Question
Name the five major organ systems of the human body. For each, state its main function, one key organ, and what would happen if it stopped working.
(CBSE Class 7 Science)
Solution — Step by Step
| System | Main function | Key organ | If it fails |
|---|---|---|---|
| Skeletal | Support and protection | Bones (206 in adults) | Body cannot stand or protect organs |
| Muscular | Movement | Muscles (over 600) | No movement, no heartbeat |
| Digestive | Break down food | Stomach, small intestine | Body cannot get nutrients from food |
| Respiratory | Gas exchange (O₂ in, CO₂ out) | Lungs | Cells cannot get oxygen, die within minutes |
| Circulatory | Transport of materials | Heart | Blood stops flowing, organs fail |
No system works alone. The digestive system breaks food into nutrients. The circulatory system carries these nutrients (via blood) to every cell. The respiratory system provides oxygen that cells need to burn those nutrients for energy. The skeletal and muscular systems work together to move the body.
Think of it as a delivery network: food is the raw material, oxygen is the fuel, blood is the truck, and muscles are the workers.
- The heart beats about 72 times per minute (1 lakh times per day)
- Lungs take in about 500 mL of air per breath
- Food takes 6-8 hours to pass through the stomach and small intestine
- The smallest bone is the stapes (in the ear), smallest muscle is the stapedius
Body Systems Interconnection Map
flowchart TD
A["Digestive System"] -->|"Nutrients absorbed into blood"| B["Circulatory System"]
C["Respiratory System"] -->|"O₂ enters blood, CO₂ exits"| B
B -->|"Delivers O₂ and nutrients"| D["All body cells"]
D -->|"CO₂ waste returned"| B
E["Muscular System"] -->|"Moves bones"| F["Skeletal System"]
F -->|"Provides framework"| E
B -->|"Blood supplies muscles"| EWhy This Works
The human body is like a factory with departments. Each organ system handles one major job, but they constantly communicate through blood (circulatory system) and nerves (nervous system). If any one system shuts down, the others are affected quickly — which is why doctors monitor multiple vital signs simultaneously.
Common Mistake
Students often list the heart as part of the respiratory system. The heart belongs to the circulatory system — it pumps blood. The respiratory system includes the lungs, windpipe (trachea), and diaphragm. The two systems work closely together (the heart pumps blood to the lungs for oxygenation), but they are separate systems.