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Fungi and Plants: The Diversity of Life 2

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1 Fungi and Plants: The Diversity of Life 2

2 22.1 The Fungi: Life as a Web of Slender Threads

3 The Fungi Fungi do not make their own food, as plants do, but instead are heterotrophs—they consume existing organic material in order to live.

4 The Fungi Fungi consist largely of webs of slender tubes, called hyphae, that grow toward food sources. Collectively, hyphae make up a branching web, called a mycelium, that forms the bulk of most fungi.

5 The Fungi Fungi cannot immediately ingest the food the hyphae reach since only small molecules can pass through the cell walls of fungal cells. Fungi thus digest their food externally, through release of digestive enzymes, and then bring the resulting small molecules into the hyphae.

6 The Fungi Many fungi have a reproductive structure called a fruiting body that produces and releases reproductive cells called spores. All fruiting bodies are organized collections of hyphae.

7 The Fungi fruiting body (mushroom) spore hyphae mycelium Figure 22.3

8 The Fungi Most fungi are sessile or fixed in one spot, but their hyphae grow toward food sources. Such growth comes only at the tips of the hyphae, not throughout their length.

9 The Fungi Most fungi are multicellular.
The primary exception to this, the single-celled yeasts, are thought to have evolved to the single-celled state from an earlier multicelled condition.

10 22.2 Roles of Fungi in Society and Nature

11 Roles of Fungi Fungi are the cause of many crop diseases, human infections, and forms of damage to buildings and homes. They are also sources of medicines and are used extensively in food processing.

12 Roles of Fungi In nature, fungi join bacteria as major decomposers of the living world. They break down the organic material in such objects as fallen trees and recycling the inorganic products that result back into the soil.

13 22.3 Structure and Reproduction in Fungi

14 Structure and Reproduction in Fungi
Individual cells that form hyphae often are separated from one another by dividers called septa.

15 Structure and Reproduction in Fungi
Septa are porous enough to allow for a fairly free flow of cellular material between one hyphal cell and the next. Hyphae can bring resources very quickly to the point of growth at the hyphal tips. As a result, fungi can grow very quickly.

16 Structure and Reproduction in Fungi
The fruiting body of the toadstool mushroom fungi, the mushroom cap, is made up on its underside of accordion-like gills. The gills produce spores and release them into the wind, which carries them to new locations.

17 Structure and Reproduction in Fungi
Only a tiny fraction of fungal spores will successfully germinate, or sprout new mycelia. Because of this, fruiting bodies release huge quantities of spores as a means of ensuring new fungal growth.

18 Life Cycle of Fungi Many fungi have a so-called dikaryotic phase of life in which the fusion of cells from different parental hyphae produces a single hypha with cells that each have two nuclei— one nucleus coming from one parental hypha, the other nucleus coming from the second parental hypha. Each of these nuclei is haploid, meaning each contains only a single set of chromosomes.

19 Life Cycle of Fungi When the below-ground mycelium in a mushroom fungus sprouts into the above-ground mushroom cap, all the cells in the cap initially are dikaryotic. This includes those in the reproductive structure called the basidium.

20 Life Cycle of Fungi Figure 22.5 Fusion of nuclei (fertilization) gills
Meiosis and spore formation diploid dikaryotic basidium spore from another mushroom gills spores haploid Life cycle of a fungus dikaryotic hyphae Germination Mushroom formation dikaryotic Fusion Figure 22.5

21 Life Cycle of Fungi The nuclei in certain cells of the basidia then undergo fusion, which is a step in carrying out sexual reproduction. These cells are now diploid—they have a single nucleus that contains a paired set of chromosomes.

22 Life Cycle of Fungi These same cells then undergo meiosis, and the result is four haploid spores attached to tip of the basidium. These spores are then released and blown by the wind to new locations, where they may germinate and result in new mycelia.

23 Life Cycle of Fungi A spore is a reproductive cell that can develop into a new organism without fusing with another reproductive cell. Unlike human eggs and sperm, which fuse to make a fertilized egg, fungal spores do not need to fuse with any other cell to give rise to a new generation of fungi.

