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| Life Science | Living System 7D2.00 | Unifying Concepts of Science | Interactions 2.4 ab |
GRADES: Seventh
CONTENT STANDARD: Life Science
CONTENT TOPIC: Living System
CONCEPT: The cell is the basic unit of living things.
CONTENT OBJECTIVE: 7D2.00 To understand the importance of microscopic life
INSTRUCTIONAL OBJECTIVES: The student will be able to
TN COMPONENT OF SCIENCE: Unifying Concepts of Science
TN GOAL:
BENCHMARK: Viruses, bacteria, fungi, and parasites may alter the function of an organism.
2.4b Interactions of matter and energy shape our world.
BENCHMARK: In any particular environment, the growth and survival of organisms depend on the physical conditions.
BENCHMARK: The relationships between two organisms may be competitive or mutually beneficial.
TIME REQUIRED:
This classroom connector addresses Instructional Objective 2.01.
Viruses are not made of cells as are other organisms. They are composed of nucleic acids and proteins.
Nucleic acid is in the center surrounded by a layer of protein. Viruses do not need nutrients like other living cells, and they do not need energy.
The only way viruses are similar to other living organisms is that they can reproduce; however, the virus must invade a live cell in order to reproduce. Once inside the cell, the virus seems to take control and change the normal activities of the cell.
The electron microscope has been very useful in studying viruses. They are so small that viruses were not actually seen until the invention of the electron microscope. Viruses must be magnified thousands of times in order to be seen. Viruses have been observed to be rod-like, spherical and many-sided in their shapes. Some have a tail.
Most diseases that people get today are caused by viruses. Colds, cold sores, chicken pox, flu, and possibly some forms of cancer are caused by viruses. Many viral diseases do not respond to normal treatments with antibiotics or other drugs effective in treating other illnesses caused by microscopic organisms. Some viral diseases such as polio, measles and smallpox can be prevented with the use of vaccines which give people resistance to these diseases. Viruses can also cause diseases in plants.
Scientists have found that there are viruses in people and other animals that do not appear to cause disease. They can destroy cells, but do not seem to cause disease. Because of this, scientists think there is a possibility that not all viruses are harmful. There is still a great deal of information to be learned about these tiny, but possibly very dangerous organisms.
2. Do demonstration to show effect of Tobacco Mosaic Virus.
This demonstration might be prepared by teacher in advance or assigned to students.
Materials needed: 1 cigarette, mortar and pestle, distilled water, sugar, 1 tomato plant in soil
Procedure:
b. Grind tobacco with mortar and pestle so that it is a fine powder
c. Place powder in prepared solution of distilled water and sugar.
d. Gently rub some leaves of tomato plant with abrasive material so leaf surface is scratched
e. Place powder solution on leaves
f. Observe plants daily
g. What happens to leaves of a plant before the plant dies (Mosaic pattern should appear on leaves within two weeks or sooner.)
2. Reports of contribution made by Edward Jenner related to viruses )
Anton van Leeuwnehoek is given credit for the discovery of bacteria in 1667. Bacteria are unicellular monerans, most not having chlorophyll. There are about 3000 different kinds of bacteria.
Bacteria occur in three basic shapes. They are 1) Coccus bacteria are round, 2) Bacillus bacteria are rod-shaped, and 3) Spirillum and spiral shaped bacteria can be seen with the use of a light microscope, but because they are so small, they must be stained in order to see them. Bacteria can be found almost every where on earth. They have been found deep in the ocean and high in the atmosphere. They are on our skin and in the air we breathe.
Most bacteria need oxygen, warmth, food and water to grow. Some can survive temperatures below freezing while others can survive temperatures as high 60 degrees Celsius. Most bacteria need oxygen to live. These are called aerobic bacteria. There are some bacteria that can live without oxygen, and they are called anaerobic bacteria. Some contain chlorophyll and can make their own food, while others are saprophytes or parasites. Many bacteria can survive unfavorable growing conditions by forming a protective wall around itself called an endospore. When conditions for growth improve the endospore will develop into the bacterium.
