(This should be done two weeks before it is needed for the study of succession.) Prepare a hay infusion -- study a hay infusion, observing any protists which may be present.
Materials: distilled water or boiled tap water; glass slide and coverslip; jar (with screw cap, 1000 ml, quart); malt tablet (grocery store item); medicine dropper; microscope; pond water with mud and debris; timothy hay (available from a farmer or biological supply house or use dried grass); optional: apple core; yeast.
(The student makes a hay culture and observes the culture with a microscope. Water from a bird bath or any stagnant water may be used in place of the pond water. Paramecia and other ciliates will be observed in the culture. The number of different kinds of organisms observed will change over time due to ecological succession of species. Hay is dried grass or legumes. Fifteen minutes should be allowed during future class periods for follow-up viewing.)
Directions: Standard simplified technique for culturing:
Half fill a screw cap jar with distilled water (or boiled tap water). Add several pieces of cut timothy hay.
Drop half a malt tablet into the water.
Add a small amount of pond water containing mud and debris.
Cover and allow to remain in the dark at about 22C for one to two weeks.
Prepare slides of the hay infusion. Remove a drop of liquid from the infusion using the dropper. Place on a glass slide, cover with a coverslip, and observe under the low power magnification. Use subdued light. (This should be done twice a week, for five to six weeks, to study succession.)
Record the approximate number, use such terms as few (1-10), moderate (11-50), many (50-100), teaming (over 100), of each organism's type seen under a single low power viewing. That is, how many can be seen without moving the slide to a new area.
Attempt to diagram one example of each type of protozoa observed. (Use reference books to identify protozoa.)
(A data chart which organizes the observations is suggested, see below.) The type and number of each kind of protozoa observed should change as the infusion ages, and succession continued.
DATA SHEET: (example)
|
Date |
Number of Days since start of INFUSION |
Number of different PROTOZOANS observed |
Approximate number seen |
Diagram |
(Students should observe these types of changes:)
Weeks 1-2 -- Number of protozoan types shown below will rise to teaming and then drop to none by the third week. Protozoans will be small in size having this characteristic shape:
DRAW VORTICELLA HERE
Weeks 2-4 -- Number of protozoan types shown below will rise to many and then drop to none by the fourth week. Protozoans will be medium in size having this characteristic shape:
DRAW BLEPHARISMA HERE
Week 3-6 -- Number of protozoan types shown below will rise from a few to moderate, then drop to very few by week 7-10. Protozoans will be medium in size having this characteristic shape:
DRAW PARAMECIUM HERE
WEEKS 5-7 -- Number of protozoan types shown below will rise from few to many and then drop to none by week 7. Protozoans will be large in size having this characteristic shape:
DRAW EUPLOTES HERE
(Possible) Questions
The changes in protozoan numbers, size, and types is natural and is SUCCESSION. Change in protozoa type is the result of many factors such as: buildup of waste products, supply of available food, type of food, crowding, etc. (Just as succession happens on land, it also happens in this hay infusion.)
1. Did the types of protozoa change during the weeks you studied the infusion? (yes)
2. Did the numbers of protozoa change in time as you studied the infusion? (yes)
3. Give one reason why the type and number may have changed in a closed community such as this. (different foods available at different times, limited food supply, buildup of waste, etc.)
4. If the first protozoa to appear were consumers, what might they be feeding on? (Microscopic life in pond water such as yeast and bacteria. These in turn feed off of the hay.)
5. What name is given to the observation that the number and type of organisms changes with time in a community? (Succession)
(Questions listed above.)
SUCCESSION IN A MOLASSES SOLUTION
Materials:
Bottle of molasses (without preservatives); distilled water; package of yeast; 1000 milliliter Erlenmeyer flask; 500 milliliter graduated cylinder; stirring rod; microscope; medicine dropper; culture dish; microscope slides; cover slips; lens cleaning tissue; ethylene blue solution; blue litmus paper; red litmus paper; notebook; pen; pencil.
Directions:
1. Measure 10 milliliters of distilled water in the graduated cylinder,
pour it into the culture dish.
2. Add a pinch of yeast to the distilled water in the culture dish, stir
water and yeast well with stirring rod.
3. Prepare a slide of the yeast and water, staining with methylene
blue.
4. Examine slide under both low and high powers of microscope. Make
drawings of some yeast cells in your notebook.
5. Measure 500 milliliters of distilled water in a graduated cylinder, pour it into the Erlenmeyer
flask.
6. Add the remainder of the package of yeast to the water in the flask, stir the water and yeast well with the stirring rod.
7. Test yeast-in-water culture with blue and red litmus paper to find out if culture is acidic,
basic, or neutral. Record data in your notebook.
8. Put the culture in a warm (200 Celsius to 350 C), dark place.
9. Examine the culture once each day as follows: -Smell the culture, noting the presence of an odor like vinegar or alcohol. -Test the culture with litmus paper as in number 7
above -Prepare a microscope slide of the culture, stained with methylene
blue, examine under microscope. Note any increase or decrease in the number
of yeast cells. Note the presence and relative numbers of bacteria, which
will probably be rod-shaped, but may be spherical. -Record your data in
your notebook.
10. Write a description of the changes that take place in the culture.
11. Explain your results.
