CBSE - Biological Classification

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.

(a) Heterotrophic bacteria

(1) They act as decomposers and help in the formation of humus.

(2) They help in the production of curd from milk.

(3) Many antibiotics are obtained from some species of bacteria.

(4) Many soil bacteria help in fixation of atmospheric nitrogen.

(b) Archaebacteria

(1) Methane gas is produced from the dung of ruminants by the methanogens.

(2) Methanogens are also involved in the formation of biogas and sewage treatment.

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 filtration of oils, sugars, and for other industrial purposes.

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 fishes.

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.

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.

Plants have 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 required nutrients derived from insects, causing proliferation of growth.
The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

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.

(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 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. It occurs through asexual spores called conidia.

Sexual reproduction is absent in deuteromycetes.

Some characteristic features of Euglenoids are as follows.

• Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.

• Instead of 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 absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.

• They have both plant and animal-like features, which makes them difficult to classify.

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, small pox, mumps, and influenza are some common examples of viral diseases.

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.

Diatoms are the chief producers in marine environment. Hence, they are also called the ‘pearls of ocean’.
As walls of diatoms are made of silica, they have left behind a large amount of cell deposits in their habitat.
This accumulation is called diatomaceous earth.
Diatomaceous earth is gritty in nature and hence is used for polishing and, in filtration of oils and syrups.  
 

The mycelium of mushrooms absorbs nutrients from the ground. When nutrients at the centre get exhausted they grow in diameter and form a circle.
The ring grows in diameter  every year which are actually fruiting bodies of the fungus. This is called the ‘Fairy Ring’  especially in Europe.
 

Neurospora is used as a model organism to study plant genetics. Several characteristic of this organism make it ideal to be used for genetic studies. Some of these features are as follows:

(a) It reproduces quickly
(b) It is easy to culture
(c) It can survive on minimum media 
 

All the prokaryotes have been kept under the kingdom Monera. Both cyanobacteria and heterotrophic bacteria are prokaryotes and hence are being kept under the same  kingdom. Mode of nutrition is the major difference between cyanobacteria and heterotrophic bacteria. So, this classification is justified. 

The fruiting body of ascomycetes is called ascocarp. Ascocarp can be divided into three types, viz. apothecium perithecium and cleistothecium.

(a) Apothecium is a saucer-shaped structure which is open from the upper side.
(b) Perithecium is a flask-shaped structure with a pore-like opening.
(c) Cleistothecium is a closed structure with no opening.

Following characters of Trypanosoma make us classify it under kingdom Protista:

(a) Unicellular organism
(b) Centrally located nucleus
(c) Asexual reproduction
(d) Reserve food material in the form of granules 

Role of fungi is daily life:

(a) Many fungi spoil food materials; like stale bread, fruits and vegetables.
(b) Yeast is used in fermentation.
(c) Some fungi cause dangerous diseases of plants and animals.
(d) Some fungi are used for making antibiotics.

Many species of cyanobacteria can carry out nitrogen fixation in soil. Hence, they are used in agricultural fields for crop improvement. 

All unicellular eukaryotes belong to the kingdom Protista. Hence, this organism belongs to Protista. 

In two-kingdom classification many unrelated organisms were kept under the same kingdom. This anomaly has been removed after the introduction of five-kingdom classification.

For example; the bacteria were kept under plant kingdom previously but many bacteria are heterotrophic. Now, a separate kingdom has been made for bacteria.

These organisms get plenty of nutrients in polluted water. Hence, they often bloom in such conditions and are found in abundance in polluted water.

Chemosynthetic bacteria are autotrophic because they can synthesize their own food. 
During chemosynthesis it uses chemicals as source of energy. 

The common name ‘pea’ is an English word and this can have different names in different languages. It is easier to remember a standard scientific name as compared to so many names. Hence, instead of using simple common names; it is preferred to use scientific names which may appear complicated but universally accepted.

Characters of virus that are similar to non-living objects:
(a) They have inert crystalline structure outside the living cell.
(b) They do not have any cell organelles.

