What are the main characteristics of living organisms according to the IB MYP Science curriculum?

In the IB MYP Science curriculum, living organisms are defined by several key characteristics: they are made up of cells, they grow and develop, they reproduce, they respond to stimuli, they require energy, they maintain homeostasis, and they adapt to their environment. These characteristics help distinguish living organisms from non-living matter.

How do cells play a role in the characteristics of living organisms?

Cells are the basic unit of life and are fundamental to all living organisms. They perform essential functions that support the characteristics of life, such as growth, reproduction, and response to stimuli. For instance, cells divide to enable growth and repair, and they contain genetic material necessary for reproduction. Additionally, cells interact with their environment, allowing organisms to respond to changes and maintain homeostasis.

Why is homeostasis considered a vital characteristic of living organisms?

Homeostasis is the process by which living organisms maintain a stable internal environment despite external changes. This characteristic is vital because it ensures that conditions within the organism remain optimal for cellular functions and overall survival. For example, humans regulate body temperature and blood pH to support metabolic processes. Without homeostasis, organisms would not be able to function properly and could not survive.

How do living organisms demonstrate the characteristic of adaptation?

Adaptation is a characteristic of living organisms that involves changes over time to better suit their environment. This can occur through evolutionary processes where advantageous traits become more common in a population. For example, some plants have adapted to arid environments by developing deep root systems to access water. Adaptation enhances an organism's ability to survive and reproduce in its specific habitat.

Can you explain how energy is utilized by living organisms?

Living organisms require energy to perform various life processes, such as growth, reproduction, and maintaining homeostasis. This energy is primarily obtained through cellular respiration, where cells convert nutrients into usable energy in the form of ATP (adenosine triphosphate). Plants, for example, capture energy from sunlight through photosynthesis to produce glucose, which is then used in cellular respiration to fuel their activities.

Why is "Saying plants don't move." a common mistake in Characteristics of Living Organisms?

Why it happens: They look still. How to avoid it: Plants move — slowly, mostly parts of themselves (leaves toward light, roots toward water). All seven MRS GREN features apply.

Why is "Calling a grape absorbing water 'growth'." a common mistake in Characteristics of Living Organisms?

Why it happens: It does get bigger. How to avoid it: Growth means adding NEW cells or cell material — not just inflating with water.

CellsIB MYP Sciences (Years 1-5)

Characteristics of Living Organisms

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Characteristics of Living Organisms — IB MYP Sciences: MRS GREN and what defines life

What makes something 'alive'? Biologists list seven core characteristics — Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. This MYP Sciences note covers each one and how they appear in animals, plants and bacteria.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — State and explain the seven characteristics of life.
MYP Sciences A — Give an example of each in an animal, plant and bacterium.
MYP Sciences D — Discuss whether viruses are alive based on the seven characteristics.

The seven characteristics — MRS GREN

Every living thing does all seven.

M — Movement: change of position. Animals move their whole body; plants move parts (leaves to follow the sun, roots to follow water).

R — Respiration: chemical release of energy from food. All living things respire — even plants (in addition to photosynthesis). Aerobic respiration: glucose + O₂ → CO₂ + H₂O + energy.

S — Sensitivity: detecting and responding to changes (stimuli). Animals have nerves and senses; plants respond to light (phototropism) and gravity (gravitropism).

G — Growth: increase in size and mass that is permanent. Different from just absorbing water — growth involves adding new cells or material.

R — Reproduction: making new individuals. SEXUAL (combining DNA from two parents) or ASEXUAL (one parent, identical clones). Plants do both; bacteria mostly asexual; animals mostly sexual.

E — Excretion: getting rid of toxic waste from chemical reactions. Animals excrete CO₂ (lungs), urea (kidneys), salts (sweat). Plants excrete O₂ from photosynthesis.

N — Nutrition: obtaining materials and energy. Animals (HETEROTROPHS) eat other organisms; plants (AUTOTROPHS) make their own food by photosynthesis.

Note: GROWTH (G) is about MORE cells or more cell material, NOT just inflating with water. A grape soaking up water expands, but doesn't grow biologically.

M-R-S-G-R-E-N: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
All living things share all seven.
Plants do all seven too — including movement and excretion, just differently from animals.

