Life Processes

Look around you. A cat, a houseplant, a pencil and a stone — which of these are alive?

It can be tricky. A parked car can move, and a flame seems to grow and feed. So how do scientists decide?

The answer is simple: a living thing carries out a whole set of special activities called life processes. A non-living thing does not — it might do one or two things that look alive, but never all of them.

Some things were once alive but are not now — like a dead leaf or a wooden table. We call these once-living. Things that were never alive — like rock and water — are simply non-living.

Every living thing — a whale, a daisy or you — carries out seven life processes. Scientists agreed on this list because these activities are shared by all life on Earth.

There are seven words to remember, so we use a memory aid: MRS GREN. Each letter stands for one process.

• M — Movement
• R — Respiration
• S — Sensitivity
• G — Growth
• R — Reproduction
• E — Excretion
• N — Nutrition

If you can picture "MRS GREN", you have the whole list ready whenever you need it.

Now let's see what each process actually means.

• Movement — all living things move at least part of themselves. Animals walk or swim; plants slowly turn their leaves towards the light.
• Respiration — releasing energy from food inside cells. This is not the same as breathing! Even plants respire.
• Sensitivity — sensing changes around you and responding. You blink in bright light; a plant grows towards a window.
• Growth — getting bigger and developing over time. A kitten becomes a cat; a seed becomes a tree.
• Reproduction — making new living things of the same kind, so the species continues.
• Excretion — removing the waste that life processes make. You breathe out carbon dioxide and pass urine.
• Nutrition — taking in or making food to give the body energy and materials to grow.

It is easy to think only animals are truly alive, because plants move so slowly and stay rooted in one spot. But plants are fully living things — they carry out all seven life processes.

Let's check MRS GREN for a plant:

• Movement — a plant slowly turns its leaves and stems towards the light.
• Respiration — every plant cell releases energy from food, day and night.
• Sensitivity — roots grow downwards and shoots grow towards light.
• Growth — a tiny seed develops into a towering tree.
• Reproduction — plants make seeds, spores or bulbs to create new plants.
• Excretion — plants release waste gases such as oxygen and carbon dioxide.
• Nutrition — plants make their own food using sunlight, in photosynthesis.

The big difference is nutrition. Animals must eat other living things, but a green plant makes its own food. That is special — but it is still nutrition, so the rule holds: plants do all seven.

There are millions of different living things on Earth. To make sense of them, scientists sort them into groups based on the features they share. This is called classification.

The two big groups you will meet first are:

• Animals — they cannot make their own food, so they must take in food by eating. Most can move their whole body from place to place. Examples: fish, birds, insects, humans.
• Plants — they are usually green and make their own food using sunlight. They stay rooted in one place. Examples: grass, ferns, trees, flowers.

There are other groups too — such as fungi (like mushrooms) and tiny microorganisms (like bacteria) — which you will explore more later.

Sorting living things helps scientists study them, name them clearly, and spot how different living things are related. Whenever you meet a new living thing, ask: what features does it have, and which group do they place it in?

Understanding life processes now makes later biology much clearer:

• Cells — each life process happens because of the work cells do inside a living thing.
• Photosynthesis and respiration — you will study nutrition and respiration in much more detail.
• Ecosystems — you will see how living things feed, grow and depend on one another.
• Classification — sorting living things into groups builds straight on the idea of shared features.

Whenever a topic feels confusing later, come back to MRS GREN and ask which life process is involved. Take your time — really understanding this list is worth far more than rushing through it.