In the five-kingdom system of Whittaker, four kingdoms are eukaryotes which are as follows:
(a) Protista
(b) Fungi
(c) Plantae
(d) Animalia  

All eukaryotic unicellular organisms belong to
(a) Monera
(b) Protista
(c) Fungi
(d) Bacteria 

ANS (b) Protista
Monera contains all prokaryotic organisms and bacteria come under monera. Fungi can have unicellular as well as multicellular organisms. Hence, option ‘b’ is the correct option. 

Ans. (a) R. H. Whittaker

R. H. Whittaker proposed five kingdom classification in 1959. Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms according to R. H. Whittaker.

(b) Halophiles

Halos means salt and phile means loving.

(d) Slime molds 

Slime molds were earlier kept under kingdom fungi but due to multinucleate character and naked protoplasm, they are now considered as belonging to monera. 

Ans. (c) Mycorrhiza

Lichen is the association between fungi and algae, ferns belong to Pteridophyta and BGA is short form of Blue-Green Algae. Hence, option ‘c’ is the correct answer. 
 

Ans. (b) The two haploid cells do not fuse immediately

‘Di’ means two and ‘karyon’ means nucleus. 

Ans. (b) M.W. Beijerinek

Beijerinek demonstrated that extracts of infected tobacco plant can cause infection in healthy plants and termed the fluid as contagium vivum fluidum (infectious living fluid). 

Ans. (c) Lichens

In a lichen; the fungal component is called mycobiont and algal component is called phycobiont.

Ans. (a) Absence of protein coat in viroid but present in virus

Ans. (c) Plasmogamy, Karyogamy and Meiosis

Ans. (d) None of the above
Since viruses are considered as borderline case between living and nonliving things; no kingdom has been specified for them.

Members of phycomycetes are found in
(i) Aquatic habitats
(ii) On decaying wood
(iii) Moist and damp places
(iv) As obligate parasites on plants
Choose from the following options
(a) None of the above
(b) (i) and (iv)
(c) (ii) and (iii)
(d) All of the above 

Ans. (d) All of the above
Phycomycetes belong to fungi. They live in aquatic habitats, moist and damp places, as obligate parasites on plants and on decaying wood. 

Algae reproduce asexually by variety of spores under different environmental conditions.
These spores and the conditions under which they are produced are as follows:

Algae have many other pigments in their chloroplast; in addition to chlorophyll. The following table shows various pigments in algae and color imparted by them:

Some algae of commercial importance: 

Some fungi of commercial importance:

Peat is an accumulation of partially decayed vegetation or organic matter.
Formation of Peat: When plant material; usually in wet areas; in inhibited from decaying fully because of acidic and anaerobic conditions, it results in formation of peat. Peat is mainly composed of wetland vegetation. Sphagnum is the main producer of peat; but many other plants may also be involved in peat formation. Most of the modern peats formed in high latitudes after the retreat of glaciers at the end of the last Ice Age. This
happened about 12,000 years ago. Peat accumulation is usually slow; at the rate of 1 millimeter per year.

Peat is an important source of domestic fuel in several countries; especially in Europe and America. Peat is also used in agriculture to improve soil fertility. This is also used as water purified in septic tanks.
 

This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms.
At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by
Robert Whittaker.
The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four kingdoms. All the photosynthetic autotrophs have been kept under plank kindom and all the eukaryotic heterotrophs (without cell wall) are kept under animal kingdom.
However, even this system of classification has certain limitations.
For example; the chemosynthetic autotrophs have been kept under the kingdom Protista.
Recently, some scientists have also suggested three domains of life and some others have suggested a Six-Kingdom classification. Such attempts of classification are in tune with our changing understanding of life forms. 

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.

(a) Heterotrophic bacteria

(1) They act as decomposers and help in the formation of humus.

(2) They help in the production of curd from milk.

(3) Many antibiotics are obtained from some species of bacteria.

(4) Many soil bacteria help in fixation of atmospheric nitrogen.

(b) Archaebacteria

(1) Methane gas is produced from the dung of ruminants by the methanogens.

