Fungi that obtains nutrients from non-living organic matter are called saprobes. Other fungi obtain nutrients directly from a living host, these are parasites. In either case, the fungi secretes enzymes that allow digestion to take place outside of the fungal body. Nutrients are then absorbed across the cell membranes. Together with bacteria, fungi are the decomposers of the earth. Fungi include yeast, bread mold, and mushrooms.
How many times have you looked for an orange to eat and found that the last one left had grown soft, blue-green fuzz? Have you ever left a wet towel at the bottom of your clothes hamper and at the time of washing you found that it had green "freckles" all over it? Or how many times have you found bread that has gone stale and has grown black "whiskers?" The green fuzz on the orange, the green freckles on the towel and the black whiskers on the bread are all known as molds. Molds are really tiny fungi belonging to one of the 5 kingdoms. "Molds" are a term that is not really a natural grouping, but until scientists figure out exactly where they belong, we will consider them fungi. Molds are so tiny that we cannot see them unless there are many of them bunched together. To see just one mold you need a microscope. There are many kinds of molds. One of the most common molds is the one which turns oranges into green fuzzy balls. It is called penicillium. This is where the drug penicillin comes from.
here is a world of tiny living things called microbes, which live all around us. They are almost everywhere and on almost everything you can think of. They're in the air, the water, the soil, your food, your clothes, on your hands, even on your desk and pencil! Microbes are small, too small for us to see with our eyes. People who study microbes use microscopes to see them.
Students should observe different stages of mold growth. Thin, transparent threads growing all over the slice of bread are a mold garden. The cluster will look like a tangled spider web. If you single out one of the threads and observe it with a microscope you will see many branches of threads. At the ends of some of these branches are little round balls. These balls are hollow round cases and each one is filled with tiny seeds called spores. The spores are the mold's seeds. In a 2-3 day old mold you will begin to see the spores on the garden. The spores are the black substances sitting on top of the threads. Each black ball or spore contains more than 20,000 smaller spores of their own. The threads and their cases have no color but the spores within the cases are all colored. So mold plants have no color, their spores make them appear to have different colors. The 3-4 day old mold should have produced hundreds of millions of new spores. Later they may fall on moist food left out somewhere, sprout threads of their own, and give rise to new spores.
fresh mushrooms from the store
black construction paper
slides and cover slips
Mushrooms are the largest group of the fungi. Mushrooms belong to the club fungus group due to their club-like structures. Mushrooms have 4 basic parts. The top of the mushroom, the umbrella or the part that grows above the ground is called the CAP. Under the cap are the GILLS. Inside the gills are the spores. A spore is a reproductive cell protected by a hard casing. A spore can live through very hot, dry or cold weather and still form a new plant. The STALK holds the mushroom upright. HYPHAE anchor the mushroom to the ground. The growing part of the mushroom is underground - this is called the MYCELIUM. The mushroom grows a cap in order to produce spores. The actively growing portion is the mycelium. Mushrooms are important decomposers in our environment, although some are poisonous to humans.
Fungi are heterotrophs, that is they cannot make their own food. Fungi obtain food by decomposing anything that is organic in nature. Fungi live everywhere. They grow best in warm, moist places. They are not green and do not possess chlorophyll. Fungi can grown on vegetables, bread, meat, fur, wood, leather, or anything that can be warm and moist. Fungi that obtain nutrients from nonliving organic matter are saprobes. Other fungi obtain nutrients directly from a living host, these are parasites. In either case, the fungi secrete enzymes that allow digestion outside the fungal body. Nutrients are then absorbed across the cell membranes. Together with bacteria, fungi are the decomposers of the earth. There are three major types of fungi: yeast, bread mold, and mushrooms.
Fungus itself is made up of a fungal body or the mycelium. The mycelium is a mesh of filaments that branch out in any direction living over or within the organic matter. Each filament is a hypha. Hypha are transparent thin walled tubes.
Fungi reproduce asexually through the formation of spores, through fragmentation of the mycelium or by budding. Some reproduce sexually through the formation of male and female gametes.
In this activity you will examine fresh mushrooms brought from a supermarket. Gently have the students shake the mushroom stalk over a piece of black paper. If any spores fall out, have students examine them with their hand lens or a microscope.
Have them following the procedures on their lab sheet.
PROBLEM: Is the function of a mushroom obvious?
MATERIALS: mushroom, hand lens, black construction paper, microscope
1. Using the microscope or hand lens draw a picture of the mushroom in the space provided. Label the following parts: cap, stalk, gills, hyphae (if visible)
2. Gently shake the stalk over a piece of black paper. Draw what you see. Label this drawing SPORES.
3. What is the difference between the hyphae and the mycelium?
Sac fungus reproduce by spores in sac like structures. These sac like structures usually contain eight spores which are formed as a result of sexual reproduction. Sac fungi range in size from single celled organism such as yeast to multi-celled organisms such as powdery mildew.
Yeast are sac fungi that grow in chains of cells instead of forming mycelia. Yeast cells can form spores in groups of four or eight. Yeast can also reproduce by fission or by budding. Budding occurs when some of the yeast material pushes out of the cell wall, forming a BUD. Several cells may form and force the bud to break away from the parent. This is asexual reproduction or reproduction. In some species of yeast, the parent cell simply divided in two, forming two new cells.
Yeast cause fermentation, a process by which enzymes change sugars to ethyl alcohol and carbon dioxide. Yeast is used for baking bread because carbon dioxide is given off causing the bread to rise.
Follow the instructions on students sheet.
BIOLOGICAL SCIENCE S-FUNGI
PROBLEM: How do mushrooms differ from yeast?
MATERIALS: dry yeast, small test tube, water, 2 droppers, sugar, glass slide, cover slip, microscope, iodine solution toothpick
Part 1. Fill the test tube 1/4 full of water. Use the big end of the toothpick as a scoop. Add 6 scoops of sugar to the vial. Add one scoop of dry yeast. Let sit in a warm spot for 15 to 20 minutes.
Part 2. On a clean slide, place one grain of dry yeast. Turn the microscope to high power. DRAW WHAT YOU SEE UNDER HIGH POWER. Label this drawing as part 2 and the magnification power. Part 1: After 15 to 20 minutes have passed, place one drop of the sugar solution on a clean slide, add one drop of iodine and examine under low and high power. DRAW WHAT YOU SEE UNDER HIGH POWER. Label this drawing as part 1 and the magnification power.
1. Why are yeast cells sac fungi?
CONCLUSIONS: Mushrooms and yeast are both fungi. What do they have in common?
How do they differ?