Why do plants have cell walls and animals don't?

Plants have cell walls, while animals do not, due to differences in their evolutionary history, structure, and the functions of their cells.

Plants:

1. **Structural Support:**

   • The primary function of plant cell walls is to provide structural support to plant cells. Plant cells have a rigid cell wall composed mainly of cellulose, a complex carbohydrate. This rigid structure helps plants maintain their shape and withstand the pressure generated by the influx of water during osmosis.

2. **Protection:**

   • Cell walls protect plant cells from external mechanical damage and pathogens. The tough and rigid cell wall acts as a barrier, preventing physical damage and helping to resist the entry of pathogens.

3. **Water Regulation:**

   • The cell wall also plays a role in regulating water balance. It allows water to pass through while preventing the cell from bursting due to excessive water uptake. This is crucial for turgor pressure, which helps maintain cell and plant rigidity.

4. **Support for Growth:**

   • As plants grow, new cells are continuously added. The cell walls allow for the elongation of cells while maintaining structural integrity.

Animals:

1. **Extracellular Matrix:**

   • Instead of cell walls, animal cells are surrounded by an extracellular matrix (ECM) made up of proteins and other molecules. The ECM provides structural support to animal tissues, but it is more flexible than the rigid cell walls of plants.

2. **Cell-to-Cell Communication:**

   • Animal cells rely on direct cell-to-cell communication through tight junctions, desmosomes, and gap junctions. The absence of rigid cell walls allows for greater flexibility and mobility in animal tissues.

3. **Adaptation to Environment:**

   • Animals have evolved a wide range of adaptations for mobility, and the absence of a rigid cell wall allows for more flexibility and the ability to change shape. This is crucial for processes like muscle contraction and the movement of cells during development.

4. **Phagocytosis:**

   • Animal cells, particularly certain immune cells, use a process called phagocytosis to engulf and digest particles. The flexibility of the cell membrane is essential for this process.

In summary, the presence of cell walls in plants and their absence in animals are adaptations that have evolved to suit the specific needs and lifestyles of each group of organisms. The rigid cell walls of plants provide structural support and protection, while the absence of cell walls in animals allows for greater flexibility, mobility, and adaptability to diverse environmental conditions.