Name _______________________________
These questions refer to the lab exercise we are doing this week.
1. What is the source of energy for the primary producers?
2. From Activity 2, how would you define plankton?
3. What is the difference between phytoplankton and zooplankton?
4. In Activity 3, what is the biotic potential of the bacteria (maximum rate of division)?
5. Why are the actual numbers of bacteria in the population, (after a certain amount of time), much less than the theoretical numbers based on the biotic potential?
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Work in groups of two Name __________________________
The interactions among the biotic (living) and abiotic (non-living) factors that affect the abundance and distribution of life are called the study of ecology.
Summary of Activities
1. Understand food web diagrams and energy pyramids.
2. Examine and draw planktonic creatures collected from our coastal waters.
3. Compare exponential and logistic growth curves of an imaginary population of bacteria.
A. Food Webs
The role of organisms in an ecosystem can be demonstrated by examining a food web (see below).
Light from the sun is the primary source of energy for the producers ( autotrophs ) which transfer some of the energy they capture to the primary consumers ( heterotrophs ) or herbivores. Energy is then passed to the secondary and tertiary consumers, carnivores or in some cases omnivores.
1. Write the numbers of each labeled organism according to its role in the food web.
_____________Decomposer _____________Herbivore _____________Primary consumer
____________ Producer _____________Top predator _____________Secondary consumer
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B. Pyramid of Production (Use this diagram to answer the questions at the end of the lab).
Any marine organism that drifts passively along with the ocean currents is said to be a member of the marine plankton . Some cannot swim at all while others swim, but not strongly enough to overcome the currents. Planktonic organisms are at the mercy of the currents and are unable to control their movement or distribution.
Some plankton are plant-like organisms, called phytoplankton , that carry out photosynthesis (they are in the Kingdom Protista). Phytoplankton are the producers of the open ocean and form the base of the food web in that marine ecosystem. Other plankton are animals, called zooplankton . They may be primary consumers that feed on phytoplankton or secondary consumers that feed on other zooplankton.
Some remain microscopic in size all their lives, but others are tiny larvae that will grow into much larger, non-planktonic organisms (such as fish, barnacles, jellies and crabs).
1.
Withdraw a small sample of plankton from the collection bottle (a few drops) and place it in a small glass dish to observe under the dissecting microscope.
2.
Make a wet mount slide of a drop or two and observe under low and high power of the compound microscope.
3.
One a separate sheet of paper, draw and label the following (use guidebooks to help you identify what you are drawing). a.
One consumer that you find (will be a larger organisms that may be moving). b.
One producer that you find (will be smaller and probably not moving).
In nature a population is kept in balance by the action of two opposing factors. The biotic potential or maximum reproductive capacity of the population, and the limiting factors which prevent the maximum from being attained (such as food, water, accumulated wastes, and disease.)
Consider a population of bacteria in a nutrient solution in a test tube that can divide every 30 minutes. In an ideal world the population has the potential of doubling every half hour. However, the actual growth in nature will be limited by factors such as space, amount of food, and a build-up of waste.
1. Complete the column labeled Theoretical in the following table.
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TIME (hrs)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Theoretical
1
2
4
8
16
32
Bacteria in 1,000’s per ml
Actual TIME (hrs) Theoretical Actual
1
2
4
8
15
29
3.5
4.0
4.5
5.0
5.5
6.0
_______
_______
_______
_______
_______
_______
54
62
63
61
54
38
64 46
2. Plot the data from the Theoretical growth and from the Actual growth on the semi-log graphs below, showing what happens to the population of bacteria over time. Label each curve: one for the theoretical population growth, and the other for the actual population growth. Use circles for each data point of the theoretical growth and triangles for each data point of the actual growth.
Theoretical Growth Curve
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Actual Growth Curve
( Type the questions and your answers on separate paper)
1. Based on the pyramid of production, which trophic level has the most energy? Explain why.
2. Where does the trophic level of detritivores fit in the pyramid of production? In other words, what trophic level do detritivores feed on? Explain your answer and include some examples of detritvores in the aquatic ecosystem.
3. Explain why there are very few predators at the top trophic level. Use your understanding from concepts discussed in lecture and from your text book.
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4. Which of the following food chains would support the larger population of humans? Explain your answer in terms of energy available. How does your answer apply to the issues concerning human population growth? a.) corn ---> cattle ---> humans b.) corn ---> humans
5. Most of the animals in the world, some say 90%, are invertebrates (they have no skeleton backbone). Based on what you saw and your own experience, why do you think this is so?
6. Which of the two curves that you drew, theoretical or actual, best represents the current growth of the human population? Explain why using concepts and information discussed in lecture and your text book.
7. Discuss 3 differences between the ecosystem of the bacteria in a test tube and the ecosystem of humans on the Earth. Why are these differences important?
8. What factor(s) do you think are most likely to limit human population growth in the next 100 years?
Come up with at least 3 factors and explain why those factors are important.
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