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CHAPTER 2
THE DIVERSITY OF LIFE
How are they classified?
Biologists classify organisms to study unity and diversity in an organized way. Things such as the
physical structure are important ways that organisms are classified. The division of biology that deals
with the classification and naming of living and extinct organisms is called taxonomy.
The Classification Scheme
Since early times organisms were grouped into just two kingdoms, plant and animal. They were
classified by how they ate and what they did, however, with the invention of the microscope new
categories for classifying was evolved. Through the microscope they were able to classify organisms
even further starting the kingdom Protista.
Bacteria are different than other living things because they do not have a nucleus. Biologists consider
the development of a nuclear membrane and other cell organelles to be so important an evolutionary
step that they group bacteria into a separate kingdom. This kingdom is called Monera. However, today
this kingdom is grouped into two separate kingdoms, Archaebacteria and Eubacteria.
A fifth kingdom was started, Fungi. Bread molds, yeasts, and mushrooms are different in some ways
but they do resemble each other so thus creating the fifth/sixth kingdom.
Nomenclature
Categories of classification are known as taxons. There are seven categories begin at most
general and go to most specific.
There is a two-name system for all organisms. The name consists of its Genus and
Species. This system is called Binomial Nomenclature. In the actual name itself the first word
must be capitalized and the second word should not be, however, they both need to be
either italicized or underlined.
Comparing Cat and Human Classification
Cat
Kingdom
Phylum
Class
Order
Family
Genus
Species
Animalia
Chordata
Mammalia
Carnivora
Felidae
Felis
Felis domesticus
Human
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
Homo sapiens
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In the year 1753 the Swedish naturalist Carolus Linnaeus (originally Karl von Linne) published a book in
which he classified and named all plants and animals the known in Europe.
The Roll Call of Living Things
Bacteria has its own kingdom because they are so different from anything in all the other
kingdoms. The main reason is because of the difference between the cells of Monera and any of the
other kingdoms. Monerans lack a distinct membrane-bound nucleus. Cells that lack this distinct
membrane-bound nucleus are called prokaryotes. Cells with a distinct nucleus are called eukaryotes.
Organisms that con produce their own food from simple materials are called autotrophs. Heterotrophs
are organisms that their food is preformed high-energy molecules obtained from dead or living things.
Kingdom Protista
This kingdom was developed to include microscopic organisms that could not be classified with
certainty as plants or animals. Some are heterotrophs and others are autotrophs. Most of them are
unicellular. The protists include algae, protozoans, and slime molds.
Euglena. Euglena is and unusual organism that possesses characteristics of both animal and plant cells.
Algae. Unlike the blue green algae, the algae have true nuclei and specialized organelles. Some algae
form large, many-celled structures. Algae live in the ocean, fresh water, and moist places on land.
Protococcus is a green alga that lives on the moist bark of trees and moist surfaces of rocks.
Protozoa
Protozoa are unicellular, complex, and animal like protists that lack chlorophyll. They reside in
fresh water, salt water, and moist soil. They are classified by the method of movement. Among fresh
water protozoa are Ameba and Paramecium, single celled organisms large enough to be seen with the
naked eye.
Ameba is an irregularly shaped organism classified with the protozoa. It can be seen with the naked eye
and appears under the microscope as a translucent mass of protoplasm that slowly changes shape. I
lives in water and may be found on the underside of the leaves of plants which grow near the bottom of
freshwater ponds.
Paramecium is smaller than ameba and cannot be seen with the naked eye. These organisms live in
ponds and lakes.
Slime Molds are named because at one stage of their existence they are like a slimy mass of protoplasm.
Slime molds are a good example of protists because they cannot clearly be defined as plants or animals.
Viruses are much smaller than bacteria. Viruses were classified as a type of disease causer in the early
years scientists knew about them. Most biologists do not consider viruses to be organisms and they are
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not included in either the Protista or the Monera kingdoms. They live only within living cells of a host. A
virus particle l directs the host cell’s chromosomes to cause the production of additional virus particles
instead of carrying on the cell’s normal metabolism. Viruses cause a number of human diseases
including lethal illnesses such as AIDS, and forms of cancer such as T-cell leukemia. They cause things
such as the flu, influenza, and the common cold those nasty little buggers!
Kingdom Fungi
Fungi is a group of plantlike organisms lacking chlorophyll. Fungi are heterotrophs, some act as
parasites getting their food from living things. Others get food from dead organisms. Molds are a form
of fungus coming in many different ways on human’s everyday food such as bread, fruits, and
vegetables. Mildew is a mold that forms black spots on damp towels jammed into a hamper and other
sorts of things that are damp. Mushrooms are also forms of fungus however we can eat them
Lichens. These things look like a thin, gray crustlike pancake growing on rocks or trees. It is a
combination of fungus and alga. This growing together helps each other in a relationship called
mutualism. The death of lichens enriches soil by the addition of organic matter.
