Question 1

Discuss how classification systems have undergone several changes over a period of time.

Accepted Answer

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) Monera2) Protista3) Fungi4) Plantae5) Animalia

Question 2

State two economically important uses of: (a) Heterotrophic bacteria(b) Archaebacteria

Accepted Answer

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.

Question 3

What is the nature of cell walls in diatoms?

Accepted Answer

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.

Question 4

Find out what do the terms algal bloom and red-tides signify.

Accepted Answer

Algal bloom refers to the vigorous growth of algae or blue-green algae in the water, due to the enrichment of water body with mineral nutrients coming from fields, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals, due to suffocation.Red-tide is a phenomenon caused by algal blooms during which algae become so numerous that they discolour coastal waters (hence, the name "red tide").

Question 5

How are viroids different from viruses?

Accepted Answer

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.

Question 6

Describe briefly the four major groups of Protozoa.

Accepted Answer

The Protozoans which are included in the kingdom Protista, are single-celled hetrotrophic eukaryotic organisms. Depending on their mode of locomotion they are grouped into four; The amoeboid protozoans - which use pseudopodia for movement e.g. Amoeba, EntamoebaThe flagellated protozoans - which have flagella assisting their movement. e.g. TrypanosomaThe ciliated protozoans - which have thousands of cilia whose coordinated movement helps the organism to move. e.g. ParamoeciumThe sporozoans - which do not have movement but are carried around by flow of fluids. They are usually parasites with spore-like stage in their life cycle. e.g. Plasmodium

Question 7

Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Accepted Answer

Plants are the autotrophs as they have the ability to synthesize their own food by the process of photosynthesis due to the presence of green pigments.During this process, they utilize carbon dioxide and water in the presence of sunlight. However, some plants are partially heterotrophic and are called as insectivores. They have various means of capturing insects so as to supplement their diet with nitrogen derived from insects, as they live in nitrogen-deficient soil. Examples include the pitcher plant (Nepenthes), Venus flytrap, bladderwort, and sundew plant (Drosera).

Question 8

What do the terms phycobiont and mycobiont signify?

Accepted Answer

Phycobiont refers to the algal component of the lichens and mycobiont refers to the fungal component. Both of these are present in a symbiotic relationship in which algae prepare food for fungi due to the presence of chlorophyll whereas the fungus provides shelter to algae and absorbs water and nutrients from the soil.

Question 9

Give a comparative account of the classes of kingdom Fungi under the following:(i) Mode of nutrition(ii) Mode of reproduction

Accepted Answer

(A) Phycomycetes- This group of fungi includes members such as Rhizopus, Albugo, etc.(i) Mode of nutrition:They are obligate parasites on plants or are found on decaying matter such as wood.(ii) Mode of reproduction:Asexual reproduction takes place through motile zoospores or non-motile aplanospores produced endogenously in a sporangium.Sexual reproduction may be of isogamous, anisogamous, or oogamous type resulting in the formation of thick-walled zygospore.(B) Ascomycetes- This group of fungi includes members such as Penicillium, Aspergillus, Claviceps and Neurospora.(i) Mode of nutrition:They are sporophytic, decomposers, parasitic or coprophilous (growing on dung).(ii) Mode of reproduction:Asexual reproduction occurs through asexual spores produced exogenously, such as conidia produced on conidiophores.Sexual reproduction takes place through ascospores produced endogenously in sac-like asci and arranged inside ascocarps.(C) Basidiomycetes- This group of fungi includes members such as Ustilago, Agaricus and Puccinia.(i) Mode of nutrition:They grow as decomposers in soil or on logs and tree stumps. They also occur as parasites in plants causing diseases such as rusts and smuts.(ii) Mode of reproduction:Asexual reproduction takes place commonly through fragmentation. Asexual spores are absent.Sex organs are absent but sexual reproduction takes place through plasmogamy. It involves fusion of two different strains of hyphae. The resulting dikaryon gives rise to a basidium. Four basidiospores are produced inside a basidium. (D) Deuteromycetes- This group of fungi includes members such as Alternaria, Trichoderma and Colletotrichum.(i) Mode of nutrition:Some members are saprophytes while others are parasites. However, a large number act as decomposers of leaf litter.(ii) Mode of reproduction:Asexual reproduction is the only way of reproduction in Deuteromycetes, which occurs through asexual spores called as conidia.Sexual reproduction is absent in Deuteromycetes.

Question 10

What are the characteristic features of Euglenoids?

Accepted Answer

Some characteristic features of Euglenoids are as follows.• Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.• Instead of the cell wall, a protein-rich cell membrane known as pellicle is present.• They bear two flagella on the anterior end of the body.• A small light sensitive eye spot is present.• They contain photosynthetic pigments such as chlorophyll and can thus prepare their own food. However, in the absence of light, they behave similarly to heterotrophs by capturing other small aquatic organisms.• They have both plant and animal-like features, which makes them difficult to classify and hence they are called as connecting link between plants and animals.

Question 11

Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Accepted Answer

Viruses are sub-microscopic, infectious, nucleoprotein particles that can infect all living organisms. A virus consists of genetic material either in the form of RNA or DNA surrounded by a protein coat.Most of the viruses, infecting plants, have single-stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double-stranded RNA or double-stranded DNA.Bacteriophages or viruses infecting bacteria mostly have double- stranded DNA. Their protein coat called as capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.AIDS, smallpox, mumps, and influenza are some common examples of viral diseases.

Question 12

Organise a discussion in your class on the topic, are viruses living or nonliving?

Accepted Answer

Viruses are microscopic organisms that have characteristics of both living and non-living. A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) and protein suggests that viruses are alive. In addition, they can also respond to their environment in a limited manner inside the host cell.However, some other characters, such as their inability to reproduce without using the host cell machinery and their acellular nature indicate that viruses are non-living. Therefore, classifying viruses has remained a mystery for modern systematics.

Chapter 2 : Biological Classification