class 11 biology chapter 2 biological classification
EXERCISE : 2
1.DISCUSS HOW CLASSIFICATION SYSTEMS HAVE UNDERGONE SEVERAL CHANGES OVER A PERIOD OF TIME ?
The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.
Therefore, Linnaeus gave a two-kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.
So, Ernest Haeckel, then, separated unicellular eukaryotic organisms into separate kingdom named Protista and hence, gave three kingdom classification.
After that Copeland separated all prokaryotic organisms into a separate kingdom named Monera and hence, Four-Kingdom systems of classification came into existence.
And lastly, a five kingdom system of classification was proposed by R.H. Whittaker in 1969 to separate achlorophyllous, decomposer organism into a separate kingdom named Fungi. So five kingdoms now are:
1) Monera
2) Protista
3) Fungi
4) Plantae
5) Animalia
2.STATE TWO ECONOMICALLY IMPORTANT USES OF :(a).hetero tropic bacteria (b).archaebacteria
Heterotrophic bacteria are microorganisms which survive by deriving their energy using organic matter from other sources rather synthesizing their own organic matter. The Heterotrophic bacteria have several economic applications; Lactobacillus and Streptococcus are widely used for the production of milk products like curd and cheese. Streptomyces is a genus of Gram-positive bacteria with the ability to produce bioactive secondary metabolites such as antifungals, antivirals, antitumoral, anti-hypertensives, and mainly antibiotics and immunosuppressives. Many different kinds of heterotrophic bacteria are used for sewage treatment. Some heterotrophic bacteria like Alcanivorax or Methylocella Silvestris have an important applications in bio-remediation (cleaning the oil spills).
Archaebacteria are a group of prokaryotes which live under very harsh and hostile conditions. Since the enzymes from these organisms can survive harsh conditions they have many industrial applications in biotechnology; Many of the thermostable enzymes used in the manipulation of DNA are derived from Archaebacteria, Methanogens of the Archaebacteria are mainly involved in the biogas production.
3.WHAT IS THE NATURE OF CALL-WALL IN DIATOMS ?
The process of cell walls construction of diatoms is known as Frustule. It has two thin overlapping shells fitting into each other just as a soap-box. Their walls are made up of silica. The dead and decomposed diatoms deposit the sillica present in their walls in form of diatomaceous earth. This diatomaceous earth is very soft and quite inert. It is used in filtration of oils, sugars, and for other industrial purposes.
4.FIND OUT WHAT DO THE TREMS “ALGAL- BLOOM ” AND “RED-TIDES” SIGNIFY ?
ALGAL-BLOOM refers to an increase in the population of algae or blue-green algae in water due to an enrichment of nutrients , resulting in discoloration of the water body. This casus an increses in the BIOLOGICAL OXYGENDEMEND (BOD), resulting in the death of fish’s and other aquatic animals.
RED-TIDES are caused by dinoflagellates (gonyaulax) that multiply rapidly. There large numbers in the sea makes the sea appear red in color .these realize the larger amount of toxin with result in the death of other marine organisms.
Both of these signify on the pollution of the water body
5.HOW ARE VIROIDES DIFFERENT FROM VIRES ?
Viroids are free RNA molecules of low molecular weight without any protein coat while viruses can have either RNA or DNA molecules encapsulated in a protein coat. Viroids are smaller in size than the viruses. Viroids infect only plants whereas virus infects all types of organisms. In viroids, protein coat is absent whereas in viruses a protein covering or a coat called as capsid is present around the genetic material.
6. DESCRIBE BRIEFLY THE FOUR MAJOR GROUPS OF PROTOZOA ?
- Viruses are complicated assemblies of molecules, including proteins, nucleic acids, lipids, and carbohydrates, but not their own they can do nothing until they enter a living cell.
- Without cells, viruses would not be able to multiply.
- Therefore, viruses are not living things.
