Lesson 15: A Fungus Among Us

Well, we’ve looked at two of the five kingdoms so far – the bacteria of kingdom Monera and the one-celled creatures of kingdom Protista.  Now we are on to the third – Kingdom FUNGI.

You probably already know a few things about fungi.  For example, you probably know that a mushroom is a type of fungus.  But  what else do you know?  Click and PLAY THIS  GAME to find out.

Do you recognize any other fungi from these pictures? 

We don’t,  of course, want a moldy fungus growing on our bread.  And some fungi can cause serious diseases.  But others are useful and important…yeast, for example, makes bread rise.  Some important medicines such as penicillin are derived from fungi.  (Watch the video on Alexander Fleming in the sidebar to learn more).  Other fungi  are important in the manufacture of cheeses and wine. 

I want to spend a few minutes learning about some general characteristics of fungi, but first we need to start growing a sample fungus to look at later. It will take five days or more to grow, so, fellow mycologists,  start it now:

You will need a slice of bread (freshly baked bread works fastest, but any bread will do – the fresher the better) and a self-seal plastic bag.  Sprinkle the bread with water.  Leave it uncovered for several hours, and then sprinkle on a little more water.  Place the bread into a plastic bag.  Seal the bag, trapping in a small amount of air.  Place the bag in a dark place at room temperature (such as under the kitchen sink.) We’ll pull it out in a few days to check for any fungal growth.

Okay, now we are ready to talk about some characteristics of typical fungi.  In a few minutes we will look more specifically at three sample phyla in this kingdom, but all of the phyla have some things in common, so lets start by pointing out the similarities. For example, most fungi, no matter to what phylum they belong,   are heterotrophic, specifically saprophytic.   Do you remember what “saprophytic” means?  Saprophytic organisms, also known as decomposers,  derive their nourishment by breaking down dead or decaying organisms.  In fact, fungi are the most important decomposers in the world.  If it weren’t for the fungi all around us that are constantly decomposing them, we’d be buried in dead leaves, animal waste, and trash.

Fungi break down their food by secreting special chemicals into the food so that it will digest.  Then they absorb the digested food into their bodies.  This type of digestion is called “extracellular digestion” because it takes place outside of the organism.  In most fungi this digestion is performed in a structure called the mycelium.  We will look more closely at the mycelium when we examine specific fungal phyla.

Most fungi reproduce by producing spores, tiny oval-shaped structures  which are designed to survive even in unfavorable conditions.  Mushrooms produce their spores in gills or pores – so, before we look more closely at spores,  maybe it’s time to look at the structure of mushrooms in a little more detail.  Print the picture below, and follow the instructions to color:

 

 Mushrooms are members of the fungal phylum Basidiomycota.  The main part of the mushroom, unlike what you might expect, is the underground mycelium which performs the extracellular digestion.  The mycelium is made up of many individual rootlike strands called hyphae.  Color the mycelium BROWN.   The stalk of the mushroom is called the stipe.   Color it GRAY.  The cap is the umbrella-shaped cup on the top of the mushroom.  Color it  RED.  Underneath the cap the reproductive spores are formed – either in slits called gills or behind holes called pores.  Color the gills in the drawing PINK.  Do you see the flap of tissue attached near the top of the stipe?  This structure is called the ring.  When mushrooms newly sprout, the cap and stipe are inside a thin covering of tissue called the veil.  As the mushroom grows it breaks through the veil and sometimes leaves a rim of fleshy tissue surrounding the stipe, like you can see in the picture.  Color the ring BLUE. 

Now see if you can find a few sample live-growing mushrooms to study – or buy some at  a grocery store.

Let’s look at the external anatomy first.  Print this chart and fill it out as you examine each specimen.  Wear gloves if you gathered your samples from outdoors – mushrooms can be toxic!  Use a tape measure to measure the cap width and stalk length.  Use tweezers and a magnifying glass to check out the gills.  See how many specimens you can find to examine.  Scan your chart and send it to me and I will publish it on our website.

The next thing we want to do is look at some spores under a microscope.  The easiest way to gather some is to make a spore print. To do this you will need a mushroom cap with open gills (not pores). Older mushrooms work best.   Break off the stipe and lay the mushroom cap, gill side down, on a sheet of white paper.  Cover the cap with a glass or bowl and leave overnight.  In the morning it should look something like this:

  Scrape up a bit of the residue with a toothpick and tap onto a clean slide.     Add a drop of water and a coverslip and check it out under your microscope.  Don’t forget to draw what you see on a sheet of microscope paper. 

    Puffballs are also members of phylum Basidiomycota.  Can you see the spores in this video?

     Members of phylum Basidiomycota are obviously multicellular, but some fungi are unicellular.  Yeast, a member of phylum Ascomycota, is an example of a unicellular fungus.  Yeasts often reproduce by a process called budding, in which their cell walls swell to form a pouch, fill with cytoplasm, and eventually pinch off to form new yeast cells. 

See if you can see any budding cells in this short video, and then lets look at some actual yeast cells budding. 

 

To make a wet-mount slide you will need a packet of active dry yeast like the kind used in making bread.  The spores in the packet will grow into yeast cells when mixed with water, so you will need some warm water to “wake up” the inactive spores.  You will also need some sugar.   The reason bread dough rises is that the yeast feeds on the sugar in the dough and breaks it down into alcohol and carbon dioxide.  Carbon dioxide is a gas, and when the gas tries to bubble out of the dough lump, the lump grows larger due to the gas bubbles trapped inside.  Interestingly, no oxygen is necessary for this process to occur – so it is an anaerobic process.  We call this fermentation.  You can understand now why fungi are also used to make wine and beer.  Fermentation not only produces carbon dioxide gas but also alcohol. 

 Now, here’s what we will do: 

• In a glass or measuring cup, mix your packet of yeast into a cup of warm water.
• Add a tablespoonful of sugar.
• Wait five to ten minutes. What do you see? You should see bubbles form – what do you think they are?
• Place a drop of the solution onto a clean slide and cover with a cover slip.
• Start on scanning power, and then observe on medium and high powers. Draw what you see on a sheet of microscope paper.  Look for oval shaped cells that are attached in the middle (like the picture above). 
• Wait thirty minutes and observe again.  What differences do you see? Can you find any chains of yeast cells?

Yeast isn’t the only edible member of phylum Ascomycota.  Have you ever heard of truffles? Not chocolates, but fungus. CLICK HERE to learn about members of this fascinating phylum.

 Ready to see how much you remember so far?  Before we check out our bread mold,  CLICK HERE  for a crossword puzzle to test yourself: