Fill in the blanks:
1. In plant cells the vacuoles can occupy up to …a… of the volume of the cell.
2. In plants, the tonoplast facilitates the transport of a number of ions and other materials …b… concentration gradient into the vacuole, hence their concentration is significantly …c… in the vacuole than in the cytoplasm.
3. In Amoeba the …d… vacuole is important for excretion.
4. In many cells, as in protists …e… vacuoles are formed by engulfing the food particles.