24 Life Cycle of Fungi PLAY Animation 22.1: Life Cycle of Fungi

25 22.4 Categories of Fungi

26 Categories of Fungi There are four major categories or “phyla” of fungi: Basidiomycetes Ascomycetes Zygomycetes Chytrids

27 Categories of Fungi The first three of these phyla are defined by reproductive structures. Any fungus that reproduces through use of the reproductive structure called a basidium is a basidiomycete, for example. The ascomycetes and zygomycetes are defined by their own reproductive structures.

28 Basidiomycetes The basidiomycetes, also known as the club fungi, include “toadstool” mushrooms, “shelf ” fungi that often can be seen sprouting from trees, and the agricultural pathogens called smuts and rusts.

29 Basidiomycetes Figure 22.7

30 Ascomycetes The ascomycetes, also known as the sac fungi, include truffles, morel mushrooms, and fungi that attack stone fruits.

31 Ascomycetes Figure 22.8

32 Zygomycetes The zygomycetes, also known as the bread molds, include many fungi that form associations with plant roots, but also include one group of fungi that live by parasitizing insects.

33 Zygomycetes Figure 22.9

34 Chytrids The chytrids are a primitive group of mostly aquatic fungi, all of which are mobile at one point in their life cycle. The chytrids probably give us an idea of what the earliest fungi were like, as the sessile fungi that are so common today seem to have evolved from chytrid-like ancestors. Early fungi were probably very similar to early animals.

35 Chytrids Figure 22.10

36 Yeasts A yeast is any single-celled fungus that tends to reproduce by the process known as budding. In this process, fungal daughter cells are produced as outgrowths of parental cells.

37 Yeasts Yeast species exist within three of the four fungal phyla—the ascomycetes, the basidiomycetes, and the zygomycetes. The majority of yeasts are ascomycetes, but many are basidiomycetes.

38 Yeasts The yeast Saccharomyces cerevisiae has been very important to human beings because of the critical roles it has played in the production of beer, wine, and bread and because of the important role it has played in scientific research.

39 Yeasts Figure 22.11

40 22.5 Fungal Associations: Lichens and Mycorrhizae

41 Lichens Lichens are composite organisms made up usually of fungi and algae but sometimes of fungi and bacteria.

42 Lichens Within a lichen, the photosynthesizing algae are supplying the fungi with food, while the fungi are supplying the algae with water, minerals, carbon dioxide, and protection from the elements.

43 Lichens fungal hyphae algal cell dense hyphae algal layer loose hyphae
rock lichen Figure 22.13

44 Lichens Lichens can establish themselves in barren environments, and some lichens have been alive for thousands of years. Lichens grow at an extremely slow pace, however, thanks to their practice of entering a state of dormancy during periods when water is scarce.

45 Lichens Figure 22.12

46 Mycorrhizae Up to 90 percent of seed plants live in a cooperative association with fungi that links plant roots with fungal hyphae. Associations of plant roots and fungal hyphae are called mycorrhizae.

47 Mycorrhizae In this relationship, plants supply fungi with food produced in photosynthesis, while the fungi supply plants with minerals and water, gathered by the web of fungal hyphae.

48 Mycorrhizae Figure 22.14

49 22.6 Plants: The Foundation for Much of Life

50 Plants are the foundation for much of life on Earth because they are responsible for much of the living world’s production of food and oxygen. In addition, they stabilize soil, provide habitat for animals, and lock up carbon dioxide.

51 Characteristics of Plants
All plants are multicelled, and almost all are fixed in one spot and carry out photosynthesis. All plant cells have a cell wall and contain organelles called chloroplasts, which are the sites of photosynthesis.

52 Characteristics of Plants
cell wall (made of lignin and cellulose) cell membrane nucleus central vacuole (contains mostly water) chloroplast (site of photosynthesis) Figure 22.15

53 Characteristics of Plants
Plants reproduce through an alternation of generations: a life cycle in which successive plant generations produce either spores (the sporophyte generation) or gametes (the gametophyte generation). Within a given species, these two generations can differ greatly in size and structure.

