Q1. Discuss how classification systems have undergone several changes over a period of time.
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 the 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 the 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.
Q2. State two economically important uses of:
(a) heterotrophic bacteria
(b) archaebacteria
Answer: (a) Heterotrophic bacteria
i) They act as decomposers and help in the formation of humus.
ii) They help in the production of curd from milk.
iii) Many antibiotics are obtained from some species of bacteria.
iv) Many soil bacteria help in the fixation of atmospheric nitrogen.
(b) Archaebacteria
i) Methane gas is produced from the dung of ruminants by the methanogens.
ii) Methanogens are also involved in the formation of biogas and sewage treatment.
Q3. What is the nature of cell walls in diatoms?
Answer: The cell walls of diatoms are made of silica. Their cell wall construction is known as frustule. It consists of two thin overlapping shells that fit into each other such as a soap box. When the diatoms die, the silica in their cell walls gets deposited in the form of diatomaceous earth. This diatomaceous earth is very soft and quite inert. It is used in the filtration of oils, sugars, and for other industrial purposes.
Q4. Find out what do the terms ‘algal bloom’ and ‘red tides’ signify.
Answer: Algal bloom: Algal bloom refers to an increase in the population of algae or blue-green algae in water, 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.
Red-tides: Red tides are caused by red dinoflagellates (Gonyaulax) that multiply rapidly. Due to
their large numbers, the sea appears red in colour. They release large amounts of toxins in water that can cause death of a large number of fish.
Q5. How are viroids different from viruses?
Answer: Viroids were discovered in 1917 by T.O. Denier. They cause potato spindle tuber disease. They are smaller in size than viruses. They also lack the protein coat and contain free RNA of low molecular weight.
Q6. Describe briefly the four major groups of Protozoa.
Answer: Protozoa are microscopic unicellular protists with heterotrophic mode of nutrition. They may be holozoic, saprobic, or parasitic. These are divided into four major groups.
(1) Amoeboid protozoa or sarcodines
They are unicellular, jelly-like protozoa found in fresh or sea water and in moist soil.
Their body lacks a periplast. Therefore, they may be naked or covered by a calcareous shell. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia. These pseudopodia or false feet help in movement and capturing prey. They include free-living forms such as Amoeba or parasitic forms such as Entamoeba.
(2) Flagellated protozoa or zooflagellates
They are free-living, non-photosynthetic flagellates without a cell wall. They possess flagella for locomotion and capturing prey. They include parasitic forms such as Trypanosoma, which causes sleeping sickness in human beings.
(3) 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. They include organisms such as Paramoecium, Vorticella, etc.
(4) 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.
Q7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer: Plants have an autotrophic mode of nutrition as they contain chlorophyll pigment. Thus, they have the ability to prepare their own food by the process of photosynthesis. However, some insectivorous plants are partially heterotrophic. They have various means of capturing insects so as to supplement their diet with the required nutrients derived from insects, causing the proliferation of growth. Examples include pitcher plants (Nepenthes), Venus fly trap, bladderwort, and sundew plant.
Q8. What do the terms phycobiont and mycobiont signify?
Answer: Phycobiont refers to the algal component of the lichens and mycobiont refers to the fungal component. Algae contain chlorophyll and prepare food for fungi whereas the fungus provides shelter to algae and absorbs water and nutrients from the soil. This type of relationship is referred to as symbiotic.
Q9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition
(ii) mode of reproduction
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 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.
(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 saclike 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 the 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. It occurs through asexual spores called conidia.
Sexual reproduction is absent in deuteromycetes.
Q10. What are the characteristic features of Euglenoids?
Answer: Some characteristic features of Euglenoids are as follows.
Q11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also, name four common viral diseases.
Answer: Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.
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 capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.
A.I.D.S., smallpox, mumps, and influenza are some common examples of viral diseases.
Q12. Organise a discussion in your class on the topic – Are viruses living or nonliving?
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) suggests that viruses are alive. In addition, they can also respond to their environment (inside the host cell) in a limited manner. 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.
NCERT EXEMPLAR
VERY SHORT ANSWER TYPE QUESTIONS
Q1. What is the principle underlying the use of cyanobacteria in agricultural fields for crop improvement?
Answer: Cyanobacteria (BGA) are autotrophic microbes. Cyanobacteria are widely distributed in aquatic and terrestrial environments. Nostoc, Ariabaena and Oscillatoria are BGA that can fix atmospheric nitrogen. These organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., Nostoc and Anabaena. In paddy fields cyanobacteria serve as an important biofertiliser. BGA also add organic matter to the soil and increase its fertility.
Q2. Suppose you accidentally find an old preserved permanent slide without a label. In your effort to identify it, you place the slide under microscope and observe the following features :
a. Unicellular
b. Well defined nucleus
c. Biflagellate-one flagellum lying longitudinally and the other transversely.
