Protista

Phagocytosis is used to bring large particles into the cell and involves a bulging out of part of the cell membrane. Pinocytosis is used to bring in small particles and liquids and involves the pinching off of an invagination of the cell membrane.

The protozoa responsible for the sleeping sickness, Trypanosoma gambiense, lives in the blood of animals. When an infected animal is bitten by a tsetse fly, the trypanosoma are sucked into the fly's intestines. Here they undergo a physiological change that allows them to invade the salivary glands of the fly. Every animal that is bitten by this fly now receives an injection of Trypanosoma gambiense.

Eukaryotic cilia are similar in internal structure to flagella, but are much shorter and hair-like. They can be connected at the base to contractile fibers that allow them to beat in fixed patters. Cilia may be used for locomotion or to sweep food particles toward the oral groove.

Conjugation begins when individuals of opposite mating types meet, the adhere to each other at the oral groove. The micronuclei then divide meiotically, producing four haploid nuclei each. All but one nucleus from each paramecium disintegrate. The macronucleus also disintegrates, leaving each cell with one haploid micronucleus. These remaining nuclei then divide mitotically and the two cells swap copies of their nuclei. The cells separate and the haploid nuclei fuse, leaving each cell with a new diploid micronucleus. To form a new macronucleus, the micronucleus divides several times and the resulting nuclei develop into a macronucleus.

Helped by filaments of a structural protein called actin, the cytoplasm of a cell flows beneath the cell membrane into new pseudopods, causing the cell to move in a given direction.