Multicellularity = Multiple Cells, Single Unit
Definition
Multicellularity
Multicellularity refers to organisms composed of multiple cells functioning together as a single unit.
- Cells cooperate, specialize, and typically cannot survive independently.
- This adaptation has evolved multiple times independently, demonstrating convergent evolution (e.g., animals, fungi, plants).
These independent origins suggest that the benefits of multicellularity outweigh its challenges.
Multicellularity Provides Advantages
1. Larger Body Size
- Allows organisms to grow larger, offering evolutionary benefits:
- Predator avoidance: Larger size deters smaller predators.
- Resource access: Increased size provides better access to sunlight or prey.
- Environmental stability: Larger bodies buffer against temperature or moisture fluctuations.
- Imagine a single-celled alga floating in a pond.
- It is highly susceptible to being eaten by a predator like a ciliate.
- In contrast, multicellular algae like kelp grow large enough to escape most predators, allowing them to dominate their habitats.
To support their larger size, multicellular organisms often develop structural adaptations, such as skeletons in animals or rigid cell walls in plants.
2. Cell Specialization and Division of Labor
- Specialization enables complex tasks that unicellular organisms cannot perform.
- This increases efficiency by allowing cells to focus on specific functions.
- Animals: Muscle cells enable movement, nerve cells transmit signals; red blood cells transport oxygen.
- Plants: Photosynthetic cells produce energy, xylem cells transport water and nutrients.
3. Longer lifespan
- Organisms can replace damaged cells.
