A human gamete, for example, has only 23 chromosomes. The full complement of chromosomes is restored when a male gamete fertilizes an egg. Consequently, the offspring resembles both parents. Spherical or dumbbell-shaped nuclei containing DNA have been found in the cytoplasm of some bacteria. The cytoplasm of bacteria also contains grains of stored food, vacuoles, and ribosomes.
Many types of bacteria live as parasites on higher organisms.
Bacteria are plantlike, but most lack the chlorophyll to make their food. However, some types of one-celled plants called algae do bear chlorophyll. Although there are about 20,000 species of protozoans, the amoeba and the paramecium are perhaps the most commonly known. Many species of protozoans can hunt and catch food. Large plants and animals are made up of millions or billions of cells.