lesson seven eight

1、Lesson Seven(4学时) Fungi: The Great Decomposers Characteristics of FungiThe 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 nutr

2、ients from living hosts; or they may live in symbiotic relationships with algae or with the roots of higher plants. 包括最简单的多细胞生物在内，真菌大概有175，000种。真菌有多种生命形式。他们可能是分解无生命的腐生菌；也可能是寄生菌；或者与藻类共生，或者与高等植物共生。In spite of these variations veri:enz, however, all fungi carry out extracellular digestion ekstrseljul d

3、adestn : they secrete enzymes that digest organic matter, and then they absorb the resulting nutrients. 不管如何变化，所有真菌都是细胞外消化。他们分泌酶消化有机物，然后吸收有效的营养物质。 Most fungi have the same basic body structure consisting of a main body or thallus ls composed of filaments called hyphae hafi:. In most species the wall

4、s of hyphal hafl cells contain chitin katn. Hyphae in certain species may become specialized to form rhizoids razdz, which serve as rootlike anchors, or they may become the feeding structures known as haustoria h:st:r. 大多数真菌有同样的基本结构，即由菌丝组成的菌体。大多数真菌的细胞壁含有明角质。某些种类的菌丝可能特化形成假根，具有根样的固定作用，或者他们成为饲喂结构称吸器。Fi

5、nally, 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:nstk; that is, they are one mass of cytoplasm that contains multiple nuclei. 菌丝或有细胞隔膜或没有细胞隔膜，但至少有一个细胞核。低级真菌是多核体的，即，一大团细胞质含有多个细胞核。 分子孢子Hyphae grow

6、 and branch to form a filamentous network called a mycelium masi:lm. Food is digested and absorbed at the tip of each hyphae; more hyphae 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 mitosi

7、s is unique in that it occurs within the nucleus. 菌丝生长形成分支，进而形成网状结构称为菌丝体。在菌丝尖端，食物被消化并吸收；这个过程能持续产生更多菌丝。结果，真菌生长很快。生长靠有丝分裂和细胞质的快速产生。真菌的有丝分裂很独特，即它只发生在细胞核里。Hyphae from genetically distinct individuals may fuse to form a heterokaryonhetrkrn -a single cytoplasm with dissimilar nuclei. 遗传学明显不同的菌丝个体融合形成异核体同一

8、个细胞质中含有不同的细胞核。 As nonmotile heterotrophs, fungi must eventually be able to find new sources of nutrients. This function is fulfilled by spores, the fungal reproductive bodies. Spores may be home on aerial eril hyphae, which discharge spores into the air, and depending on the species they may haploid

9、 or diploid. 作为不会移动的异养生物，真菌最终能够发现营养新资源的。这个过程由孢子来完成，即真菌的生殖体。孢子可能是在气生菌丝的中心，将孢子释放到空气中，依赖物种不同，可能是单倍体也可能是二倍体。There are two main categories of spores: (1) dispersal spores, which are usually short-lived and are produced in large numbers during active fungal growth; and (2) survival spores, which are usual

10、ly produced in smaller numbers and at a time in the life cycle when the fungus is under some kind of environmental stress. 有两种主要的孢子：（1）分散的孢子，通常生命期短，数量大，主要存在于活跃的菌丝生长阶段；（2）存活孢子，通常产生很少的数量，在生存压力条件下的一种生命循环。 Classification of fungi As with some of the other groups you have studied, it is difficult to grou

11、p fungi according to actual evolutionary relationships. In general, they are classified according to morphology, methods of reproduction, and modes of spore production. On the basis of these features, the single division of the kingdom Fungi, Mycota, is divided into six principal classes. 对真菌依据实际进化关

12、系进行分类是很困难的。总体来说，它们是依据形态学，生殖方式，孢子产生的模式来分类。基于这些特性真菌界的门被分成6个基本纲。 The lower fungi comprise the groups Chytridiomycetes, Oomycetes, and Zygomycetes zamsets. All lack septate hyphae are commonly coenocytic si:nstk; spores are formed by asexual means. Of the six fungal classes, only the oomycetes u:msets u

