Fungi

1. Fungi

2. Learning Objectives • Define the terms: saprophytic & parasitic • State the structure & life cycle of Rhizopus • Explain nutrition in fungi. • Outline the structure & reproduction of Yeast • Name 2 Beneficial & 2 Harmful fungi • Mention that there are Edible and Poisonous fungi • Identify and state functions for the following structures: rhizoid, sporangium, gametangium, zygospore.

4. Features of Fungi • They do not make their own food • They are mostly multi-cellular • They are made up of threads called hyphae • Hyphae combine in masses to form a mycelium • Their walls are made of a carbohydrate called chitin

5. Nutrition • All fungi are heterotrophs i.e. they take in food made by other organisms Fungi are either: • Parasitic • Saprophytic

6. Saprophytic fungi • Most fungi are saprophytic • obtain nutrients from dead material • As they digest it minerals are released and recycled • Play a vital role in the environment as they are responsible for decay • E.g. mushrooms and moulds

7. Parasitic Fungi • Absorb their food from live hosts • They get their food mostly from plants although some fungal parasites live on animals e.g. athlete’s foot

8. Parasitic Fungi • Obligate parasites • live on live hosts but do not normally kill them • Facultative parasites • kill the host and feed on the remains

9. Some fungi e.g. form symbiotic relationships with other organisms • A lichen is an organism which is a combination of a fungus and an alga

10. Edible and poisonous fungi • Some fungi are edible, but many are poisonous if eaten • It is often difficult to distinguish between the edible and poisonous varieties growing in the wild

11. Rhizopus

12. Rhizopus growing on agar

13. Structure of Rhizopus

14. Consists of threadlike structures called Hyphae Hypha

15. They are tubular with no cross walls and are multinucleate. Each nucleus is haploid. Nucleus

16. Large numbers of hyphae are called a mycelium • The hyphae digest the substrate on which they grows • Rhizoids provide extra surface area for absorption of the digested material • Stolons are arial hyphae which allow Rhizopus to spread sideways

17. Structure of Rhizopus

18. Sporangium Spores Columella Apophysis Sporangiophore

19. Life cycle of Rhizopus

20. Asexual reproduction • Sporangiophores grow up from the substrate after a number of days • Cells within the sporangium divide by mitosis to produce spores (haploid)

21. Asexual reproduction • Cells within the sporangium divide by mitosis to produce spores (haploid)

22. Asexual reproduction • The sporangium dries out in the right conditions and opens releasing many spores. • Each spore will grow into a new hypha and mycelium if it lands on a suitable substrate

24. Sexual reproduction + Strain - Strain • Sexual reproduction in Rhizopus can only occur between a plus and a minus strain.

25. Sexual reproduction + Strain - Strain • When hyphae from opposite strains grow close together swellings grow on both strains and touch each other.

26. Sexual reproduction + Strain - Strain • Nuclei from both hyphae move into these swellings which are now called progametangia.

27. Sexual reproduction + Strain - Strain • Cross-walls form to produce gametangia.

28. Sexual reproduction + Strain - Strain • The walls of the gametangia dissolve and a number of fertilisations take place producing diploid zygote nuclei.

29. Sexual reproduction + Strain - Strain • A zygospore forms around these nuclei. • When conditions are suitable the zygospore germinates by meiosis.

30. Sexual reproduction + Strain - Strain • A zygospore forms around these nuclei. • When conditions are suitable the zygospore germinates by meiosis.

31. Sexual reproduction • A hypha grows out of the zygospore and produces a sporangium at the tip. • The sporangium opens releasing many haploid spores which grow into new individuals.

33. Review of sexual reproduction • Sexual reproduction in Rhizopus can only occur between a plus and a minus strain • When hyphae from opposite strains grow close together swellings grow on both strains and touch each other • Nuclei from both hyphae move into these swellings which are now called progametangia • Cross-walls form to produce gametangia

34. Review of sexual reproduction • The walls of the gametangia dissolve and a number of fertilisations take place producing diploid zygote nuclei • A zygospore forms around these nuclei • When conditions are suitable the zygospore germinates by meiosis • A hypha grows out of the zygospore and produces a sporangium at the tip • The sporangium opens releasing many haploid spores which grow into new individuals

35. Yeast

36. Structure of yeast

37. Reproduction in Yeast

38. Asexual reproduction in yeast occurs by budding. The nucleus of the parent cell divides by mitosis. One of the daughter nuclei enters a small developing bud on the outside of the yeast cell. Asexual reproduction in yeast

39. This bud can separate from the parent to become a new individual Asexual reproduction in yeast

40. This bud can separate from the parent to become a new individual In some cases the bud does not separate, but can itself bud. In this way long colonies of yeast cells can develop Asexual reproduction in yeast

41. Budding

42. Budding

43. Economic importance of fungi Beneficial fungi • Yeasts can be used to make bread and alcohols such as wine and beer • Fungi can be used as a source of food e.g. mushroom

44. Economic importance of fungi Harmful fungi • Fungi can attack crops e.g. corn and wheat and cause major financial losses as a result • Fungi such as athletes foot and ringworm can infect animals • Fungi can spoil food e.g. rhizopus grows on bread

45. Depth of treatment • Saprophytic and parasitic forms • Rhizopus (Structure and life cycle) • Nutrition • Yeast: structure and reproduction (budding).

46. Contemporary issues and Technology • Mention of edible and poisonous fungi. • Economic importance of fungi: examples of any two beneficial and any two harmful fungi. Practical Activities • Investigate the growth of leaf yeasts using agar plates and controls