When bacteria grow they tend to form colonies. Colonies are groups of cells living together. Many species can divide as often as once every 20 minutes, thus causing the colonies to become apparent and seen without a microscope.
Many people associate bacteria with germs meaning that they all cause disease in people. This is not so as there are many bacteria which are of value and are beneficial to man.
Let's look at some ways bacteria are helpful to man. Many bacteria live in the soil and cause the decay of plants and animals. The compounds produced in the decay process are added back to the environment. Another important value of bacteria to the environment are the nitrogen-fixing bacteria. These bacteria live in the soil or in root of legume plants such as peanuts, peas, and clover. Plants need nitrogen to grow, but cannot get the nitrogen in the air which is in the form of a gas. Nitrogen-fixing bacteria can take nitrogen from the air and change it into nitrogen compounds that plants can use.
People have learned to make use of bacteria in the production of foods such as yogurt, sauerkraut, pickles, and some cheeses. (Swiss cheese gets its flavor from acid produced by a certain type of bacteria.)
Bacteria are used in industrial processes for commercially producing acetic acid (vinegar), acetone, lactic acid, and several vitamins. Bacteria are also used to change animal skins into leather and to prepare plant fibers for use in making linen.
Another important beneficial use of bacteria is in the production of medicines. Many antibiotic drugs used to treat bacterial diseases are produced by the use of bacteria.
Animals also need bacteria. Plant-eating animals cannot break down the cell walls of plants they eat; however, animals such as cattle, goats, sheep and rabbits have certain kinds of bacteria in their digestive tract. These bacteria are able to break down the cell walls for the animals to use the plant cells for food.
There are some bacteria which are harmful. Some cause diseases in humans such as the bacteria that cause tetanus or lockjaw. This kind of bacteria normally live in the soil, but when in the body cause disease. Other well known diseases caused by bacteria are pneumonia, strep throat which sometimes causes rheumatic or scarlet fever, skin infections like boils and pimples, and some venereal diseases such as gonorrhea and syphilis.
Another harmful group of bacteria cause food poisoning. They either cause the food to rot or form poisons in the food. People who eat this food may become very ill. The most dangerous kind of food poisoning is celled botulism. Which usually results from eating canned foods that have not been properly sterilized.
Blue-green algae make up the second group of Monerans. These unicellular organisms may live alone or in chains, or some live in colonies. The cells are surrounded by a jellylike covering. The chlorophyll is not found in chloroplast which makes the blue-green algae different from other kinds of algae.
Not all of these algae are blue-green in color. Some are black, brown, yellow, red, or green. The periodic redness of the Red Sea is due to a red colored algae in this group.
Blue-green algae is found in many environments. Many live in fresh water and a few are marine. Some live in the soil, some can be found in deserts, others grow on the sides of damp rocks, flower pots, and on backs of trees, and on wet cliffs.
Ponds or lakes containing a rich supply of organic matter often develop huge populations called blooms. These blooms can make water so green that objects can only be seen a few centimeters below the water surface. These blooms can give water a bad odor and can sometimes be toxic to livestock.
2. View prepared slides of Blue-green algae such as Nostoc or Oscillatoria.
3. Show how bacteria can be grown:
Materials: Four petri dishes with sterile nutrient agar
Procedure:
b. Open dish one and leave it open to the air for two or three hours. Then close.
c. Open dish two and lightly rub a finger over the surface of the agar. Then close the dish.
d. Wash hands thoroughly. Open dish three and rub a finger over the surface of the agar. Replace the cover.
e. Do not open dish four.
f. Place all four dishes upside down in a warm, dark place for three days.
g. After three days examine the dishes.
h. Count and record the number of colonies of bacteria in each dish.
i. Answer these questions:
2. Where did the bacteria come from?
3. Which of the dishes you touched with your fingers contained the greatest number of colonies?
Do not allow students to open the petri dishes.
