A simple organism is a living thing that is made up of one cell and is not complex. ALGA, with four letters, is a type of simple organism that is typically found in water and is photosynthetic. MONAD, with five letters, is another type of simple organism that is also single-celled and is usually found in water. AMOEBA, with six letters, is a type of single-celled organism that moves by changing its shape and is found in water or soil. Ameba, with five letters, is another type of single-celled organism that moves by changing its shape and is found in water or soil.