(e) Aplcomplexans
Apicomplexans are a large group of parasitic protozoa, some of which cause serious diseases such as malaria in humans. Apicomplexans lack specific structures for locomotion but move by flexing. At some stage in their lives, they develop a spore, a small infective agent transmitted to the next host, many apicomplexans spend part of their life in one host and part in a different host species (fig. 7.7).
Fig. 7.7the life cycle of the malarial parasite (plasmodium).
Plasmodium, the apicomplexan that causes malaria, enters human blood through the bite of an infected female anopheles mosquito. Plasmodium first enters liver cells and then red blood cells, where it multiplies. When each infected red blood cell bursts, many new parasites are released. The released parasites infect new red blood cells, and the process is repeated. The simultaneous bursting of millions of red cells causes the symptoms of malaria; a chill, followed by high fever caused by toxic substances that are released and affect other organs of the body (Fig. 7.7).
The algae : Plant like protists
Algae (singular alga) are photosynthetic protists, carrying out probably 50 to 60 percent of all the photosynthesis on earth (plants account for most of the rest).
Algae differ from the plants in their sex organs which are unicellular and the zygote is not protected by the parent body. A plant zygote, on the other hand, grows into a multicellular embryo that is protected by parental tissue.
Algae exhibit a remarkable range of growth forms. Some are unicellular; others are filamentous. Filaments are composed either of distinct cells or coenocytes (multinucleate structures that lack cross-walls), still others (e.g. seaweeds) are multicellular and intricately branched or arranged in leaf-like extensions. A body which is not differentiated into true roots, stems and leaves and lacks xylem & phloem is called a thallus.
In addition to green chlorophyll a, yellow and orange carotenoids, which are photosynthetic pigments are found in all algae, other algal phyla possess a variety of other pigments (such as xanthophylls and phycoerythrin) that are also important in photosynthesis. Classification into phyla is largely based on their pigment composition.
Algal life cycles show extreme variation, but all algae except members of the phylum Rhodophyta (red algae) have forms with flagellated motile cells in at least one stage of their life cycle.
Almost all algae are aquatic. When actively growing, algae are restricted to damp or wet environments, such as the ocean; freshwater ponds, lakes, and streams; hot springs; polar ice; moist soil, trees, and rocks. Table 7.2 summarizes the classification of algae.
Table 7.2classification of the photosynthetic protoctists
phylum | Common name | Form | Locomotion | Pigments | Examples |
| Euglenophyta | Euglenoids | Unicellular | Two flagella one long one short | Chl.a, Chl.bCarotenoids | Euglena |
| Pyrrophyta | Dinoflagellates | Unicellular | Two flagella | Chl.a, Chl. c carotenes including Fucoxanthin | Gonyaulax, Cratium |
| Chrysophyta | Diatoms | Usually unicellular | Usually none | Chl. a, Chl. cCarotenes including Fucoxanthin | Diatoma, Frequilaria Pinnularia |
| Phaeophyta | Brown algae | Multicellular | Two flagelia on reproductive cells | Chl.a, Chl. cCarotenes including Fucoxanthin | Focus, Macroeystis |
| Rhodophyta | Red algae | Multicellular or unicellular | None | Chl.a, carotenes Phycoerythrin | Chondrus Polysiphonia |
| Chlorophyta | Green algae | Unicellular, colonial, multicellular | Most have flagella | Chl.a,Chl.b, carotene | Chlorella, ulva, Acetabularia |