Biological
Classification
NCERT Solutions
Exercises
Page - 22
1. Discuss how classification systems have undergone several changes over
a period of time?
Answer 1: 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.
To solve these problems, a five kingdom system of classification was
proposed by R.H Whittaker in 1969. On the basis of characteristics, such as
cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms,
Monera, Protista, Fungi, Plantae, and Animalia were formed.
2. State two economically important uses of:
(a) Heterotrophic bacteria
(b) Archaebacteria
Answer 2: Two economically important uses of Heterotrophic bacteria are:
→ They help in the production of curd from milk.
→ Many antibiotics are obtained from some species of bacteria.
Two economically important uses of Archaebacteria are:
→ Methane gas is produced from the dung of ruminants by the methanogens.
→ Methanogens are also involved in the formation of biogas and sewage
treatment.
3. What is the nature of cell-walls in diatoms?
Answer 3: The cell walls in diatoms are embedded with silica, which makes
them indestructible. They form two thin overlapping shells which fit together
as in a soap box. Thus diatoms have left behind large amounts of cell wall
deposits in their habitat.
4. Find out what do the terms 'algal bloom' and 'red-tides' signify.
Answer 4: Algal bloom refers to an increase in the population of algae or
blue-green algae in water, resulting in discoloration of the water body.
Red tides are caused by red dinoflagellates that multiply rapidly. Due to their
large numbers, the sea appears red in colour. Toxins released by them can
kill other marine species.
5. How are viroids different from viruses?
Answer 5: Viroids are free RNAs without the protein coat, while virus have a
protein coat encapsulating the RNA.
6. Describe briefly the four major groups of Protozoa.
Answer 6: The four major groups of Protozoa are:
• Amoeboid protozoans: These organisms live in fresh water, sea water or
moist soil. They move and capture their prey by putting out pseudopodia
(false feet) as in Amoeba. Marine forms have silica shells on their surface.
Some of them such as Entamoeba are parasites.
• Flagellated protozoans: The members of this group are either free-living or
parasitic. They have flagella. The parasitic forms cause diaseases such as
sleeping sickness. Example: Trypanosoma.
• Ciliated protozoa or ciliates: They are aquatic individuals that form a large
group of protozoa. Their characteristic features are the presence of
numerous cilia on the entire body surface and the presence of two types of
nuclei. All the cilia beat in the same direction to move the water laden food
inside a cavity called gullet. Example: Paramoecium, Vorticella,etc.
• Sporozoans: They include disease causing endoparasites and other
pathogens. They are uninucleate and their body is covered by a pellicle. They
do not possess cilia or flagella. They include the malaria causing parasite
Plasmodium.
7. Plants are autotrophic. Can you think of some plants that are partially
heterotrophic?
Answer 7: Some insectivorous plants, like bladderwort and venus fly trap are
partially heterotrophic.
8. What do the terms phycobiont and mycobiont signify?
Answer 8: Lichens are good examples of symbiotic life of algae and fungi.
Phycobiont is the name of the part composed of algae and Mycobiont is the
name of the part composed of fungi. Fungi provide minerals and support to
the alage, while algae provide nutrition to the fungi.
.
9. Give a comparative account of the classes of Kingdom Fungi under the
following:
(i) Mode of nutrition
(ii) Mode of reproduction
Answer 9: → Phycomycetes- This group of fungi includes members such as
Rhizopus, Albugo, etc.
• Mode of nutrition: They are obligate parasites on plants or are found on
decaying matter such as wood.
• Mode of reproduction: Asexual reproduction takes place through motile
zoospores or non-motile aplanospores that are produced endogenously in
sporangium.
Sexual reproduction may be of isogamous, anisogamous, or oogamous type.
It results in the formation of thick-walled zygospore.
→ Ascomycetes- This group of fungi includes members such as Penicillium,
Aspergillus,Claviceps, and Neurospora.
• Mode of nutrition: They are sporophytic, decomposers, parasitic or
coprophilous.
• 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.
→ Basidiomycetes- This group of fungi includes members such as
Ustilago,Agaricus and Puccinia.
• 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.
• 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.
→ Deuteromycetes - This group of fungi includes members such as
Alternaria, Trichoderma, and Colletotrichum.
• Mode of nutritionSome members are saprophytes while others are
parasites. However, a large number act as decomposers of leaf litter.
• Mode of reproduction: Asexual reproduction is the only way of reproduction
in deuteromycetes. It occurs through asexual spores called conidia.
Sexual reproduction is absent in deuteromycetes.
10. What are the characteristic features of Euglenoids?
Answer 10: Characterisitic Features of Euglenoids:
→ Fresh water organisms found in stagnant water.
→ Instead of cell wall they have a protein rich layer called pellicle whick
makes their body flexible.
→ They are autotrophs in the presence of sunlight and heterotrophs in the
absence of sunlight.
→ A small light sensitive eye spot is present.
11. Give a brief account of viruses with respect to their structure and nature
of genetic material. Also name four common viral diseases.
Answer 10: Viruses have a protein capsule and genetic materials inside the
capsule. These genetic material become active once they are inside the
nucleus of a host cell. They start replicating themselves and in turn spreading
the disease.
Generally viruses that infect plants have single stranded RNA. Viruses
infecting animals have double stranded RNA or DNA. Viruses which infect
bacteria have double stranded DNA.
A.I.D.S, small pox, mumps, and influenza are some common examples of viral
diseases.
