The high concentration of materials in the vacuole causes water to diffuse into the cell, increasing its volume. Because of the cell wall, however, the amount of space into which the cell can expand is limited. The cell thus exerts outward pressure on its cell wall, and when all cells are maintaining this pressure, the plant gains rigidity. You can notice this by comparing crisp fresh celery with celery that has sat around and grown limp. The old celery has lost fluids, and is no longer rigid.
Plastids manufacture food through photosynthesis.
Plastids are perhaps the most important feature of plants, that is, from the perspective of animals that live on land. The plastid is an organelle which contains chlorophyll . The chlorophyll captures the energy of light, and makes it accessible to the plant for photosynthesis . This provides the energy plants use to manufacture sugars, which are then used as a fuel source for continued growth. The sugars are often linked together for easy storage into a complex carbohydrate called starch .