Introduction to biology – what is life?

Characteristics that distinguish living things from non-living things:

growth / development

moves on its own

reproduction – continuity



excrete – processing the energy taken in –> conversion to another material –> passed out of system

responds to stimuli – maintain equilibrium with environment



Inanimate objects that have characteristics of living organisms:


  1. takes in energy (fuel)
  2. excretes (emits exhaust)
  3. moves on its own
  4. responds to stimuli (when reversing, it beeps faster when it gets nearer an object)
  5. death (engine is powered down)


  1. takes in energy (electricity)
  2. responds to stimuli (when you move the mouse, the cursor on the screen moves)
  3. interdependent (needs a mouse to move cursor and a keyboard to enter words)
  4. death (when battery runs out)

Living things that seem utterly lifeless:

Seeds – they do not reproduce, move on their own or respond to stimuli

Embryos in eggs – they do not reproduce or move on their own

Plants and fungi – they move on their own, but very slowly. Most do not respond to stimuli quickly, with exceptions such as the mimosa.

What about these organisms? they do not fulfill all characteristics.

Anaerobic organisms – do not need oxygen to respire (e.g. yeast)

Virus – do not need to feed, respire, excrete. It only reproduces.


Therefore how can you gather evidence and develop criteria to decide if something is living or non-living?

(The specimen being tested shall be called “A”.)

Criteria: A has to fulfill at least 4 of the characteristics of living things, one of which must be death.

To gather evidence:

  1. Movement – Mark the location of A over a period of time and observe whether it changes. Also observe whether A grows. If it does, A can move on its own.
  2. Growth – measure A’s length and mass daily over a period of time. If they increase, this means A is growing.
  3. reproduction – confine A in an enclosed space with ample air, food and water for survival; and observe whether the number of A multiplies after a period of time.
  4. Taking in of energy – observe whether A takes in any organisms or materials.
  5. Excrete – observe whether A releases any substances
  6. Responds to stimuli – set up 3 experiments with 2 specimens of A. In each experiment, expose one specimen to heat, light and drop in temperature for a period of time respectively while using the other as a control. Observe whether A responds in any way towards the stimuli.
  7. Death – cut off all supply of air, food and water to A for an extended period of time and observe if it continues to show any of the above characteristics. If it does not, A has died. *the criteria of death only applies if A has shown any of the characteristics above*

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