What are fungi?
Fungi (one is a fungus) are a kingdom of living things. They are not plants and not animals.
- Their cells have a nucleus (they are eukaryotes).
- Their cell wall is made of chitin, the same tough stuff found in insect shells.
- They have no chlorophyll, so they cannot make food from sunlight.
- They store food as glycogen, like animals, not as starch.
Fungi live almost everywhere: soil, dead wood, food, water, and even on our skin.
Hyphae and mycelium: the body of a fungus
Most fungi are built from very thin threads called hyphae (one is a hypha). Many hyphae together make a net called a mycelium.
In a cap mushroom, the mycelium lives hidden in the soil. When there is enough food and water, hyphae pack tightly together and push up a fruit body: the mushroom we see. It has a cap, gills under the cap and a stalk. Picking a mushroom is like picking an apple: the tree (mycelium) stays alive.
Try it at home
Put a slice of moist bread in a closed plastic bag in a warm place. Look at it each day for a week (do not open or smell it). Draw the white threads and black dots you see. Throw the bag away sealed when you finish.
How fungi feed
Fungi are heterotrophs: they need ready-made food. They feed by absorption. Hyphae release enzymes (digestive juices) onto the food. The food breaks down into small pieces outside the fungus, and the hyphae soak them up.
- Saprotrophs feed on dead things: fallen leaves, dead wood, old bread. They are nature's recyclers and return minerals to the soil.
- Parasites feed on living hosts and harm them: rust and smut on wheat, ergot on rye, ringworm and athlete's foot on people.
- Mutualists live with a partner and both gain: lichens (fungus + alga) and mycorrhiza (fungus + plant roots).
Moulds, yeast and the main groups
Fungi make many tiny, light spores. Wind, water and animals carry spores far. A spore that lands on damp food grows hyphae. Fungi also grow from broken bits of hyphae, and yeast makes new cells by budding.
- Mucor and Rhizopus (pin moulds, zygomycetes): white threads on bread with black round spore cases on top.
- Penicillium and Aspergillus (ascomycetes): blue-green or yellow-green moulds; spores form in chains. Penicillium gave the antibiotic penicillin.
- Yeast (an ascomycete): one cell. In fermentation it turns sugar into alcohol and carbon dioxide. The gas makes dough rise.
- Cap mushrooms and bracket fungi (basidiomycetes): spores form on the gills under the cap.
Edible and poisonous mushrooms
Some mushrooms are good food: button mushroom, oyster mushroom, shiitake. Others are deadly: the death cap and fly agaric. Their poison is not destroyed by cooking. There is no simple test (colour, smell, silver spoon) that shows if a wild mushroom is safe. Rule: never eat a wild mushroom unless an expert has checked it. Eat only mushrooms bought from a shop.
Lichens and why fungi matter
A lichen is a fungus and a green alga (or cyanobacterium) living as one body. The alga makes food by photosynthesis. The fungus holds water, takes up minerals and grips the surface. Lichens grow on bare rock and tree bark and are often the first settlers there; they slowly break rock into soil. Many lichens die in dirty air, so they are used as indicators of air pollution.
Uses and harms of fungi: decomposers in every ecosystem; food (mushrooms, yeast bread, cheese); medicines (penicillin); but also food spoilage, crop diseases and some human infections.
Key formulas and definitions
- Hypha = one thin thread; mycelium = net of many hyphae
- Fruit body (mushroom) = cap + gills + stalk
- Feeding: enzymes out → food digested outside → absorbed
- Fermentation by yeast: sugar → alcohol + carbon dioxide + energy
- Lichen = fungus + alga (both gain: mutualism)
- Saprotroph = feeds on dead matter; parasite = feeds on a living host
Worked examples
1. Bread left in a warm, damp kitchen grows white threads with black dots. Name the fungus and explain the dots.
It is a pin mould such as Mucor or Rhizopus. The white threads are hyphae; the black dots are spore cases full of spores.
2. Why does dough with yeast rise in a warm place?
Yeast ferments the sugar in the dough and gives off carbon dioxide gas. The gas makes bubbles that puff up the dough. Warmth makes yeast work faster.
3. A forest floor never fills up with dead leaves. Which living things help, and how?
Saprotrophic fungi (and bacteria). Their hyphae digest the dead leaves with enzymes, absorb the food and return minerals to the soil.
4. Lichens disappear from trees near a busy road. What does this tell us?
The air there is polluted (for example with sulfur dioxide). Many lichens cannot survive dirty air, so they act as pollution indicators.
Common mistakes
- Calling fungi plants. Fungi have no chlorophyll and their wall is chitin, not cellulose.
- Thinking the mushroom is the whole fungus. It is only the fruit body; the mycelium in the soil is the main body.
- Believing cooking or a silver spoon test makes wild mushrooms safe. It does not.
- Thinking a lichen is a single organism. It is a partnership of a fungus and an alga.