How Cells Are Organised (KS3)
What does “Cell Organisation” mean?
In organisms made of lots of cells (called multicellular organisms, like animals and humans), the cells aren’t just randomly placed — they are organised into levels.
Each level has a special job and builds up into the next one.
🧱 Levels of Organisation (from smallest to largest):
Cell
🔸 The basic unit of life
🔸 Example: Epithelial cell (lines the stomach and intestines, helps absorb nutrients)
Tissue
🔸 A group of similar cells working together
🔸 Example: Epithelial tissue (made up of epithelial cells, protects internal surfaces)
Organ
🔸 A group of different tissues working together to do a specific job
🔸 Example: Stomach (contains muscle, epithelial, and glandular tissues)
Organ System
🔸 A group of organs working together
🔸 Example: Digestive system (includes stomach, intestines, liver)
Organism
🔸 A whole living thing made of many organ systems
🔸 Example: A human or any animal
🐾 Example from an Animal:
➡️ Epithelial Cells
make up →
➡️ Epithelial Tissue
which forms part of →
➡️ Stomach (Organ)
which is part of →
➡️ Digestive System (Organ System)
which belongs to →
➡️ The Whole Animal (Organism)
💡 Key Terms
| Term | Definition |
|---|---|
| Cell | Smallest unit of life |
| Tissue | Group of similar cells |
| Organ | Group of different tissues working together |
| Organ System | Group of organs working together for a bigger function |
| Organism | The complete living thing (like a human or animal) |
Cells → Tissues → Organs → Organ Systems → Organism
MORE INFO
🧱 Levels of Organisation in Animals
1️⃣ Cells – The Basic Units of Life
An animal cell has:
- Nucleus – controls the cell
- Cytoplasm – site of chemical reactions
- Cell membrane – controls what enters and exits
- Mitochondria – releases energy
- Ribosomes – makes proteins
👉 Example: Epithelial cells
- Found lining the stomach and intestines
- Their job: absorb nutrients and protect internal organs
2️⃣ Tissues – Groups of Similar Cells Working Together
A tissue is a group of similar cells with a common function.
👉 Example: Epithelial tissue
- Made of epithelial cells
- Covers and protects body surfaces and lines internal organs
🧠 Other examples of tissues in animals:
- Muscle tissue – contracts to cause movement
- Nervous tissue – sends signals
- Connective tissue – holds parts together (like blood or fat)
3️⃣ Organs – Groups of Tissues Working Together
An organ is made of different types of tissue working together for a job.
👉 Example: Stomach
- Made of:
- Muscle tissue (to churn food)
- Epithelial tissue (to protect and absorb)
- Glandular tissue (to produce digestive juices)
4️⃣ Organ Systems – Organs Working Together
An organ system is a group of organs that perform a big function together.
👉 Example: Digestive (Alimentary) System
- Includes:
- Mouth – chews food
- Esophagus – carries food to stomach
- Stomach – breaks down food
- Small intestine – absorbs nutrients
- Large intestine – absorbs water and forms waste
🧠 This system works to digest food and absorb nutrients to give energy to the body.
5️⃣ Organism – A Complete Living Animal
All the organ systems (like digestive, circulatory, respiratory) work together to make a full organism.
👉 Example: A human or any animal