Monera Kingdom
Monerans are one-celled organisms that lack a nucleus, but do have nuclear material within the cell wall. They also lack many of the cell parts found in plant and animal cells. The two groups of monerans, bacteria and blue-green bacteria, are found everywhere around you. They live as single cells or in groups of cells.
Traits of Bacteria
What are bacteria? Bacteria are very small, one-celled monerans. They are larger than viruses, but are too small to be seen without a microscope. They are so small that 300 could fit side by side across the period at the end of this sentence.
Bacteria can be found almost everywhere. They live in water, air, soil, food, and on almost every object. They are on your skin and even inside your body. Bacteria have been found in arctic ice as well as in hot springs. Bacteria are so widespread because almost any material may be food for some kind of bacteria.
Bacteria are classified into three groups according to shape. Some bacteria are round. Some are shaped like rods.
Others are spiral. Bacteria can be found as single cells, in pairs, or in clusters. Some singles and pairs may join together in a cluster or chain. The cells in a rapidly growing cluster or chain can make a colony. A colony is a group of similar cells growing next to each other that do not depend on each other.
Under a microscope, bacteria look very different from other cells you have studied. It has one main chromosome. The animal cell does have a nucleus. The bacterial cell also does not have most cell parts seen in the animal cell.
Even without certain cell parts, bacteria carryon the same jobs as other cells. Bacteria still reproduce, grow, and carry out cellular respiration.
Bacterial cells have a cell wall as well as a cell membrane. Some bacteria have a sticky outer layer called a capsule. The capsule keeps the cell from drying out and helps the cell stick to food and other cells. Some bacteria move with a long, whiplike thread called a flagellum (fluh JEL um).
Bacteria reproduce by fission (FIHSH un). Fission is the process of one organism dividing into two organisms. Fission is a kind of asexual (ay SEK shul) reproduction. . Asexual reproduction is the reproducing of a living thing from only one parent. Bacteria reproduce by asexual reproduction. The circular chromosome of the bacterial cell makes a copy of itself, and the cell divides. The time that it takes a bacterial cell to grow and divide into two cells varies. If growing conditions are right, it can take only about 20 minutes.
What do bacteria need to live? They need moisture, a certain temperature, and food. A few bacteria can live at O°C and others can live at temperatures of 75°C. Those that cause disease in humans live at 37°C, normal body temperature. Most bacteria grow best in darkness. Most need oxygen to live. Others cannot live in the presence of oxygen.
If living conditions are not right for bacteria to grow, they can survive by forming endospores (EN duh sporz). An endospore is a thick-walled structure that forms inside the cell, enclosing all the nuclear material and some cytoplasm. Some endospores can survive for many years. They can withstand boiling, freezing, and extremely dry conditions without damage. When conditions return to normal, endospores develop into bacteria. Endospores are not used for reproduction. They let bacteria survive when living conditions are not ideal.
Most bacteria feed on other living things or on dead things. Bacteria that feed on living things are parasites. Bacteria that live on dead things are called saprophytes (SAP ruh fites). Saprophytes are organisms that use dead materials for food. They get energy by breaking down, or decomposing, dead materials. Decomposers are living things that get their food from breaking down dead matter into simpler chemicals. Decomposers are important because they return minerals and other materials to the soil, where other organisms can use them.
Some bacteria can make their own food. Some use the energy of the sun to make food. Others use the energy in substances containing iron and sulfur to make food.
Bacteria and Disease
Some bacteria are parasites in humans. They can cause a variety of diseases. Human diseases caused by bacteria include strep throat, tuberculosis, certain kinds of pneumonia (noo MOH nyuh), gonorrhea (gahn uh REE uh), and meningitis.
Plants and animals other than humans also may have bacterial diseases. Fire blight and crown gall are plant diseases caused by bacteria. The bacteria that cause fire blight are spread by rain.
Some bacterial diseases that occur in animals can be passed on to humans. Anthrax, a disease found in livestock, is one example. It is usually passed on to people who work with animals, such as butchers and handlers of wool and leather.
How do we know that bacteria cause disease? In 1876, a German doctor named Robert Koch used a scientific method to show that anthrax was caused by a bacterium. He made a hypothesis that a bacterium caused the disease. He experimented to test the hypothesis. The experiments supported his hypothesis, so he formed a theory about the cause of disease.
Koch's postulates (KAHKS P AHS chuh lutz) are steps for proving that a disease is caused by a certain microscopic organism. Here are Koch's postulates:
1. The organism must be present in a living thing when the disease occurs.
2. The organism must be taken from the host and grown in the laboratory.
3. When the organisms from the laboratory are injected into healthy hosts, they must cause the same disease in the healthy hosts.
4. The organism must be removed from the new hosts, grown in the laboratory, and shown to be the same as the organism from the first host.
Scientists still use Koch's postulates today. The procedure helps identify bacteria and other disease-causing organisms.
Some diseases caused by bacteria and viruses are called communicable (kuh MYEW nih kuh bul) diseases. Communicable diseases are ones that can be passed from one organism to another. They may be spread in several ways. Some diseases are spread by air when a person sneezes or coughs. Pneumonia, strep throat, and tuberculosis are spread through the air. Communicable diseases can also be spread by touching anything an infected organism has touched. Common items that might have bacteria are clothes, food, silverware, or toothbrushes. Another way of spreading diseases is by drinking water that contains bacteria. Some of the more serious diseases are those spread by sexual contact. Syphilis (SIHF uh lus) and gonorrhea are sexually transmitted diseases caused by bacteria.