Kingdom Plantae
This kingdom has only two phyla…the bryophytes and the tracheophytes, mostly land plants.
The bryophytes are small green plants that grow in moist places. They have no true leaves and lack a
stem or have a very simple stem. The tracheophytes (tube plants) have a vascular (conducting) system
of tubes for conducting water. This lets plants grow taller than the low-lying liverworts and mosses.
More advanced ones have roots, stems, and leaves. Ferns if examined closely you can see the stem or
roots grow in the ground. They require water for fertilization and thus are usually found in moist places.
Kingdom Animalia
This kingdom contains only multicellular organisms. They don’t have chlorophyll or cellulose cell
walls and most of them move their bodies by means of contracting fibers. This kingdom has nine phyla
The porifera, or sponges, are simple animals that spend their lives attached to solid objects
under water. Most of them are marine, however, a few are freshwater types. The sponges eat by
drawing food in through their pores and filtering out food particles. Flagellated cells cause a current to
get the movement of the water through the sponge. The filtered water passes out through the osculum.
They are the least complex of the animal phyla.
The coelenterates include the hydra, jellyfish, sea anemones, and corals. Coral is common in
tropical waters. It is formed by millions of layers of exterior skeletons of millions of tiny Hydra-like
animals.
The Platyhelminthes are the simplest of the three phyla of wormlike animals. Their body is flat
hence the name flatworms. Planaria secretes a slimy mucus layer glides over underwater objects by the
beating of cilia on it ventral surface. Many flatworms are parasites that cause great damage to humans
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and other higher animals. A tapeworm grows as a long flat ribbon consisting of rectangular sections
called proglottids. Humans may get tapeworm larvae by eating undercooked meat from infected
animals such as a little helpless pig.
The nematodes or roundworms have bodies that are round in cross section. They have bilateral
symmetry and three layers of cells. They can be identified by their thrashing around. These can also be
consumed by humans in the same way tapeworms are. They can be really harmful and even cause
death. So be sure to cook your pork super well. The hookworm is a parasite that usually enters the
human body through the feet. Walking bare foot on the soil is one way to get these. Elephantiasis is a
disease caused by the minute nematode, Filaria. They cause terrible swelling of the limbs of a human
being.
The annelid worms are the segmented worms. The most visible sign of segmentation is the
series of rings encircling the body as seen in the common earthworm. They have bilateral symmetry,
three cell layers, a body cavity and a well-developed closed circulatory system. Leeches live in
freshwater ponds and streams are in a separate group of the annelid phylum. They have suckers at each
end of their bodies so that the posterior sucker can anchor the leech temporarily while the anterior on
sucks the blood of the host animal.
The mollusks are soft-bodied, unsegmented animals that have three layers of tissue and welldeveloped organ systems. The bodies are protected by a shell. Clams, oysters, mussels, and scallops are
called bivalves because they have two shells. Most of these mollusks are marine although some live in
the fresh water. They get their food by filtering food particles through. Many mollusks are used as food
for humans but some cause us trouble. The anatomy of mollusks differs greatly from that of other
phyla.
The arthropods are “the join-legged animals.” This phylum contains 90 percent of the species of
the animal kingdom. More than 900,000 species have been identified, and the number of species is
estimated to be in the millions. They are the most complex and successful of the animals without
backbones. Arthropods inhabit most places on earth in fresh water, salt water, on the surface of the
land, in the soil, and on or inside animals and plants. The living arthropods are divided into five main
classes.
1. Class Chilopoda – the centipedes are elongated flattened wormlike arthropods with
little external difference in the numerous segments
2. Class Diplopda – the millipedes are founder than the centipedes and they have two
pairs of walking legs for each segment except the first one and the last two.
3. Class Crustacea – most crustaceans are water-dwelling animals that breathe by
means of gills and have two pairs of antennae.
4. Class Arachnida – the arachnids include ticks, mites, spiders, daddy longlegs,
horseshoe crabs, and scorpions.
5. Class Insecta – insects make up the largest class of the phylum arthropoda.
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The echinoderms are called the “spiny-skinned animals” because of the spines that cover their
skins. The vascular system of a starfish draws sea water into a system of canals that end in many tube
feet at the ventral surface of the radiating arms. Oysterfishers who found starfish used to hack them up
with a knife and toss the paerts into the sea.
The chordates take their name from the notochord. This stiff supporting rod of cartilage in the
dorsal part of the body is present at some stage in their lives. They have vertebrates unlike the other
organisms we’ve gone over.
The End!