Name _____________________________________________________________ Date_________________________________ Per_________
Paramecium Population Growth Activity: 35pts
Background Information
The genus Paramecium consists of unicellular species of protists that live in freshwater
environments. Under ideal conditions-sufficient food, water, and space-populations of these species grow
rapidly and follow a pattern known as exponential growth. Exponential growth is explosive population
growth in which the total number of potentially reproducing organisms increases with each generation.
However, populations of organisms will not increase in size forever. Eventually, limitations on food,
water, and other resources will cause the population to stop increasing.
When a population arrives at the point where its size remains stable, it has reached the carrying
capacity of the environment. The carrying capacity is the greatest number of individuals a given
environment can sustain. Competition for resources among members of a population (intraspecific
competition) places limits on population size. Competition for resources among members of two or more
different species (interspecific competition) also affects population size. This principle states that if two
species are competing for the same resource, the species with a more rapid growth rate will outcompete
the other.
In order to test these ideas, you conducted an experiment by growing 2 species of the Paramecium
alone and together. This was done to demonstrate how competition for natural resources in the
environment can affect population growth and how the availability of food can be a limiting factor for a
population. You set up three test tubes each with the same amount of food. In test tube 1 you put P.
Aurelia, in test tube 2 you put P. caudatum, and in test tube 3 you put both P. aurelia and P. caudatum. You
then watched their growth for 16 days.
Pre-Experiment Questions (4pts)
1. What is the purpose of this experiment? 2pts
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2. Make a hypothesis about how you think the two species of Paramecium will grow alone and how
they will grow when they are grown together. 2pts
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Procedure
Use the data sheets for each test tube to complete the data table below.
Make sure you count correctly! When in doubt, ask!
Data Table: 7pts
P. aurelia grown
alone, # of cells
(Test Tube 1)
P. caudatum grown
alone, # of cells
(Test Tube 2)
P. aurelia grown in
mixed culture, # of
cells
(Test Tube 3)
P caudatum grown in
mixed culture, # of
cells
(Test Tube 3)
Day O
Day 2
Day 4
Day 6
Day 8
Day 10
Day 12
Day 14
Day 16
Graph (10pts)
 Create a single graph that accurately reflects the number of each Paramecium species when they
were grown in the same test tube.
Analysis Questions (17pts)
1. On what day did the Paramecium caudatum population reach the carrying capacity of the
environment when it was grown alone? How do you know? (2pts)
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2. What is carrying capacity? (2pts)
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3. When an organism reaches the carrying capacity of its environment does this mean that it is no
longer reproducing? _______________________________ (1pt) Explain. (2pts)
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4. Explain the differences in the population growth patterns of the two Paramecium species when
grown separately. What does this tell you about how Paramecium aurelia uses available
resources? (2pts)
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5. Describe what happened when the Paramecium populations were mixed in the same test tube.
(2pts)
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6. What other things, beside food, can act as limiting factors for a population? (2pts)
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7. What factors are used to describe a population? (2pts)
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