IGCSE Biology 0610 - 2.1 Cell Structure

Objective: Describe the meaning of the terms: cell, tissue, organ, organ system and organism.

1. Cell

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that can replicate independently.

• Cells are microscopic.
• They carry out all the life processes.
• Examples: animal cells, plant cells, bacterial cells.

2. Tissue

A tissue is a group of similar cells that perform a specific function. Cells within a tissue are usually similar in structure and function.

• Tissues are composed of many cells working together.
• Different types of tissues exist in multicellular organisms.
• Examples: epithelial tissue, connective tissue, muscle tissue, nervous tissue.

3. Organ

An organ is a structure made up of different tissues that work together to perform a specific function.

• Organs are composed of multiple tissue types.
• Examples: heart, lungs, stomach, brain.

4. Organ System

An organ system is a group of organs that work together to perform a major function in the body.

• Organ systems are essential for survival.
• Examples: digestive system, circulatory system, respiratory system, nervous system.

5. Organism

An organism is a complete, living being. It is made up of one or more organ systems working together to maintain life.

• Organisms can be unicellular (single-celled) or multicellular (many-celled).
• Examples: bacteria, fungi, plants, animals.

Level of Organization	Definition	Examples
Cell	The basic structural and functional unit of life.	Animal cells, Plant cells, Bacterial cells
Tissue	A group of similar cells performing a specific function.	Epithelial tissue, Connective tissue, Muscle tissue
Organ	A structure made up of different tissues working together.	Heart, Lungs, Stomach, Brain
Organ System	A group of organs working together to perform a major function.	Digestive system, Circulatory system, Respiratory system
Organism	A complete, living being.	Bacteria, Plants, Animals