Characteristics of Living Organisms
BiologyΒ· 1.1 (2017 Spec Issue 3)Β· 12 min read
1. The 8 Defining Characteristics of Living Organismsβ βββββ± 4 min
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All living organisms share 8 core characteristics, as specified in the Edexcel IGCSE Biology syllabus. You are expected to define each of these correctly and use exact terminology in exam answers to score full marks.
Characteristic | Definition |
|---|---|
Require nutrition | Obtain food to provide energy and materials for growth |
Respire | Break down food molecules to release energy for cellular processes |
Excrete their waste | Remove toxic metabolic waste products produced by cell reactions |
Respond to their surroundings (sensitivity) | Detect and react to changes (stimuli) in their environment |
Move | Change position or move parts of their body, even if movement is slow |
Control their internal conditions | Maintain stable internal conditions (e.g. temperature, water levels) |
Reproduce | Produce offspring to continue the species |
Grow and develop | Increase in size and mass, and mature into adult form |
List 3 characteristics of living organisms that a human exhibits, with a 1-sentence example for each.
- 1
- Respiration: Humans break down glucose from food to release energy for walking, thinking and other processes.
- 2
- Excretion: Humans excrete urea (a waste product from protein breakdown) in urine.
- 3
- Sensitivity: Humans pull their hand away quickly if they touch a hot object (responding to the stimulus of heat).
Exam tip:
Mark schemes only accept the exact 8 characteristics listed in the syllabus. Do not include egestion, as this is not counted as a core characteristic.
2. Distinguishing Excretion and Egestionβ β ββββ± 3 min
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A common mark scheme trap is confusing excretion with egestion. The two processes are fundamentally different, and only excretion counts as one of the 8 characteristics of living organisms.
Excretion
Removal of waste products that are produced by chemical reactions inside the body's cells (metabolic waste), e.g. carbon dioxide from respiration, urea from protein breakdown.
Example:
Humans exhaling carbon dioxide is an example of excretion.
Egestion, by contrast, is the removal of undigested food that has never been absorbed into the body's cells. For example, humans passing faeces is egestion, not excretion. You will lose marks if you list egestion as a characteristic of living organisms, or if you define excretion incorrectly as removal of undigested food.
A student writes that 'excretion is the removal of waste food from the body'. Explain why this answer would not receive full marks in an Edexcel IGCSE Biology exam.
- 1
- The student's definition describes egestion, not excretion.
- 2
- Excretion is specifically the removal of metabolic waste produced by reactions inside body cells, not undigested food that never entered cells.
- 3
- To score full marks, the student would need to refer to metabolic waste, and give a correct example such as urea or carbon dioxide.
Exam tip:
If you are asked to define excretion, always include the phrase 'metabolic waste' to make your answer clear to examiners.
3. Applying Characteristics to Classify Entitiesβ β β βββ± 4 min
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You will often be asked to justify whether a given entity is living or non-living by referencing the 8 characteristics. You must give specific examples of which characteristics are present or absent to support your conclusion.
Use the 8 characteristics of living organisms to justify why a car is classified as non-living.
- 1
- A car may look as though it 'moves' and 'gives off waste gases', but neither is a biological life process: biological movement is powered by energy from respiration, and excretion is the removal of waste made by the organism's own metabolism β a car's motion and its exhaust both come only from burning fuel.
- 2
- Checking all 8 characteristics (MRS GREN): a car does not respire (combustion is not cellular respiration), does not truly move using its own respiration, does not sense and respond independently (it only reacts to the driver), does not grow, does not reproduce, does not excrete metabolic waste, does not require nutrition, and does not control its internal conditions.
- 3
- Conclusion: a car genuinely exhibits none of the 8 characteristics of living organisms, so it is non-living; its superficial resemblances (moving, giving off gases) are products of combustion, not of life.
When answering extended response questions on classification, aim to reference at least 3 characteristics to support your conclusion, as mark schemes usually award 1 mark per valid characteristic example.
Exam tip:
If you are asked about a less familiar organism (e.g. a fungus or a cactus), use general characteristics rather than specific ones you may not be sure of: all living organisms respire, excrete waste and reproduce, so these are always safe to reference if you are unsure about movement or sensitivity for that organism.
4. Classifying Viruses as Non-Livingβ β ββββ± 2 min
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Edexcel IGCSE Biology classifies viruses as non-living particles, and you may be asked to justify this classification using the 8 characteristics of living organisms.
Explain why viruses are classified as non-living, using the 8 characteristics of living organisms.
- 1
- Viruses only carry out one of the 8 characteristics: reproduction. They can only reproduce when they are inside a living host cell, by hijacking the host cell's machinery to make copies of themselves.
