Let us look at
another main group of unicellular or multicellular organisms: Fungi. This group
includes the well-known mushrooms
and moulds, so you can imagine that
these are not edible or pleasant as a rule. Most fungi are decomposers, making their living on breaking down dead organic
matter, using oxygen. They release energy in the process, and liberate some
organic molecules they can use for growth, and the rest goes into the soil,
available for plants to incorporate into their tissues. Fungi, together with
many decomposing microorganisms, thus make up an essential component of the
flow of matter through an ecosystem, by liberating matter from the dead so that
the new generation can use it.
Other fungi are parasites, stealing nutrients from a host animal or plant, some with the agenda of keeping the host alive, forever parasitized upon, others that prefer to kill the host and move on to another.
Perhaps surprisingly, the fungi are closer to humans than plants in the evolutionary tree. This actually surprised me even more when we learned about their detailed biology at university last year, because they don’t seem quite like anything. The wicked thing is that many fungus groups can share cytoplasm, organelles and even nuclei between individual cells: they are basically interconnected through pores in their cell walls (made up of chitin, by the way, another large sugar, like cellulose, but different), where the cell contents can flow around as needed.
Other fungi are parasites, stealing nutrients from a host animal or plant, some with the agenda of keeping the host alive, forever parasitized upon, others that prefer to kill the host and move on to another.
Perhaps surprisingly, the fungi are closer to humans than plants in the evolutionary tree. This actually surprised me even more when we learned about their detailed biology at university last year, because they don’t seem quite like anything. The wicked thing is that many fungus groups can share cytoplasm, organelles and even nuclei between individual cells: they are basically interconnected through pores in their cell walls (made up of chitin, by the way, another large sugar, like cellulose, but different), where the cell contents can flow around as needed.
Chytridiomycota is the
most primitive. The chytridiomycetes are commonly known as the water moulds.
They are defined by a certain type of spores, but are otherwise quite diverse. Their
spores are motile, meaning they are designed to swim around in water, in
contrast to e.g. being spread by wind, which means that chytridimycetes need to
grow near water (hence their common name). Some forms are unicellular, others
grow as sheets or mats; however, chytridiomycetes do not form the typical
filamentous (thready) hyphae present in most other fungi. Cytridiomycota
includes both decomposers and parasites.
Microscope view of a chytridiomycete. Image from http://s668.photobucket.com/user/fungiblog/media/chytridio.jpg.html
Zygomycota, the pin moulds, have immobile spores, and do form hyphae, which are basically the thready bits, perhaps more easily seen on moulds, but if you take apart a mushroom, you can feel its ‘flesh’ is tightly packed threads. More specifically, the zygomycetes can be recognised by their dormant, heterokaryotic zygosporangium, which is basically a capsule for a new individual, but whose nucleus halves still have not fused properly (crazy, I know!), where they lie protected until the outside conditions are favourable. The zygosporangium looks pretty cool, though I doubt you would be able to see it unless under a microscope.
Zygomycota, the pin moulds, have immobile spores, and do form hyphae, which are basically the thready bits, perhaps more easily seen on moulds, but if you take apart a mushroom, you can feel its ‘flesh’ is tightly packed threads. More specifically, the zygomycetes can be recognised by their dormant, heterokaryotic zygosporangium, which is basically a capsule for a new individual, but whose nucleus halves still have not fused properly (crazy, I know!), where they lie protected until the outside conditions are favourable. The zygosporangium looks pretty cool, though I doubt you would be able to see it unless under a microscope.
A zygomycete. Image from http://mushroomhobby.com/Gallery/Zygomycota/
The zygosporangium of a zygomycete. Image from http://vdshahane.hpage.co.in/gallery27137_2.html
Next are the glomeromycetes, the mycorrhizal fungi. They
typically form a symbiotic relationship with plants, living in tight
association with their roots (sometimes even inside them), helping the plants
to take up nutrients from the soil, while the plants share some of their
products of photosynthesis. This is incredibly common, and it has been
estimated that 90% of all plants have mycorrhizal associations.
A glomeromycete. Image from
http://website.nbm-mnb.ca/mycologywebpages/NaturalHistoryOfFungi/Glomeromycota.html
Ascomycetes, sac fungi, might be more familiar. They keep their spores in a sac, giving them their common name. Some sacs are open, others closed, ether to protect the spores, or to allow them to be shot out explosively by building up pressure in the camber. Lichens, which can easily be mistaken for mosses, are symbiotic associations between ascomycete fungi and some photosynthetic microorganism, either a chlorophyte (green alga) or cyanobacterium (blue-green alga).
Ascomycetes, sac fungi, might be more familiar. They keep their spores in a sac, giving them their common name. Some sacs are open, others closed, ether to protect the spores, or to allow them to be shot out explosively by building up pressure in the camber. Lichens, which can easily be mistaken for mosses, are symbiotic associations between ascomycete fungi and some photosynthetic microorganism, either a chlorophyte (green alga) or cyanobacterium (blue-green alga).
An ascomycete. Image from http://www.clarku.edu/faculty/dhibbett/tftol/content/1introprogress.html
Finally, Basidiomycota, or ‘higher fungi’, includes
the familiar mushrooms. They typically keep their spores under the cap, which
protects them from above. We all know what these look like.
A basidiomycete. Image from http://renewablekinabalu.blogspot.co.uk/2013/04/mushrooms-could-be-used-to-curb.html
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