What Makes Something Alive

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 1.1 — The eight characteristics shared by all living organisms

Specification section 1(a) Characteristics of living organisms — also taught in The Four Eukaryote Groups.

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Everyone thinks they know what 'alive' means until they are asked to define it. Is a seed alive? Is a virus? Is fire? Biology needs an answer that works every time, so it does not try to define life in one sentence. Instead it lists the jobs a living thing does, and says: do all of these, and you are alive.

Think of it like a checklist for a working car

A pile of car parts is not a car. A car is a thing that steers, brakes, burns fuel, cools itself and moves. Take away any one of those and you have a broken car, not a different kind of car. Life works the same way: an organism is something doing all eight jobs at once. A seed is doing them very slowly, which is why it counts. A fire burns fuel and grows and moves — but it never reproduces itself with instructions, never excretes waste it made from its own chemistry, and never controls its own conditions. Three out of eight is not alive.

The eight, and what each one actually means

1. Nutrition — taking in materials to build with and to release energy from. Plants make their own; animals eat other organisms.
2. Respiration — releasing energy from food, inside every cell, all the time. This is a chemical reaction, not breathing.
3. Excretion — getting rid of the waste your own chemistry made, such as carbon dioxide and urea.
4. Growth — a permanent increase in size, because you built more of yourself.
5. Movement — some part of the organism moves. Plants move; they just do it slowly.
6. Sensitivity — detecting changes in your surroundings and responding to them.
7. Reproduction — making more organisms like yourself, using stored instructions.
8. Control of internal conditions — keeping the inside steady even when the outside changes.

Two of these are the ones that cost marks all the way through the course, so meet them properly now. Respiration is NOT breathing: breathing (ventilation) is moving air in and out of lungs, and plenty of living things have no lungs at all, while every living cell respires. Excretion is NOT going to the toilet: faeces is food that was never absorbed, so getting rid of it is egestion. Excretion is only for waste your body actually made.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

The eight characteristics — learn them as a list you can write in ten seconds

• Nutrition
• Respiration
• Excretion
• Growth
• Movement
• Sensitivity (control / response to surroundings)
• Reproduction
• Control of internal conditions

What each characteristic actually means

Nutrition

taking in materials for energy and growth

Respiration

releasing energy from glucose in every cell

Excretion

removing the waste products of metabolism

Growth

a permanent increase in size

Movement

some part of the organism moves

Sensitivity

detecting and responding to the surroundings

Reproduction

making more organisms of the same kind

Control of internal conditions

keeping the inside steady as the outside changes

Learn this definition · Respiration

The chemical process, occurring in all living cells, that releases energy from glucose. It is not breathing.

Taught in full in Respiration and ATP.

Learn this definition · Excretion

The removal of the waste products of metabolism (for example carbon dioxide and urea) from the body.

Taught in full in Excretion: Getting Rid of What You Made.

Excretion vs egestion

A. Excretion removes waste MADE BY the body's own reactions — carbon dioxide, urea.

B. Egestion removes undigested food that was never absorbed into the body at all.

Not this: 'Plants do not move, so they fail the movement test.'

This: Plants move: shoots grow towards light, roots grow downwards, some leaves fold at night. Movement does not have to mean walking.

Learn this definition · Egestion

The removal of undigested food from the body as faeces. It is not excretion, because the material was never absorbed into the body's cells.

The three things examiners use, and exactly which characteristics each one fails

Respiration vs breathing

A. Respiration is a CHEMICAL reaction in every living cell, releasing energy from glucose. Plants, bacteria and fungi all do it.

B. Breathing (ventilation) is a MECHANICAL movement of air into and out of lungs. Only some animals do it, and it is not one of the eight.

Deciding whether something is alive — the routine that scores

1. Take the eight characteristics one at a time, in the order you learned them.
2. For each one, say whether the evidence you were GIVEN shows it, and quote that evidence.
3. Name every characteristic the thing does NOT show — those are the marks.
4. State the conclusion in the form the evidence supports: alive, not alive, or not demonstrated on this evidence.
5. If a characteristic is only slow rather than absent, say so. A dormant seed respires slowly; it does not stop.

