Chapter

21 Fungi

What are Fungi?• The way in which Fungi grow from the

ground once led scientists to classify them as nonphotosynthetic plants

• However, they are not plants at all, fungi are very different

• Fungi are eukaryotic heterotrophs that have cell walls

Chitin

• A complex carbohydrate that makes up the cell walls of fungi

Fungi Nutrition• Remember that heterotrophs depend on other

organisms for food• Unlike animals, fungi do not ingest their food• Instead they digest food outside their bodies

and then absorb it• Many feed by absorbing nutrients from

decaying matter in the soil (decomposers)• Others live as parasites, absorbing nutrients

from their hosts

Structure and Function of Fungi

• All fungi are multicellular with the exception of yeast

• Multicellular fungi are composed of thin filaments called hyphae

Structure and Function of Fungi

Fungus Structure• The bodies of multicellular fungi

are composed of many hyphae tangled together into a thick mass called a mycelium

Fungus Structure

Fruiting body

• The reproductive structure growing from the mycelium in the soil that you recognize as a mushroom

Fungi reproduction• Most fungi reproduce both

asexually and sexually

Spore

• A reproductive cell that is capable of growing into a new organism by mitosis alone

• This is how fungi spread

Fungal spore

Fungi reproduction• Sexual reproduction involves two

different mating types (+ and -)

• When two hyphae of opposite mating types meet, their nuclei fuse together

Types of fungi

zygomycetes

Sac Fungi

Yeast

Club Fungi

Imperfect fungi

Ecology of Fungi• Fungi have been around since life first

moved onto land• Paleontologists think that fungi helped early

plants to obtain nutrients from the ground• Their early appearance suggests that fungi

may have been essential to plants successful colonization of the land

• Overtime, fungi have become an important part of virtually all ecosystems

Edible and Inedible Mushrooms

• Many types of mushrooms are considered delicious

• Although wild mushrooms are edible, many are poisonous

• You should never pick or eat mushrooms in the wild

• Leave mushroom gathering to the experts

All Fungi Are Heterotrophs

• Many are saprobes

• Others are parasites

• Others are symbionts that live in close and mutually beneficial association with other species

Saprobes • Organisms that obtain food from

decaying organic matter

Carnivorous Fungi• Pleurotus ostreatus

Fungi as Decomposers• Fungi play an essential role in

maintaining equilibrium in nearly every ecosystem

• They recycle nutrients by breaking down the bodies and wastes of other organisms by releasing digestive enzymes

Fungi as Parasites• As useful as many fungi are

others can infect both animals and plants and cause diseases

• Ex.) Wheat rust, athelets foot, Candida, Cordyceps

Cordyceps

Symbiotic Relationships

• Some fungi form symbiotic relationships in which both partners benefit

Lichens

• Symbiotic association between a fungus and a photosynthetic organism

Lichens• The algae or cyanobacteria - Carries out

photosynthesis providing the fungus with food

• The fungus provides the algae or bacteria with – water and minerals that it collects and also protects the delicate algae cell

• Lichens are often the first organisms to enter barren environments

Mycorrhizae

• Symbiotic relationship between plant roots and fungi

• Fungi allow plants to – absorb more water and minerals

• Fungi also release enzymes that – free nutrients into the soil

• Plants provide fungi with – the products of photosynthesis