54 The Alternation of Generations in Plants
Human reproduction Plant alternation of generations meiosis egg multicellular gametophyte multicellular diploid adults spores gametes sperm 1n 1n meiosis fertilization 2n fertilization 2n mitosis and development zygote multicellular sporophyte zygote haploid (1n) diploid (2n) Figure 22.16

55 22.7 Types of Plants

56 Types of Plants The four principal categories of plants are:
bryophytes seedless vascular plants gymnosperms angiosperms

57 green algae (ancestors)
Types of Plants Moss Ferns flowering plants mosses ferns conifers flowers seeds vascular tissue Conifers Flowering plants multicellularity green algae (ancestors) Figure 22.17

58 Types of Plants Bryophytes include mosses.
Seedless vascular plants include ferns. Gymnosperms include coniferous trees. Angiosperms include a wide array of plants, such as orchids, oak trees, rice, and cactus.

59 Bryophytes Bryophytes are close living relatives of the earliest plants that made the transition from living in water to living on land. They lack a fluid transport or vascular system and thus tend to be low lying.

60 Bryophytes Bryophyte sperm get to eggs primarily by swimming through water, although it’s recently been discovered that tiny animals sometimes transport sperm among mosses. Bryophytes tend to inhabit damp environments.

61 Bryophytes Figure 22.18

62 Seedless Vascular Plants
Seedless vascular plants have a vascular system but do not produce seeds in reproduction. Their sperm must move through water to fertilize eggs.

63 Seedless Vascular Plants
Figure 22.19

64 Gymnosperms Gymnosperms are seed-bearing plants with seeds that are not encased in tissue called fruit. There are only about 700 gymnosperm species, but their presence is considerable, particularly in northern latitudes, where gymnosperm trees, such as pine and spruce, often dominate landscapes.

65 Gymnosperms Figure 22.20

66 Gymnosperms The sperm of gymnosperms is encased in pollen grains that are carried to female reproductive structures by the wind. Gymnosperms produce seeds in carrying out reproduction. Seeds are structures that include a plant embryo, its food supply, and a tough, protective casing.

67 Gymnosperms wing protective seed coat seed embryo nutritional tissue
Figure 22.21

68 Gymnosperms male cone Wind carries pollen to female cone. pollen
mature tree Sperm within the pollen fertilizes one egg within the cone. seedling Embryo begins to develop within seed. seed New pine tree begins to grow. Seed germinates. Figure 22.22

69 Angiosperms Angiosperms, or flowering plants, are seed plants with seeds that are encased in tissue called fruit. Angiosperms are easily the most dominant group of plants on Earth, with some 260,000 species having been identified to date.

70 Angiosperms Angiosperm species include not only plants with flowers, such as roses, but almost all trees except for the conifers, all important food crops, cactus, shrubs, and common grass.

71 Angiosperms Figure 22.23

72 22.8 Angiosperm–Animal Interactions

73 Angiosperm-Animal Interactions
Angiosperm pollen grains generally are transferred from one plant to another by animals, such as insects and birds.

74 Angiosperm-Animal Interactions
To induce animals to carry out this pollination, angiosperm flowers produce nectar and have developed attractive colorations and fragrances.

75 Angiosperm-Animal Interactions
Figure 22.24

76 Endosperm Angiosperm seeds contain tissue called endosperm, which functions as food for the growing embryo. Endosperm supplies much of the food that human beings eat. Rice and wheat grains consist largely of endosperm.

77 Endosperm wheat endosperm seed coat (bran) embryo (wheat germ)
Figure 22.26

78 Fruit Angiosperm seeds are unique in the plant world in being wrapped in a layer of tissue called fruit. Fruit that is edible functions in angiosperm seed dispersal because animals will eat and digest the fruit but then excrete the tough seeds inside, often in a different location.

79 Seed Carriers Figure 22.27

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