Chapter 31Chapter 31

FungiFungi

Heterotrophic Metabolism

Heterotrophic Metabolism

• Fungi are heterotrophs, but they do not ingest their food.

• They release exoenzymes that digest their food while it’s still in the environment.

• Then they absorb the nutrients.

• Fungi are heterotrophs, but they do not ingest their food.

• They release exoenzymes that digest their food while it’s still in the environment.

• Then they absorb the nutrients.

Characteristics of Fungi:Characteristics of Fungi:

• Some are multicellular• Others are small and single celled• The morphology of fungi is primed to take up nutrients

• The bodies form a network of hyphae– Hyphae are composed of tubular cell walls surrounding the plasma membrane and cytoplasm of cells.

– The cell walls contain chitin.

• Some are multicellular• Others are small and single celled• The morphology of fungi is primed to take up nutrients

• The bodies form a network of hyphae– Hyphae are composed of tubular cell walls surrounding the plasma membrane and cytoplasm of cells.

– The cell walls contain chitin.

HyphaeHyphae

• The fungal hyphae form a network of interwoven fibers called mycelium.

• The mycelium surrounds and infiltrates the material on which the fungus feeds.

• This acts to increase the surface area to volume ratio of the fungus– Makes feeding more efficient.

• The fungal hyphae form a network of interwoven fibers called mycelium.

• The mycelium surrounds and infiltrates the material on which the fungus feeds.

• This acts to increase the surface area to volume ratio of the fungus– Makes feeding more efficient.

FungiFungi

• Fungi are immobile, thus it is important for them to be able to increase the length of the hyphae quickly and efficiently to obtain food.– In some fungi, individual cells are separated by septa which usually contain large pores that allow many things through.

– In other fungi, the bodies are huge, multinucleated masses with no cytoplasmic divisions.

• Fungi are immobile, thus it is important for them to be able to increase the length of the hyphae quickly and efficiently to obtain food.– In some fungi, individual cells are separated by septa which usually contain large pores that allow many things through.

– In other fungi, the bodies are huge, multinucleated masses with no cytoplasmic divisions.

MycorrhizaeMycorrhizae

• These are beneficial relationships between fungi and plant roots.– The benefit comes from the ability of the fungus to provide the plant with nutrients that it couldn’t otherwise obtain.

– The plants provide the fungus with organic nutrients.

• These are beneficial relationships between fungi and plant roots.– The benefit comes from the ability of the fungus to provide the plant with nutrients that it couldn’t otherwise obtain.

– The plants provide the fungus with organic nutrients.

HaustoriaHaustoria

• Specialized hyphae that penetrate the roots of their hosts (plants).

• Site of nutrient exchange.

• Specialized hyphae that penetrate the roots of their hosts (plants).

• Site of nutrient exchange.

MycorrhizaeMycorrhizae

• 2 Different Types of mycorrhizae:– Ectomycorrhizal fungi form sheaths of hyphae over the surface of the roots and also grow into the extracellular spaces of the root cortex

– Endomycorrhizal fungi extend their hyphae through the root cell wall and into the tubes by pushing the root cell membrane inward.

• 2 Different Types of mycorrhizae:– Ectomycorrhizal fungi form sheaths of hyphae over the surface of the roots and also grow into the extracellular spaces of the root cortex

– Endomycorrhizal fungi extend their hyphae through the root cell wall and into the tubes by pushing the root cell membrane inward.

MycorrhizaeMycorrhizae

• Almost all vascular plants have mycorrhizae. The fungi provide essential nutrients to the plant; the plant provides nutrients to the fungus.

• Almost all vascular plants have mycorrhizae. The fungi provide essential nutrients to the plant; the plant provides nutrients to the fungus.

Fungal ReproductionFungal Reproduction

• Fungi reproduce both sexually and asexually.

• Either way, they produce large numbers of spores.

• Fungi reproduce both sexually and asexually.

• Either way, they produce large numbers of spores.

Fungi: Sexual ReproductionFungi: Sexual Reproduction• Sexual reproduction in fungi begins when hyphae from two distinct mycelia release pheromones.

• The fungi perceive the chemical signal and extend hyphae toward the source of the pheromone.

• This acts to attract different mycelia towards one another.

• During the sexual life cycle of a fungi, the haploid nuclei of the hyphae and their spores become diploid.

• Sexual reproduction in fungi begins when hyphae from two distinct mycelia release pheromones.

• The fungi perceive the chemical signal and extend hyphae toward the source of the pheromone.

• This acts to attract different mycelia towards one another.

• During the sexual life cycle of a fungi, the haploid nuclei of the hyphae and their spores become diploid.

Fungi: Sexual ReproductionFungi: Sexual Reproduction• When the mycelia meet they perform a compatibility test to ensure mycelium and hyphae from the same fungus don’t fuse.

• They want to sexually reproduce with other fungi.

• When the mycelia meet they perform a compatibility test to ensure mycelium and hyphae from the same fungus don’t fuse.

• They want to sexually reproduce with other fungi.

Fungi: Sexual ReproductionFungi: Sexual Reproduction• Plasmogamy is the union of the cytoplasm of two parent mycelia.

• Even though their cytoplasm is joined, the haploid nuclei don’t fuse right away.

• The mycelia are said to be heterokaryotic.

• Sometimes, haploid nuclei pair off two to a cell and the mycelia are said to be dikaryotic.

• Plasmogamy is the union of the cytoplasm of two parent mycelia.

• Even though their cytoplasm is joined, the haploid nuclei don’t fuse right away.

• The mycelia are said to be heterokaryotic.

