Chapter 16 Fungi

1. Chapter 16 Fungi

2. Fungi contribute to food, to medicine, and to the recycling process. The Kingdom Fungi includes microscopic yeast as well as giant puffball, which can grow the size of a basketball. Multicellular, eukaryote heterotrophs

3. The cell walls of most fungi are made of chitin. Chitin is a tough, flexible carbohydrate that also makes up the hard outer skeleton of insects. Yeast is a typical unicellular fungi. There are no typical multicellular fungi.

4. A mushroom typically consists of a stalk (stipe) and a cap (pileus). As the mushroom develops from an underground mycelium and pushes upward, it is protected by a thin membrane (universal veil), which eventually ruptures, leaving fragments on the cap. Another membrane, attaching the cap to the stalk, also ruptures, allowing the cap to expand and leaving a remnant ring (annulus) on the stalk. Radiating rows of gills are found on the cap's undersurface; these bear the club-shaped reproductive structures (basidia) which form minute spores known as basidiospores, of which a single mushroom may produce millions.

5. Multicellular fungi are composed of a mass of tiny, individual filaments, barely visible to the unaided eye. The individual filaments, called hyphae, are tubules filled with cytoplasm and nuclei. Some hyphae may be divided into segments by walls called septa.

6. Septa have holes through which cytoplasm and organelles move. Some fungi do not have septa in their hyphae, and each hypha is one continuous filament containing cytoplasm and nuclei. Hyphae are the living growing part of fungi.

7. Hyphae can weave together in a variety of ways, thereby producing many different forms of fungi. Hyphae can grow quickly; certain fungi produce about 35 to 40 m of hyphae in only one hour. The mass of tangled, interwoven hyphae that forms the body of a fungus is called a mycelium.

8. Fungi are heterotroph ( extra-cellular digestion ) Fungi obtain nutrition by absorbing it - that is, they take food in by the diffusion of small organic molecules. Fungi produce enzymes in their hyphae, which they secrete directly into their environment. The enzymes break the large organic molecules into small organic molecules that the fungus can easily absorb. These enzymes can break down large, complex organic molecules such as lignin, which is a major component of wood.

9. How fungi obtain their food.

10. Other fungi depend on living things for their nutrition. Parasitic fungi absorb nutrients from living hosts, a process that often causes diseases in, and sometimes death of, the host. A few fungi are predators, they trap and kill their prey.

11. Fungi differ in the types of organisms that they use as a source of nutrition. Most fungi are saprophytes. Saprophytes are organisms that digest and absorb nutrients from dead organisms.

12. Examples of mutualistic relationships with a fungi might be a lichen or a mycorrhizae.

13. Fungi grow very rapidly, as nutrient transport to the actively growing areas of hyphae is extremely efficient. Materials move quickly through a fungal mycelium because the hyphae of the mycelium share the same cytoplasm. This means the materials from the entire mycelium are available to all hyphae.

14. Growth in the hyphae occurs at the tips. The mycelium spread outward quickly, occupying an increasingly large area. The visible mushrooms of a single, underground mycelium can spread to cover more than 1000 acres.

15. Origin of fungi Many mycologists hypothesize that fungi evolved at least 400 million years ago from a protist ancestor. Fungi Plants cell walls made of chitin cell walls made of cellulose Heterotroph autotroph

16. Kingdom Fungi is divided into groups called divisions instead of phylum. Fungi are grouped in one of four divisions based on their method of reproduction.

17. Three of the divisions are classified according to the structures used in sexual reproduction. Zygomycota Ascomycota Basidiomycota The fourth division includes fungi that have only been observed reproducing asexually. Deuteromycota

18. Fungi in all four divisions have been observed reproducing asexually. Asexual reproduction can occur in three ways. Budding Regeneration Spore production

19. During budding, a parent cell divides and produces offspring by forming a small bud, which separates from the parent. The most common budding in fungus is yeast and athlete’s foot. Budding -

20. Regeneration - Regeneration occurs when a piece of mycelium breaks off from a fungus and grows on its own. Most fungi reproduce asexually by producing spores in a structure called a fruiting body. Spores are reproductive cells that can remain dormant or develop into new organisms. A typical mushroom makes 16 billion spores. Fruiting bodies are above ground stalks that support the structures in which spores are made.

21. Sexual Reproduction Sexual reproduction involves combining the genes of two different parents. In fungi there are no males or females. Instead, fungi have two different mating types of hyphae: plus and minus. Sexual reproduction in fungi occurs by the fusion of two hyphae with different mating types and the resulting production of spores.

22. Spore production occurs in both asexual and sexual reproduction. Although the spores of both methods look the same, spores that are produced sexually contain a new combination of genetic information.

23. Zygomycota - common molds You might have noticed mold on bread or mildew on shower curtains. Zygomycetes are generally found in soil or on dead animals or plants. Common molds are structurally unique. Their hyphae lack septa.

24. There are three kinds of specialized hyphae in common molds. Rhizoids - absorb nutrients and hold common molds to their food source like roots anchor plants to the soil. Stolons - connect groups of rhizoids to one another. They transport cytoplasm containing nutrients through the body of the fungus. Sporangia - produces spores during reproduction. Nuclei from the two mating types fuse to form a diploid structure called a zygospore. Zygospores can survive for many years in harsh conditions.

25. Ascomycota - sac fungi This is a very diverse group that includes unicellular yeasts, powdery mildews, lichens and morels. The characteristic that links the members of this group together is the production of saclike structures called asci during sexual reproduction. This characteristic gives the group its name.

26. The sexual reproduction cycle includes two mating types fusing together to form a cell called an ascogonium. This structure develops hyphae that grow upward. Asci forms at the tips of ascogonium. In favorable environmental conditions, these spores grow into new fungal organisms.

27. Sexual reproduction in sac fungi is rare. In most cases, sac fungi reproduce asexually by spores. Unicellular fungi reproduce by budding or by cell division.

28. Basidiomycota - club fungi Mushrooms and toadstools are club fungi. One of their most distinguishing characteristics is their tendency to reproduce sexually. Asexual is possible but very rare.

29. The visible parts of the mushroom are made of tightly packed mycelia. The stalk, cap and gills. These structures form the fruiting bodies that house the tiny spore producing basidia.

30. Spores that are produced in the basidia are released, and if environmental conditions are favorable, new mushrooms grow. As a result of the genetic recombination that occurred during the process of sexual reproduction, there is variation among these offspring.

31. Deuteromycota - imperfect fungi Some fungi apparently reproduce only asexually. These are commonly called imperfect fungi. Examples would be ringworm, athlete’s foot and penicillium.

32. Imperfect Fungi

33. Athlete’s foot is a parasitic fungus that is breaking down and decomposing the skin of the living host. Ringworm is actually a fungus. It looks like a worm because of the curved growing tips of the mycelium.

34. Penicillium produces the antibiotic penicillin, which you may have taken to fight a bacterial infection.

35. Imperfect Fungi reproduce asexually by producing spores called conidia in specialized hyphae called conidiophores. These asexually produced spores are released into the environment. If they land in a suitable place, they start growing. Most imperfect fungi are moldlike in appearance. Since Ascomycotes also reproduce asexually using conidiophores, mycologists believe they are related.

36. Fungi are key members of stable ecosystems. They break down organic materials, converting them into a form that can be used by the fungi and other living things. In this way fungi recycle the nutrients needed to keep communities alive.

37. Fungi often participate in symbiotic relationships. For example lichens (which you already know about) and mycorrhizae. Mycorrhizae result from mutually beneficial relationships between plants and fungi. Mycorrhizae form when the tiny hyphae of a fungus grow on and in the roots of a host plant.

38. Over time, mycorrhizae can account for as much as 15 percent of the total mass of the roots. The mycorrhizae absorb the nutrients made by the photosynthetic plant. The fungus helps the plant by acting as root extensions, increasing the ability of the roots to absorb water and nutrients from the soil.

39. In addition, the fungus secretes digestive enzymes that help break down organic matter in the soil. The plant can then absorb the decomposed material as nutrients and minerals. Many biologists hypothesize that mycorrhizae were instrumental in the evolution of land plants. Today, more than 90% of tree species and 80% of all other plant species have mycorrhizae.

40. Diseases caused by fungi. Fungal diseases can occur in both plants and animals.

41. Plant diseases In some regions of the world disease causing fungi destroy large amounts of harvested food crops each year. Smuts and rusts are both club fungi that attack grain crops.

42. Dutch elm disease has killed millions of American elm trees. This disease was accidentally imported to the U.S. from Europe after W.W.I. The fungus is spread from tree to tree by bark beetles. Haustoria are specialized hyphae that grow into the living cells and absorb the nutrients directly. Once the tree is dead, the fungus takes over as a decomposer.

43. Human Diseases Some fungal diseases in humans are ringworm, athlete’s foot, thrush and yeast infection.

44. Human uses There are many edible mushrooms. Morels, matsutake, button, potrabella and yeast are a few examples. Although some wild mushrooms are edible, many are poisonous. For this reason, gathering and eating wild mushrooms should be left to experts who can distinguish the poisonous mushrooms from those that are harmless.

45. There are about 10,000 different kinds of mushrooms, but relatively few -- perhaps about 100 -- are considered good to eat. If you plan on eating a mushroom, you'd better be absolutely sure of its identity, because 100 out of 10,000 isn't many (1%). And some of those other 9.900 are poisonous. So be very careful: check the identification with a truly knowledgeable person before you heat up the frying pan.

46. Fungi provide many of the distinct aromas and tastes in our foods. The flavor of many cheeses results from the presence of fungal molds.

47. Beneficial Fungi

48. In 1928 a Scottish scientist Alexander Fleming was Staphylococcus , a bacteria that causes skin infections. He grew the bacteria in culture dishes. One day he noticed that a Penicillium mold was growing in some of the culture dishes. In the area around the fungal mold there was a clear zone with no bacteria.