13、sually have a diploid vegetative state. 低级真菌包含壶菌，卵菌纲和接合菌。所有缺乏隔膜的菌丝是通用的多核细胞的；孢子通过非性方式产生。只有卵菌纲通常有二倍体的营养状态。Oomycetes and chytrids katrd (sometimes called water molds) produce motile, flagellated spores in sporangia sprnd.They also produce gametes in gametangia; oomycetes are distinguished by their larg

14、e, immobile egg cells.在配子囊中产生配子；卵菌纲具有非寻常大的静止的卵细胞。卵菌纲和壶菌在孢子囊中产生能动的带鞭毛的孢子。In fact, both these groups have such distinctive features that some biologists prefer to classify them as protists rather than fungi. Zygomycetes resemble the other two classes in this group but have nonmotile spores. They are a

15、lso completely terrestrial trestril, and some form mycorrhizal associations with plant roots. 实际上，这两大群具有不同的特征，生物学家宁愿把它们归为原生动物而不是真菌。接合菌与其它两纲相似，但它的孢子不会动。它们完全是陆生的，一些菌根与某些植物的根形成共生关系。The higher fungi include the class Ascomycetes skmsets, the largest class of fungi. Most ascomycetes are either saprobes o

16、r parasites. Asexual reproduction produces spores called conidia knd, which develop on the tips of specialized aerial eril hyphae. In the ascomycete sexual cycle, hyphae of different mating strains fuse, giving rise to ascospores that form in a small, saclike ascus sks. 高级真菌包括子囊菌纲，最大的真菌纲。大多数子囊菌要么是腐生

17、菌，要么是寄生菌。非性繁殖产生的孢子称分生孢子子实体，其依赖特化的气生菌丝尖。在子囊菌性循环过程中，不同的菌丝通过株融合进行匹配，产生的子囊菌存在于小类子囊中。Groups of asci si: form fruiting bodies. Ascomycetes of interest to humans include truffles trflz, yeasts, and Penicillium species. Most members of the class Basidiomycetesthe second group of higher fungi form visible fr

18、uiting bodies. A prime characteristic distinguishing basidiomycetes from ascomycetes is the dense mass of dikaryotic hyphae called the basidiocarp-the mushroom seen on damp lawns and the forest floor.子囊群形成果实体。对人类有利的子囊菌包括块菌，酵母和产青霉素菌。 纲中大多数菌为担子菌，第二大类高级真菌，能形成可见的果实体。担子菌与子囊菌相比，最基本不同是它具备浓密的双核菌丝，称担子果。Club-

19、shaped basidia, each bearing four haploid basidiospores, line the surfaces of the gills gls on the underside of the mushroom cap. Members of this group undergo both sexual and asexual reproductive processes at different times in their life cycle, and in response to varying environmental influences.

20、棒形担子，每个都含有4个单倍体的担子孢子，线形地排列在蘑菇帽下的菌褶表面。大多数成员有性和非性繁殖两种，在不同生命循环中有不同形式，并依据环境变化而变化。 The class Deuteromycetes dtrmasets, or Fungi Imperfecti, includes a variety of fungi that lack modes of sexual reproduction. Most are known to reproduce asexually by means of conidia. knd Deuteromycetes important to humans

21、 include those used to ferment soybeans and rice to make soy sauce and sake respectively, and those responsible for producing citric acid and the highly dangerous aflatoxin fltksn. 半知菌纲，包括大量无性繁殖的真菌。分生孢子完成非性繁殖。对人类很重要的半知菌纲包括发酵大豆成酱油和大米发酵成清酒的菌类，它们也产生柠檬酸和有毒的黄曲霉毒素。 Lichens: The Ultimate Symbionts smbjntsL

22、ichens lakn are composite organisms in which about 90 percent of the lichen mass consists of one species of fungus, while the remaining 10 percent is made up of one or two species of algae. The algal ll portion of the lichen provides the fungal portion with essential nutrients, while the presence of

23、 the fungal component may enable the alga to exploit an otherwise unavailable ecological niche nt. Lichen fungi are usually ascomycetes, although the other two higher fungi are sometimes found in lichens. 共生体。 地衣是复合生物，大概90%的地衣团由一种地衣组成，10%含有一两种藻类。藻类为真菌提供必要的营养，真菌为藻类提供了难得的小生态环境。地衣真菌通常是子囊菌，有时在地衣中也能发现其他两

