Classification of the Living World

Classification makes the study of living organisms systematic and simple.

Classification gives an idea about the evolution of organisms from simpler to more complex ones.

The Greek philosopher, Aristotle was the first to classify animals.

Linnaeus classified all living organisms in two separate Kingdoms.

In Linnaeus’ general plan of classification, a class has a number of Orders.

The members of a genus are much more similar than those of a Family.

Each genus is divided into Species.

R. H. Whittaker suggested the five-kingdom classification.

Lactobaccilus is rod-shaped bacteria.

Azotobacter is a bacterium that lives in the root nodules of the leguminous plants.

Finger-like projections in Amoeba are known as pseudopodia.

Sporulation is the other name given to multiple fission.

Carolus Linnaeus

Reason — The binomial system of naming organisms was given by Carolus Linnaeus which consists of Genera and species.

kingdom

Reason — The largest unit of classification is Kingdom. Living organisms have been classified into five kingdoms.

species

Reason — The smallest unit of classification is species.

Monera, Protista, Fungi, Plantae, Animalia

Reason — Monera are unicellular prokaryotes, Protista are unicellular eukaryotes, Fungi are multicellular heterotrophs, Plants are multicellular autotrophs and animals are multicellular and motile.

a single cell without nucleus

Reason — Organisms of Kingdom Monera are unicellular prokaryotes.

a single cell with nucleus

Reason — Organisms of Kingdom Protista are unicellular eukaryotes.

cell wall

Reason — Cell wall is only present in plants and some bacteria.

Groups of similar genera are grouped together into a Family.

Closely-related species resembling each other are grouped into a Genera.

Kingdom Monera contains prokaryotic, unicellular organisms.

The organisms belonging to Kingdom Plantae have chlorophyll.

Kingdom animalia includes all organisms that are multicellular and heterotrophic.

True

False

Corrected statement — Rod-shaped bacteria are called bacilli.

False

Corrected statement — Protists are single-celled organisms with a nucleus.

True

False

Corrected statement — Yeasts do not contain chlorophyll. They are saprophytic i.e., they feed on dead decaying organic matter.

False

Corrected statement — Bread mould reproduces by spore formation, budding and fragmentation.

True

Bacteria

Reason — Bacteria is classified under kingdom Monera while others are classified under kingdom Protista.

Amoeba

Reason — Amoeba is classified under kingdom Protista while others are classified under kingdom Fungi.

Blue green algae

Reason — Blue green algae is classified under kingdom Monera while Rhizopus and Mucor are classified under kingdom Fungi.

The scientific way of identifying, naming and grouping of living organisms based on similarities and differences is known as (biological) classification.

Two advantages of classification are:

1. It makes the study of living organisms systematic and simple.
2. It highlights the relationship between different organisms.

Protozoa is a phylum of unicellular, eukaryotic organisms. They are classified under kingdom Protista.

Kingdom Plantae consists of all green plants. They perform photosynthesis with the help of chlorophyll present in the chloroplasts of their cells.

Cryptogams are those plants that do not produce flowers and seeds. They do not have special male and female reproductive units to produce seeds.

The five-kingdom classification was proposed by R. H. Whittaker.

The five kingdoms with example are :

1. Kingdom Monera —
   1. They are unicellular and prokaryotic organisms.
   2. Their mode of nutrition is mainly autotrophic and sometimes heterotrophic.
2. Kingdom Protista —
   1. They are unicellular and eukaryotic organisms.
   2. Some show plant characters, for example Algae is autotrophs with cell wall and chloroplast; while others show animal like characters, for example Paramecium is motile with flagella.
3. Kingdom Fungi —
   1. They are eukaryotic and heterotrophic (without chlorophyll) organisms.
   2. Their cells have a cell wall made of tough, complex sugar called chitin.
4. Kingdom Plantae —
   1. They are multicellular organisms. They can prepare their own food by photosynthesis. Hence, they are autotrophic.
   2. The cell wall of plant cells is made of cellulose.
5. Kingdom Animalia —
   1. They are multicellular and heterotrophic organism.
   2. They do not have cell wall but contain cell membrane.

One characteristic feature of kingdom fungi is that they are unicellular as well as multicellular and heterotrophs (either parasite or saprophyte).

Fungi are not a part of Kingdom Plantae because they are heterotrophs and plants are autotrophs. They do not have chloroplast and thus they cannot produce their own food.

Useful effects of Bacteria

1. Production of butter and cheese — Some bacteria such as Streptococcus and Lactobacillus are used to produce curd, butter and cheese.
2. Production of vitamins — Many bacteria living in the intestine of humans synthesize vitamins such as vitamin B.

Harmful effects of Bacteria

1. They cause diseases in plants. e.g. bacterial leaf blight of rice is caused by Xanthomonas oryzae pv. oryzae and Angular leaf spot in cotton is caused by Xanthomonas malvacearum.
2. They cause diseases in humans. e.g. Tuberculosis is caused by Mycobacterium tuberculosis and Diphtheria is caused by Corynebacterium diptheriae.

Useful effects of Fungi

1. Fungi are called nature's scavengers. They decompose the dead, decaying bodies of plants and animals and their waste products. This also helps in making the soil fertile.
2. Morels and some mushrooms are enjoyed as palatable food.

Harmful effects of Fungi

1. Fungi can attack tissues of plants and animals and cause diseases. Mould spores can cause allergies in some people leading to sneezing, sniffling and other respiratory problems.
2. Some fungi damage paper and paper products, leather and even clothes.

(a) Two disease causing bacteria in plants along with the disease caused by them are:

(b) Two disease causing bacteria in animals along with the disease caused by them are:

Nitrogen fixation — The process of conversion of atmospheric nitrogen into nitrates is called Nitrogen fixation. Nitrogen fixation is done by bacteria present in root nodules of leguminous plants. For example, Rhizobium is found in root nodules of legumes and convert the atmospheric nitrogen into nitrates.

Nitrification — The process of conversion of ammonia into nitrates is called Nitrification. For example, Nitrosomonas converts ammonia into nitrates which is used by the plants.

Asexual reproduction in amoeba takes place in two ways — binary fission and multiple fission.

Binary fission — A fully grown Amoeba multiplies by binary fission. In this process, one parent Amoeba divides into two daughter Amoebae. First, the nuclear membrane disappears and the nucleus becomes larger. The nucleus then divides into two daughter nuclei and the cytoplasm surrounds each nucleus. Then a plasma membrane is formed outside the cytoplasm. As a result, the two daughter Amoebae are formed, which start growing separately.

Multiple fission — Under unfavourable environmental conditions, Amoeba produces a thick wall around its body. This is called the cyst wall. The nucleus divides several times producing many nuclei. The cytoplasm then separates, creating multiple daughter cells inside the cyst. These daughter cells are called spores, so this process is also known as sporulation. Under favourable conditions, the cyst bursts open releasing the daughter cells that grow into independent amoeba.

Bacteria were placed in the plant kingdom according to the two-kingdom classification because they have following characteristics resembling plants:

1. They have cell wall.
2. Some are autotrophic.
3. They are usually non-movable.

Viruses have very few characteristics of life. They behave like a link between living and non-living. When independent they behave like non-living and when in living cell, they behave like living. Also they are unique as they have no proper cellular structure and protoplasm. Hence, they are not classified into any of the kingdoms.