4. Show students how to stain bacteria so that they can be easier to see.
Procedure:
b. Heat an inoculating needle in a burner flame until it is red hot.
c. Carefully open the petri dish of cultured bacteria, touch the hot needle to the agar to cool it.
d. Then touch one of the colonies with the needle. Remove needle and close dish. Stir the needle in the water on the slide spreading water over a larger area.
e. Holding one end of slide, slowly pass it over the burner flame until the smear on the slide dries. Do not let glass slide get so hot that it is too hot to hold.
f. Examine the slide through the high-power objective of a microscope. Can you see any bacteria?
g. Cover the smear on the slide with some methylene-blue stain and let it stand for about a minute.
h. Rinse off excess stain and gently blot slide dry with a paper towel.
i. Examine under the microscope.
j. Can you see any bacteria?
k. Were the stained bacteria easier to see than the unstained bacteria?)
(Bacteria and blue-green algae) How many different shapes are there of bacteria? (Three) Name them. (Round, rod, spiral) Are all bacteria harmful? (No) Describe some helpful bacteria. (response) Describe some harmful bacteria. (response)
There are several different kinds of Protist algae. Most green algae live in fresh water, however, some can live on snowbanks, damp soil, rocks or tree bark. Another kind of algae are the golden algae. A well known member of this group are the diatoms. Diatoms have a shell made of silica. (A material used to make glass.) The shells have 2 parts that fit together and the shells are in many shapes, designs, and sizes. The glassiness of the shells have led some people to call the diatoms the jewels of the sea.
Another algae group are the euglenoids. These organisms are like other algae because they contain chlorophyll and can make their own food, but are different in that they can move. This helps them catch their food when conditions for photosynthesis are not favorable for them to make their own food.
The most important feature of the algae is that they provide food for so many tiny animals which are in turn eaten by larger animals. Algae are found in such large numbers on the earth and they have the ability to make food by photosynthesis. Another important benefit from the process of photosynthesis is the production of oxygen.
Some algae can have harmful effects on the environment. For example, sometimes the large numbers of certain dinoflagellates cause red tides off the coast of Florida and other areas. These red tides kill fish and poisons formed may cause people to become sick if they eat contaminated fish or shellfish.
Other algae can cause harm in large numbers such as making drinking water unfit for people or other animals. A sudden growth of algae called an algae bloom prevents light from reaching the lower levels in the water causing plants and algae below the surface to die. Bacteria then cause decaying to take place which uses a great deal of the oxygen in the water. This lack of oxygen in the water then causes the fish and other animals in the water to die.
People can benefit from certain kinds of algae. Shells of diatoms are used to test microscope lens. Each marking on the shell can be seen with a good lens, and not with a poor lens.
When diatoms die, their shells do not decay, but settle to the bottom of the ocean floor and build up in layers called diatomaceous earth. Diatomaceous earth is used in filters, toothpaste, metal polishes and in dynamite. Also, oil is often found in some areas here diatomaceous earth is found.
Water purification plants often use bacteria to break down wastes. Bacteria need oxygen to break down the wastes so green algae is added to the water to be treated. The green algae provides oxygen for the bacteria.
Since so many fish depend on algae for food, fish are often more abundant in numbers where large amounts of algae are found. The best fishing is often in areas where large amounts of algae live.
Another group of organisms in the Protist kingdom are called the Protozoans. These are the protists that have animal-like characteristics. These unicellular organisms carry on the same life functions as the larger organisms. There are four groups of protozoans based on the different method each has for moving. The Sarcodines move by sending out a stream of cytoplasm to move them in a certain direction and the rest of the cell follows. These streams of cytoplasm are called pseudopods or false feet.
A common example of a Sarcodine is the amoeba. Most amoebas live in water and are free-living. There are some that are parasites and can cause disease in people. Amoebic dysentery is one such disease which is caused by an amoeba that can live in the intestine. When conditions for living become unfavorable, an amoeba can form a cyst. A cyst is a cell enclosed in a thick protective covering. Amoebic dysentery can be caused by cysts that are spread by people, infected food, or polluted water. when the cysts enter the intestines, the growing conditions are favorable so the amoebas begin growing causing the disease.
