ï§Most protists are single celled â Protists include any eukaryote that is not a plant, animal, or fungus âMost protists are single-celled and microscopic in size âSome are large aggregations or colonies of single-celled individuals; others are multicellular organisms.Table 20-1.Protists use diverse modes of nutrition âProtists that ingest food are typically predators âThey use extensions of the cell membrane called pseudopods to surround and engulf prey items.
Girls usually complete puberty by ages 15â17, while boys usually complete puberty by ages 16â17. The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12â13; for males, it is the first ejaculation, which occurs on average at age 13.n boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche). Testes in prepubertal boys change little in size from about 1 year of age to the onset of puberty, averaging about 2â3 cm in length and about 1.5â2 cm in width.
Usually the capability to ejaculate semen comes about one to two years after puberty starts -- often about the time pubic hair begins to grow and a boy begins his growth spurt. The average age for starting puberty is 11 1/2. This makes the average age to ejaculating semen around the age of 13. But this is only an average.