Fungi and Plant Biology

• Fungi, often mistaken as similar to plants, are distinct organisms.
• Fungi are decomposers, breaking down organic material and absorbing nutrients.
• Fungi reproduce by releasing spores.
• Fungi are heterotrophs, obtaining energy from organic substances.
• They secrete digestive enzymes to break down organic material and absorb nutrients.
• Fungi cell walls are made of chitin for structural support.
• Chitin is a polysaccharide found in insect exoskeletons and other invertebrates.
• Truffles, molds, yeasts, mushrooms, and mildews are examples of fungi.
• Plants are autotrophs, producing their own energy through photosynthesis.
• Plants are producers, using radiant energy to create food.
• Chlorophyll in chloroplasts converts carbon dioxide and water into glucose using sunlight.
• Plants reproduce through seeds or spores.
• Plant cell walls are made of cellulose, providing structural support.
• Grass, trees, flowers, and ferns are examples of plants.
• Plants and fungi evolved from protists, single-celled eukaryotic organisms.
• Eukaryotic organisms have cells with membrane-bound organelles and DNA in a nucleus.
• Both plants and fungi are immobile, and fungal hyphae resemble plant roots.
• Fungi lack chloroplasts and have chitin cell walls, unlike plants.

Evolution of Fungi

• The fungi kingdom has significant biological diversity, with approximately 3.8 million species, but only 100,000 identified.
• Fungi are essential decomposers, breaking down organic matter and releasing nutrients into the soil.
• Earliest fungi species were likely aquatic, with symbiotic relationships with photosynthetic bacteria.
• Approximately 460 million years ago, fungi adapted to land, becoming some of the first terrestrial organisms.
• Fungi aided plant evolution by releasing nutrients into the soil by breaking down detritus.
• Detritus is waste matter from rocks, minerals, and organic material.
• During the Devonian Era (419.2 to 358.9 million years ago), Prototaxites, gigantic fungi as tall as 26 feet, existed.
• The K-T extinction event (65 million years ago) favored fungi growth due to plant decay.
• Mammals survived the K-T extinction because they were too hot for fungal pathogens that affected reptiles.
• Fungi are adaptable and can survive in hazardous conditions.
• Most fungi are terrestrial decomposers, thriving on dead organic matter.
• Parasitic fungi can cause diseases, such as ringworm on humans.
• Fungi are found in Antarctica, cockroaches, and nuclear power plants.

When Did Fungi First Appear?

• Fungi first appeared about one billion years ago, diverging from animals.
• Microscopic organisms with chitin-containing filaments were discovered in Arctic Canada.
• This suggests fungi are older than the previously thought 600 million years.
• However, some researchers are skeptical about the ancient fungi findings in Arctic Canada.

Phylogeny of Fungi

• The phylogeny of fungi explains common ancestry and evolutionary development.
• There are five phyla of fungi and one informal group called Deuteromycota:
  • Chytridiomycota (the Chytrids):
    • Appeared about 500 million years ago and are a group of simple true fungi.
    • Mostly unicellular and reproduce sexually and asexually.
    • Live in aquatic environments, some parasitically on land.
  • Zygomycota (the conjugated fungi):
    • Saprobes that thrive on decaying organic matter.
    • Some are parasitic on insects and found on bread, fruit, and vegetables.
  • Ascomycota (the sac fungi):
    • Have sac-like structures that disperse ascospores.
    • Yeasts are commonly used in baking and brewing.
    • Some species are parasitic on plants and animals.
  • Basidiomycota:
    • Characterized by a fruiting body and gill-like structures under the cap.
    • A network of mycelium grows underground.
    • Reproduce through alternation of generations, with both sexual and asexual spore production.
  • Glomeromycota:
    • Live in mutualistic symbiotic relationships with plant life.
    • Require plant roots to survive.
    • DNA suggests they descended from a common ancestor (monophyletic lineage).
  • Deuteromycota (the imperfect fungi):
    • Reproduce asexually.
    • Considered a polyphyletic group with multiple ancestral relationships.
    • Very diverse and known as mold.
    • Mold grows in hyphae, which are multicellular structures.