What would you identify it as? Can you name the kingdom it belongs to?
Answer: Dinoflagellates are unicellular eukaryotes. Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates. Dinoflagellates belongs to kingdom protista.
Q3. How is the five-kingdom classification advantageous over the two kingdom classification?
Answer: Two Kingdom system of classification with Plantae and Animalia kingdoms.
1. Two kingdom classification did not distinguish between the prokaryotes and eukaryotes. E.g.: It brought together the prokaryotic bacteria and blue green algae with other groups (like plant, fungi and animals) which were eukaryotic.
2. Two kingdom classification did not distinguish between the unicellular and multicellular organisms. E.g.: Chlamydomonas (unicellular) and Spirogyra (multicellular) were placed together under algae.
3. This system did not distinguish between autotrophic/photosynthetic (green algae and plants) and the heterotrophic/non-photosynthetic organisms (fungi).
Five Kingdom Classification:
1. Fungi were placed in a separate kingdom-kingdom fungi.
2. It has put together organisms which were placed in different kingdoms in earlier classifications. Kingdom Protista brought together Chlamydomonas, Chlorella (earlier placed in algae within plants and both having cell walls) with Amoeba and Paramoecium (earlier placed in the animal kingdom and both lacking cell walls).
3. Animal and plant kingdoms become more homogenous than they are in the two kingdom classification. So, it is the advantageous over the two kingdom classification.
Q4. Polluted water bodies have usually very high abundance of plants like Nostoc and Oscillitoria. Give reasons.
Answer: Polluted water bodies (Ponds, ditches and rivers etc.) have usually nutrient contents (such as nitrate, phosphates) domestic sewage primarily contains biodegradable organic matter. Presence of large amount of nutrients in waters also causes excessive growth of Planktonic (free floating algae) called an algal bloom, which imparts a distinct colour to water bodies. Algal bloom causes deterioration of the water quality and fish mortality. Some bloom forming algae mainly Nostoc and Oscillitoria are extremely toxic to human beings and animals.
Q5. Are chemosynthetic bacteria-autotrophic or heterotrophic?
Answer: Chemosynthetic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. So chemosynthetic bacteria are autotrophic in nature.
Q6. The common name of pea is simpler than its botanical (scientific) name Pisum sativum. Why then is the simpler common name not used instead of the complex scientific/ botanical name in biology?
Answer: As we know that pea (vernacular name or local name) is simpler than its botanical (scientific) name Pisum sativum. These local names would vary from place to place, even within a country. Probably one would recognise the confusion that would be created if we did not find ways and means to talk to each other, to refer to organisms we are talking about.
Hence, there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world.
Q7. A virus is considered as a living organism and an obligate parasite when inside a host cell. But virus is not classified along with bacteria or fungi. What are the characters of virus that are similar to non-living objects?
Answer: Virus are living organisms inside a host cell. But virus is not classified along with bacteria or fungi because they having an inert crystalline structure outside the living cell. They are inert outside their specific host cell and cannot multiply of their own because they lack cellular machinery to use its genetic material.
Q8. In the five kingdom system of Whittaker, how many kingdoms are eukaryotes?
Answer: In the five kingdom system of Whittaker, four kingdoms (Protista, fungi, plantae and animalia) belong to eukaryotes.
SHORT ANSWER TYPE QUESTIONS
Q1. Diatoms are also called as ‘pearls of ocean’, why? What is diatomaceous earth?
Answer: The diatoms are the unique organisms, because of their distinctive cell walls. The walls are embedded with silica and thus the walls are indestructible. It show sculpturing and ornamentation that why Diatoms are also called as ‘Pearls of Ocean’. Diatoms have left behind large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’. Being gritty this soil is used in polishing, filtration of oils and syrups. Diatoms are the chief ‘producers’ in the oceans.
Q2. There is a myth that immediately after heavy rains in forest, mushrooms appear in large number and make a very large ring or circle, which may be several metres in diameter. These are called as ‘Fairy rings’. Can you explain this myth of fairy rings in biological terms?
Answer: After heavy rains in forest, moisture and nutrients pass down in soil and activates the growth of mushroom mycelium. The basidiocarps of Agaricus (mushroom) arise from the mycelium present in the soil. They appear in a circle like a ring. As these basidiocarps resemble buttons and grow in rings, they are known as fairy rings.
Q3. Neurospora – an ascomycetes fungus has been used as a biological tool to understand the mechanism of plant genetics much in the same way as Drosophila has been used to study animal genetics. What makes Neurospora so important as a genetic tool?
