Is it alive? - Living things and Protocols (27 June 2012)

1. List the characteristics of living things.

• Can respond to changes (matter of how fast)
• Can die
• Can move on its own
• Ability to reproduce
• Can grow
• Respire
• Evolve
• Made of cells
• Have hereditary information

2. List the conditions needed to support life.

• Air
• Food
• Water

A common mistake is that people think warmth is a condition needed to support life. However, this is not true! A good example is cold-blooded animals. Cold-blooded animals have the ability to adapt to their surrounding temperature and hence, these animals may be inhabiting in a cold environment but can still survive. Moreover, some plants grow better in cold surroundings. It depends on their breed. Hence, it is not right to conclude that warmth is needed to support life.

3. Discuss with your partner how you would carry out experiments to find out whether some unknown pellets or powdered substances are actually living things.

• Which characteristics of the living things are you using in your experiment?

We are using the characteristic "Made of cells".

• How would you carry out the experiment?

We will examine the specimen under a microscope and look out for cells in the specimen. 

• What kind of evidence will you collect to show that it is living?

We will be unable to collect solid evidence but only pictures. We can take pictures through the lens of the microscope to observe and study the contents of the specimen. Alternatively, we can just look through the lens of the microscope and examine the substance, however, we will be unable to produce solid evidence if we do so. 

• From the evidence, can you infer that it is a living thing?

Yes, we can. If we are able to spot cells in the specimen under the microscope, we can conclude that it is a living thing since all living things are made of cells. However, if there is no sign of cells in the substance, we can deduce that the specimen is non-living.

Experimental methods from other groups:

• Using the characteristic "Living things respire", we can fill up a bag with a fixed amount of oxygen, put the substance in and seal the bag tightly. After 30 minutes, use a datalogger to check the amount of oxygen in the bag. If the oxygen amount has reduced, we can conclude that the substance is a living thing.
• Using the same characteristic "Living things respire", we can pour lime water into a transparent bag, put the substance into the bag and then seal the bag tightly. After 10 minutes, if the lime water appears to be chalky, we can deduce that the substance is a living thing because respiration produces carbon dioxide and when lime water absorbs carbon dioxide, it turns chalky.