24、类真菌。Lichens have a number of remarkable features, including their ability to become almost completely desiccated without drying dra and their ability to absorb inorganic nutrients. Reproduction in lichens is not well understood.地衣有大量的显著特征，包括在几乎脱水条件下仍能吸收无机养分。地衣繁殖方式还不清楚。 Fungal EvolutionThe various fu

25、ngi fnda may have arisen rzn independently from prokaryotes, since some evidence suggests that ascomycetes and basidiomycete did not evolve from known lower forms. However, all fungi do show the same dependence on nutrients produced by plants, animals, or algae. 各种真菌可能都独立进化于原核生物，有证据表明，子囊菌和担子菌没有进化。但所

26、有真菌都依赖由植物，动物或藻类产生的营养。 coenocytic si:nstk;Myceliumheterokaryonhetrkrnon aerial eril hyphaeSeptateOomycetes, and Zygomycetes zamsets.be saprobesSymbioticDigestionof a main body or thallushyphae hafi:.chitin katn.rhizoids razdz,haustoria h:st:r.SporangiaTerrestrialMycorrhizalAscomycetes skmsetstruffles

27、 trflz, yeasts, and PenicilliumBasidiomycetesof dikaryotic hyphaebasidiaconidia.ferment soybeanscitric aciddangerous aflatoxinLichens laknThe algalniche nt.Lesson EightAnimal Development sperm精细胞 Cells that develop from the spermatids by losing much of their cytoplasm and developing long tails; the

28、male gamete. ovum 卵，卵子（复数,ova） vmAn unfertilized non-motile female gamete. In many animals it is produced in the ovary. spermatogenesis 精子发生 sp:mtdenssThe specific name given to the gametogenesis process that leads to the formation of sperm. oogenesis 卵子发生- The specific name given to the gametogenes

29、is process that leads to the formation of eggs. ovaries 卵巢，子房 The female sex organs the produce haploid sex cells, the eggs or ova. yolk 卵黄jk ，蛋黄 yoke, yogurt The store of food material, mostly protein and fat, that is present in the eggs of most animals oviduct 输卵管 vdktThe tube (fallopian tube) tha

30、t carries the primary oocyte to the uterus.子宫gene amplification 基因扩增 A temporary dramatic increase in the numbers of a particular gene in a genome during one developmental period. fertilization 受精 The joining of haploid nuclei, usually from an egg and a sperm cell, resulting in a diploid cell called

31、 the zygote. Zygote受精卵 A diploid cell that results from the union of an egg and a sperm. acrosome krsm reaction 顶体反应 That series of observable, structural changes undergone by a sperm when in the vicinity of an ovum in the oviduct. Specifically, many openings appear in the sperm head membrane, throu

32、gh which the contents of the acrosome appear to be released. Parthenogenesis p:ndenss单性生殖，孤雌生殖 Reproduction in which eggs develop normally without being fertilized by a male gamete, producing an individual usually genetically identical to the parent. cleavage 卵裂kli:vd The mitotic division of the zyg

33、ote that occurs immediately after fertilization and produces a ball of smaller cells without an overall increase in size. blastula 囊胚，囊胚泡 blstlThe stage of the early animal embryo that succeeds cleavage and precedes gastrulation. 原肠胚形成A blastula is usually made up of a hollow ball blastomere 卵裂球 One

34、 of several small cells formed from an animal zygote during cleavage. gastrulation 原肠胚形成 gstrlenThe process in the animal embryo by which a blastula囊胚is converted into a gastrula, with the laying down of the germ layers. gastrula 原肠胚 The stage in the development of animal embryos that follows the bl

35、astula and results from gastrulation. The cells of a gastrula are differentiated into the germ layers and the central cavity opens to the exterior by the blastopore. ectoderm ektd:m外胚层，内层 The outermost of the germ layers胚层of metazoan后生动物embryos. It develops mainly into epidermal tissue, the nervous

36、system, sense organs, and (in lower forms) the nephridia肾的. endoderm 内胚层，内层 The innermost of the germ layers of metazoan embryos. Mesoderm中胚层，中层 mesd:mThe middle layer of the three germ layers of triploblastic三胚层 animal embryos. It develops into cartilage软骨, bone, muscle, blood, kidneys, and gonads.