- 2
- Viruses do not exhibit the other 7 characteristics: They do not respire, do not excrete waste, do not require nutrition, do not move on their own, do not grow or develop, do not control their internal conditions, and do not respond to stimuli outside of a host cell.
- 3
- Conclusion: Since viruses lack 7 of the 8 core characteristics of living organisms, and only reproduce inside a host, they are classified as non-living.
Exam tip:
Do not state that viruses are 'neither living nor non-living' in your exam answers. The Edexcel mark scheme explicitly requires you to classify them as non-living, with justification referencing the 8 characteristics.
5. Common Pitfalls
Wrong move:
Listing egestion as a characteristic of living organisms, or defining excretion as removal of undigested food.
Why:
Egestion is the removal of undigested food that never entered cells, not metabolic waste, so it is not a core characteristic.
Correct move:
Only list excretion as a characteristic, and define it as the removal of metabolic waste produced by cell reactions.
Wrong move:
Writing only the MRS C GREN mnemonic letters in exam answers instead of the full characteristic names.
Why:
Mark schemes do not award marks for the mnemonic alone, you must use the full specification terminology.
Correct move:
Use the mnemonic to recall the characteristics, but write out the full name of each characteristic in your answer.
Wrong move:
Stating that viruses are living because they can reproduce.
Why:
Viruses only reproduce inside a living host cell, and do not exhibit any of the other 7 core characteristics of living organisms.
Correct move:
Classify viruses as non-living, and justify by explaining they only carry out reproduction inside a host, and lack all other 7 characteristics.
Wrong move:
Claiming that plants are not living because they do not move from place to place.
Why:
The definition of movement includes moving parts of the organism, not moving the entire body. Plants move their leaves towards sunlight, for example.
Correct move:
Reference that plants exhibit movement (e.g. sun tracking, root growth) as one of their characteristics.
Wrong move:
Using non-specification terminology for characteristics, e.g. writing 'homeostasis' instead of 'control their internal conditions' when asked to list the 8 characteristics.
Why:
The Edexcel specification explicitly uses the phrase 'control their internal conditions' for this characteristic, and mark schemes may reject non-standard terminology for direct list questions.
Correct move:
Use the exact wording from the specification when listing the 8 characteristics, and only use the term homeostasis if specifically asked for it in later questions on the topic.
6. Quick Reference Cheatsheet
Characteristic | Key Exam Detail | Example |
|---|---|---|
Require nutrition | Obtain food for energy and growth | Plants make glucose via photosynthesis |
Respire | Break down food to release energy | Humans respire to get energy for exercise |
Excrete waste | Removal of metabolic waste only (no egestion) | Plants release oxygen as waste |
Sensitivity | Respond to stimuli in surroundings | Snails pull into their shell when touched |
Move | Whole body or parts of body can move | Sunflowers turn to face the sun |
Control internal conditions | Maintain stable internal state | Humans sweat to cool down |
Reproduce | Produce new offspring | Bacteria split into two new cells |
Grow and develop | Increase in size/mass, mature | A seed grows into a mature tree |
7. Frequently Asked
What order should I list the 8 characteristics in for exam answers?
There is no required order in Edexcel mark schemes. You can list them in any sequence as long as you use the exact specification terminology: require nutrition, respire, excrete waste, respond to surroundings, move, control internal conditions, reproduce, grow and develop. You may use the MRS C GREN mnemonic to recall them, but do not write the mnemonic as your answer.
Is egestion counted as one of the characteristics of living organisms?
No. Egestion is the removal of undigested food that was never absorbed into the body's cells. Excretion (the removal of metabolic waste produced by cell reactions) is one of the 8 characteristics, while egestion is not, so do not mix these terms in your answers.
Why are viruses classified as non-living in Edexcel IGCSE Biology?
Viruses only carry out one of the 8 characteristics (reproduction) and only when inside a living host cell. They do not respire, excrete, grow, move, respond to their surroundings, control their internal conditions, or require nutrition outside of a host, so they are classified as non-living particles.
Going deeper
What's Next
Now that you have mastered the 8 characteristics of living organisms, you are ready to move on to the next topic in Section 1 of Edexcel IGCSE Biology: the classification of living organisms into groups including plants, animals, fungi, protoctists, bacteria and viruses. This builds directly on the characteristics you have learned, as classification is based on shared traits between organisms. You will also later apply these characteristics to more detailed topics such as nutrition, respiration and homeostasis in Section 2 of the syllabus, where you will learn the cellular mechanisms behind each of these processes. Practice past paper questions on this topic first to reinforce your knowledge before moving on to more complex content.