How to Proceed

• Read through the introductory materials below.
• Open the Unit 8 Experiment Answer Sheet and complete the following Experiment exercises this unit:
  • Experiment 8 Exercise 1 – Species Interactions: Competition
  • Experiment 8 Exercise 2 – Biomes

Species Interactions: Competition – Introduction

This unit we are learning about species-species interactions and how species influence each other (see pp 428-432 and our online lecture). One important interaction is interspecific competition, in which two or more species compete for limited resources. Competition, along with predation and symbioses (e.g., commensalism, mutualism, and parasitism) are important biological interactions that affect the size of species populations.

In the first exercise, we will examine the population growth of two species of freshwater ciliates. Populations of these species initially grow exponentially (see p 408), but the population does not increase in size forever. Eventually it reaches what is known as the carrying capacity of the environment, or the maximum population size the environment can support due to limitations in food, water or other resources.

Competitive exclusion (see p 429) may occur between two species that compete for the same resources. In this situation, only one species will be successful, such that the other species is forced to move elsewhere or die out. This rarely happens in nature though, since the species on the losing end typically switches to an alternate resource. However, under artificial situations, elimination of one species can occur.

The purpose of this exercise is to use a simulation to model competitive exclusion using the microscopic organisms that Gause used to come up with his competitive exclusion principle (see p 429). You will need to use the following website. Be sure you can access it and use it:

Glencoe/McGraw Hill. No date. Population Biology
http://www.mhhe.com/biosci/genbio/virtual_labs/BL_04/BL_04.html (Links to an external site.)

When you are ready to begin, go to the above website and open the Unit 8 Experiment Answer Sheet and follow the instructions.

In Biomes – Introduction

This unit we have learned about the large scale ecosystems called Biomes. They have developed over millions of years and the flora and fauna found in each biome type have adapted to the long term climate conditions (e.g., average rainfall, average temperatures). The purpose of this exercise is to see how well you understand the biotic and abiotic factors that shaped the various biomes. Review pp 384-390 and our online lecture this unit before beginning.

You will need to use the following websites. Be sure you can access them and use them:

NASA. No date. The Great Graph Match
http://earthobservatory.nasa.gov/Experiments/Biome/graphmatch_advanced.php  (Links to an external site.)

NASA. No date. To Plant or Not to Plant
http://earthobservatory.nasa.gov/Experiments/Biome/plant_it.php (Links to an external site.)

When you are ready to begin, open the Unit 8 Experiment Answer Sheet to complete this exercise.

WEEK 8 EXPERIMENT ANSWER SHEET Please submit to the Week 8 Experiment dropbox no later than Sunday midnight.

SUMMARY OF ACTIVITIES FOR WEEK 8 EXPERIMENT ASSIGNMENT

· Experiment 8 Exercise 1 – Species Interactions: Competition

· Experiment 8 Exercise 2 – Biomes (Part I and II)

Experiment 8 Exercise 1: Species Interactions: Competition

In this exercise you will be evaluating the effect of competition on the population size of two species of microorganisms. Be sure you have read through the readings for Week 8 as well as the introductory information for the Week 8 Experiment. When you are ready to begin, open in the following website:

Glencoe-McGraw Hill. No date. Population Biology http://glencoe.mcgraw-hill.com/sites/dl/free/0078759864/383928/BL_04.html

Procedure

A. Click on the Information button on the bottom and read through the material before beginning. You will need to scroll down to read all of the information. Close the window when you are done. Note that the two species we will be using will be competing for the same food source; bacteria.

B. First, you need to set up the experiment by distributing the two species to the three test tubes.

a. Click on the pipette (the purple bulb) in the flask containing P. caudatum, fill it and place the contents in Tube #1.

b. Then click on the pipette in the flask containing P. aurelia, fill it and place the contents in Tube #2.

c. Finish by putting a pipette full of both species in the Tube #3.

C. Answer the question below before proceeding.

Question

1. The number of P. caudatum and P. aurelia grown alone would be expected to increase until the population size reaches the carrying capacity of the test tube. What do you think will happen in terms of population growth in Tube #3 that contains both species combined and why (2 pts)?

