Question

1. To apply what you have learned about fungi, answer the following questions (1.75)

a)Why would a fungus make and secrete an antibiotic?

           

b). Describe the anatomy of a mushroom, and explain how it serves as the reproductive organ of the fungi.

           

c). Why would ergot, a parasite of grains like wheat, produce an animal toxin?

           

d). Explain, in detail, why the addition of brewer’s yeast (S. cerevisiae) makes bread rise.

           

e). Are lichens pure fungi? Why or why not?

           

f). What feature of members of the Mucorales lineage makes them able to have a mutualistic relationship with cattle and other herbivores?

           

g). How can black bread mold begin to grow on bread in a house that does not currently contain moldy bread?

Answer 1

Answer a):

Fungi secret natural antibiotics.

Fungi are slow growing organisms and in natural habitats have to face tough competition from other fast growing microorganisms like bacteria. In order to survive and grow they need to reduce this competition and have enough resources of nutrients they need. This they seem to achieve by secreting the antibiotic substances in the surrounding area and eliminate maximum fast growing bacteria from the medium / natural habitat.

In fact the first antibiotic was known to man when Alexander Flemming saw a contaminant fungi (Penicillium) on his culture plate and noted a zone of bacterial inhibition around it (Penicillin).

Answer b):

Mushroom is a fruiting body.

Certain fungi (Basidiomycetes) grow a fruiting body known as mushroom. Mushroom is part of the fungus and produces spores which are the basic reproductive units of the fungus.

The fungal mycelium remains hidden underground. When two hyphae come near to each other, their cells fuse making a cell with two nuclei. This fused cell grows into a fruiting body called mushroom. Soon small plates appear under the caps of the mushroom called gills. In the gills of the mushroom cap the haploid nuclei fuse to form a diploid zygote. This is followed by meiosis to produce haploid spores in the gills. These haploid spores are released in the surrounding producing new fungal mycelia.

Parts of Mushroom (Fruiting Body):

Answer c):

Ergot, fungal disease of cereal grasses is caused by fungi belonging to Ascomycetes group. They are parasites of cereal grasses like wheat, Rye, etc. They produce toxic substances called ergot alkaloids. All animals are affected by these chemical compounds but cattle are the most affected. As cattle and ergot share the same food (cereal grass), they are competition for each other for food and nutrients. Hence these fungi produces substances to protect themselves from being ingested by cattle as well as to protect their own food supply of cereal grass from cattle.

Some ergot alkaloids cause vasoconstriction of small arteries and affect the extremities of the cattle like lips, tails, tips of ears etc. Some also produce hallucinations, irrational behaviour, convulsions and even death. The neurotropic activities of these alkaloids can also affect humans. (A hallucinogen LSD a popular drug is actually secreted by Ergots)

Answer d) :

Brewer's yeast and baker's yeast is made from one celled fungus called Saccharomycetes cerevisiae. This fungus ferments the starch and other sugars present in the dough and converts it to alcohols and CO2 is released as a by product in the process. This carbon dioxide gets trapped in the strands of fibre and starch in the dough and makes it rise.

Answer e)

No, Lichens are not pure fungi.
They are symbiotes having a fungal element and a algal component.
The algal component of lichen synthesize carbohydrates by the process of photosynthesis and provides nutrition to the fungal component. The fungal component in turn provides shelter and minerals & water that it absorbs through its hyphal roots from the soil for the algal component.
Nowadays, this association is called Helotism (master-slave relationship) instead of symbiosis.