(2) Methanogens are also involved in the formation of biogas and sewage treatment.

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 filtration of oils, sugars, and for other industrial purposes.

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 fishes.

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.

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.

Plants have 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 required nutrients derived from insects, causing proliferation of growth.
The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

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.

(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 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. It occurs through asexual spores called conidia.

Sexual reproduction is absent in deuteromycetes.

Some characteristic features of Euglenoids are as follows.

• Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.

• Instead of 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 absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.

• They have both plant and animal-like features, which makes them difficult to classify.

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, small pox, mumps, and influenza are some common examples of viral diseases.

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.

Diatoms are the chief producers in marine environment. Hence, they are also called the ‘pearls of ocean’.
As walls of diatoms are made of silica, they have left behind a large amount of cell deposits in their habitat.
This accumulation is called diatomaceous earth.
Diatomaceous earth is gritty in nature and hence is used for polishing and, in filtration of oils and syrups.  
 

The mycelium of mushrooms absorbs nutrients from the ground. When nutrients at the centre get exhausted they grow in diameter and form a circle.
The ring grows in diameter  every year which are actually fruiting bodies of the fungus. This is called the ‘Fairy Ring’  especially in Europe.
 

Neurospora is used as a model organism to study plant genetics. Several characteristic of this organism make it ideal to be used for genetic studies. Some of these features are as follows:

(a) It reproduces quickly
(b) It is easy to culture
(c) It can survive on minimum media 
 

All the prokaryotes have been kept under the kingdom Monera. Both cyanobacteria and heterotrophic bacteria are prokaryotes and hence are being kept under the same  kingdom. Mode of nutrition is the major difference between cyanobacteria and heterotrophic bacteria. So, this classification is justified. 

The fruiting body of ascomycetes is called ascocarp. Ascocarp can be divided into three types, viz. apothecium perithecium and cleistothecium.

(a) Apothecium is a saucer-shaped structure which is open from the upper side.
(b) Perithecium is a flask-shaped structure with a pore-like opening.
(c) Cleistothecium is a closed structure with no opening.

Following characters of Trypanosoma make us classify it under kingdom Protista:

(a) Unicellular organism
(b) Centrally located nucleus
(c) Asexual reproduction
(d) Reserve food material in the form of granules 

Role of fungi is daily life:

(a) Many fungi spoil food materials; like stale bread, fruits and vegetables.
(b) Yeast is used in fermentation.
(c) Some fungi cause dangerous diseases of plants and animals.
(d) Some fungi are used for making antibiotics.

Many species of cyanobacteria can carry out nitrogen fixation in soil. Hence, they are used in agricultural fields for crop improvement. 

All unicellular eukaryotes belong to the kingdom Protista. Hence, this organism belongs to Protista. 

In two-kingdom classification many unrelated organisms were kept under the same kingdom. This anomaly has been removed after the introduction of five-kingdom classification.

For example; the bacteria were kept under plant kingdom previously but many bacteria are heterotrophic. Now, a separate kingdom has been made for bacteria.

These organisms get plenty of nutrients in polluted water. Hence, they often bloom in such conditions and are found in abundance in polluted water.

Chemosynthetic bacteria are autotrophic because they can synthesize their own food. 
During chemosynthesis it uses chemicals as source of energy. 

The common name ‘pea’ is an English word and this can have different names in different languages. It is easier to remember a standard scientific name as compared to so many names. Hence, instead of using simple common names; it is preferred to use scientific names which may appear complicated but universally accepted.

Characters of virus that are similar to non-living objects:
(a) They have inert crystalline structure outside the living cell.
(b) They do not have any cell organelles.

In the five-kingdom system of Whittaker, four kingdoms are eukaryotes which are as follows:
(a) Protista
(b) Fungi
(c) Plantae
(d) Animalia  

All eukaryotic unicellular organisms belong to
(a) Monera
(b) Protista
(c) Fungi
(d) Bacteria 

ANS (b) Protista
Monera contains all prokaryotic organisms and bacteria come under monera. Fungi can have unicellular as well as multicellular organisms. Hence, option ‘b’ is the correct option. 

