Explanation:
Protists are mostly one-celled organisms. Some make
their own food, but most take in or absorb food. Most
protists move with the help of flagella, pseudopods, or
cilia. Some protists, like the one-celled amoeba and paramecium, feed on other
organisms.
Fungus-like protists share many features with fungi. Like fungi, they are heterotrophs, meaning they must obtain food outside themselves. They also have cell walls and reproduce by forming spores.
Ciliates reproduce asexually by division: the micronucleus undergoes mitosis, while in most ciliates the macronucleus simply pinches apart into two. This process is shown in the drawing above. However, ciliates also reproduce sexually, through a process known as conjugation. Conjugation is often induced by lack of food. Two ciliates of opposite mating types come close together and form a cytoplasmic bridge between the two cells; the micromuclei divide by meiosis, the macronuclei disintegrate, and the conjugating cells exchange haploid micronuclei over the cytoplasmic connection. They then separate, reform new macronuclei from their micronuclei, and divide, but remember that the essence of sexual reproduction is forming a new organism from the combined genetic material of parents. After conjugation, each ciliate partner has acquired new genetic material, and divides to give rise to progeny with a new combination of genes. This is essential to the survival of ciliate lineages; most ciliates cannot reproduce indefinitely by asexual fission, and eventually die out if prohibited from conjugating.
One convenient way to categorize protozoans is by how they move. Some move rapidly, while others creep slowly. Still others are not capable of active movement at all, but instead rely on a host organism to supply their food.
Protozoans With Flagella
Zooflagellates (zoh oh FLAJ uh lits) move by means of one or more flagella. (Recall from Chapter 6 that flagella are long, thin, whip-like cellular projections.) Zooflagellates generally reproduce asexually by binary fission. Recall that asexual reproduction results in genetically identical offspring.
Sarcodines reproduce sexually by syngamy (fusion of two gametes) and asexually by division or budding. In multinucleate forms, cytoplasmic division with distribution of the nuclei occurs.Members of the phylum Sarcodina are ameboid. They move about by using pseudopods and usually eat by phagocytosing food particles, usually bacteria. Some amoeba form calcium carbonate or silica skeletons called tests to protect themselves.
The sporozoans are able to form spore-like cells, from which they get their name. Sporozoans do not have flagella, cilia, or pseudopodia. They are capable of gliding movements. ... The apical complex secretes enzymes which allow the sporozoan to enter a host cell.Apicomplexan, also called sporozoan, any protozoan of the (typically) spore-producing phylum Apicomplexa, which is called by some authorities Sporozoa. ... Apicomplexans feed by absorbing either dissolved food ingested by the host (saprozoic nutrition) or the host's cytoplasm and body fluids.Protozoa reproduce asexually by fission, schizogony, or budding. Some protozoa can also reproduce sexually. Relatively few protozoa cause disease
