Biological Classification Test - 89

In higher fungi, karyogamy is delayed and occurs just before meiosis. In the stage intervening between plasmogamy and karyogamy the cells often contain two nuclei or Dikaryons (n+n). Such cells are called dikaryotic cells. The phase is known as Dikaryophase which takes place in Ascomycetes and Basidiomycetes.

The teacher was explaining the advent of lichen formation. A lichen is made up of a simple photosynthesising organism, usually green algae or cyanobacteria, surrounded by filaments of a fungus. Generally, most of lichens bulk is made of interwoven fungal filaments, although in filamentous and gelatinous lichens this is not the case. The fungus is called as a mycobiont. The photosynthesizing organism is called as a photobiont. Algal photobionts are called as phycobionts. Cyanobacteria photobionts are called as cyanobionts. The part of a lichen that is not involved in reproduction, the "body" or vegetative tissue" of a lichen, is called as the thallus. The thallus form is very different from any form, where the fungus or alga are growing separately. The thallus is made up of filaments of the fungus called as hyphae. The filaments grow by branching then rejoining to create a mesh, which is called being. The mesh of fungal filaments may be dense or loose.

In some species of Mucor, e.g., M. racemosus, if grown in liquid media with a high concentration of sugar, the hyphae breakup into short segments known as oidia. These oidia further increase by budding in yeast like fashion. This is called as torula condition. Thus, the correct answer is option C.

The short twisted strands of hyphae which are primarily involved in providing anchorage to the lichens are called as rhizines. Unlike the roots of higher plants, they do not absorb nutrients from the soil but serve only as anchors.
So the correct answer is option B.

In some fungi, true sexual cycle involving nuclear fusion and meiosis is absent. Instead of that, other form of reproduction is seen i.e., plasmogamy. In this fusion of cytoplasm takes place followed by meiosis (haploidisation only). Thus, the correct option is 'Fusion of cytoplasm.'

Red rot of sugarcane is a severe disease traced in sugarcane. It is caused by Colletotrichum falcatum. The mycelium of the fungus infects the parenchymatous cells of the host tissue. The pathogen enters through the nodes at the leaf scars, through any kind of wound, through root primordia and seed-cuttings. It produces conidia which grow into mycelium and infects the host.

Asexual reproduction in fungi takes place by the germination of a type of exospore called Conidiospores which are formed on the Conidiophores of the fungi.
So the correct answer is Conidiospores.

Lichens usually reach maturity and produce ascocarps at 4-8 years of age. The age of some lichens in alpine-arctic area is 1000-4500 years. Their longevity can be partially attributed to their ability to survive long periods of drought unharmed.

Correct Answer: A

Blakslee (1904) discovered the phenomenon of sexual incompatibility in fungi. Since, the two compatible strains could not be distinguished morphologically, he labelled one '+' and the other '-'. Later, Burgeff (1924) demonstrated that a diffusable substance is responsible for the initiation of sexual reproduction and has been chemically identified to be trisporic acid.