How Are Cells Organized in Multicellular Organisms?
- Multicellular organisms don't function as loose collections of cells.
- Instead, cells are arranged in a hierarchical structure, where each level builds on the one below:
- Cells form tissues,
- Tissues form organs,
- And organs form organ systems.
| Level | Description | Example |
|---|---|---|
| Cell | Basic unit of life, specialised for a specific job | Muscle cell, nerve cell |
| Tissue | Group of similar cells performing one function | Muscle tissue, epithelial tissue |
| Organ | Several tissues working together | Heart, stomach |
| Organ system | Multiple organs coordinating to perform major tasks | Circulatory system |
Tip
- A single cell cannot pump blood or digest food.
- Only groups of cells arranged in the correct structure can perform complex functions.
How Do Specialized Cells Form Tissues?
Definition
Tissue
A group of similar, specialised cells working together to perform one function.
- Tissues form when many cells of the same type organise themselves to cooperate.
- This cooperation allows tissues to perform tasks that no single cell can manage alone.
- For example, one muscle cell contracts weakly, but millions together create strong movement.The structure of the tissue always reflects its function.
Analogy
- Stronger in numbers.
- A single person pushing a car achieves nothing.
- A coordinated group can move it easily.
- Tissues use the same principle.
What Are the Main Tissue Types in Animals?
- All animal tissues fall into four major categories, each serving a distinct biological purpose.
- The table below summarizes them clearly.
| Tissue Type | What It Does | Example |
|---|---|---|
| Epithelial | Covers surfaces and protects organs | Skin, lining of gut |
| Connective | Supports, binds, or stores materials | Bone, cartilage, fat |
| Muscular | Contracts to produce movement | Skeletal muscle, heart muscle |
| Nervous | Sends signals and coordinates responses | Brain, spinal cord |
Note
All four tissue types appear in most organs, but in different proportions depending on the organ’s purpose.
What Are the Main Tissue Types in Plants?
- Plant tissues are organized differently from animal tissues because plants do not move and have different survival needs.
- Plant tissue types include:
| Tissue Type | What It Does | Example |
|---|---|---|
| Epidermal | Protective outer layer | Leaf surface |
| Xylem | Transports water and provides support | Wood, veins in leaves |
| Phloem | Moves sugars through plant | Stem vascular bundles |
| Mesophyll | Performs photosynthesis | Palisade and spongy mesophyll |
Tip
- Mesophyll tissue contains many chloroplasts.
- This is why most photosynthesis happens in the leaves, not roots.
Self review
- What is the hierarchy of organisation in multicellular organisms?
- Why do multicellular organisms need specialised cells?
- What makes a tissue different from a single specialised cell?
- What are the four main tissue types in animals?
