Only dust - is there a sign of life?

This experiment should take around two hours. 

Equipment

Materials per group Dust:

• Sand
• Vermiculite
• D-fructose Each sample should contain ca 5 g D-fructose. (Alternatively, amino acids can be used.)
• For calibrating polarimeter: 10 g D-fructose, deionised water

Equipment per group

• Items from the junk list, including:
• Sealing wax
• Rubber bands
• Rubber tubing
• Glass tubing and rods (various)
• Protractor
• Paper
• Test tubes
• Test tube holder and rack
• Beakers (various)
• Weighing bottles (various, flat bottomed)
• Filter funnel
• Filter paper
• Measuring cylinders, 25 cm³ and 100 cm³ 
• Petri dishes
• Pasteur pipettes
• Optical filters (coloured, polarizing, clear, diffuse)
• Clamps and stands
• Corks
• Copper wire
• Light source
• Wash bottle
• Mirrors (small)
• Bunsen burner
• Plastic gloves
• Safety glasses

Health, safety and technical notes

• Read our standard health and safety guidance here. 
• Wear eye protection.
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.

Commentary

Some students may need help in remembering that the building blocks of proteins and carbohydrates  – amino acids and sugars  – are chiral and therefore stereospecific. They may also need help in recalling how a polarimeter works. However, the instruction to test a physical property of organic compounds from living sources, plus the presence of optical filters in the equipment, prompted most students to test for optical activity by constructing a polarimeter. This problem has been used successfully in competitions.

Possible approach

The hand-outs, including a list of the contents of the kits, can be given to groups the previous day. The main challenge must be seen as the construction of an arrangement capable of giving a reliable estimate of the optical activity in the sample. A possible design for a polarimeter is sketched below; a way of measuring the angle of rotation must be devised.

Possible extension

If this method was used to analyse dust from a meteoric crater for signs of extra terrestrial life, what assumptions would the students have to make to analyse their results?

Evaluation

This problem was set as a competition and marks were awarded as follows.

1. Marks were awarded for the construction of the polarimeter.
2. Marks were awarded for use and demonstration of optical activity in the dust.
3. Marks were deducted for hints that were given.

Notes

This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.