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Biology: The Nature and Variety of Living Organisms

Updated: Apr 12, 2021

What is a 'Living Organism?'

You might think there is an easy answer to this question. Humans, animals and plants are all living things, right? Yes... but it’s not quite as simple as that.

You are alive as you read this. If you have a pet at home, they are alive. The flowers and trees outside your window are alive too, but what about a wooden chair? It once belonged to a tree, so is it a living organism? How about the clouds as they move across the sky or rain as it falls? What about a fire that dances while it burns - are these things alive?

You see, the answer to the question, 'what is a ‘living organism?' is a little more complicated than you might originally think. We cover everything you need to know about living organisms in the Biology IGCSE course and corresponding STEM Semester-End Revision Courses.

Characteristics of living organisms

To be considered a living organism, the 'thing' in question needs to share a few common characteristics. You will come to know these as 'Mrs Gren' – a helpful acronym to make them easier to remember.

Movement - An action by an organism causing a change of position or place

Respiration - The chemical reactions in cells that break down nutrient molecules and release energy

Sensitivity - The ability to detect and respond to changes in the environment

Growth - A permanent increase in size

Reproduction - The processes that make more of the same kind of organism

Excretion - Removal from organisms of toxic materials and substances in excess of requirements