Are viruses alive?

Viruses have some but not all of the seven characteristics — biologists are divided.

Viruses present a fascinating challenge:

Outside a host cell, a virus is just a protein shell containing DNA or RNA. It can't move, respire, grow, reproduce or do anything else.
INSIDE a host cell, a virus hijacks the cell's machinery to make copies of itself. It reproduces, in a sense.

Counting against viruses being 'alive':

They DON'T respire alone.
They DON'T grow.
They DON'T excrete.
They can't make their own materials or get energy.

Counting in favour:

They have GENETIC MATERIAL (DNA or RNA).
They REPRODUCE (using the host's machinery).
They EVOLVE (mutation + selection — that's why we get new flu strains).

Most biologists treat viruses as ON THE BORDER of life — not quite alive in the way cellular organisms are, but not just chemistry either. This kind of edge case is a great MYP criterion D discussion: how do we define life when nature doesn't fit neat boxes?

Viruses: have DNA, reproduce, evolve — but only inside a host.
They don't respire, grow or excrete on their own.
Biologists divided on whether to count them as 'alive'.

How it’s examined

Criterion A tests recall and identification. Criterion D often asks about viruses or other edge cases.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

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Step-by-step worked examples — Characteristics of Living Organisms

Step-by-step solutions to past-paper-style questions on characteristics of living organisms, written exactly the way a tutor would explain them at the board.

1Recall MRS GREN
Getting started• MRS GREN
Question
What do the letters in MRS GREN stand for?
Step-by-step solution
1. Step 1
  M = Movement, R = Respiration, S = Sensitivity, G = Growth, R = Reproduction, E = Excretion, N = Nutrition.
Answer
Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
2Plants and MRS GREN
Building confidence• plants
Question
Give one example of each MRS GREN feature in a plant.
Step-by-step solution
1. Step 1
  M: leaves turn toward light. R: respires using glucose + O₂ → CO₂ + H₂O + energy. S: responds to gravity (roots down). G: grows taller and adds woody tissue. R: produces seeds. E: releases O₂ from photosynthesis. N: photosynthesis makes glucose.
Answer
Movement: phototropism. Respiration: in mitochondria. Sensitivity: gravitropism. Growth: stem and roots. Reproduction: seeds/flowers. Excretion: O₂. Nutrition: photosynthesis.
3Are viruses alive?
Stretch• viruses
Question
Use MRS GREN to argue whether a virus should be classified as living.
Step-by-step solution
1. Step 1
  Outside a host, viruses don't respire, grow or do anything else — they fail several characteristics.
2. Step 2
  Inside a host, they DO reproduce (hijack host machinery) and they evolve.
3. Step 3
  Conclusion: viruses are on the border of life. They have SOME features but not all — most biologists count them as 'biological entities' rather than fully alive.
Answer
Viruses meet some MRS GREN features (reproduce, evolve, have DNA) but only inside a host. They lack respiration, growth and excretion on their own. Most biologists treat them as borderline.

Key Definitions and Keywords — Characteristics of Living Organisms

Definitions to memorise and the exact keywords mark schemes credit for characteristics of living organisms answers — sharpened from recent examiner reports for the 2026 IB MYP Sciences sitting.

MRS GREN
Examiner keyword
Mnemonic for the seven characteristics of living organisms: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
Autotroph
Examiner keyword
An organism that makes its own food, usually by photosynthesis (e.g. plants, algae).
Heterotroph
Examiner keyword
An organism that obtains food by consuming other organisms (e.g. animals, fungi).

Common Mistakes and Misconceptions — Characteristics of Living Organisms

The traps other students keep falling into on characteristics of living organisms questions — taken from recent IB MYP Sciences examiner reports and mark schemes — and how to avoid them.

✕Saying plants don't move.
Why it happens
They look still.
How to avoid it
Plants move — slowly, mostly parts of themselves (leaves toward light, roots toward water). All seven MRS GREN features apply.
✕Calling a grape absorbing water 'growth'.
Why it happens
It does get bigger.
How to avoid it
Growth means adding NEW cells or cell material — not just inflating with water.

Practice questions

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Characteristics of Living Organisms — frequently asked questions

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