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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Fungi Structure and Nutrition
Fungi make up one of the five kingdoms of living organisms and include familiar examples like mushrooms, moulds and yeasts. Unlike plants, fungi cannot make their own food through photosynthesis. Instead, they have unique ways of feeding and growing that make them fascinating to study!
Key Definitions:
Though fungi were once classified as plants, they're actually quite different! Fungi:
The fungal kingdom is incredibly diverse, including:
Fungal cells have several unique features that distinguish them from plant and animal cells. Understanding these structures helps explain how fungi grow and feed.
Fungal cells are eukaryotic, meaning they have a true nucleus and membrane-bound organelles. Here are their key features:
Made of chitin, a tough polysaccharide also found in insect exoskeletons. This gives fungi rigidity and protection but is different from the cellulose walls in plants.
Controls what enters and leaves the cell. Contains ergosterol (rather than cholesterol found in animal cells), which is why many antifungal medications target this molecule.
Contains ribosomes for protein synthesis, mitochondria for cellular respiration and vacuoles for storage. May contain multiple nuclei in some fungal cells.
Most fungi grow as a network of thread-like structures that spread through their food source. This growth pattern is key to how fungi feed and reproduce.
Hyphae are microscopic filaments that grow through the fungus's food source. Each hypha is:
The tip of each hypha grows and extends into new areas, allowing the fungus to explore for food.
When many hyphae grow together, they form a tangled mass called a mycelium. This network:
Unlike plants that make their own food or animals that ingest food, fungi have a unique feeding method called saprophytic nutrition.
Most fungi are saprophytes, which means they feed on dead or decaying organic matter. This feeding process involves several steps:
This method of feeding is perfect for fungi because:
In a forest ecosystem, fungi play a crucial role as decomposers. When trees fall or leaves drop, fungi like bracket fungi and turkey tail mushrooms colonize the dead plant material. Their hyphae penetrate the wood, releasing enzymes that break down tough compounds like lignin and cellulose that few other organisms can digest. Without fungi, dead plant material would accumulate, locking away nutrients and preventing new growth. Scientists estimate that a single cubic centimetre of soil can contain up to 1 kilometre of fungal hyphae, all working to recycle nutrients back into the ecosystem!
Fungi can reproduce both asexually and sexually, but all methods involve the production of spores – tiny, lightweight cells that can grow into new fungi.
Many fungi reproduce asexually through:
This allows fungi to reproduce quickly when conditions are favourable.
Spores are perfectly adapted for dispersal:
Fungi may seem unimportant, but they're actually essential for healthy ecosystems and human society.
Fungi break down dead material, recycling nutrients back into the ecosystem. Without fungi, we'd be buried in dead leaves and trees!
Many fungi form mycorrhizal associations with plant roots, helping plants absorb water and nutrients in exchange for sugars.
Fungi are used to make bread, cheese, medicines (like penicillin) and are being explored for bioremediation to clean up pollution.
Students often confuse fungi with plants. Remember these key differences for your exam:
Make sure you can explain how fungal nutrition works through external digestion and absorption!
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