an important basis for any future studies in ecology.

Learning Objectives

Upon completion of this module, you should be able to:

10A Describe the evidence used to suggest an extraterrestrial source for life on earth.
10B State the most probable physical conditions on early Earth and the changes thought to have happened before life could exist.
10C Differentiate between the concepts of spontaneous generation and biogenesis.
10D Examine the chemical and physical events that must have occurred to have life originate on Earth.
10E Describe the different hypotheses for what the first living thing might have been like.
10F Identify the way in which organisms have caused the atmosphere of the earth to change.
10G State the order and approximate times for major evolutionary events.
10H Examine the endosymbiotic theory.
10I Explain the experimental evidence for the origin of life from organic and inorganic material.
10J Distinguish between taxonomy and phylogeny.
10K Describe the kinds of tools used to establish phylogenetic relationships.
10L Distinguish among viruses, viroids, and prions.
10M Describe the scientific method for naming organisms.
11A List and give distinguishing characteristics of the kingdoms within the Domain Eukarya.
11B Distinguish between Bacteria and Archaea.
11C Explain the features that differentiate organisms as microbes.
11D List the basic characteristics of members of the Protista, Archaea, Bacteria, and Fungi.
11E Identify the type of environments in which microorganisms live. 


Module 7 Reading Assignment

Enger, E. D., Ross, F. C., & Bailey, D. B. (2012).  Concepts in biology (14th ed.). New York: McGraw-Hill. Chapters 19, 20, and 21.

Optional Reading Assignment:

Chapter 22, The Plant Kingdom, and Chapter 23, The Animal Kingdom.

Origin and Classification of Life

Scientists have broken down life into domains of organisms.  Scientists believe that at first life, there was first the bacteria domain.  The bacteria domain was followed by the archaea domain and finally, the eucarya domain.  Domain bacteria and domain archaea remain the same and have not been further broken down.  Domain eucarya was further broken down into the plant kingdom, the fungi kingdom, and the animal kingdom.

Organisms live on, in, and within all types of environments.  Organisms can be found from pole to pole and everywhere in between.  This includes deserts, rocks, geysers, the deep sea, and so much more.  There are also organisms that are considered extremophiles.  Extremophiles are organisms that have adapted to extreme environments such as high and low temperatures, acid and alkaline, extreme pressure, and even radiation.

Bacteria, archaea, Protista, and fungi are all microorganisms.  Generally, they are so tiny that you almost always have to use a microscope to see them.  Many of them are single-celled organisms.  The domain bacteria are made up of a very assorted group of organisms that carry different purposes.  Scientists have predicted that there could be millions of different bacteria, but only about 2,000 have been named.  Bacteria come in the form of spheres, which are either rod-shaped or spiral-shaped.  Many of them also have flagellum that they use to move.

Under the domain bacteria are several subgroups that are further broken down.  Many kinds of bacteria are decomposers.  Decomposers are able to break down nonliving organic materials into inorganic molecules.  Decomposers also allow for producers to reuse them.  This is a very primitive way of recycling, but it also keeps the ecosystem moving by recycling all the inorganic molecules back to the producers where they can create energy again.  A commensal bacterium is a bacterium that lives in or on another living organism, but does not otherwise seem to have a function.  This type of bacteria does not cause harm nor do any good for the host.  Photosynthetic bacteria use photosynthesis to break down carbon dioxide and water and then release oxygen.  This type of bacteria does not cause harm.  Another bacteria is known as mutualistic bacteria.  This type of bacteria actually works to help its host by blocking disease-causing bacterium and also helps to produce antibiotics.

The domain archaea used to be grouped with bacteria, but it was discovered that they were their own diverse group of organisms.  Archaea’s cell walls, cell membranes, and DNA are very different from bacteria’s.  While archaea are like bacteria in that they too are shaped in sphere, rod-shaped and spiral-shaped formations, they also exist in lobed, platelike or irregular shapes.  They can be found everywhere from water, both salt and fresh, to extreme temperatures and high acid counts.  Please watch the Three Domain Classification System video.

Protista is a strange grouping because scientists do not believe that they actually belong together as a whole, but it is convenient to place them together.  It is so challenging to separate the Protista into accurate subgroups because of their diversity and that they are always evolving.  Still, scientists have them broken down into three different categories: algae, protozoa, and fungus-like protists.  These categories are basically only good for the purpose of deliberating on their major roles.

Fungi are non-photosynthetic, which means that they do not use photosynthesis to gain energy.  Fungi differ from other organisms because of the compounds that their cells walls are made up of.  They are not capable of moving independently, but they spread fairly easily because of the large amount of spores and their tiny size.  The spores are moved by wind and water.

Viruses are acellular (not made of cells), infectious particles.  Viruses are not considered to be living because they can only function if they are within a living thing.  Viruses can be rod-shaped, sphere-shaped, or in coils, and are characterized by the symptoms that they cause in the infected.  They are even smaller than microorganisms, and you cannot see them with a normal microscope; they can only be seen with an electron microscope.  Viruses replicate rather than divide, which makes it much easier to spread the illness.

viroid is an infectious particle that is even smaller than a virus particle.  Scientists believe that a viroid is made up of just one strand of RNA, or ribonucleic acid.  Viroids attack plants and have never been shown to affect animals.  When a plant is infected, the plant’s growth can become underdeveloped or malformed or the entire plant can be killed.  Scientists believe that a viroid may mimic DNA, which makes it easier to spread and damage more.

The basics of viroids are still being studied, even less to truly known about prions.  Prions are hypothesized to be a protein that is able to be passed from one organism to another.  These proteins then cause damage to the brain.  An example of a prion is mad cow disease.  It is still unclear if environmental factors are responsible for prions, or if the actual organisms are responsible for causing the diseases.

Required Presentations:

Click on the links below to view the Module 7 presentations.

Click on the links below to view optional presentations.


Posted in Uncategorized

Leave a Reply