7.2.4 Importance of Protists to Humans Protists are both useful and harmful to humans.
Useful protists:
Dinoflagellates: They are a great source of food for small marine and freshwater animals which are used as palatable food by humans.
Diatoms are also a source of oxygen for aquatic animals. Brown algae are used as food and fertilizer in many countries, from it we also get vitamins A, C, D, and E.
Red algae is used as a source of agar (algine) which is produced from the mucilaginous cell wall. Agar is used to make capsules for vitamins and drugs, dental impressions, base for cosmetics and also used in the laboratory as culture media for bacterial growth.
Antiseptic role:
Algae is used in medicines, Chlorella is used in the synthesis of antibiotics, and its agar is also used for stomach diseases. Chlorella has been used as an experimental organism in research for photosynthesis.
Green algae are important producers and are used as experimental organisms for photosynthesis in research laboratories (Such as Chlorella).
Algae are used as a new food source; single-cell protein (SCP) is derived from algae. Chlorella is sold as "health food" especially in Taiwan and Japan. Protists are used for the study of genetics and other physiological processes.
In aquatic ecosystems, zooplanktons (protozoans) feed on phytoplanktons and are the most important primary consumers in a food c
Harmful effects of protists:
In some places, protists act as pollutants. Sometimes they become the reason for the closing of pipes. Phytophthora causes late blight disease in potatoes. Many, protozoans cause diseases in human beings, such as malaria is caused by Plasmodium. According to the World Health Organization about one to two million people die each year from this infectious disease.
Entamoeba histolytica causes amoebic dysentery while Trypanosoma causes African sleeping sickness. Many protozoans also cause diarrhea. Acanthamoeba, a protozoan causes eye infections in contact lens users.
7.3 Kingdom Fungi
Fungi are eukaryotic spore-bearing thallophytes which lack chlorophyll. They are either saprotrophic or parasitic and possess a chitinous cell wall. They live both in dark and light environments. The study of fungi is called mycology and the person who studies fungi is called mycologist. 7.3.1 General characteristics of fungi.
Fungi have a wide range of habitats, may be aquatic or terrestrial, and many are parasites of plants and animals. Fungi range in size from microscopic (such as yeast) to very large up to two meters (such as toadstool).
Modes of life in fungi:
They live as saprotrophs, parasites, or mutualists, few are predatory. Fungi morphologically differ from other organisms: Their plant body is thallus which is mostly a multicellular structure known as mycelium (Gk. Filaments). The mycelium is an interwoven mass of thread-like filaments called hyphae (Gk. Web).
There are two types of hyphae, septate or aseptate (coenocytic hyphae) are made of one cell with many nuclei that is no cross wall or septum between nuclei, e.g. Rhizopus. Septate hyphae are made up of many cells separated by a porous partition called septum, e.g., in Penicillium.
Their cell wall contains chitin, which has high tensile strength and prevents the osmotic bursting of cells. It has also more resistance to decay than cellulose and lignin (found in plants' cell walls).
All fungi being nutritionally absorptive heterotrophs, digest organic food outside the body and then absorb the digested food into body cells. Many are decomposers. They store carbohydrates in the form of glycogen.
Fungi are non-motile in all stages of their life i.e., lack flagella, move towards a food source by growing take durch towards it. Flagella are also absent both in fungi and in red algae, thus most mycologists believe that fungi probably evolved from red algae. A fungus reproduces both asexually and sexually."
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