7 蒋悟生生物专业英语 第七课.docVIP

Lesson Seven Fungi: The Great Decomposers Characteristics of Fungi The approximately 175,000 species of fungi include some of the simplest multicellular organisms. Fungi have a variety of lifestyles. They may be saprobes that decompose dead organic matter; they may be parasites which obtain nutrients from living hosts; or they may live in symbiotic relationships with algae or with the roots of higher plants. In spite of these variations, however, all fungi carry out extracellular digestion: they secrete enzymes that digest organic matter, and then they absorb the resulting nutrients. (存在的)大约175,000种真菌包括一些最简单的多细胞生物。真菌有各种各样的生活方式。它们可能是分解死有机物的腐生生物;它们可能是寄生虫，从活的宿主那里获取营养;或者它们可能与藻类或高等植物的根存在共生关系。尽管存在这些变化，所有的真菌都进行细胞外消化:它们分泌消化有机物的酶，并吸收产生的营养物质。 Most fungi have the same basic body structure consisting of a main body or thallus（菌体） composed of filaments called hyphae（菌丝）. In most species the walls of hyphal cells contain chitin（几丁质）. Hyphae in certain species may become specialized to form rhizoids（假根）, which serve as rootlike anchors, or they may become the feeding structures known as haustoria. Finally, hyphae may or may not be septate-having cross walls that segregate independent cells, each with at least one nucleus. Lower fungi are coenocytic [si:n?sitik]; that is, they are one mass of cytoplasm that contains multiple nuclei. 大多数真菌具有相同的由菌体形成的基本结构，菌体由称做菌丝的细丝组成。大多数种类菌丝细胞壁含有几丁质。某些物种的菌丝可以特化形成假根，充当根状锚（固定物），或者它们可以成为被称为吸器的取食结构。最后，菌丝可能是不分隔的，也可能是分隔的——即具有分隔独立细胞的横隔，每个细胞至少有一个核。低等真菌是多核体;也就是说，它们是包含多个核的一团细胞质。 Hyphae grow and branch to form a filamentous network called a mycelium（菌丝体）. Food is digested and absorbed at the tip of each hyphae; more hyphae ?[ˋhaifi?] are generated as this process continues. As a result, fungi may grow very rapidly. Growth depends on mitosis and the rapid manufacture of cytoplasm; fungal mitosis is unique in that it occurs within the nucleus. Hyphae from genetically distinct individuals may fuse to form a heterokaryon?[het?r?uk?ri?n] -a single cytop