Materials Included In Kit

Additional Materials Required

Safety Precautions

Hydrochloric acid solution is corrosive to skin and eyes and toxic by ingestion or inhalation. Dispense the HCl very carefully and have students wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Solutions from this lab can be disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs. If solutions are shared, many more students can be served with the kit. The laboratory activity can easily be completed in one 50-minute class period, including discussion time.

• Make the gelatin solution and gum arabic solution prior to the lab. Add 100 mL of warm deionized water to the dry powder in the bottles provided. Cap the bottle and shake until all the powder has dissolved.
• If students add acid too quickly or do not mix between each drop, they will miss the cloudy phase at about pH 3–4.
• Have students observe a living amoeba or bacteria under the microscope and compare the organisms to the coacervate droplets.
• Encourage students to experiment with other conditions that might affect coacervate formation. Heat, cold, light, dark, and other chemical conditions that might affect coacervate formation. If materials are available, allow students to experiment with other dissolved materials. Some interesting results might be secured with: gelatin solution in alcohol, gelatin solution in sodium sulfate, egg albumen with gum arabic, sucrose or alcohol and egg yolk in sugar water. In all cases it may be necessary to adjust the pH by adding acid or base before coacervates will form.
• A lively discussion can ensue after this lab about the likelihood of “creating” life in a test tube. How close are we to doing it? Students will enjoy reading about Miller’s and Fox’s experiments. (Found in most biology texts.)

Answers to Questions

(Draw sketches of your observations. Label each drawing.)

Observations will vary.

1. How do the materials used to make coacervates compare with those that might have been present in ancient oceans?

These materials could easily be found in ancient oceans after polymerizing from simpler building blocks.

2. At what pH did the coacervates form? How might this compare with ancient Earth conditions?

Answers will vary but they usually form in pH range from 3–5, which would be like conditions predicted for ancient oceans.

3. It has been found that coacervates similar to those found in this lab are capable of decomposing starch to sugar. How might this be significant?

Since sugars serve as energy sources for most living animals, the ability to digest starch into sugars might be an important first step in digestion.

4. Where did the methylene blue end up with respect to the coacervates? Why might this be significant?

Methylene blue seems to accumulate at the inner surfaces of the coacervates much like the inside of the membrane in living cells.

Introduction

Scientists and philosophers have long pondered the origin of life on Earth. Scientists have found that under prescribed conditions, proteins and other chemical materials can aggregate into forms with an organization resembling simple forms of life such as bacteria. In this activity, these organized droplets, called coacervates, will be observed.

Concepts

• Coacervates

• Microspheres
• Polymerization

Background

Records show that very early people believed in abiogenesis (often called spontaneous generation). Abiogenesis beliefs held that life could originate spontaneously from non-living matter. It was believed, for example, that frogs came from mud and maggots came from meat. The later controlled experiments of Redi (middle of 17th century) and Pasteur (middle of 18th century) disproved these anciently held beliefs and cast doubt on the concept of abiogenesis.

Given the current conditions on Earth, it is not likely that life forms are originating by abiogenesis. In recent years biochemists have tried to simulate conditions in the laboratory that might have been present early in the Earth’s history. Under these presumed conditions (e.g., volcanic eruptions, violent storms, heating/cooling, lighting) it has been found that amino acids polymerize to form viscous, protein-like substances. These polymerized proteins and other molecules, when placed under primitive Earth conditions, can form self-organized microspheres, with cell-like properties, resembling spherical bacteria. Under microscopic examination, the microspheres resemble these primitive bacteria in many ways.

Materials

Safety Precautions

Hydrochloric acid solution is corrosive to skin and eyes and toxic by ingestion or inhalation. Dispense the HCl very carefully and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Mix 5 mL of gelatin solution and 3 mL of gum arabic solution in a test tube. (Gelatin is a protein; gum arabic is a carbohydrate.)
2. Measure the pH of this mixture by placing a drop on a clean microscope slide. Use a 1-cm strip of pH test paper and dip the end into the drop of liquid on the slide. Record the pH on the Coacervate Worksheet.
3. Observe the drop on the slide using a microscope on low power. Record your observations on the Coacervate Worksheet.

Caution: Dispense hydrochloric acid very carefully. It is corrosive to skin and eyes, toxic by ingestion or inhalation and will damage clothing and other materials.

4. Use a Beral-type pipet to carefully add HCl, drop by drop, to the test tube. After each drop of acid, mix the contents of the test tube (either by tapping or with a stirring rod) and then wait a few seconds to see if the mixture becomes cloudy.
5. When the mixture becomes cloudy, take another pH reading with a fresh strip of pH test paper.
6. Place a drop of the cloudy mixture on a clean microscope slide and observe it under a microscope. Use high and low powers and adjust the light so that it is extremely reduced.
7. Record and sketch your observations on the Coacervate Worksheet.
8. Add a drop of very dilute methylene blue stain to a drop of coacervate mixture on a microscope slide and view it under a microscope. Record your observations.
9. Complete the questions on the Coacervate Worksheet.
10. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10249_Student1.pdf