Insects also spread diseases. Flies, fleas, cockroaches, and mosquitoes carry disease organisms.
Helpful Bacteria
You may be surprised to learn that there are more helpful bacteria than harmful ones. Most kinds of bacteria are helpful to humans. Bacteria are needed to decompose dead matter. Bacteria get energy from dead matter as they break it down into materials that other living things can use. In this way, the chemicals that are found in dead matter are recycled so that other organisms can use them to grow.
Some bacteria grow in other living things and help them. Bacteria in the stomach of a cow break down grass and hay. In this way, the grass and hay can be used as food by both the bacteria and the cow. Without the action of bacteria, plants would have little food value for cows, sheep, and deer. Bacteria in your intestine make vitamins that you need.
Bacteria are used to make many products that are useful to us. Some bacteria break down the fibers of plants used to make linen and rope. Some are used in making leather from skins. Some of today's most useful antibiotics (an ti bi ART iks) are produced by bacteria. Antibiotics are chemical substances that kill or slow the growth of bacteria. Some antibiotics have a specific effect, working only on certain types of bacteria. Others destroy many types of bacteria.
Some foods owe their taste or texture to bacteria. Many dairy products are made by adding certain species of bacteria to milk. For example, cottage cheese, Swiss cheese, yogurt, sour cream, and buttermilk are all made by bacteria growing in milk. The flavors of coffee and cocoa are due to bacteria. Sauerkraut is made by the action of bacteria on chopped cabbage. Bacteria also help change alcohol to vinegar.
Bacteria are very important in the field of biotechnology (bi oh tek NAHL uh jee). Biotechnology is the use of living things to solve practical problems. Bacteria are being used to produce natural gas and detergents. Some are used to produce human insulin. Insulin is a chemical that the body normally makes to control the level of sugar in the blood. Some people cannot make insulin, so they must use the insulin produced by bacteria.
Controlling Bacteria
If food is put into containers and heated to a high enough temperature, the bacteria inside can be destroyed. The containers can then be sealed while they are hot. Food can remain in them for long periods of time without spoiling, as long as the seals are not broken and the cans remain airtight. The process of sealing food in airtight cans or jars after killing the bacteria is called canning. Endospores can be killed by the canning process. They are a major cause of food poisoning.
The process of heating milk to kill harmful bacteria is called pasteurization (pas chuh ruh ZA Y shun). The milk you buy in stores is pasteurized. Even pasteurized milk that has not been opened will finally spoil. Can you explain why?
Cooling food to a low temperature slows the growth of bacteria. You keep food in the refrigerator to slow bacterial growth. Freezing food is also used to slow bacterial growth. Frozen food can be stored safely for several months. Items kept in a freezer last longer than those kept in the refrigerator. Why?
If water is taken from food, bacteria can't live in the food. Bacteria need the water for growth. For this reason, uncooked noodles and dry cereals can be left open without spoiling. These foods have very little water. Removing the water from food is called dehydration (dee hi DRAY shun). What other foods do you know of that are dehydrated?
Why do you put iodine, hydrogen peroxide, or alcohol on a cut, scrape, or other skin injury? These chemicals are called antiseptics (an ti SEP tiks). The word antiseptic means against infection. Antiseptics are chemicals that kill bacteria on living things. Disinfectants (dihs un FEK tunts) are stronger chemicals that are used to destroy bacteria on objects that are not living.
What do we do to get rid of bacteria on or in our bodies? We wash with soap, we brush our teeth, and we use mouthwash. Each time this is done, we wash, brush, kill, or rinse away millions of bacteria. The bacteria can cause body and breath odor and tooth decay.
Some medicines help stop bacterial infections after you become sick. You may have been given an antibiotic or other medicine to fight a bacterial infection when you were sick. Vaccines prevent bacterial infections from happening. They protect the body from invading organisms.
Blue-green Bacteria
Blue-green bacteria are small, one-celled monerans that contain chlorophyll and can make their own food. For many years they were called blue-green algae and were classified as plants. Their cell structure is more like that of bacteria than of plants. They do not have nuclei or other typical plant cell parts. Each has a cell wall outside a cell membrane. The cell wall of a blue-green bacterium is made of materials different from the cell wall of a plant cell.
Blue-green bacteria contain colored pigments. They are usually a blue-green color, but some blue-green bacteria may appear red, black, brown, or purple. The blue-green bacteria in the Red Sea grow rapidly at certain times of the year, giving the sea its red color and its name.
Where do blue-green bacteria live? They are found in ponds, lakes, moist soils, swimming pools, and sometimes around leaky faucets. Some can even live in salt water and on snow. Others grow in the acid water of hot springs.
Blue-green bacteria occur as single cells, colonies, and long, threadlike chains. Many have an outer jellylike layer that holds the cell to other cells. Some have gas bubbles that let the cells float at the surface, where they get sun.
Blue-green bacteria serve as food for animals that live in water. They produce oxygen as they make their own food. They are also important in recycling nitrogen that can then be used by plants.
Blue-green bacteria may .grow too rapidly and cover an entire pond. When this happens, they can use up the oxygen in the pond and kill other living things. Many blue-green bacteria produce a bad odor. The odor is one clue that the water is unfit for drinking. Substances that pollute water are often used by blue-green bacteria for food. The amount of pollution in water is measured by counting the number of blue-green bacteria.
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