Procedure (continued)

D. You now need to count the number of organisms in each Tube beginning on Day 0 and continuing every 2 days until you reach Day 16. These values will need to be recorded in Table 1 below (do NOT use the Table provided by the website).

a. Click on the Microscope to get started.

b. Click on Clean microscope slides and then Take Sample.

c. Click on the first slide and drag it on to the microscope. Count the number of P. caudatum (note its shape) and multiply by 2 to get the number of cells per ml (your slide holds 0.5 ml). Record this number in the Table below; this is Day 0.

d. Next, click on the second slide and drag it to the microscope. Count the number of P. aurelia (note its shape), multiply by 2 and record this number in the Table for Day 0.

e. Finally, drag the third slide on to the microscope and count the number of each type of organism, multiply by 2 and enter the data into the Table.

f. Click on Clear Slides (on the bottom) and then on the Calendar that says Day 0 to advance it two days.

g. Repeat steps b – f until you reach 16 days.

h. As the days go on, you will have more and more individuals to count. Click on the Grid On button on the microscope to make them easier to count.

Table 1. Results (4 pts).

E. Now it is time to analyze your data.

a. You will need to generate two graphs, one which depicts the number of both species per day of culture when grown separately and one that depicts the number of both species per day of culture when grown together.

b. You must use the Scatter type graph in Excel and each graph should have two lines (one for each species).

c. Be sure you label your axes and your series; meaning you will need to indicate which line pertains to P. caudatum and which to P. aurelia.

Paste your two graphs below (4 pts):

Questions

2. What were the carrying capacities (maximum population size) for the two species when grown separately and on what day were they reached (1 pts)?

3. Describe what happened when the two species were grown together and explain why. Be sure to discuss the magnitude and timing of each species’ carrying capacity compared to when they were grown separately (3 pts).

4. Do these results support the principle of competitive exclusion; why or why not? Be sure to cite your sources. (4 pts).

Experiment 8 Exercise 2: Biomes

In these two relatively short exercises, we will be examining the biotic and abiotic factors that define a biome. You should have completed the readings for this week before beginning.

Procedure – Part I: The Great Graph Match

A. Open the following website:

NASA. No date. The Great Graph Match http://earthobservatory.nasa.gov/Experiments/Biome/graphmatch_advanced.php

B. In the Great Graph Match, you will need to match abiotic information (annual rainfall and temperatures) to the appropriate biome. Follow the instructions on the page and fill-in the Table below. For the Explanation column, you need to briefly explain why you chose the biome you did based on the data presented.

C. Be sure to provide complete citations for the sources used.

Table 2. Locations, biomes and explanations (4 pts).

Citations:

Procedure – Part II: To Plant or Not to Plant

A. Open the following website:

NASA. No date. To Plant or Not to Plant http://earthobservatory.nasa.gov/Experiments/Biome/plant_it.php

B. In the To Plant or not to Plant, you will need to determine which in which biomes to plant various plants, based on the information presented. Follow the instructions on the page and fill-in the Table below. For the Explanation column, you need to briefly explain why you chose the biome you did.

C. Be sure to provide complete citations for the sources used.

Table 3. Plants, biomes and explanations (4 pts).

Citations:

Week 8 Questions

1. Are most invasive (exotic) species K-selected or r-selected species? Explain your choice and why that makes sense in terms of their ecological success.

Citation(s):

2. Briefly define a community and an ecosystem and describe how the two are interrelated.

Citation(s):

3. Which of the following levels of organization are in order, from simplest to most complex.

a.  population, organism, community, ecosystem b.  community, ecosystem, population, organism c.  organism, community, population, ecosystem d.  population, ecosystem, organism, community e.  organism, population, community, ecosystem

4. Mosses growing on bare rock will eventually help to create soil.  These mosses are involved in ___ succession.

a.  primary b.  secondary c.  tertiary

5. If a farmer sprays a pesticide onto a field and kills half of the insect pests, he has caused a reduction in________.

a.  field capacity b. carrying capacity c. population size d. More than one of the above

6. What type of survivorship curve would you expect for a plant species in which only a few seeds are produced and most of these survive to produce adult plants?

a.  type I b.  type II c.  type III

7.  An ecological niche is an organism’s_______ in an ecosystem.

a. location b.  habitat         c.  resources         d.  function

8. No matter how rapidly populations grow, they eventually reach a limit and begin to stabilize. This is called the ______________.

9. Unicellular algae live in the tissues of coral animals.  The algae provide food for the coral, while the coral provides a stable home for the algae. This is an example of

a.  Parasitism b.  Commensalism c.  Mutualism

10. The vast majority of energy taken into an ecosystem is____________.

a.  converted into biomass by plants. b.  utilized by secondary consumers. c.  lost as heat. d.  used by the primary consumers. e.  concentrated in the decomposers.

