The correct answer is option 2: Hyphae are thin threads formed by many fungi.

Hyphae are the main structural units of fungi. They are long, thread-like structures that are typically made up of cylindrical cells called hyphens. These hyphens are connected end to end to form a network of hyphae, which is known as mycelium.

Hyphae allow fungi to grow and spread. They are responsible for absorbing nutrients from the environment, as well as providing support and structure to the fungus. The mycelium of a fungus can extend and penetrate through various substrates, such as soil, decaying matter, or living organisms.

Unlike yeast, which is a single-celled fungus, hyphae are multicellular and have a branched or filamentous structure. This branching allows fungi to explore a larger area and maximize their nutrient absorption.

Overall, hyphae are essential for the growth, nutrition, and reproduction of fungi. They play a vital role in the ecological processes of decomposition, nutrient cycling, and symbiotic relationships with other organisms.