Plastids are absent in cheek cells because cheek cells are animal cells, and plastids are organelles specific to plant cells (as stated in the provided reference).
Understanding Plastids and Cell Types
To understand why cheek cells lack plastids, it's crucial to understand the fundamental differences between plant and animal cells.
Plant Cells vs. Animal Cells
| Feature | Plant Cells | Animal Cells |
|---|---|---|
| Cell Wall | Present (made of cellulose) | Absent |
| Chloroplasts | Present (a type of plastid) | Absent |
| Vacuoles | Large, central vacuole | Small, multiple vacuoles |
| Shape | Relatively fixed | Irregular and flexible |
| Plastids | Present (chloroplasts, chromoplasts, leucoplasts) | Absent |
What are Plastids?
According to the reference, plastids are membrane-bound organelles that perform crucial tasks like the production and storage of significant chemical substances. They are primarily responsible for:
- Photosynthesis: Chloroplasts contain chlorophyll and are the site of photosynthesis.
- Storage: Plastids store substances like starch, lipids, and proteins.
- Pigment Synthesis and Storage: Chromoplasts are responsible for the color of fruits and flowers.
Cheek Cells: Function and Characteristics
Cheek cells, which line the inside of the mouth, are animal cells. Their primary function is to:
- Provide a protective barrier.
- Participate in limited absorption and secretion.
Since cheek cells don't need to perform photosynthesis or store large amounts of substances like starch, they don't require plastids. Their structure is optimized for protection and limited transport, not for the functions that plastids perform.
