CDS (I) 2022 General Knowledge · Question 30 of 120

Correct — B, thin threads formed by many fungi. A hypha is a long, branching, filamentous structure, and it is the basic building unit of the fungal body. Hyphae grow at their tips, branch as they go, and mat together into the network called a mycelium — the white fuzz on a slice of stale bread, or the fine web running through leaf litter and soil, is exactly that. The walls are built largely of chitin, which is what separates them from the cellulose-walled filaments of plants and oomycetes. Some hyphae are divided into cells by cross-walls called septa, as in Aspergillus; others have no cross-walls at all and are one long multinucleate tube, as in Mucor.

• (a)produced by yeast. — Yeasts are the fungi that do not do this. They live as single cells and, when they do grow in chains, typically form pseudohyphae rather than true hyphae, though a few species can make true septate ones. In any case the option describes who makes hyphae rather than what a hypha is, which is what the question asks.
• (c)reproductive cells. — The reproductive units of a fungus are its spores. Hyphae are vegetative structures that grow, absorb and spread; some of them go on to bear the spore-producing bodies, but the thread itself is not a reproductive cell.
• (d)responsible for preventing the cell from losing water in wet conditions. — Incoherent as stated, since a cell in wet conditions is not losing water in the first place — the risk there runs the other way. Where a fungal cell does need protection against water loss, it is the chitin wall that provides it, not the shape of the filament.

The body of a typical fungus is not made of tissues but of hyphae — fine tubes bounded by a chitin wall, growing at the tip and branching behind it. Their collective mass is the mycelium, and the whole design is built around absorption: a mat of thin threads presents an enormous surface area to whatever the fungus is growing in, and digestive enzymes secreted out of that surface break food down where it lies so the products can be taken back in. The mushroom that appears above ground is only the fruiting body of a mycelium that has been growing unseen; the same architecture makes fungi the principal decomposers of dead plant material in most ecosystems.

The trap here is the first option, because yeast is the fungus every candidate has met and the association is quick. Reading the question strictly settles it — the stem asks what hyphae ARE, so the answer has to be a definition, and 'produced by yeast' would be an incomplete one even if it were true. It is not: yeasts are precisely the fungi that live as single cells. The fourth option is worth pausing on for a different reason, since it is self-contradictory as printed, describing protection against water loss in wet conditions. Ruling it out on its internal logic costs nothing and is faster than recalling any biology.

• A hypha is a long, branching, filamentous structure of a fungus, growing at its tip.
• A mass of hyphae together forms the mycelium, which is the main vegetative body of a fungus.
• Fungal hyphal walls are built largely of chitin, unlike the cellulose walls of plants.
• Septate hyphae are divided by cross-walls, as in Aspergillus; aseptate or coenocytic hyphae are not, as in Mucor.
• Yeasts are the fungi that live as single cells and typically form pseudohyphae rather than true hyphae.

• Attaching hyphae to yeast, which is the one common fungus that does not form them.
• Confusing hyphae with spores, so that a vegetative structure is treated as a reproductive one.
• Assuming fungal walls are cellulose like a plant's, when they are chitin.

As a definition question like this one, as a characters-of-fungi statements item, or through the mycelium and the role of fungi as decomposers.

• practice — not a real PYQ

  The mass of branching threads that makes up the vegetative body of a fungus is called the

  • (a)thallus
  • (b)mycelium
  • (c)sporangium
  • (d)rhizome

  Answer(b) mycelium — the network of hyphae growing through the substrate, of which a mushroom is only the fruiting body.

• practice — not a real PYQ

  Hyphae that are divided into cells by cross-walls are described as

  • (a)septate
  • (b)coenocytic
  • (c)aseptate
  • (d)unicellular

  Answer(a) septate — the cross-walls are called septa; hyphae without them, forming one long multinucleate tube, are coenocytic or aseptate.