Lessons 5–6 · 2 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
6
The world of fungi
Textbook: pp. 19–24
GoalExplain the structure, reproduction and importance of fungi and lichens.
Fungi are heterotrophic eukaryotes: they lack chlorophyll and plastids and absorb nutrients over the whole surface of the mycelium. The body, the mycelium, consists of separate threads, the hyphae; in lower fungi (Mucor) the hyphae have no cross-walls, in higher fungi (Penicillium) they do. Yeast is unicellular, reproduces by budding and breaks sugar down into alcohol and carbon dioxide; this gas makes dough rise. Parasitic fungi (rust on wheat, wilt on cotton) cause great crop damage, while saprophytic fungi, together with bacteria, decompose plant and animal remains. Mycorrhiza is a mutually beneficial union of a tree root with a fungus; lichens are a symbiosis of a fungus and an alga (or cyanobacterium) and can be indicators of clean air. Picking and eating unknown mushrooms is dangerous because some are poisonous; only a specialist can identify them.
Worked examples
When yeast is added to dough, sugar is broken down and CO₂ is released; gas bubbles make the dough porous, and the alcohol evaporates during baking.
The mycelium of the Penicillium mould is multicellular with cross-walls; the antibiotic penicillin was obtained from it (A. Fleming, 1928).
Class activity
“Mycelium and hypha”. Make a model of a mycelium with paper or thread: each thread is a hypha. Then two groups show a “lower” (no cross-walls) and a “higher” (with cross-walls) hypha. Do not collect real mushrooms on your own.
Practice
1
What is the main difference between fungi and plants?
They are heterotrophs and have no chlorophyll or plastids, so they do not photosynthesise.
2
How does yeast reproduce and what process does it carry out?
By budding; it breaks sugar down into alcohol and CO₂ (alcoholic fermentation).
3
Cotton in a village is infected with wilt. Name two agrotechnical control measures.
Proper crop rotation and growing new wilt-resistant cotton varieties.
4
Why are lichens common where the air is clean but rare in polluted city centres?
They take up substances directly from the air and are sensitive to harmful gases, so they die in polluted air, which makes them indicators.