STUDYING AN OCEANIC BACTERIAL POPULATION
PURPOSE:
-To observe the growth and decline in a population of bacteria.
BACKGROUND:
Questions
- What is a population?
- List three properties of a population.
- What is carrying capacity?
- What are some common limiting factors that prevent populations from exceeding (going beyond) their carrying capacity?
- In density –dependent factor, as the population gets bigger the stronger or more pressure the limiting factor is on the population.Which of the characteristicsfrom the above question (#4)are density- dependent?
Information
-The ocean contains all forms of life. Living along the surface of the ocean is plankton.
-Plankton is made up of bacteria, animals, and plants that either float passively in the water, or possess limited powers of swimming.
-One type of plankton is phytoplankton, which are classified as plants. The second type of plankton is zoo-plankton, which feed on phytoplankton. These are microscopic animals. Phytoplankton form the basis of the food chain in the ocean.
-Plankton can also include tiny microbes (bacteria), which are invisible to the naked eye, to jellyfish metres long.
-Pure oceanic bacterial cultures can be grown with a medium(nutrient broth) of sugars, proteins, minerals, and water.
PROCEDURE:
What you didn’t do but should know
-Approximately 1mL of the oceanic bacterial cell culture was added to a test tube containing nutrient broth (food for thebacteria). The cells in the broth were allowed to grow for one hour. Products, or wastes, include CO2and ammonia waste. The ammonia waste results from breaking down the proteins.
-Every hour a 1 mL sample was taken from the broth. Using a microscope, the number of cells was counted in that sample.
-Underneath is a picture of what some of these cells might look like through a high powered microscope (left). E.Coli is normally not found in oceanic waters except for after heavy rains (right).
What you need to do
-Below (Data Table) is the number of cells counted at each hour.
-Graph the following data with the time (hrs) in the x-axis and the bacterial cell population size on the y-axis ( x 1000/ mL).
-Be sure to label axes, title it, and take up the whole paper when graphing.
DATA TABLE. Estimated number of bacterial cells in a 1mL sample per hour.
TIME(hrs) / POPULATION
(x 1000/mL) / TIME
(hrs) / POPULATION
(x 1000/mL) / TIME
(hrs) / POPULATION
(x 1000/mL)
1 / 10 / 11 / 520 / 21 / 660
2 / 20 / 12 / 560 / 22 / 660
3 / 30 / 13 / 600 / 23 / 660
4 / 50 / 14 / 640 / 24 / 660
5 / 80 / 15 / 650 / 25 / 660
6 / 120 / 16 / 660 / 26 / 650
7 / 180 / 17 / 660 / 27 / 640
8 / 260 / 18 / 660 / 28 / 630
9 / 360 / 19 / 660 / 29 / 620
10 / 450 / 20 / 660 / 30 / 610
ANALYSIS AND CONCLUSION:
- When was the most rapid growth? Between what hours?
- Between 7 and 14 hours, is the birth rate higher or the death rate higher? How do you know?
- When was the maximum growth rate reached? At what hour?
- What is it called when a population reaches the maximum growth rate?
- Describe the relationship between the death and birth rate at this point (Number 4).
- Towards the end of the 24 hours, does the population appear to be increase, decrease, or stay the same?
- Look at your graph. Does the growth of the bacterial population follow a logistic model or an exponential model?
- What limiting factors might cause the trend you see between hours 16 and 24? In the last six hours?
- Is this density dependent or independent?
- Now you’re going to design an experiment. Pick a limiting factor from question number nine (above) to test.
- What’s your problem? You can write it in question form?
- State your hypothesis (not a prediction).
- What are your variables? What would be the control in this experiment?
- Briefly discuss the methods you would use in this experiment. What kind of materials might you use?
- What type of data would you need to gather?