Ans. (a) R. H. Whittaker

R. H. Whittaker proposed five kingdom classification in 1959. Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms according to R. H. Whittaker.

(b) Halophiles

Halos means salt and phile means loving.

(d) Slime molds 

Slime molds were earlier kept under kingdom fungi but due to multinucleate character and naked protoplasm, they are now considered as belonging to monera. 

Ans. (c) Mycorrhiza

Lichen is the association between fungi and algae, ferns belong to Pteridophyta and BGA is short form of Blue-Green Algae. Hence, option ‘c’ is the correct answer. 
 

Ans. (b) The two haploid cells do not fuse immediately

‘Di’ means two and ‘karyon’ means nucleus. 

Ans. (b) M.W. Beijerinek

Beijerinek demonstrated that extracts of infected tobacco plant can cause infection in healthy plants and termed the fluid as contagium vivum fluidum (infectious living fluid). 

Ans. (c) Lichens

In a lichen; the fungal component is called mycobiont and algal component is called phycobiont.

Ans. (a) Absence of protein coat in viroid but present in virus

Ans. (c) Plasmogamy, Karyogamy and Meiosis

Ans. (d) None of the above
Since viruses are considered as borderline case between living and nonliving things; no kingdom has been specified for them.

Members of phycomycetes are found in
(i) Aquatic habitats
(ii) On decaying wood
(iii) Moist and damp places
(iv) As obligate parasites on plants
Choose from the following options
(a) None of the above
(b) (i) and (iv)
(c) (ii) and (iii)
(d) All of the above 

Ans. (d) All of the above
Phycomycetes belong to fungi. They live in aquatic habitats, moist and damp places, as obligate parasites on plants and on decaying wood. 

Algae reproduce asexually by variety of spores under different environmental conditions.
These spores and the conditions under which they are produced are as follows:

Algae have many other pigments in their chloroplast; in addition to chlorophyll. The following table shows various pigments in algae and color imparted by them:

Some algae of commercial importance: 

Some fungi of commercial importance:

Peat is an accumulation of partially decayed vegetation or organic matter.
Formation of Peat: When plant material; usually in wet areas; in inhibited from decaying fully because of acidic and anaerobic conditions, it results in formation of peat. Peat is mainly composed of wetland vegetation. Sphagnum is the main producer of peat; but many other plants may also be involved in peat formation. Most of the modern peats formed in high latitudes after the retreat of glaciers at the end of the last Ice Age. This
happened about 12,000 years ago. Peat accumulation is usually slow; at the rate of 1 millimeter per year.

Peat is an important source of domestic fuel in several countries; especially in Europe and America. Peat is also used in agriculture to improve soil fertility. This is also used as water purified in septic tanks.
 

This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms.
At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by
Robert Whittaker.
The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four kingdoms. All the photosynthetic autotrophs have been kept under plank kindom and all the eukaryotic heterotrophs (without cell wall) are kept under animal kingdom.
However, even this system of classification has certain limitations.
For example; the chemosynthetic autotrophs have been kept under the kingdom Protista.
Recently, some scientists have also suggested three domains of life and some others have suggested a Six-Kingdom classification. Such attempts of classification are in tune with our changing understanding of life forms. 

Peat is an accumulation of partially decayed vegetation or organic matter.
Formation of Peat: When plant material; usually in wet areas; in inhibited from decaying fully because of acidic and anaerobic conditions, it results in formation of peat. Peat is mainly composed of wetland vegetation. Sphagnum is the main producer of peat; but many other plants may also be involved in peat formation. Most of the modern peats formed in high latitudes after the retreat of glaciers at the end of the last Ice Age. This
happened about 12,000 years ago. Peat accumulation is usually slow; at the rate of 1 millimeter per year.

Peat is an important source of domestic fuel in several countries; especially in Europe and America. Peat is also used in agriculture to improve soil fertility. This is also used as water purified in septic tanks.
 

