Biology Exam Paper

Whitney Wilson 24 November, 2009 Biology I Population Biology of Two Species of the Freshwater Protozoan Paramecium Introduction In this experiment, two species of Paramecium will be tested alone and together. Their growth will be observed and recorded every two days until sixteen days is complete. The environment of the Paramecium caudatum and Paramecium aurelia will include the freshwater they survive in and rice as the source of food. Under perfect conditions, organisms will continue to grow at an exponential growth. When there is an abundance of food, space to continue to grow, and a water source, exponential growth will occur. Competition occurs between species. This competition for resources is a population limitation. Intraspecific competition is competition among one single species. Interspecific competition is competition among two or more species. Both affect the population size. “For most species, resources become limiting as populations grow...The upper boundary for the population size is known as the carrying capacity.”(Brooker 1208) Once the carrying capacity is reached, the genetic make-up of the organism can change to adapt to another niche. “The “competitive exclusion principle” states that if two non-interbreeding populations occupying the same ecological niche are sympatric, one will ultimately exclude the other.”(Hutchinson 1965) In this experiment, the Paramecium will continue to grow in their own environment until carrying capacity has been reached where a continual number will then be recorded. With the mixed species, one species will continue to grow as the other one will decrease or even cease to exist. Methods Methods of the experiment included the two species of Paramecium, Paramecium caudatum and Paramecium aurelia. Equipment used in this experiment included the following: two species of Paraecium, rice, three test tubes, five milliliters of water in each test tube, two flasks, two pipettes, a microscope, wet mount slides, and a calendar. In the procedure, three test tubes were filled with rice as the source of food for the Paramecium. The two flasks were filled with the two different species of Paramecium, each in their own flask. The pipettes were used to transport five milliliters of each species to the test tubes. P. caudatum was transported

Wilson 2 to the first flask. P. aurelia was transported to the second flask. Each contained five milliliters. In the third flask, five milliliters of each Paramecium were placed in the same flask so the total amount in the flask measured to ten milliliters. Each flask was made into a wet mount slide with the slides provided. There were three slides, one containing species from each of the three flasks. Slide one containing P. caudatum was placed under the microscope and counted. P. aurelia was placed under the microscope and counted. Last, the mixed species were placed under the microscope and counted as well. For every 1 species counted on each slide, they were multiplied by two to acquire the appropriate number for one milliliter. This is because each slide only contained 0.5 milliliters. These calculations were recorded onto a data sheet. This recording occurred on day zero. Every two days this information was recorded from each slide; new slides were made every two days. A calendar kept track of the days. Results In the results, both species continued to grow and reach their carrying capacity in their own flasks alone. Paramecium caudatum reached its carrying capacity the fastest. This species reached its carrying capacity on day eight while Paramecium aurelia reached its carrying capacity on day ten. In the mixed flask with both species, P. aurelia continued to grow while P. caudatum's growth increased a little and then decreased to being nonexistent. Data Table 1:

Day

P. caudatum alone, cells/mL

P. aurelia alone, cells/mL

P. caudatum mixed, cells/mL

P. aurelia mixed, cells/mL

0

2

2

2

2

2

10

8

10

6

4

28

54

24

36

6

28

86

18

64

8

60

98

18

84

10

56

100

8

94

12

60

100

4

90

14

60

92

0

98

16

60

100

0

100

Wilson 3 Graph 1: Amount of Paramecium caudatum and aurelia Separate and Mixed for Sixteen Days

Size of Population (cells/mL)

120

100

80

P. caudatum alone P. aurelia alone

60

P. caudatum mixed P. aurelia mixed

40

20

0 0

2

4

6

8

10

12

14

16

Days Discussion/Conclusion In conclusion, both species survived on their own in separate flasks. This proves the fact that a species can survive without competition and the proper food source, water, light, etc. needed to survive. Both species of Paramecium reached carrying capacity in their own separate flasks, which also proves that with the ideal conditions, a species can continue to grow and reach the maximum amount of species possible in a given area. Both species also experienced exponential growth. In the two flasks, the two separate species had perfect conditions with a supply of food, room to grow, and no competition. In the mixed flask, the Paramecium were given the same amount of food that was supplied when they were separated. Although this is true, the results showed that Paramecium aurelia survived and dominated over the Paramecium caudatum. These results prove the competitive exclusion principle that states if two non-interbreeding populations live in the same niche, one population will exterminate the other. On day ten, P. caudatum lowered to a count of only eight and on day twelve lowered to four. By day fourteen and sixteen, their entire population had become extinct. On the other

Wilson 4 hand, P. aurelia experienced the competitive exclusion principle and dominated over the other species causing them to become extinct. Intraspecific competition also occurred. P. aurelia had to compete with one other species, P. caudatum, and succeeded. The hypothesis that the Paramecium will continue to grow in their own environment until carrying capacity has been reached where a continual number will then be recorded and that with the mixed species, one species will continue to grow as the other one will decrease or even cease to exist has been proven true with this experiment. To further test this hypothesis, more species could be added. They would be placed in their own flask as well as added to the mixed flask. Another way to further test this is to study the perfect conditions of the environment and how it affects the population and competition. The rice as the food supply could be decreased or replaced with another food source. The flasks could be smaller causing the space to grow to have been decreased. All of these tests could further test the hypothesis.

Wilson 5 Works Cited Brooker, Robert J., Eric P. Widmaier, Linda E. Graham, Peter D. Stiling. Biology. New York: The McGraw-Hill Companies, Inc., 2008.

Zaret, Thomas M., A. Stanley Rand. “Competition in Tropical Stream Fishes: Support the Competitive Exclusion

Principle.” Ecology, Vol. 52, No. 2 (1971): pg. 336. jstor. Web. 18 November 2009.