11. A farmer is using an insecticide to treat his crops. While most insects do not survive their first exposure to the insecticide some have a gene that enables them to survive. When these survivors reproduce they will likely pass along this resistance to their offspring. This results in an increase in numbers of the insects over time. Which of the following processes applies to this survival?

a. cloning b. mutation c. natural selection d. genetic engineering

12. What is the ecological relationship between insects and crops?

a. mutualism  b. competition c. predation

13. Sea anemones growing on the backs of crabs without damaging the crabs are an example of

a.  Parasitism b.  Commensalism c.  Mutualism

14. Which of these is a population density-independent regulating factor?

a.  Competition b.  Predation c.  Size of population d.  Weather e.  Resource availability

15. Producers are_________.

a.  Autotrophs b.  Herbivores c.  Omnivores d.  Carnivores

16.If biological magnification occurs, the ___ will have the highest levels of toxins in their systems.

a.  producers b.  herbivores c.  primary carnivores d.  top carnivores

17. Given the amount of sunlight that hits the plants on our planet, and the ability of plants for rapid growth and reproduction, how come we aren’t all hip deep in dead plants?

Citation(s):

Week 8 Experiment Grading Rubric

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This unit’s Experiment exercises will deal with Diffusion and Osmosis. Read through the introductory material located below and complete the questions found in the Unit 3 Experiment Answer Sheet.

How to Proceed

• Read through the Experiment Exercise Introductions below.
• Open the Unit 3 Experiment Answer Sheet and complete the following Experiment exercises this unit:
  • Experiment 3 Exercise 1 – Diffusion (~1 hr)
  • Experiment 3 Exercise 2 – Osmosis (~1.5 hrs)
• Save your completed Unit 3 Experiment Answer Sheet and submit it no later than Sunday midnight (CT).

Diffusion – Introduction

This unit we are learning about the structure and function of cells. The plasma membrane, for example, is an important structure of all cells and it is responsible for regulating the passage of materials into and out of the cell. Plasma membranes are differentially (selectively) permeable, meaning some substances are allowed to enter and exit the cell, while the movement of other materials is either carefully regulated or blocked. Two ways in which materials can move freely across the cell membrane are diffusion and osmosis.

Diffusion is the movement of solutes (material dissolved in liquid) from an area of high concentration to an area of low concentration. If these areas are separated by a membrane, that membrane may or may not be permeable to the solute. The membrane is always permeable to water though and the movement of water across a membrane is a special form of diffusion called osmosis.

In our first exercise, we will examine diffusion of solutes through a semipermeable membrane and the factors that affect their movement. You’ll want to be sure to review our online lecture this unit on Cell Structure and pp 83 – 86 in your book. View the following two animations BEFORE starting this exercise:

McGraw-Hill. 2006. How Diffusion Works
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html (Links to an external site.)

McGraw-Hill. 2006. How Osmosis Works
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html (Links to an external site.)

When you are ready to begin, open the Unit 3 Experiment Answer Sheet and answer the questions associated with the first exercise.

Osmosis – Introduction

In our second exercise this unit, we will to take a closer look at osmosis; the movement of water across a membrane. The direction water moves depends on the relative concentration of solute molecules on either side of the membrane (in this case, these solutes are not able to cross the membrane). Furthermore, the presence or absence of cell walls (e.g., in plant cells) influences how cells respond to osmotic fluctuations in their environment. This exercise will examine the forces that determine whether water moves into or out of a cell.

We will be using the following website in this exercise. Be sure you are able to access and use this website before starting.

The Biology Place. No Date. Osmosis: Movement of Water across Membranes
http://www.phschool.com/science/biology_place/biocoach/biomembrane1/osmosis.html  (Links to an external site.)

Open the Unit 3 Experiment Answer Sheet and complete the questions for this exercise.

WEEK 3 EXPERIMENT ANSWER SHEET Please submit to the Week 3 Experiment dropbox no later than Sunday midnight.

SUMMARY OF ACTIVITIES FOR WEEK 1 EXPERIMENT ASSIGNMENT

· Experiment 3 Exercise 1 – Diffusion: Movement of Solutes across a Membrane

· Experiment 3 Exercise 2 – Osmosis: Movement of Water across a Membrane

Experiment 3 Exercise 1: Diffusion – Movement of Solutes across a Membrane

We will be using dialysis tubing to simulate a semipermeable membrane. This tubing allows small molecules (e.g., water, ions, glucose) to pass while preventing large molecules (e.g., macromolecules like proteins, starch, glycogen) from moving across. Be sure you have read over the suggested material before starting this exercise and that you have reviewed the following animations:

McGraw-Hill. 2006. How Diffusion Works https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

McGraw-Hill. 2006. How Osmosis Works https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Experimental Design

A. The dialysis bag we will use is permeable to water and small molecules (e.g., less than 500 g/mol) and impermeable to large molecules (e.g., more than 500 g/mol).