This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms.
At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by
Robert Whittaker.
The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four kingdoms. All the photosynthetic autotrophs have been kept under plank kindom and all the eukaryotic heterotrophs (without cell wall) are kept under animal kingdom.
However, even this system of classification has certain limitations.
For example; the chemosynthetic autotrophs have been kept under the kingdom Protista.
Recently, some scientists have also suggested three domains of life and some others have suggested a Six-Kingdom classification. Such attempts of classification are in tune with our changing understanding of life forms. 

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.

(a) Heterotrophic bacteria

(1) They act as decomposers and help in the formation of humus.

(2) They help in the production of curd from milk.

(3) Many antibiotics are obtained from some species of bacteria.

(4) Many soil bacteria help in fixation of atmospheric nitrogen.

(b) Archaebacteria

(1) Methane gas is produced from the dung of ruminants by the methanogens.

(2) Methanogens are also involved in the formation of biogas and sewage treatment.

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 filtration of oils, sugars, and for other industrial purposes.

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 fishes.

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.

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.

Plants have 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 required nutrients derived from insects, causing proliferation of growth.
The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

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.

(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 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. It occurs through asexual spores called conidia.

Sexual reproduction is absent in deuteromycetes.

Some characteristic features of Euglenoids are as follows.

• Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.

• Instead of 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 absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.

• They have both plant and animal-like features, which makes them difficult to classify.

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, small pox, mumps, and influenza are some common examples of viral diseases.

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.

Diatoms are the chief producers in marine environment. Hence, they are also called the ‘pearls of ocean’.
As walls of diatoms are made of silica, they have left behind a large amount of cell deposits in their habitat.
This accumulation is called diatomaceous earth.
Diatomaceous earth is gritty in nature and hence is used for polishing and, in filtration of oils and syrups.  
 

The mycelium of mushrooms absorbs nutrients from the ground. When nutrients at the centre get exhausted they grow in diameter and form a circle.
The ring grows in diameter  every year which are actually fruiting bodies of the fungus. This is called the ‘Fairy Ring’  especially in Europe.
 

Neurospora is used as a model organism to study plant genetics. Several characteristic of this organism make it ideal to be used for genetic studies. Some of these features are as follows:

(a) It reproduces quickly
(b) It is easy to culture
(c) It can survive on minimum media 
 

All the prokaryotes have been kept under the kingdom Monera. Both cyanobacteria and heterotrophic bacteria are prokaryotes and hence are being kept under the same  kingdom. Mode of nutrition is the major difference between cyanobacteria and heterotrophic bacteria. So, this classification is justified. 

The fruiting body of ascomycetes is called ascocarp. Ascocarp can be divided into three types, viz. apothecium perithecium and cleistothecium.

(a) Apothecium is a saucer-shaped structure which is open from the upper side.
(b) Perithecium is a flask-shaped structure with a pore-like opening.
(c) Cleistothecium is a closed structure with no opening.

Following characters of Trypanosoma make us classify it under kingdom Protista:

(a) Unicellular organism
(b) Centrally located nucleus
(c) Asexual reproduction
(d) Reserve food material in the form of granules 

Role of fungi is daily life:

(a) Many fungi spoil food materials; like stale bread, fruits and vegetables.
(b) Yeast is used in fermentation.
(c) Some fungi cause dangerous diseases of plants and animals.
(d) Some fungi are used for making antibiotics.

Many species of cyanobacteria can carry out nitrogen fixation in soil. Hence, they are used in agricultural fields for crop improvement. 

All unicellular eukaryotes belong to the kingdom Protista. Hence, this organism belongs to Protista. 

In two-kingdom classification many unrelated organisms were kept under the same kingdom. This anomaly has been removed after the introduction of five-kingdom classification.

For example; the bacteria were kept under plant kingdom previously but many bacteria are heterotrophic. Now, a separate kingdom has been made for bacteria.

These organisms get plenty of nutrients in polluted water. Hence, they often bloom in such conditions and are found in abundance in polluted water.

Chemosynthetic bacteria are autotrophic because they can synthesize their own food. 
During chemosynthesis it uses chemicals as source of energy. 