Mushroom Evolution

• Mushrooms are fungi with fruiting bodies and underground mycelium.
• Mycelium is a network of hyphae that absorbs and transports nutrients.
• Mushrooms reproduce by releasing spores.
• Mushrooms are part of the Basidiomycota phylum.
• The earliest mushrooms evolved approximately 815 to 715 million years ago.
• They possibly played a key role in plant evolution on land.
• Mycelium remains have been found in rocks dated between 810 to 715 million years old.
• Mushroom fossils are rare due to their delicate structure, resulting in gaps in the fossil record.
• The earliest mushroom fossils are approximately 460 million years old.
• Fruiting body development was an evolutionary step in sexual reproduction in fungi.
• Gill-like structures under the cap of mushrooms increased the surface area for spore production.
• Some mushroom species developed toxicity as a defense mechanism.

Evolution of Plants

• Photosynthetic eukaryotic protists resembling algae were early plant species that evolved from cyanobacteria.
• Fossils of these organisms are dated to be about 1700 million years old.
• Early plant life was aquatic until 510 to 439 million years ago.
• Bryophytes, including mosses and liverworts, were some of the earliest nonvascular land plants.
• Nonvascular plants lack specialized structures for transportation.
• Lacking a vascular system, nonvascular plants grow on the ground surface and are smaller than vascular plants.
• Vascular plants evolved approximately 425 million years ago.
• Vascular plants have xylem and phloem for water and food transport.
• Vascular plants grow larger than nonvascular plants and include trees, angiosperms, and gymnosperms.
• Nonvascular plants reproduce through the alternation of generations.
• The sporophyte generation produces spores for asexual reproduction.
• The gametophyte generation produces sperm and eggs.
• Gymnosperms (naked-seed plants) evolved 305 million years ago and reproduce through seeds.
• Male and female reproductive organs are cones without flowers or fruits.
• Gymnosperms mostly reproduce through wind dispersal.
• Angiosperms (flowering plants) evolved 140 million years ago and reproduce through seeds in fruit.
• Angiosperms contain flowers that house reproductive organs and aid in pollination.
• Angiosperms are the most evolutionarily advanced plants, with flowers and fruit for seed dispersal.

When Did Plants First Appear?

• The earliest evolutionary relationship with plants is with prokaryotes.
• Prokaryotes are unicellular organisms without membrane-bound organelles and DNA not in a nucleus.
• Prokaryote evidence was discovered in stromatolites dated 2700 million years ago.
• Cyanobacteria, blue-green algae, formed ancient stromatolites and contributed to atmospheric oxygen.
• Cyanobacteria contained photosynthetic pigments like chloroplasts in algae and plants, suggesting an evolutionary relationship.

Classification of Plants

• Plants are classified by spore or seed reproduction, the presence of a vascular system, flowers, and the number of seed leaves.
  • Spore-reproducing plants: include ferns, mosses, liverworts, and algae.
  • Seed-bearing plants: include angiosperms and gymnosperms.
  • Vascular plants: have vascular tissues for transport and include trees, angiosperms, and gymnosperms.
  • Non-vascular plants: include mosses and liverworts.
  • Angiosperms: house seeds in fruit and produce flowers.
  • Gymnosperms: have naked seeds not contained within a fruit and reproduce through cones (conifers).
  • Angiosperms: categorized into monocots (one seed leaf, petals divisible by three) and dicots (two seed leaves, four, five, or more petals).

Similarities in Fungi and Plant Evolution

• Fungi and plants are eukaryotic organisms that evolved from single-celled organisms.
• They both evolved from early protists, share a cell structure, and have similar root structures and growth patterns.
• Plants and fungi have symbiotic relationships with other organisms, both beneficial and parasitic.
• Fungi and animals are heterotrophs, gaining nutrition from other sources.
• DNA evidence suggests a close ancestral relationship between fungi and humans, branching away from plants about 1.1 billion years ago.
• Animals and plants later branched off from each other, sharing ancestry with a single-celled organism with flagella.

Fungi are distinct from plants, acting as decomposers that break down organic material. They reproduce via spores and have chitin-based cell walls. Plants, such as grass and trees, are autotrophs that produce energy through photosynthesis and have cellulose-based cell walls.