B. The dialysis bag is filled with a mixture of glucose (molecular weight = 180 g/mol) and protein (molecular weight = 10,000 g/mol) dissolved in water. A small subsample of the dialysis bag contents is saved and will be used in Step 4.

C. The dialysis bag is then placed into a beaker of water. A small subsample of beaker water is also saved and is to be used in Step 4 as well.

The presence or absence of glucose and protein will be determined using indicators. Indicators change colors in the presence certain materials. The two tests that we’ll use are the Benedict’s test for simple sugars (e.g., glucose) and the Biuret test for the presence of proteins.

· If glucose is present, the Benedict’s indicator will turn green. If no glucose is present, the solution will be blue.

· If protein is present, the Biuret indicator will turn violet. If the solution remains clear, then no protein is present.

D. The subsample of dialysis bag solution and the beaker water are tested for the presence of glucose and protein. See Table 1 below for the results.

E. The dialysis bag is then left in the beaker of water for 60 minutes.

F. At the end of 60 minutes, the dialysis bag solution and the beaker water are again tested for the presence of glucose and protein. See Table 1 below for the results.

Table 1. Results of testing of the dialysis bag and beaker contents at the beginning and end of the Experiment.

Questions

1. Summarize the results regarding the presence (+) or absence (-) of glucose and protein in the dialysis bag and beaker in Table 2 below (4 pts):

Table 2.

2. Explain the movement or lack of movement of protein and glucose across the dialysis bag membrane (4 pts)

3. Which solution, that in the bag or that in the beaker, is hypotonic compared with the protein solution (2 pts)?

4. What factors affect the movement of molecules across a semipermeable membrane? Which factor plays the greatest role in biological systems (4 pts)?

5. Briefly explain what active transport is and how it differs from passive transport, especially in terms of concentration gradients (4 pts).

Experiment 3 Exercise 2: Osmosis – The Movement of Water across a Membrane

Before starting, let’s see what you know about the terms hypotonic, isotonic and hypertonic. Examine the diagrams below. Note that the small green circles represent dissolved solutes like salt, glucose, and amino acids. You can assume that the additional space surrounding the solutes is water and that the tan area is INSIDE the cell.

Question

1. Define each term below in terms of solute concentration outside compared to the inside of the cell. You do not need to explain which direction water will move (3 pts).

a. Hypotonic –

b. Isotonic –

c. Hypertonic –

Procedure

A. Open the following website to get started:

The Biology Place. No Date. Osmosis: Movement of Water across Membranes http://www.phschool.com/science/biology_place/biocoach/biomembrane1/osmosis.html

B. Read over the information presented and then Click on 

C. Then, Click on . Read through the information presented and be sure to click on Animate beneath the illustration.

Questions

2. What concentration of salt is isotonic to animal cells (1 pts)?

3. When cells are in isotonic solution, is there movement of water into or out of the cell? If so, describe this movement (3 pts).

Procedure (continued)

D. Click on .

E. Read through the information presented and be sure to click on Animate beneath the illustration. When ready, answer the following question.

Question

4. Describe the net movement of water molecules when cells are placed in a hypotonic solution. Explain why water moves this way (3 pts).

Procedure (continued)

F. Click on 

G. Read through the information presented and be sure to click on Animate beneath each of the illustrations. Answer the following questions. Your answers should incorporate the terminology used in the animations.

Questions

5. What happens to an animal cell when placed in a hypotonic solution (2 pts)?

6. What happens to plant cells when placed in a hypotonic solution? What accounts for the difference in outcomes between animal cells and plant cells (3 pts)?

Procedure (continued)

H. Click on 

I. Then, Click on . Read through the information presented and be sure to click on Animate beneath the illustration. Answer the following question.

Question

7. Describe the net movement of water molecules when cells are placed in a hypertonic solution. Explain why water moves this way (3 pts).

Procedure (continued)

J. Click on 

K. Read through the information presented and be sure to click on Animate beneath the illustration. Answer the following questions.

Questions

8. Compare and contrast what happens to plant and animal cells when placed in a hypertonic solution. Be sure to use proper terminology (4 pts).

9. Based on what you learned in this exercise, explain why salt might make a good weed killer (3 pts).

Week 3 Experiment Grading Rubric

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