Taxonomy Lecture Notes
Do all plants and animals have the same genes?
No, but some organisms are closely related. Grouping organisms into categories helps scientists
find information about living things more easily. For instance, if you know that a cobra is a snake,
you know that it has scaly skin and no legs. Biologists group organisms into categories based
on how closely related the organisms are. Classifying living things in this way helps biologists
study how organisms have changed over time.
What are these categories?
First of all, living things are classified into large groups called kingdoms. Each kingdom is divided
into smaller groups, these smaller groups are divided into even smaller groups, and so on. These
groups,from largest to smallest, are kingdom, phylum, class, order, family, genus, and species.
How many kingdoms are there? And what’s in them?
Today the most widely used classification system contains six kingdoms. This system has
changed over the years to include new information. The following list shows the names and major
characteristics of the six kingdoms.
● Archaebacteria: This kingdom includes unicellular (one-celled)prokaryotes that often
live in extreme environments. Some archaebacteria are autotrophs (make their own
food), and some are heterotrophs (cannot make their own food). Examples of
archaebacteria include the bacteria that live in hot springs.
● Eubacteria: This kingdom also includes unicellular prokaryotes that may or may not
make their own food. However, most eubacteria do not live in extreme environments.
Examples of eubacteria include the bacteria that cause strep throat.
● Protista: This kingdom includes mostly one-celled eukaryotes. However, there are a
few protists that are multicellular. Protists may be autotrophs or heterotrophs. Examples
of protists include amoebas, slime molds, and algae.
● Fungi: Most fungi are multicellular eukaryotes, although there are a few unicellular
fungi. All fungi are heterotrophs with cell walls. Examples of fungi include mushrooms,
yeasts, and molds.
● Plantae: Plants are multicellular eukaryotes. They have cell walls and specialized
tissues and organs. Plants can make their own food, so they are autotrophs. Examples of
plants include mosses, ferns, trees, and grasses.
● Animalia: Like plants, animals are also multicellular eukaryotes with specialized
tissues and organs. However, animals are heterotrophs and lack cell walls. Examples of
animals include worms, insects, fish, birds, reptiles, and mammals, including humans.
How do scientists know which group to place organisms in?
Scientists classify organisms based on a variety of characteristics, including genetic makeup,
body chemistry, physical structures, and more. Let’s use the transportation of materials as an
example of one characteristic that scientists use to classify some types of organisms.
All living things must be able to transport materials such as nutrients and oxygen within their
bodies. Organisms that are closely related have similar structures to accomplish transport.
Archaebacteria, eubacteria, and most protists are one-celled organisms.
Because they are so small, they do not need to transport materials great
distances, and they do not have well-developed transport systems.
Some protists, however, have organelles called contractile vacuoles.
These organelles collect excess water and pump it out of the cell.
Even though many fungi are multicellular, they also lack circulatory systems. Instead, materials
within fungi are transported directly from cell to cell. By contrast, many plants have specialized
transporting tissues called xylem and phloem. Xylem transports water and minerals throughout a
plant, and phloem transports sugars from one part of a plant to another. We’ll talk more about this
in Objective 3.
Animals have the most-developed transport systems of all. In animals the transport system is
called the circulatory system. The circulatory system of many animals includes a heart that
pumps blood throughout the body. The blood travels in vessels and carries nutrients, oxygen,
and waste products such as carbon dioxide.
Fish have a two-chambered heart, amphibians have a three-chambered heart, and birds and
mammals have a four-chambered heart. Fish have a circulatory system with a single loop.
Amphibians, birds, and mammals have a circulatory system with two loops, one to the lungs and
one to the body.