Fungi – AEAS精读 (Y10-12)

Fungi, of which there are over 100,000 species, including yeasts and other single-celled organisms as well as the common molds and mushrooms, were formerly classified as members of the plant kingdom. However, in reality they are very different from plants and today they are placed in a separate group altogether. The principal reason for this is that none of them possesses chlorophyll, and since they cannot synthesize their own carbohydrates, they obtain their supplies either from the breakdown of dead organic matter or from other living organisms. Furthermore the walls of fungal cells are not made of cellulose, as those of plants are, but of another complex sugarlike polymer called chitin, the material from which the hard outer skeletons of shrimps, spiders, and insects are made. The difference between the chemical composition of the cell walls of fungi and those of plants is of enormous importance because it enables the tips of the growing hyphae, the threadlike cells of the fungus, to secrete enzymes that break down the walls of plant cells without having any effect on those of the fungus itself. It is these cellulose-destroying enzymes that enable fungi to attack anything made from wood, wood pulp, cotton, flax, or other plant material.

The destructive power of fungi is impressive. They are a major cause of structural damage to building timbers, a cause of disease in animals and humans, and one of the greatest causes of agricultural losses. Entire crops can be wiped out by fungal attacks both before and after harvesting. Some fungi can grow at +50°C, while others can grow at -5°C, so even food in cold storage may not be completely safe from them. On the other hand, fungi bring about the decomposition of dead organic matter, thus enriching the soil and returning carbon dioxide to the atmosphere. They also enter into a number of mutually beneficial relationships with plants and other organisms. In addition, fungi are the source of many of the most potent antibiotics used in clinical medicine, including penicillin.

 

真菌,其中有超过10万种,包括酵母和其他单细胞生物以及常见的霉菌和蘑菇,以前被归类为植物界的成员。然而,实际上它们与植物非常不同,而今天它们完全被放在一个单独的组中。其主要原因是它们都没有叶绿素,由于它们不能合成自己的碳水化合物,它们可以从死有机物质或其他生物体的分解中获得它们的供应。此外,真菌细胞的壁不是由纤维素制成的,如植物的那些,而是由另一种复杂的糖状聚合物制成,称为几丁质,制造虾,蜘蛛和昆虫的坚硬外骨骼的材料。真菌细胞壁的化学成分与植物细胞壁的化学成分之间的差异非常重要,因为它使生长的菌丝(真菌的线状细胞)的尖端能够分泌分解植物细胞壁的酶,而不会对真菌本身的影响。正是这些破坏纤维素的酶使真菌能够攻击由木材,木浆,棉花,亚麻或其他植物材料制成的任何物质。
   真菌的破坏力令人印象深刻。它们是造成木材结构损坏的主要原因,是造成动物和人类疾病的原因,也是造成农业损失的最大原因之一。在收获之前和之后,可以通过真菌攻击消灭整个作物。有些真菌可以在+ 50°C下生长,而其他真菌可以在-5°C下生长,因此即使是冷藏食品也可能无法完全避免。另一方面,真菌导致死有机物分解,从而富集土壤并将二氧化碳返回大气。他们还与植物和其他生物建立了许多互利关系。此外,真菌是临床医学中使用的许多最有效的抗生素的来源,包括青霉素。