• Sometimes, haploid nuclei pair off two to a cell and the mycelia are said to be dikaryotic.

Fungi: Sexual ReproductionFungi: Sexual Reproduction• Karyogamy is the next stage of the sexual life cycle. In this stage, the two haploid nuclei fuse and a diploid cell is formed.

• This is usually the only diploid stage in most fungi.

• Meiosis restores the haploid condition and the mycelium produces specialized reproductive structures to disperse the spores.

• Karyogamy is the next stage of the sexual life cycle. In this stage, the two haploid nuclei fuse and a diploid cell is formed.

• This is usually the only diploid stage in most fungi.

• Meiosis restores the haploid condition and the mycelium produces specialized reproductive structures to disperse the spores.

Fungi: Sexual ReproductionFungi: Sexual Reproduction• The processes of karyogamy and meiosis generate a lot of genetic variation within fungi.

• The processes of karyogamy and meiosis generate a lot of genetic variation within fungi.

The Asexual Life CycleThe Asexual Life Cycle

• Many fungi reproduce asexually through the production of a large number of spores.

• The spores are clones and spread by air and/or water.

• When they land in a suitable place, they grow.– Molds are examples of asexually reproduced fungi--spores.

– Yeasts are another example of asexual reproduction by a fungi-budding.

• Many fungi reproduce asexually through the production of a large number of spores.

• The spores are clones and spread by air and/or water.

• When they land in a suitable place, they grow.– Molds are examples of asexually reproduced fungi--spores.

– Yeasts are another example of asexual reproduction by a fungi-budding.

The Importance of FungiThe Importance of Fungi• Fungi are important decomposers.

• They are responsible for recycling the organic matter in an ecosystem.

• They make inorganic nutrients available for plant growth.

• Fungi are important decomposers.

• They are responsible for recycling the organic matter in an ecosystem.

• They make inorganic nutrients available for plant growth.

The Importance of Fungi: SymbiosisThe Importance of Fungi: Symbiosis• Mycorrhizae are common symbionts of plants that are often essential for vigorous growth.

• Some animals make use of fungi in their guts to help them break down food.

• Some insects actually “raise” fungi to assist them in the breakdown of certain plants.

• Mycorrhizae are common symbionts of plants that are often essential for vigorous growth.

• Some animals make use of fungi in their guts to help them break down food.

• Some insects actually “raise” fungi to assist them in the breakdown of certain plants.

LichensLichens

• Lichens are symbiotic associations of millions of photosynthetic microorganisms held in a mass of fungal hyphae.

• They form a surface-hugging carpet often seen on logs and rocks.

• Lichens are symbiotic associations of millions of photosynthetic microorganisms held in a mass of fungal hyphae.

• They form a surface-hugging carpet often seen on logs and rocks.

LichensLichens

• The photosynthetic portion is often a unicellular or filamentous green algae or cyanobacteria.

• The fungus is usually an ascomycete; but some are basiodiomycetes.

• The algae or cyanobacteria usually occupies the inner layer below the lichen’s surface.

• The photosynthetic portion is often a unicellular or filamentous green algae or cyanobacteria.

• The fungus is usually an ascomycete; but some are basiodiomycetes.

• The algae or cyanobacteria usually occupies the inner layer below the lichen’s surface.

LichensLichens

• In most lichens, each partner supplies something the other couldn’t obtain on its own.– Algae provide carbon compounds– Cyanobacterial provide nitrogen fixation and organic nitrogen

– Fungi provide a suitable environment--gas exchange, water, minerals.

– Fungi secrete acids that assist in the uptake of minerals

• In most lichens, each partner supplies something the other couldn’t obtain on its own.– Algae provide carbon compounds– Cyanobacterial provide nitrogen fixation and organic nitrogen

– Fungi provide a suitable environment--gas exchange, water, minerals.

– Fungi secrete acids that assist in the uptake of minerals

LichensLichens

• Many of the fungi of lichens reproduce sexually by forming ascocarps or basidiocarps.

• Lichen algae reproduce asexually by cell division.

• Many of the fungi of lichens reproduce sexually by forming ascocarps or basidiocarps.

• Lichen algae reproduce asexually by cell division.

LichensLichens

• Lichens are a good indicator of air pollution because they don’t stand up well to poor air quality.

• Lichens are a good indicator of air pollution because they don’t stand up well to poor air quality.

Fungi: The Bad…Fungi: The Bad…

• About 30,000 fungi species are parasites and they cause a variety of ailments in humans and problems with crops.

• They cause disease– Ringworm, etc…

• They are the black mold that can cause abandonment of buildings.

• Some fungal biproducts are highly toxic to humans.

• About 30,000 fungi species are parasites and they cause a variety of ailments in humans and problems with crops.

• They cause disease– Ringworm, etc…

• They are the black mold that can cause abandonment of buildings.

• Some fungal biproducts are highly toxic to humans.

The Bad

Fungi: The Good…Fungi: The Good…

• Fungi are also important in agriculture.

• Mushrooms, morels, and truffels are delicacies in the food industry.

• Yeasts are used in the alcoholic beverage industry and for baking.

• Many medicines are derived from them--antibiotics.

• Fungi are also important in agriculture.

• Mushrooms, morels, and truffels are delicacies in the food industry.

• Yeasts are used in the alcoholic beverage industry and for baking.

• Many medicines are derived from them--antibiotics.

Fungi: The Good…Fungi: The Good…

• Fungi have numerous practical uses.

• They are decomposers of ecosystems.

• Fungi have numerous practical uses.

• They are decomposers of ecosystems.

The Good