Lesson focus: Living organismA living thing, such as a plant, animal or bacterium. share life processes, but no single observation is normally enough to decide whether an unfamiliar system is alive.
Use evidence for nutritionGetting the food or materials needed for energy, growth and repair., respirationChemical reactions in all living cells that release energy from glucose, either using oxygen (aerobic) or without it (anaerobic)., excretionRemoving the waste products of metabolism (chemical reactions in cells), such as carbon dioxide and urea, from the body., response, movement, internal control, reproduction, growth and development to evaluate whether something is living.
Build on earlier learning
Specialised cellsYear 7 compared unicellular organisms. This bridge lesson now uses life processes as an evidence framework.
You will be successful when you can…
- Name the shared life processes.
- Distinguish movement from locomotion.
- Explain internal control using an example.
- Evaluate several lines of evidence together.
Words that carry the science
- organism
- An individual living system able to carry out the processes of life.
- nutrition
- Obtaining or making materials needed for energy, growth and repair.
- respiration
- Cellular reactions that release energy from nutrient molecules.
- excretion
- Removal of waste products made by metabolism.
- sensitivity
- Detecting and responding to changes in the internal or external environment.
- homeostasis
- Regulation of internal conditions within ranges compatible with cell function.
Life is recognised through a pattern of processes
01Life is recognised through a pattern of processes
Living organismA living thing, such as a plant, animal or bacterium. require nutritionGetting the food or materials needed for energy, growth and repair., carry out respirationChemical reactions in all living cells that release energy from glucose, either using oxygen (aerobic) or without it (anaerobic)., excretionGetting rid of waste made by chemical reactions inside cells, such as carbon dioxide or urea. metabolic waste, respond to surroundings, move, control internal conditions, reproduce, and grow and develop. These processes are linked: respirationChemical reactions in all living cells that release energy from glucose, either using oxygen (aerobic) or without it (anaerobic). supports active processes, while regulation keeps conditions suitable for enzymes.
A seed may show little visible activity while dormant, yet it contains living cells and can resume metabolism and growth under suitable conditions. Evidence must therefore be gathered over an appropriate timescale.
02Responses and internal control are different ideas
A responseA reaction to a change around a living thing, such as a plant shoot growing towards light. is a change caused by a stimulus, such as a shoot growing towards light. homeostasisKeeping the internal conditions of the body, such as temperature and water content, within narrow limits. is continuing regulation, such as controlling blood glucose, water balance or body temperature.
homeostasisKeeping the internal conditions of the body, such as temperature and water content, within narrow limits. does not keep a value perfectly constant. Negative feedback usually keeps it within a limited range around a set point.
03Borderline examples require careful claims
Fire spreads, consumes fuel and releases waste, but it has no cells, inherited genetic system or regulated metabolism. Viruses contain genetic material and evolve, but lack cellular structure and reproduce only inside host cells; in this course they are treated as acellular infectious particlesInfectious particles that are not made of cells, such as viruses., not living organisms.
A defensible conclusion identifies the evidence, its limitations and what further observation would discriminate between alternatives.
Evaluate an unfamiliar sample
A sealed pond-water sample consumes oxygen, releases carbon dioxide and produces more similar units after two days.
- Identify respiration evidence: oxygen consumption and carbon dioxide release.
- Identify reproduction or growth evidence: the number of similar units increases.
- Check for non-living alternatives, contamination and measurement error.
- Use microscopy to look for cells and repeat with a sterile control experiment.
How to make the reasoning visible: Several linked observations support life more strongly than one life-like feature, but control experiments are needed before concluding that the sample itself contains organisms.
Judge evidence for life
Compare each observation and decide what it supports and what remains uncertain.
| Observation | Process suggested | Limitation | Useful next test |
|---|---|---|---|
| Seed germinates after water is added | growth and development | could be contamination | observe cells and repeat sterile |
| Pond organism swims towards light | response and movement | movement alone is insufficient | change light direction |
| Yeast warms sugar solution | respiration | chemical reaction could release heat | sterile no-yeast control experiment |
| Crystal becomes larger in solution | none securely | addition is not biological growth | test for cells and metabolism |
Why is crystal growth not equivalent to biological growth?
Why use a sterile control experiment with yeast?
Check your understanding
Answer from memory, then check against the suggested answer.
What is respiration?
What is excretion?
What is homeostasis?
A robot senses a wall, changes direction and recharges. Is it living?
Why can dormant seeds still be described as living?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A probe detects movement and carbon dioxide production in a sample from beneath Antarctic ice.
Explain why each observation may have a cause other than life.
(2)Evaluate whether the sample contains living organisms, and suggest further tests.
(3)Total for this question: 5 marks
Command word: For evaluateA command word: weigh up the good points and bad points, then give your overall judgement., weigh supporting and limiting evidence before making a qualified judgement.