Edexcel iGCSE Biology-1.1 Characteristics of Living Organisms- Study Notes- New Syllabus

Characteristics of Living Organisms 

📝 Introduction

• Living things can be recognised because they all share certain basic features.
• These features separate living organisms from non-living things.

👉 To remember them, we use the classic mnemonic MRSGREN:

Movement • Respiration • Sensitivity • Growth • Reproduction • Excretion • Nutrition (+ Control of internal conditions = Homeostasis).

🍎 Nutrition

• All living things need a source of food/nutrients.
• Nutrients provide:
  • Energy → for movement, repair, and keeping warm.
  • Raw materials → for growth and cell repair.
• Plants → make food by photosynthesis.
• Animals → eat plants/other animals.

🔥 Respiration

• A chemical process in cells that releases energy from glucose.
• Energy is used for growth, repair, movement, and temperature control.
• Two main types:
  • Aerobic (with oxygen, more energy released).
  • Anaerobic (without oxygen, less energy, produces lactic acid or ethanol + CO₂).

🚮 Excretion

• Removal of toxic waste products made inside cells.
• Key examples:
  • Carbon dioxide (from respiration, breathed out).
  • Urea (from protein breakdown, excreted in urine).
  • Oxygen (in plants, released after photosynthesis).
• ❌ Not the same as egestion (which is removal of undigested food).

👀 Sensitivity (Response to Stimuli)

• The ability to detect and respond to changes in the environment.
• Examples:
  • Plants grow towards light (phototropism).
  • Humans pull back hand from a hot object.
• Helps survival → finding food, escaping danger, adapting to surroundings.

🏃 Movement

• A change in position of the whole organism or a part of it.
• Animals → run, fly, swim, walk to find food or avoid danger.
• Plants → slower movements (roots grow down, shoots grow up, flowers open/close).

⚖️ Control of Internal Conditions (Homeostasis)

• Maintaining a stable internal environment, even if the outside changes.
• Examples:
  • Humans keep body temperature close to 37°C.
  • Cells regulate water content and pH.
• Important so enzymes can work efficiently.

👶 Reproduction

• Producing new individuals of the same species → ensures survival.
• Types:
  • Asexual reproduction → one parent, offspring are identical (clones).
  • Sexual reproduction → two parents, offspring show variation.

🌱 Growth & Development

• Growth → permanent increase in size and dry mass (new cells made by cell division).
• Development → cells change and become specialised for different functions.
• In general:
  • Animals → grow up to a certain point.
  • Plants → can keep growing throughout life.

📊 Summary Table – MRSGREN

⚡ Quick Recap
MRSGREN = Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition (+ Homeostasis)
✔ Nutrition → food for energy & growth
✔ Respiration → energy release from glucose
✔ Excretion → removal of toxic wastes
✔ Sensitivity → response to environment
✔ Movement → change in position
✔ Homeostasis → stable internal conditions
✔ Reproduction → new offspring
✔ Growth → permanent increase in size