1. The Protista have been grouped together for convenience, rather than grouped together because of evolutionary relationships to one another.
2. Eukaryotic mitochondria are probably derived from symbiotic nonsulfur purple bacteria, apparently in a single event because all mitochondria are the same. All eukaryotes but Pelomyxa and a few other groups possess mitochondria.
3. The three classes are the chloroplasts of red algae, containing chlorophyll a, carotenoids, and phycobilins; the chloroplasts of brown algae, diatoms, and dinoflagellates, containing chlorophylls a and c, carotenoids, and other yellow-brown pigments; the chloroplasts of the green algae, euglenoids, and plants, containing chlorophylls a and b and carotenoids. These were all certainly derived from bacteria-from cyanobacteria in the case of the red algae.
4. Fungi have chitinous cell walls, whereas oomycetes have cellulose walls. They are saprobes or parasites and are distinguished from other protists because they have zoospores with unequal flagella. They are considered harmful because they cause disease in aquatic plants and animals and caused the potato blight responsible for the infamous Irish potato famine.
5. Rhizopods are the amoeboid protists; they reproduce through binary fission and move via extensions of pseudopodia.
6. The Chlorophyta include the ancestors of the plants and are therefore significant in evolution. Chlamydomonas is an important member of this phylum because many other simple green algae resemble it, but may lack flagella; other colonial green algae like Volvox appear similar to colonies of Chlamydomonas-like cells. A collection of individuals is truly multicellular if there is a division of labor among the cells so that certain of them perform very specialized functions.
7. Alternation of generations in this context means that the life cycle alternates between a diploid sporophyte phase and a haploid gametophyte phase. One type of sporocyte (haploid, motile spores) and two types of gametophytes (haploid eggs and haploid sperm) are produced. Sperm and eggs fuse to produce the zygote, and the diploid zygote becomes the sporophyte.
8. Bacillariophyta have double, boxlike opaline silica shells and are commonly called diatoms. Diatoms reproduce sexually or asexually, splitting in half. Each half then regenerates another half, smaller than itself, then as a certain minimum size is reached, the diatom slips out of its shell and grows to full size. These individuals are diploid and resemble brown algae and dinoflagellates biochemically.
9. In Dinoflagellata, two flagella beat in grooves in the armorlike cellulose plates. Mitosis is unique in this group because it takes place solely within the nucleus and chromosomes include very small amounts of histones. Red tides are population explosions of dinoflagellates, which produce toxins harmful to vertebrates but not to the shellfish that concentrate them. Zooxanthellae are a symbiotic form of dinoflagellate found in jellyfish, sea anemones, and molluscs.
10. Some euglenoids that are otherwise identical have chloroplasts while others do not, and those possessing chloroplasts may lose them temporarily if grown in the dark, showing the difficulty of assigning them to any group. Only mitosis is exhibited by this group, but the nuclear membrane remains intact during the entire process.
11. Some species of trypanosomes have evolved mechanisms to change their glycoprotein coats, thus making development of a vaccine against specific antigens impossible. Trypanosome-caused diseases prevent the raising of cattle for meat and milk in much of Africa, contributing to drastic food shortages there.
12. The members of Ciliophora have cilia arranged in longitudinal rows or spirals around the body, unique among the protists. They are not so simple as evidence by the fact that they have modified their cilia for various specialized locomotive and feeding functions and possess complex digestive systems. The two vacuoles are (1) a food vacuole, which digests food particles, and (2) a contractile vacuole, which regulates water balance.
13. Malaria is the disease produced. It is transmitted from the mosquito to the human in the sporozoite form. The symptoms are produced by the merozoite form; the sporozoites invade red blood cells, divide within them, and cause them to rupture, releasing toxic substances. Gametocytes are transmitted from human to mosquito, and the gametes and fusion into zygotes occur in the mosquito.