Answer: Neurospora is used as a genetic tool because it is easy to grow and has a haploid life cycle that makes genetic analysis simple since recessive traits will show up in the offspring. Beadle and Tatum exposed Neurospora crassa to X -rays, causing mutations. This led them to propose the “one gene, one enzyme” hypothesis that specific genes code for specific proteins.
Q4. Cyanobacteria and heterotrophic bacteria have been clubbed together in Eubacteria of kingdom Monera as per the “Five Kingdom Classification” even though the two are vastly different from each other. Is this grouping of the two types of taxa in the same kingdom justified? If so, why?
Answer: Cyanobacteria and heterotrophic bacteria have been clubbed together in Eubacteria of Kingdom Monera as per the “Five Kingdom Classification” because they do not have nuclear envelope and membrane bound organelles. Their genetic material is naked. They have 70S type of ribosomes. So, cyanobacteria and heterotrophic bacteria are prokaryotes and belong, to Kingdom Monera.
Q5. At a stage of their cycle, ascomycetes fungi produce the fruiting bodies like apothecium, perithecium or cleistothecium. How are these three types of fruiting bodies different from each other?
Answer: An apothecium is a wide, open, saucer-shaped or cup-shaped fruit body. It is sessile and fleshy. A cleistothecium is a globose, completely closed fruit body with no special opening to the outside. Perithecium are flask shaped structures opening by a pore or ostiole (short papilla opening by a circular pore).
Q6. What observable features in Trypanosoma would make you classify it under kingdom Protista?
Answer: Ans: Trypanosoma is classified under the Kingdom Protista because it is unicellular eukaryotes. It has well defined nucleus with nuclear envelope, membrane bound organelles, 80 S ribosomes and flagella with 9+2 organisation.
Q7. Fungi are cosmopolitan. Write the role of fungi in your daily life.
Answer: Dough which is used for making bread, is fermented by fungi Saccharomyces cerevisiae (Baker’s yeast). Roquefort cheese are ripened by growing a specific fungi on them, which gives them a particular flavour. Microbes mainly yeasts used for the production of beverages like wine, beer, whisky, brandy or rum. For this purpose the yeast (Saccharomyces cerevisiae) used for fermenting malted cereals and juices to produce ethanol and commonly called Brewer’s yeast
\(
\begin{aligned}
&\text { Antibiotics produced by Fungi: }\\
&\begin{array}{|l|l|l|}
\hline \text { 1. } & \text { Penicillin } & \text { Penicillium notatum and Penicillium chrysogenum } \\
\hline \text { 2. } & \text { Griseofulvin } & \text { Penicillium griseofulvum } \\
\hline \text { 3. } & \text { Cephalosporin } & \text { Cephalosporium acremonium } \\
\hline \text { 4. } & \text { Gentomycin } & \text { Micromonospora purpurea } \\
\hline
\end{array}
\end{aligned}
\)
LONG ANSWER TYPE QUESTIONS
Q1. Algae are known to reproduce asexually by variety of spores under different environmental conditions. Name these spores and the conditions under which they are produced.
Answer: Asexual reproduction is by the production of different types of spores, the most common being the zoospores. They are flagellated (motile) and on germination gives rise to new plants.
Types of asexual reproduction:
Q2. Apart from chlorophyll, algae have several other pigments in their chloroplast. What pigments are found in blue-green, red and brown algae that are responsible for their characteristic colours?
Answer: Apart from chlorophyll, algae have several other pigments in their chloroplast like carotenoids, xanthophylis (fucoxanthin) and r-phycoerythrin. In blue- green algae phycocyanin and r-phycoerythrin pigments are present beside chlorophyll a.
Q3. Make a list of algae and fungi that have commercial value as source of food, chemicals, medicines and fodder.
Answer: A. Economic importance of Algae:
B. Economic importance of Fungi:
Q4. ‘Peat’ is an important source of domestic fuel in several countries. How is ‘peat’ formed in nature?
Answer: Species of Sphagnum, a moss, provide peat that have long been used as fuel and because of their capacity to hold water as packing material for trans-shipment of living material. Peat forms when plant material decaying fully by acidic and anaerobic conditions. Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as fuel.
Q5. Biological classification is a dynamic and ever evolving phenomenon which keeps changing with our understanding of life forms. Justify the statement taking any two examples.
Answer: Kingdom Protista brought together Chlamydomonas, Chlorella (earlier placed in algae within plants and both having cell walls) with Amoeba and Paramoecium (earlier placed in the animal kingdom and both lacking cell walls). Five kingdom classification has put together organism (like Chlamydomonas and Amoeba) which were placed in different kingdoms in earlier classifications. This change happened because the criteria for classification changed. This kind of changes will take place in future too depending on the improvement in our understanding of characteristics and evolutionary relationships. So, biological classification is a dynamic and ever evolving phenomenon which keeps changing with our understanding of life forms.
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