Onion cells are not green because they don't need to be; they don't get any light.
The Role of Chloroplasts and Chlorophyll
Plants are green because of structures called chloroplasts, which contain a green pigment called chlorophyll. Chlorophyll is essential for photosynthesis, the process where plants use light energy to convert carbon dioxide and water into glucose (sugar) for food.
- Chloroplasts: Organelles within plant cells where photosynthesis takes place.
- Chlorophyll: The green pigment inside chloroplasts that captures light energy.
Why Onion Cells Lack Chloroplasts
Onions typically grow underground, where they are shielded from sunlight.
| Feature | Onion Cells | Leaf Cells |
|---|---|---|
| Light Exposure | Minimal to none | High |
| Chloroplasts | Absent | Present |
| Chlorophyll | Absent | Present |
| Photosynthesis | Does not occur | Occurs |
| Primary Function | Storage of energy reserves (e.g., sugars) | Production of energy through photosynthesis |
Since onion cells get no light, they do not need chloroplasts. They obtain their energy from other parts of the plant that do photosynthesize, such as the leaves. These leaves produce sugars that are then transported to the onion bulb for storage. The onion bulb serves as a storage organ, containing energy reserves to fuel the plant's growth and reproduction.
