Module 8

Module 8—Populations, Individuals, and Gene Pools

Watch and Listen

Understanding these concepts and their graphs is essential in Biology 30. You may wish to review these concepts by watching “Patterns of Population Growth and Management: Conserving Our Future.” You should pay particular attention to the following segments:

• “Population Growth Curves”
• “Bio Review: J-shaped Population Growth Curve”
• “Natural Populations”
• “Bio Review: S-shaped Population Growth Curve”
• “Effect of Environment on Yeast Populations”
  

Self-Check

Bacterial Growth

In suitable abiotic conditions and with adequate food, E. coli bacteria (part of your normal intestinal flora) undergo binary fission every 20 minutes. Thus, with each generation, populations double and each generation is only 20 minutes long. Typically, bacteria introduced onto a growth medium will go through the following phases:

• lag phase—slow growth
• exponential growth—doubling with each generation
• death phase—population crashes due to competition for food and accumulation of toxins

SC 1. Using your calculator (using 2n as a function)

• fill out the following table
• graph the results (it is only necessary to plot every second generation on the graph)

If necessary, ask your teacher how to calculate the data for the table.

Assume the environment (the Petri dish containing the nutrient medium) can only support 1 million bacterial cells. Respond to the following questions.

SC 2. At what generation has the population outstripped its environment and will begin to crash? If generation 1 was time 0, at what time did the population crash?

SC 3. Draw a graph showing the growth curve. Label axes correctly and provide a title. Label the graph with lag phase, exponential phase, and death phase.

SC 4. With each successive generation, what happens to the difference between N of the previous population and N of the current population?

SC 5. A population of lilies is growing exponentially with a generation time of three days. The water lilies threaten the species living below the surface by cutting off sunlight. At this point in time, the lilies cover half the pond. How long before the whole pond is covered?

Watch and Listen

Exponential and Logistic Growth Simulation

Conduct an Internet search using the terms “otherwise, logistic, exponential, applet” to give you access to two excellent and easy-to-use applets that will simulate exponential and logistic growth. Both allow you to manipulate birth rates to see how the graphs of logistic and exponential growth differ.

Try This

This Population Density Factors Activity will help you check your understanding of density-dependent and density-independent factors.