Paramecium are single cell eukaryotes that live in fresh (pure) water. They have a vacuole that contracts to expel excess water that enters the cytoplasm. Eukaryotes that live in salt water do not need these vacuoles because *

1. there is more solute inside their cytoplasm than outside it
2. there is the same amount of solute outside their cytoplasm as in it
3. salt will not enter their cytoplasm
4. water can't cross their cell membrane