This foundational lesson explores the essential features that distinguish living things from non-living things.

1. Short Notes: Core Concepts

All living organisms share a set of common characteristics. There are eight key features to remember:

1. Cellular Organization: All living things are made of one or more cells. This is the basic level of organization.

   • Unicellular: Organisms made of a single cell (e.g., Amoeba, Bacteria).

   • Multicellular: Organisms made of many cells. These cells group together to form tissues, tissues form organs, organs form systems, and systems make up the organism. (Cell -> Tissue -> Organ -> System -> Organism).

2. Nutrition: The process of obtaining or making food to get energy and raw materials for growth and repair.

   • Autotrophic: Organisms that make their own food (e.g., plants through photosynthesis).

   • Heterotrophic: Organisms that consume other organisms for food (e.g., animals).

3. Respiration: This is not the same as breathing. It is the chemical process inside cells that breaks down food (glucose) to release energy.

   • Glucose + Oxygen → Carbon Dioxide + Water + Energy

4. Irritability and Co-ordination (Sensitivity): The ability to detect and respond to changes in the internal or external environment.

   • A change that causes a response is called a stimulus (e.g., light, sound, touch).

   • The reaction is the response (e.g., a plant growing towards light, you pulling your hand away from a hot object).

5. Excretion: The removal of metabolic waste products from the body. These are harmful substances produced by chemical reactions inside cells.

   • Examples: Carbon dioxide (from respiration), urea (in urine).

   • Important: Excretion is not the same as egestion (removing undigested food as faeces).

6. Movement: A change in the position of the whole organism or parts of the organism.

   • Animals usually move their whole body (locomotion).

   • Plants show movement in parts, like leaves turning to face the sun.

7. Reproduction: The process of producing new individuals (offspring) to ensure the continuation of the species.

   • Asexual: Involves only one parent; offspring are genetically identical.

   • Sexual: Involves two parents; offspring have a mix of genetic traits.

8. Growth and Development: Growth is the permanent increase in the size and dry mass of an organism. Development involves an increase in complexity.

2. Tips & Tricks for the Exam

• Mnemonic for the 8 Characteristics: A good way to remember the list is MRS C GREN.

  • M - Movement

  • R - Respiration

  • S - Sensitivity

  • C - Cellular Organization

  • G - Growth

  • R - Reproduction

  • E - Excretion

  • N - Nutrition

• Respiration vs. Breathing: This is a common point of confusion. Breathing is the physical act of taking air in and out of the lungs. Respiration is the chemical reaction in cells that releases energy.

• Excretion vs. Egestion: Another tricky pair. Excretion removes metabolic waste (from chemical reactions, like urine). Egestion removes undigested waste (faeces).

3. Important Points & Common Exam Questions

• Listing the Characteristics: You may be asked to list some or all of the eight characteristics of living organisms. Use the MRS GREN mnemonic to help.

• Why is a Car Not Alive? A common question asks you to explain why a non-living thing (like a car or a fire) is not alive, even though it shows some characteristics (e.g., a car moves, uses fuel/nutrition, and releases waste/excretes).

  • Answer: A car is not considered living because it does not possess all the characteristics of life. For example, it is not made of cells, it cannot grow on its own, and it cannot reproduce.

• The Case of the Virus: Viruses are a special case because they are on the border of living and non-living.

  • Living characteristics: They have genetic material (DNA/RNA) and can reproduce.

  • Non-living characteristics: They are not made of cells and can only reproduce inside a living host cell. Outside a host, they are inactive like a non-living particle.