Chapter 21: Protists and Fungi Section 21-4: Fungi

What are Fungi? O Heterotrophs – produce enzymes that digest food outside their bodies, then absorb the nutrients O Most feed on decaying material in the soil, some are parasitic O Cells walls made of chitin – also found in exoskeletons of insects O More closely related to animals than plants

Structure and Function O Yeasts are the only unicellular fungi O Mushrooms and other fungi are larger, with bodies made up of cells forming long, slender branching filaments called hyphae

Structure and Function O Cross walls divide the hyphae into compartments, each containing 1 or 2 nuclei O Openings in cross walls allow cytoplasm and organelles to move O Body of mushroom called fruiting body – reproductive structure of a fungus O Grows from mycelium – mass of branching hyphae below soil O Clusters of mushrooms can have same mycelium

Reproduction O Reproduce asexually, primarily by releasing spores adapted to travel through air or water O Breaking off hypha or budding also

Reproduction O Most reproduce sexually - life cycle of the bread mold Rhizopus stolonifer

Sexual Reproduction O 2 mating types - + (plus) and – (minus) O Hyphae of opposite mating types fuse, bringing + and – nuclei together in the same cell O + and – nuclei form pairs and divide as mycelium grows O Many of the paired nuclei fuse to form diploid zygotes within a zygospore

Sexual Reproduction O Zygospore germinates and sporangium emerges O Sporangium reproduces asexually, releasing haploid spores produced by meiosis O Each spore can make a new mycelium – different combo of genes

Diversity of Fungi O More than 100,000 species O Groups based on reproductive structures

Ecology of Fungi O Decomposers – extracellular digestion breaks down organic material, recycle essential nutrients into the soil O Parasites – cause plant/animal diseases O Plant diseases – corn smut, mildews O Animal diseases – Cordyceps fungus infects grasshoppers, athlete’s foot, yeast infections O Lichens

Lichens O Symbiotic relationship between a fungus and a photosynthetic organism (either green alga, cyanobacterium, or both) O Upper surface - densely packed fungal hyphae O Middle - layers of green algae or cyanobacteria, loosely woven hyphae O Bottom - small projections that attach the lichen to a rock or tree

Lichens O Extremely resistant to drought/cold O Able to survive because the green algae or cyanobacteria carry out photosynthesis O Fungus provides the green algae or cyanobacteria with water and minerals and protection O First to enter barren environments, breaking down rocks to make soil (succession) O Sensitive to air pollution

Mycorrhizae O Symbiotic association between plant roots and fungi O 80-90% of all plants have from mycorrhizae O Hyphae collect water and minerals for roots, increasing surface area of root system O Fungi release nutrients O Plants provide fungi with photosynthesis O Essential for certain plants’ survival

Mycorrhizae

O Mycorrhizal networks connect many plants O Ecologist Suzanne Simard found that mycorrhizal fungi transferred carbon from tree to tree O Findings suggest that plants/fungi may be evolving as part of an ecological partnership