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MATERIALS NEEDED:

· Solutions: Gelatin (1%), Arabic gum (1%) HCl (.1%) Methylene blue (.1%)

· Slides, Coverslips, Mixing container, Pipettes, PH paper, 1-14 range

The conditions when earth formed 4.6 billion years ago were very different from those today. The atmosphere consisted mainly of hydrogen, methane, ammonia and water vapor. Most of the light hydrogen escaped into space. There was no free oxygen and this condition caused a reducing atmosphere (rather than the oxidizing atmosphere of today. Because of volcanic activity, surface temperatures were higher than today and the thinner atmosphere allowed ultraviolet radiation and cosmic rays to reach the surface at higher intensities than they now do. Under these conditions, inorganic molecules are readily converted into organic molecules (amino acids, proteins, nucleic acid, and others), as shown by Stanley Miller in 1953.

Without oxygen to break them down, these organic molecules could join to form more complex molecules, and would build up a concentrated primordial soup. Undoubtedly many chemical reactions could occur, but without some way of compartmentalizing these reactions, life would not be possible.

In today’s lab we will explore several possible means of compartmentalization: the formation of structures known as coacervates. Although not alive by any scientific definition, coacervates do exhibit many properties in common with living cells. They form a membrane of water around themselves. This membrane acts to control the effects of the external environment on the internal coacervate environment, just as a cell membrane does. Substances can be taken up by the coacervates (eating?) and, as the substances are absorbed, the coacervates grow. When they reach sufficient size, they split (reproduce). Control of an internal environment, absorption of nutrients, growth, and reproduction are all properties of living things.

PROCEDURE for Coacervates:

1. Work in groups of three or four. Use a pipette to add 3 ml of gelatin solution (protein source) to a mixing container. Observe the solution and enter your observations in the results section. Using a second clean pipette, add 1ml of gum arabic solution (a carbohydrate source) to the mixing container. Mix gently. You shouldn’t see any evidence of coacervates at this time. These structures form only under acidic conditions. Record your observations in the results section.

2. Use a third pipette to add one drop of acid (HCl) to your mixing container. When the acidity (pH) is sufficiently low, this will promote the formation of coacervates. Use the pH paper to record the pH of your mixture. Record your observations in the results table.

3. Continue adding HCl drop-by-drop while recording your observations in the results table. Eventually coacervate droplets will form as a white precipitate. Make sure to take pH measurements as you add the HCl.

4. Once coacervates have formed, draw up a sample of the mixture and place it on a microscope slide. Note the structure, shape, and appearance of the coacervates. Make a sketch in the results section. Then place a drop of methylene blue on the slide and describe what you see. Make a second sketch in the results section. Coacervates will appear as white globular structures.

5. After you have observed the coacervates, continue to add HCl to your mixing container drop-by-drop. Take the pH and record your results in the results table until the droplets disappear.

Examination of microfossils.

1. Examine a thin section slide of the Gunflint Chert from Ontario, Canada. The cells you’ll find under the microscope are about 2 billion years old. Find and draw at least five types of cells.. Identify them, if possible, using the picture key to the Gunflint Chert. You will find bacteria, cyanobacteria, and what appears to be green algae and fungus-like organisms.

Picture key to the Gunflint Chert. (A-C) blue-green algae; Animikia, Entosphaerpoides, and Gunflintia; (D) Huroniospora, an algal spore; (E) Gunflintia and Hurionospora; (F) Euastrion, a bacterium and some unknown forms, (G) Kakabekia, an ammonia-consuming organism; (H) Eosphaera.

2. Algal Limestone. Obtain an algal limestone slide and note the gross layering of the specimen (either eye-ball it or use a dissecting microscope). The thinner layers are probably silt deposited during a rainfall while the thicker bands are the remains of algal colonies (mainly Chlorellopsis coloniata). Next, examine the slide under a compound microscope at successively higher magnification (remember to look for bacteria-sized organisms). Make sketches of your observations. These deposits are only about 65 million years old. A polished section of algal limestone is shown in the following figure. The dark bands represent the silt deposits while the thicken light bands are the algal deposits.

Algal Limestone Section

3. Conodonts. Conodont remains are common in Paleozoic through Triassic warm-water fauna. Paleontologists agree that Conodonts represent an extinct phylum of animals. They were soft-bodied marine invertebrates whose remains consist mainly of tooth-like structures that were probably used to grasp and ingest prey. The diversity of conodonts can be seen in the following photographs and illustrations.

Conodont Diversity

Conodonts

Conodonts are believed to be ancestral to vertebrates. Owing to their soft body parts, few complete fossils have been found; however, their teeth are readily fossilized. The great diversity in tooth structure suggests that members of this group were specialized for a variety of lifestyles. Transfer a small amount of conodont residue to a depression slide or watch glass. Observe using a dissecting microscope. Make drawings showing the diversity of conodont teeth.