R.H. Whittaker proposed the five kingdom classification system which divides life into five kingdoms - Animalia, Plantae, Fungi, Protista, and Monera. Protists are single-celled organisms that can move using cilia, flagella, or amoeboid movement. They may have a cell wall or nucleus and organelles like chloroplasts. Protists obtain nutrients through photosynthesis, ingesting other organisms, or both.