Organs
An organ is a structure made of two or more tissue types working together to perform a specialised function. For example, the stomach contains epithelial, connective, muscle, and nervous tissues. The tissues are arranged so that the organ can carry out digestion, movement, protection, and coordination.
Sense organs
Sense organs contain receptors that detect changes called stimuli. The eye detects light, the ear detects sound and helps with balance, the nose detects chemicals in the air, the tongue detects dissolved chemicals, and the skin detects touch, pressure, temperature, and pain.
| Sense organ | Stimulus detected | Receptor or structure involved |
|---|---|---|
| Eye | Light | Photoreceptors in the retina |
| Ear | Sound and movement | Receptors in the inner ear |
| Nose | Airborne chemicals | Olfactory receptors |
| Tongue | Dissolved chemicals | Taste receptors |
| Skin | Touch, pressure, temperature, and pain | Receptors in the skin |
Organ systems
An organ system is a group of organs that cooperate to perform a major body function. The digestive system processes food, the respiratory system exchanges gases, and the circulatory system transports substances between organs. Systems do not work independently: the circulatory system supplies oxygen from the lungs to respiring cells and carries carbon dioxide back to the lungs.
Levels of organisation
- Cells form tissues.
- Tissues form organs.
- Organs form organ systems.
- Organ systems work together in the complete organism.
Revision questions
- What is an organ?
- Name five human sense organs or sensory structures.
- State the stimulus detected by the eye, ear, nose, tongue, and skin.
- Explain why organ systems depend on one another.
