Ch 1 · Characteristics of Living Organisms · IGCSE Biology 0610
Topic 1 of 4 in Characteristics and Classification of Living Organisms — IGCSE Biology 0610 — 38 lessons.
Introduction
Biology is the study of living things, so the first job is to be clear about what "living" means. Cambridge lists seven characteristics that every living organism shows, remembered as MRS GREN. The definitions are examined word for word, and the same ideas return throughout the course: respiration, excretion and sensitivity each get a topic of their own later. Learn the exact wording now and you will keep collecting the marks for it.
Key ideas — The seven characteristics (MRS GREN)
Every living organism, from a single bacterium to a blue whale, shows all seven characteristics:
🧑🏫 Teacher's explanation
Imagine a high-security bank vault. It is a complex object, but it is not alive. Why? Because it does not do anything on its own. It does not eat, it does not breathe, and it does not fix its own broken parts. Living things are different because they are self-maintaining machines. They constantly take in energy and matter, use them to keep themselves running, and get rid of the rubbish. This constant internal activity is what separates a rock from a root.
📖 Definitions
🔍 Worked example — Easy
A student observes a crystal growing in a saturated solution of copper sulfate. The crystal increases in size over time. The student concludes the crystal is alive because it grows. Explain why this conclusion is incorrect using the MRS GREN characteristics.
🔍 Worked example — Standard
A car is driven on a road. It moves, takes in petrol (fuel), and releases carbon dioxide and water vapor from the exhaust. A student argues that because the car moves, uses fuel, and releases waste, it is alive. Use the MRS GREN characteristics to refute this argument.
🔍 Worked example — Exam-style
A virus is discovered in a sample. It has genetic material and a protein coat. When placed in a nutrient broth, it does not grow or reproduce. When placed in a culture of human cells, it causes the cells to divide and produce new viruses. Explain why the virus is often considered non-living despite its ability to reproduce inside a host.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — The Cambridge definitions
Metabolism means all the chemical reactions taking place in the cells of an organism.
🧑🏫 Teacher's explanation
Imagine a robot vacuum cleaner. It moves, it uses electricity (energy), and it can sense walls to avoid them. But is it alive? No. Why? Because it does not grow, it does not reproduce, and it does not excrete waste products of its own metabolism. It just dumps its dust bin. This is the core test: to be living, an organism must do all seven things. If it fails even one, it is not alive.
📖 Definitions
🔍 Worked example — Easy
A student observes a sunflower head turning to face the sun throughout the day. Explain why this movement does not prove the sunflower is alive, but the plant as a whole is alive.
🔍 Worked example — Standard
A student claims that a plant is heavier after drinking water, so it has grown. Explain why this statement is incorrect using the Cambridge definition of growth.
🔍 Worked example — Exam-style
A student is given a list of processes: (1) Removal of undigested food, (2) Removal of urea, (3) Removal of carbon dioxide, (4) Removal of excess water. Identify which of these are excretion and which are egestion, and explain your reasoning.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the name of the characteristic shown by the rotation of the flagellum. [1] (b) Explain why the release of ammonia is considered excretion. [2] (c) The student suggests the organism is not alive because it does not move its whole body. Explain why this conclusion is incorrect. [2] [5 marks]
Key ideas — Deciding whether something is living
Exam questions often show an unfamiliar object, such as a seed, a fungus, a flame or a robot, and ask whether it is alive. Test it against all seven characteristics, and use the definitions, not everyday meanings.
🧑🏫 Teacher's explanation
Imagine you are a detective trying to prove a suspect is a 'living' person. You cannot just look at what they are doing right now; you must check a checklist of seven biological capabilities. If the suspect is sleeping, they are not moving or eating, but they are still breathing and their body is still processing waste. Therefore, they are still alive. In biology, we use the same logic. We do not ask 'is it moving?' as the only test; we ask if it has the *capacity* for movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition.
📖 Definitions
🔍 Worked example — Easy
A student observes a candle flame. It moves (flickers), grows (gets taller), and releases gas. The student concludes it is living. Explain why this conclusion is incorrect using at least two specific characteristics from MRS GREN.
🔍 Worked example — Standard
A dormant seed is placed in a dry, dark cupboard. It shows no visible movement, no growth, and no reproduction. Is it alive? Justify your answer by referencing at least three characteristics that are still occurring or potential.
🔍 Worked example — Exam-style
A mushroom is found on a log. It does not move from place to place and does not photosynthesize. A student argues it is not living because it cannot move or make its own food. Evaluate this argument using the Cambridge definitions of nutrition and movement.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Explain why the robot is not a living organism, despite showing movement and sensitivity. (3 marks) (b) Explain why the dormant seed is considered a living organism, even though it shows no visible growth or reproduction. (3 marks) [6 marks]
Worked example
(a) Define the term excretion. [2]
🔍 Worked example — Easy
Define the term excretion in the context of human physiology.
🔍 Worked example — Standard
A student claims that plants are not alive because they do not move from place to place. Explain why this statement is incorrect using the characteristics of living organisms.
🔍 Worked example — Exam-style
A crystal of copper sulfate placed in a saturated solution increases in size over time. Explain why this is not considered growth in the biological sense.
⚠️ Common errors
Common mistakes
Practice
Answers