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 ______

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 ______

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 P. caudatum grown P. aurelia grown in P caudatum grown in alone, # of cells alone, # of cells mixed culture, # of cells mixed culture, # of cells (Test Tube 1) (Test Tube 2) (Test Tube 3) (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) ______

2. What is carrying capacity? (2pts) ______

3. When an organism reaches the carrying capacity of its environment does this mean that it is no longer reproducing? ______(1pt) Explain. (2pts) ______

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) ______

5. Describe what happened when the Paramecium populations were mixed in the same test tube. (2pts) ______6. What other things, beside food, can act as limiting factors for a population? (2pts) ______7. What factors are used to describe a population? (2pts) ______