Model answer [3 marks]

Explain why a candle flame is not a living organism. [3]

It cannot reproduce using stored instructions, it does not control its internal conditions, and it does not respond to stimuli. Its apparent growth is more fuel burning, not new material built by the flame itself.

Model answer [3 marks]

A student writes that a crystal growing in a solution is alive because it grows and gets bigger. Explain why the student is wrong. [3]

Growth in living organisms is a permanent increase in size produced by the organism building new material of its own. A crystal enlarges because more of the dissolved substance deposits on its outside — nothing is built by the crystal. It also shows none of the other seven characteristics: no nutrition, no respiration, no excretion, no sensitivity, no reproduction from stored instructions and no control of internal conditions.

Model answer [3 marks]

Explain why removing carbon dioxide from the lungs is excretion but removing faeces is not. [3]

Excretion is the removal of the waste products of metabolism — substances made by the body's own chemical reactions. Carbon dioxide is made by respiration inside the body's cells, so removing it is excretion. Faeces is mostly undigested food that was never absorbed into the body's cells, so removing it is egestion.

Mark-losing trap. Name the characteristics the thing does NOT show. 'It is not alive' scores nothing.

Mark-losing trap. Respiration is not breathing. Write 'releases energy from glucose in every cell' and the mark is safe.

Mark-losing trap. Faeces is egestion, not excretion. The test is whether YOUR chemistry made the substance.

Mark-losing trap. Plants move — shoots towards light, roots downwards. Movement does not mean walking.

Mark-losing trap. A low rate is not a zero rate. A dormant seed and a hibernating animal are alive, doing everything slowly.

Mark-losing trap. All eight are required. Five out of eight describes an interesting chemical system, not an organism.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · State [1 mark] — Which process releases energy from glucose inside every living cell?
2. Grade 7 · Explain [2 marks] — A student says that removing faeces from the body is an example of excretion. Explain why the student is wrong.
3. Grade 8 · Explain [3 marks] — A candle flame takes in oxygen, releases energy, gives out carbon dioxide, grows larger and moves. Explain why a flame is still not a living organism.
4. Grade 9 · Evaluate [3 marks] — Some biologists argue that a dormant seed should not count as a living organism because for months it shows almost no measurable respiration, no growth and no movement. Which single statement is the strongest scientific response?
5. 9+ · Suggest [4 marks] — A probe returns a sample from Mars containing objects that grow when fed sugar, move towards warmth, and release carbon dioxide — but which never produce copies of themselves and lose their structure entirely if the temperature rises by 2 °C. Which is the most scientifically defensible conclusion?

The people behind this science

Two ways into the same idea — the one who first defined life by what it does, and the one who proved life does not arise from nothing. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Aristotle — the one who first defined life by what it does

The checklist you have just learned descends from Aristotle's. He was the first to argue that living things are defined by their FUNCTIONS — nutrition, growth, sensation, reproduction — rather than by what they are made of, which is exactly the move this lesson makes.

• “How did you decide what separates a living thing from a stone?”
• “Why define life by what something does rather than what it is made of?”
• “Is a seed alive while it sits in the ground doing nothing?”
• “Which of your criteria for life do you think has survived best?”
• “Why is it so hard to write a single sentence that defines life?”

Louis Pasteur — the one who proved life does not arise from nothing

For centuries, educated people believed maggots and microbes simply appeared in rotting matter — so 'is it alive?' had no stable answer. Pasteur's swan-neck flask settled it: life comes only from life. That is what makes reproduction a non-negotiable item on your checklist.

• “How did your swan-neck flask prove that microbes do not appear from nothing?”
• “Why did so many clever people believe living things arose from mud and broth?”
• “What made your experiment more convincing than the ones before it?”
• “If life only comes from life, how did the first living thing arise?”
• “Why does reproduction have to be part of any definition of life?”

Carry on through the course

• Next lesson: The Four Eukaryote Groups
• The Four Eukaryote Groups — Plants, animals, fungi and protoctists — how to tell them apart from their features, and the named examples the specification expects.
• Bacteria, Viruses and Pathogens — What a prokaryote is, why a virus is not classed as living at all, and what the word pathogen actually covers.
• All of Biology · Biology key terms · required practicals · Incandio Science · The 4BI1 specification