The common name ‘pea’ is an English word and this can have different names in different languages. It is easier to remember a standard scientific name as compared to so many names. Hence, instead of using simple common names; it is preferred to use scientific names which may appear complicated but universally accepted.

Characters of virus that are similar to non-living objects:
(a) They have inert crystalline structure outside the living cell.
(b) They do not have any cell organelles.

In the five-kingdom system of Whittaker, four kingdoms are eukaryotes which are as follows:
(a) Protista
(b) Fungi
(c) Plantae
(d) Animalia  

All eukaryotic unicellular organisms belong to
(a) Monera
(b) Protista
(c) Fungi
(d) Bacteria 

ANS (b) Protista
Monera contains all prokaryotic organisms and bacteria come under monera. Fungi can have unicellular as well as multicellular organisms. Hence, option ‘b’ is the correct option. 

Ans. (a) R. H. Whittaker

R. H. Whittaker proposed five kingdom classification in 1959. Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms according to R. H. Whittaker.

(b) Halophiles

Halos means salt and phile means loving.

(d) Slime molds 

Slime molds were earlier kept under kingdom fungi but due to multinucleate character and naked protoplasm, they are now considered as belonging to monera. 

Ans. (c) Mycorrhiza

Lichen is the association between fungi and algae, ferns belong to Pteridophyta and BGA is short form of Blue-Green Algae. Hence, option ‘c’ is the correct answer. 
 

Ans. (b) The two haploid cells do not fuse immediately

‘Di’ means two and ‘karyon’ means nucleus. 

Ans. (b) M.W. Beijerinek

Beijerinek demonstrated that extracts of infected tobacco plant can cause infection in healthy plants and termed the fluid as contagium vivum fluidum (infectious living fluid). 

Ans. (c) Lichens

In a lichen; the fungal component is called mycobiont and algal component is called phycobiont.

Ans. (a) Absence of protein coat in viroid but present in virus

Ans. (c) Plasmogamy, Karyogamy and Meiosis

Ans. (d) None of the above
Since viruses are considered as borderline case between living and nonliving things; no kingdom has been specified for them.

Members of phycomycetes are found in
(i) Aquatic habitats
(ii) On decaying wood
(iii) Moist and damp places
(iv) As obligate parasites on plants
Choose from the following options
(a) None of the above
(b) (i) and (iv)
(c) (ii) and (iii)
(d) All of the above 

Ans. (d) All of the above
Phycomycetes belong to fungi. They live in aquatic habitats, moist and damp places, as obligate parasites on plants and on decaying wood. 

Algae reproduce asexually by variety of spores under different environmental conditions.
These spores and the conditions under which they are produced are as follows:

Algae have many other pigments in their chloroplast; in addition to chlorophyll. The following table shows various pigments in algae and color imparted by them:

Some algae of commercial importance: 

Some fungi of commercial importance:

Peat is an accumulation of partially decayed vegetation or organic matter.
Formation of Peat: When plant material; usually in wet areas; in inhibited from decaying fully because of acidic and anaerobic conditions, it results in formation of peat. Peat is mainly composed of wetland vegetation. Sphagnum is the main producer of peat; but many other plants may also be involved in peat formation. Most of the modern peats formed in high latitudes after the retreat of glaciers at the end of the last Ice Age. This
happened about 12,000 years ago. Peat accumulation is usually slow; at the rate of 1 millimeter per year.

Peat is an important source of domestic fuel in several countries; especially in Europe and America. Peat is also used in agriculture to improve soil fertility. This is also used as water purified in septic tanks.
 

This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms.
At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by
Robert Whittaker.
The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four kingdoms. All the photosynthetic autotrophs have been kept under plank kindom and all the eukaryotic heterotrophs (without cell wall) are kept under animal kingdom.
However, even this system of classification has certain limitations.
For example; the chemosynthetic autotrophs have been kept under the kingdom Protista.
Recently, some scientists have also suggested three domains of life and some others have suggested a Six-Kingdom classification. Such attempts of classification are in tune with our changing understanding of life forms.