Edexcel IGCSE Biology · Spec 1.1
Characteristics of Living Organisms
The eight life processes shared by all living organisms — the MRS GREN characteristics — and how to tell whether something is living.
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Characteristics of Living Organisms
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Explained
Eight characteristics, and the two pairs of words that decide the mark
Deciding whether something is alive is not a matter of opinion. Biologists use a set of characteristics, and Pearson names eight of them. A single feature proves nothing on its own. A car moves and a flame grows, but neither shows the whole set.
The eight
- Movement, changing position or moving part of itself.
- Respiration, chemical reactions in cells that release energy from nutrients, usually glucose.
- Sensitivity, detecting a stimulus and producing a response. The specification calls this responding to surroundings.
- Growth, a permanent increase in size and in the number of cells.
- Reproduction, producing new organisms of the same species.
- Excretion, removing the waste products of metabolism, such as carbon dioxide and urea.
- Nutrition, obtaining or making the nutrients needed for energy, growth and repair.
- Control of internal conditions, keeping the inside of the organism within limits the cells can work in.
MRS GREN gives you seven of them: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. For Edexcel you add control of internal conditions, which is the one candidates most often leave out.
Excretion is not egestion
Excretion is the removal of substances the body has made. Carbon dioxide from respiration and urea from breaking down excess amino acids are both excreted.
Egestion is the removal of food that was never absorbed. It passed through the gut and left as faeces without ever entering a cell, so nothing made it. That is why faeces are egested, not excreted.
Respiration is not breathing
Respiration is a chemical reaction inside cells that releases energy. Breathing, or ventilation, is the movement of air into and out of the lungs.
An oak tree respires and has never taken a breath. Using the words as though they were the same thing costs marks in several topics, not just this one.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Biology show these confusions costing marks elsewhere in the paper. On a question about the function of fibre in the diet, some candidates incorrectly stated that fibre helps excretion, and the report advises that candidates should give very precise, accurate answers. On a different question, a response lost a mark for writing excretion where faeces was required.
Another report notes a candidate writing activity rather than respiration and losing a mark for it. These are recall marks. The science is not difficult; the precision is.
Applying the list
When a question describes something and asks whether it is living, work through the characteristics and say which are present and which are not. A virus is the classic case. It reproduces, but only inside a host cell, and it does not respire, grow, excrete or feed. Naming what is missing is what earns the credit.
Spec 1.1
What you need to know
- List the characteristics shared by all living things
- Explain what each one means
- Use them to decide whether something is alive
Active recall
Quick check
Answer each question before opening the answer.
What does the memory aid MRS GREN stand for?
Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition — the seven life processes shared by all living organisms.
What is the difference between excretion and egestion?
Excretion is removing the waste products of metabolism (e.g. carbon dioxide, urea). Egestion is removing undigested food that never entered the body's cells.
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