37、 性腺 primitive streak 原肠胚 A longitudinal band of embryonic mesodermal cells that develops within a dorsal背的groove凹槽along the length of the gastrula of mammals and birds. organogenesis 器官形成 :gndenssThe formation of organs. morphogenesis形态发生，形态建成 The developmental processes leading to the characteristi

38、c mature form of an organism or part of an organism. differentiation 分化，鉴别 The complex of changes involved in the progressive diversification of the structure and functioning of the cells of an organism. For a given line of cells, differentiation results in a continual restriction of the types of tr

39、anscription that each cell can undertake. neurulation njrlen神经胚形成 Developmental stage in an embryo during which the cells differentiate into the brain and spinal cord.脊髓metamorphosis 变态 The transformation from larval to adult form. regeneration 再生 The replacement by an organism of tissues or organs

40、that have been lost. dedifferentiation 去分化，脱分化 The loss of differentiation, as in the vertebrate limb stump残余during formation of a blastema. compensatory kmpensetr hypertrophy 代偿式肥大 See regeneration. Animal Development Production of Sperm and EggsIn sexually reproducing organisms males and females p

41、roduce sex cells, known as gametes. These are swimming sperm in males and ova (eggs) in females. 在性繁殖过程中，生物的雄性和雌性产生性细胞，称配子。雄性是能够游动的精子，雌性是卵子。 The process of sperm production, spermatogenesis, takes place in testes testi:z.精子产生过程，即精子发生在睾丸中。The sperm originate in gonial gnl cells (spermatogonia) in the

42、 walls of seminiferous tubules. Spermatocytes produced by mitosis in spermatogonia divide meiotically to generate haploid spermatids. The mature sperm has a tail, a nucleus containing haploid chromosomes, and a front end with an acrosome, the storage site for enzymes that will aid fertilization. 精子产

43、生于输精管壁的性母细胞（精原细胞）。精原细胞经有丝分裂再减数分裂产生单倍体精子细胞，即精母细胞。成熟精子有尾部，单倍体染色体组，头部有顶体，内部储存酶类，有助于受精。 Ova, which are produced during oogenesis, are generated in gonial cells (oogonia) of the females ovaries. Oocytes then enter a stage of arrest in early meiosis. At a species-specific later point, a final ripening (ov

44、ulation) and the first meiotic division occur. A second meiotic division, followed by development of the embryo, takes place if the egg is fertilized. 在卵子发生过程中，由卵巢中的性母细胞产生。卵母细胞进入减数分裂的抑制阶段。第一次减数分裂产生一个成熟卵。如果卵受精，那么第二次减数分裂伴随胚胎的发育。 Eggs vary greatly in size from species to species and have complex struct

45、ures. Virtually all developing animal ova are surrounded by helper cells, either follicle滤泡cells or nurse cells. Depending on the species, eggs also store varying amounts of yolk, a reservoir of nutrients produced by digestive-gland cells in the mothers body. 品种间卵的大小变化很大，并且有复杂的结构。实际上，所有发育过程中的卵都辅助细胞环

46、绕，要么是滤泡细胞，要么是抚育细胞。依赖物种的不同而不同，卵黄贮备也不同，即由母体消化腺细胞产生的营养储备。Finally, follicle cells or cells of the maternal oviduct输卵管provide protective coatings for the egg, including albumen lbjumn(egg white) and various types of outer membranes and shells. 最后，滤泡或母体输卵管细胞产生保护性的卵膜，包括清蛋白和各种外部膜及壳。 Frog oocytes have served

47、 as model systems for studies of oocyte development. During maturation they produce huge numbers of ribosomes through gene amplification. Large quantities of mRNA may also be made and stored. 蛙卵母细胞作为卵母细胞发育的研究系统模型。在成熟过程中，通过基因扩增产生大量的核糖体。同时也产生和储备了大量的mRNA。 Fertilization: Initiating DevelopmentFertilizat

48、ion unites male and female gametes and initiates development. In some species fertilization is external; in others (including most terrestrial animals) it takes place internally. The first contact of the sperm head with the eggs jelly coat triggers the acrosome顶体reaction, in which enzymes are releas

49、ed to digest a hole through the eggs protective layers, and the plasma membrane of the sperm is brought into position to bind to the ovums surface. 雌雄配子结合作用称受精作用，发育开始。某些物种中，是外部受孕；另一些物种，包括大部分陆生动物，是内部受孕。当精子和卵子的胶状膜发生接触时，触发了顶体反应。释放多种酶而将卵保护膜消化出一个洞。精子的原生质膜与卵子的表面连接起来。After fusion of the egg and sperm plasm

