Download reading and questions: kingdom monera

READING AND QUESTIONS: KINGDOM MONERA
Monerans are tiny organisms that consist of a single cell. Moneran cells, which are called prokaryotic
cells, are different from all other cells because they lack a nucleus and certain other cell structures. At one
time, the term "bacteria" was used to refer only to certain kinds of monerans, while other monerans were
known as blue-green algae. Today, blue-green algae are called cyanobacteria, or blue-green bacteria.
Because all monerans are now considered to be bacteria, the terms bacteria and monerans are used
interchangeably.
Bacteria are the oldest forms of life on Earth. The first bacteria appeared about 3.8 bya, and were
Earth's only living things for about 2 billion years. They are among the most numerous organisms on Earth.
Bacteria can be found above Earth's surface in the atmosphere, on the surface of the Earth and far beneath
Earth's surface. Scientists estimate that there are about 2.5 billion bacteria in a gram of garden soil. And
the total number of bacteria living in your mouth is greater than the number of people who have ever lived!
The first characteristic used to classify bacteria is their shape. They may be rod-shaped like a
medicine capsule (called bacilli), spherical as a marble (called cocci), coiled like a stretched spring (called
spirilla), round and stalked like a candied apple on a stick, or completely shapeless (see figure 1). They come
in colors ranging from reds and yellows to blues and violets. Some bacteria live alone as single cells. Others
live in groups of cells that are attached to one another called colonies.
coccus
bacillus
spirillum
Figure 1. The three most common shapes of bacteria.
Monerans are found in water, air, soil and the bodies of larger organisms. In fact, bacteria live
almost everywhere — even in places where other living things cannot survive. For example, bacteria live in
volcanic vents at the bottom of the ocean. The temperature of the water in these vents can be as high as
250ºC — two-and-one-half times the temperature of boiling water!
Monerans are considered the simplest organisms; however, they are more complex than they may
appear. Each bacterial cell performs the same basic functions that more complex organisms, including you,
perform.
Structure of Monerans
One of the most noticeable features of a bacterium is the cell wall (see figure 2). The cell wall is a tough,
rigid structure that surrounds, supports, shapes and protects the cell. In some bacteria, in addition to the
cell wall there is a coating on the outside of the cell wall called the capsule. Lining the inside of the cell wall
is the cell membrane. The cell membrane controls which substances enter and leave the cell. Within the cell
membrane is the cytoplasm. The cytoplasm is a jellylike mixture of substances that makes up most of the
cell.
Figure 2. Structure of a typical bacterial cell.
Unlike most other cells, the hereditary material of bacteria is not confined in a nucleus. (A nucleus is
a membrane-enclosed structure that can be thought of as the "control center" of a typical cell.) In other
words, there is no membrane separating the hereditary material from the rest of the cell in monerans.
Many bacteria are not able to move on their own. They can be carried from one place to another by
air and water currents, clothing, and other objects. Other bacteria have special structures that help them
move in water surroundings. One such structure is a flagellum (pl. flagella). A flagellum is a long, thin,
whiplike structure that propels a bacterium through its environment. Some bacteria may have flagella.
Life Functions of Bacteria
Bacteria have more different ways of getting the energy they need to live than any other kingdom of
organisms. In fact, bacteria obtain energy in more ways than all of the other four kingdoms combined. Like
most other organisms, many bacteria need oxygen (aerobic) in order to get energy from food. Anaerobic
bacteria can thrive without oxygen, and other kinds of bacteria will die if they are exposed to oxygen.
Many bacteria are heterotrophs. A heterotroph is an organism that cannot make its own food. A
heterotroph gets energy by eating food, usually other organisms. Some bacteria feed on living organisms;
these bacteria are parasites. (Parasites are organisms that live and feed either inside or attached to the
outer surface of a "host" organism, thus harming the host.) Such bacteria cause infections in people, animals
and plants. Other bacteria feed on dead things. These bacteria are decomposers. Decomposers break down
dead organisms into simpler substances. In the process, they return important materials to the soil and
water.
Some bacteria are autotrophs; that is, able to make their own food. Most autotrophic bacteria use
the energy of sunlight to produce food. Other bacteria use the energy in certain substances that contain
sulfur and iron to make food. The nauseating "rotten egg" smell of mud flats or rotting food is due to the
action of such bacteria.
* When food is plentiful and the environment is favorable, bacterial cells grow and then reproduce
by dividing into two cells. Under the best conditions, most bacteria reproduce quickly. Some types can
double in number every 20 minutes. At this rate, after about 24 hours the offspring of a single bacterium
would have a mass greater than 2 million kilograms (kg), or as much as 2000 mid-sized cars! In a few more
days, their mass would be greater than that of the Earth.
When food is scarce or conditions become unfavorable in other ways, some bacteria form a small
internal resting cell called an endospore. An endospore consists of hereditary (nuclear) material, a small
amount of cytoplasm and a thick protective outer coat. An endospore can survive long periods in which the
environment is not suitable for bacterial growth. Some endospores can survive being touched by disinfectant
chemicals, blown through the atmosphere, frozen in polar ice, baked in the desert sun, boiled for an hour and
bombarded with powerful radiation. When environmental conditions improve, the endospores burst out of
their protective coats and develop into active bacteria.
Most types of bacteria are not harmful and do not cause disease. In fact, many types of bacteria
are helpful to other living things and perform important jobs in the natural world.
DIRECTIONS: Answer questions on a separate sheet of paper using complete sentences.
1.
In what way is a prokaryotic cell different from all other (eukaryotic) cells?
2.
Based on what you know about the structure of a moneran and the structure of a protist (The Cell
HW), why do you think scientists believe monerans were the first living organisms on earth?
3.
What is the first trait used to classify bacteria?
4.
How do you think the capsule of a moneran might provide protection? [Make an educated guess.]
* above does not happen.
5.
Obviously, the situation described in the paragraph
Using ecologically
6.
terms, explain why bacteria do not over-populate the world.
Explain why bacteria are found almost everywhere on earth and are extremely hard to kill.