Another kind of Sarcodine lives in salt water and is called a Foraminifer. (Forams for short) Forams build shells around themselves which are made of lime from the sea water. As forams die, their shells build up chalky lime deposits in many places in the world. The White cliffs of Dover are built from these shells over a very long period of time. Also scientists can use these shells to date layers of the ocean floor because the structure of foram shells have gradually changed over the years.
The second group of protozoans are the flagellates. These organisms move by the use of a whip-like tail called a flagellum. Most flagellates are free-living; however, some are parasitic. A parasitic flagellate that get in the blood of many vertebrates in Africa causes a disease called African sleeping sickness. This disease is transmitted by the tsetse fly when it bites a person or animal. Once in the blood, this flagellate releases poisons causing the host to become weak. If this flagellate enters the cells of the brain or spinal cord, the host will go into a deep sleep or coma and soon die.
Not all parasitic flagellates harm their host. One such flagellate lives in the intestines of a termite. The termite provides a home and food for the flagellate which in turn makes chemicals that help digest the wood eaten by the termite. This mutual relationship is called symbiosis.
The third group of Protozoans are the Ciliates. Ciliates have cilia for moving. Cilia are short, hair-like parts on the outside of the cell which may cover the entire surface. The ciliate moves by beating its cilia together.
The best known ciliate is the Paramecium which can be found both in fresh and salt water. Ciliates are sources of food for other protozoans and other tiny organisms.
The fourth group of protozoans are called the Sporozoans. These are the non-moving protozoans. They also differ from the other protozoans in that this group forms spores or resting cells at some stage of their life cycle. Since the sporozoans are incapable of moving, all are parasites.
The best known being the one that causes the sickness called malaria. This parasite lives part of its life in the Anopheles mosquito and part in a person or other mammal. The male anopheles mosquito causes no harm to people because it feeds on the nectar of flowers. It is the female mosquito that feeds on human blood. Before the female bites, she first injects saline into the blood vessels on the skin to prevent the blood from clotting. If she is carrying the sporozoan some will enter the blood with the saliva.
After entering the body, the blood carries the parasite to the liver where they will change and multiply rapidly. They then leave the liver and enter in the red blood cells where they feed and eventually cause the cells to burst. When this happens a person experiences the chills and fever.
The third group of Protists are the slime molds. A slime mold has a life cycle with many different stages. In each stage, the organism has a different form which resembles three different kinds of organisms. The slimy mass stage is like an amoeba. Production of spores in the reproductive stage is similar to spore production in fungi. The cells fuse to form a zygote that has flagella like the flagellate organisms.
The slime molds live in damp places, like the forest floor where they feed on dead decaying matter.
2. Also live specimens may be obtained from pond water or a lake.)
Most fungi are multicellular; however, one kind is unicellular. The unicellular fungi are yeasts. Yeasts are one-celled sac fungi that are able to cause sugar in some foods to change chemically or ferment. When yeasts do this, alcohol and carbon dioxide gas are formed. Brewers use the alcohol formed in this way to make beer. Bakers use the carbon dioxide formed in this way to make bread. The gas makes the bread dough rise.
Yeast cells are also important because they can produce vitamin B2, riboflavin. This vitamin is essential for normal growth, and the good health of the skin, mouth and eyes. To obtain this vitamin we must either eat yeast cells or products made of yeasts.
algae bloom - a sudden growth of algae in a body of water
anaerobic - bacteria that can live without oxygen
bacillus - rod shaped bacteria
botulism - a serious form of food poisoning caused by bacteria
cilia - short, hair-like extensions on the outside of a cell used for moving
coccus - round shaped bacteria
colony - group of organisms or cells that live together
cyst - a cell enclosed in a thick protective covering
endospore - protective wall that forms around a cell
flagellum - a whip-like tail used for moving
pseudopods - a stream of cytoplasm formed by amoebas for moving false feet
spirillum - spiral shaped bacteria
spores - resting cells; a special kind of reproductive cell
symbiosis - relationship where two organisms live together for their mutual benefit
This is the time this file has been accessed since 04/02/98.
The University of Tennessee at Martin is not responsible for the information or views expressed here.
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