Question

Scenario 1:

Upon entering the classroom you notice two small glass tanks on the table. One of them contains many active crustaceans (Daphnia) swimming around. The other tank is cloudy and it appears as though all of the Daphnia are dead! You also notice a half-empty bottle of glucose in the trashcan. Your mission is to figure out what happened and why.

You have at your disposal the following items:
   Microscope, slides, coverslips, etc.
   Biuret and Benedict’s reagents and the necessary equipment to perform these tests

1.   What are your observations?

2.   Could there be something in the water that killed the Daphnia? What could that something be?

3.   Formulate a hypothesis as to what you think might be in the “death” tank based simply on the few observations you have at the moment.

4.   What experiment would you perform to test your hypothesis?

5.   Let’s assume the results of your experiment support your hypothesis. (Check with instructor, then proceed.) State the results of your experiment.

6.   Given that your hypothesis is supported, propose an explanation as to why the Daphnia died in terms of osmosis, diffusion, tonicity and the effects of hyper/hypo-tonic solutions on living cells.

List the four steps of the scientific method and describe what you did in the above scenario as it relates to each of those steps.

Scenario 2:

1.   You are walking through the woods when you discover a small twitching blob. You think it might be alive so you bring it to class. Unfortunately by the time you get to class, it is no longer twitching. Your instructor decides to let you dissect it. When you cut the blob open you see a round mass of tissue in the center of the blob so you cut into it. You make a slide from that tissue and look at it under the microscope. What you see is a confusing mass of cells. It appears as though the cells have branches. Within the cell body you see a single nucleus. What do you think this tissue/cell type might be? And what would its function be?

2.   Next you remove a piece of some very tough tissue. Under the microscope you see linear strands of fibers that appear to have striations in them. You wonder what would happen if you applied an electric current to this tissue in the blob. Your instructor gets an electrode and applies a mild electric current. The tissue twitches! What type of tissue do you think this is? What is its function?

3.   With all of this cutting, the blob begins to leak. You examine the fluid under the microscope and see many individual cells all with a nucleus. What type of cells do you think these are? Which other animal cell type do these cells resemble?

Scenario 3:

It’s twenty past the hour and you are late to biology lab. When you arrive, you find your classmates gathered outside the door and the Professor is nowhere to be found. You then notice that everyone is hovered around some spatters of red liquid inside the doorway. Has your professor been injured? You’d better find out.

What are your observations?

What are some hypotheses you could make about the situation based on your observations?

You and your classmates decide to examine the red liquid to find out exactly what it is. Your initial thought is to see what you can find under the microscope. You first need to prepare your slide. What would you need and how would you do this?

After you get the slide on the microscope all you see is darkness. What might be the problem?

Describe how you would manipulate the microscope to first center your specimen and then focus in on your image.

After some adjustments, you are able to focus on some tiny oval shaped structures. Each contains a purple stained dot in the center. As you scan around you also see some smaller, rounder structures that are also stained purple. Could this be the blood of you missing Professor or is there no cause for alarm?

Scenario 4:

Your pet dog has a stomach ache. The veterinarian, in order to help determine the cause of the ache, will attempt to identify the contents of its stomach. What tests could the vet perform and what results might you expect him/her to find?

Scenario 5:

You return from a bathroom break during your lab class on diffusion and osmosis, having just drank half a bottle of water. You return to find that your water has been moved and your lab partners are looking your way, pointing to the bottle, and snickering. You then catch a glimpse of an empty salt packet on the table. Are your lab partners trying to be funny? How would you determine whether or not they had poured the salt in your water without drinking it?

Answer 1

Scenario 1:

1. Water in one of tanks is cloudy and the Daphnia are dead. There is half empty bottle of sugar in the trash. Microscopic observation of Daphnia with help of slide and cover slip showed dead Daphnia.

2. There is sugar in the death tank present in excess in the water.

3. Excess of sugar must have killed the Daphnia.

4. We can perform Benedict's test to know if there is excess sugar in the water tank.

5.The death tank shows reddish orange color with Benedict's reagent.

6. The cells loose water when they are in a hypertonic solution because of the phenomenon of osmosis. When there is difference in the osmolarity between two solutions, water will move from region of higher water potetnial to the region of lower water potential through a semipermeable membrane. Because of the water movement from the body cells in the tank water, Daphnia dies due to dehydration.

Steps of scientific method--

1. Make an observation.

2. Ask a question

3. Formulate a hypothesis.

4.Design and perform an experiment.

AN observation is made that the Daphnia are dead. Question is why the Daphnia died? Hypothesis is formulated seeing the water cloudy and a half glucose bottle in the trash. Benedict's test is performed to confirm if there is excess sugar in the water of the death tank.