50、a membranes, the haploid male nucleus with its chromosomes moves into the egg cytoplasm. Fusion also triggers the eggs final meiotic reduction divisions. When sperm and egg nuclei unite, the two sets of chromosomes mingle to create a diploid set. The fertilized egg is now a zygote.精卵原生质膜融合后，单倍体雄性核进入

51、卵细胞质。融合也触发了最后的减数分裂。当精卵核结合时，两套染色体混合产生一二倍体，即受精卵。 The eggs cortical皮层reaction serves as a barrier to the entry of more than one sperm. Initially, there is a temporary change in the eggs electrical state, and the egg cell is activated. The final stage of the reaction, the rapid elevation of the fertiliz

52、ation membrane, prevents further sperm penetration. 卵皮层阻止其他的精子进入，充当壁垒作用。开始时，卵电位发生暂时变化，卵细胞被激活。反应最后阶段，受精卵的膜快速隆起，阻止更多精子进入。 In some species fertilization is not necessary. Instead, parthenogenesis takes place: the egg is spontaneously activated and proceeds to normal embryonic development. 对某些物种而言，受精不是必

53、须的。孤雌生殖，即卵自发地被激活并进入正常的胚胎发育过程中。 Cleavage: An Increase in Cell Number Cleavage, the major developmental event immediately following fertilization, is a special form of cell division (mitosis). Cleavage produces a blastula, a sheet of cells rounded into a sphere that in most species surrounds a cavity.

54、 In the process, the single-celled zygote is divided into many small cells, and yolk, mRNA, ribosomes, and other materials are distributed to each cell in precise ways. 受精后，立即发生卵裂，细胞有丝分裂的特殊过程。卵裂产生一个囊胚，形成的细胞壁球形排列形成一个空腔。在这个过程中，单细胞的受精卵分裂成许多小细胞，卵黄，mRNA，核糖体和其他物质被精确分配到每个细胞中。The cells of the blastula, call

55、ed blastomeres, also each receive a full diploid set of chromosomes. 这些囊胚细胞，称卵裂球，每个细胞都有一套二倍体染色体组。 There are different patterns of cleavage in different species. 不同物种，卵裂方式不同。The amount of yolk present in the egg is a major factor in determining the pattern: in species having little yolk (such as mamm

56、als) the zygote cleaves completely through, forming cells that are roughly equivalent in size. In frogs, in which the egg has somewhat more yolk, cleavage proceeds more rapidly in regions of the embryo having less yolk. In bird eggs the yolk is so massive that cleavage divisions are restricted to a

57、tiny area of cytoplasm. 决定因素主要取决于卵黄的含量。含有少量卵黄的物种（例如哺乳动物），合子分裂得很彻底，子细胞大致平均分裂。蛙卵，卵黄稍微多点，在胚胎的卵黄较少区域发育更快些。鸟卵卵黄很大，卵裂被限制在细胞质很小区域内。 In many species the precise distribution to blastomeres卵裂球of molecular determinants in the cytoplasm is crucial to proper development of different cell types in the embryo. In

58、 mammal and bird species the fate of cells is determined by the position of a cell late in cleavage.细胞质中分子遗传因素精确分配到卵裂球中，对许多物种而言，是发育成胚中不同类型细胞关键所在。对哺乳动物和鸟类而言，细胞的命运最终由细胞分裂后所处的位置决定的。 Gastrulation: Rearrangement of Cells（原肠胚：细胞重排列）The rearrangement of the blastula囊胚into a three-dimensional organism with

59、inner, middle, and outer layers occurs during gastrulation. The resulting gastrula consists of an outer ectoderm, an inner endoderm, and a mesoderm layer positioned between them. 在原肠胚形成过程中，囊胚重新排列，形成包括内层，中层，外层的三围组织。最终原肠胚由一个外肠胚，内肠胚，和一个中肠胚构成。 Each layer gives rise to specific tissues during embryonic d

60、evelopment. A variation in gastrulation, involving the movement of cells into endodermal and mesodermal positions through the thickened primitive streak, arose in reptiles and can still be seen in bird and mammalian embryos, lending support to the theory that birds and mammals evolved from reptiles.