Biological Classification Test - 5

The cell wall is impregnated with silica.

Dinoflagellates are mostly marine and photosynthetic. The cell wall has stiff cellulose plates on the outer surface. Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.

Many dinoflagellates are known to be photosynthetic. The chloroplasts in most photosynthetic dinoflagellates are bound by three membranes. But a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy).

Fungi have nuclear mitosis. Mitosis in fungi is different from that in plants or most other eukaryotes in one key respect: the nuclear envelope does not break down and re-form. Instead, mitosis takes place within the nucleus.

Fungi have a cell wall and vacuoles. They reproduce by both sexual and asexual means, and like basal plant groups produce spores. Similar to mosses and algae, fungi typically have haploid nuclei.

The fungal cell wall is composed of glucans and chitins; while glucans are also found in plants and chitin in the exoskeleton of arthropods, fungi are the only organisms that combine these two structural molecules in their cell wall.

Most of the vascular plants have this relationship and the fungus makes phosphorus available to the plants.

(1) Archaebacteria are the most primitive form of bacteria. These live in diverse habitat, e.g. extreme hot temperature, saline condition, variable pH, etc. Saline bacteria are called Halophiles (e.g., Halobacterium, Halococcus).

Concept Enhancer: The ability of archaebacteria to survive in harsh conditions is due to the presence of branched lipid chain in their membrane, which reduces the fluidity of their membrane.

Viroids differ from viruses in having RNA molecules without protein coat. Viruses on the other hand posses DNA or RNA with a protein coat as their genetic material. Viruses can infect a wide range of organisms including plants, animals or bacteria, while viroids infect only plants.

In fungi, cell wall contains chitin or cellulose along with other polysaccharides, proteins and lipids. Only in some fungi, e.g. Phytophthora or other oomycetes a purely cellulosic cell wall is present. Hence, only option (b) is wrong, rest of the options are correct.

Concept Enhancer Chitin is chemically N-acetyl glucosamine. The exoskeleton of insects also contains this chemical.

Methanogens belong to archaebacteria. It contains three major classes of primitive bacteria, i.e., Methanogens, halophilic and thermoacidophilic. Methanogens are strict anaerobes, present in the gut of several ruminant animals (e.g., cows, etc) and are responsible for production of methane gas from the dung of these animals.

Concept Enhancer Halophilic bacteria usually occur in salt rich substrate like salt marshes, etc., and are aerobic chemoheterotrophs. Thermophilic bacteria have the dual ability to tolerate high temperature as well as high acidity. These are basically chemosynthetic.