CLASSIFICATION OF LIVING THINGS
The subject Biology deals with the study of living things – plants and animals. One of the most important aspects of its study is that, that it helps in the classification of living things. So, here in this post, we will learn – what is the classification of living things and why it is important?
There are approximate 8.7 million organisms on the planet Earth. All of these living things differ from each other in numbers of ways. No two individuals are alike. It is impossible to study them individually. So, what to do? Just think of your school library. It has thousands of books which are properly grouped into different sections based on their subjects. Within a subject, the books are further arranged in alphabetical order based on their topics or author. This helps us in easily locating the particular book we need.
Similarly, Biologists have identified, named and grouped more than millions of living things – the plant and animals. They named the groups on the basis of differences and put together similar living things in a relevant group. On the basis of this grouping, living things can be studied systematically. Thus, classification means grouping organisms together on the basis of certain common features.
The definition of classification of living things –
Classification is a system of arranging living things into groups based on similarities and difference.
Classification, not only involves grouping of living things into categories but also carries out their naming.
ADVANTAGES OF CLASSIFICATION
- We can study features of all members of a group by studying only the feature of a few members.
- Classification makes the study of living things simpler and easier.
- It helps in easy identification of different organisms and also highlights the relationship between them.
- Classification helps in tracing the possible origin of organisms.
- It also gives us an idea about the evolution of organisms from simpler to a more complex one.
OLD CLASSIFICATION OF LIVING THINGS
Originally, there were only two classifications or kingdoms or groups of living things – plants (Kingdom Plantae) and animals (Kingdom Animalia). These two kingdoms were further divided and sub-divided into lower and lower groups. The lowest group is known as the species. A species is a group of living things having common features, and which come together to produce young ones of the same kind. There are approximate 8.7 million species on the planet Earth Members of species resemble one another more than they resemble members of any other species. For example, man is one species – although all of us are unique in some way or another still we resemble each other more than we resemble any other animal on the planet Earth.
The other unique feature of members of a species is that they can breed among themselves, and not with members of other species. Each species has a specific name. Some examples of animal species are – man, dog, cat, lion, tiger, elephant, zebra, deer, cow, etc. and plant species are – mango, neem, pine, guava, apple, banyan, sugarcane, grass, etc.
NEW CLASSIFICATION OF LIVING THINGS
The classification of living things in two kingdoms as described above is no more recognized. Scientists noted that certain living things possess features of both plants and animals. For example, bacteria which were originally considered as a plant do not have chlorophyll inside its cells (a characteristic feature of a plant). Similarly, Euglena which was considered as a single cell animal possesses chlorophyll. At the same time, it has an eye-spot like animals.
Robert Whittaker, an American scientist suggested that bacteria should not be classified under plants and single cell animals like Euglena should not be under animal kingdom. He is the first one to propose a five kingdom classification of living things. Given below are five kingdoms of living things and their typical features.
01. KINGDOM MONERA
Kingdom Monera includes microscopic, single-celled organisms with cell-wall. Their nucleus is not proper because nuclear material is not enclosed in a nuclear membrane. Bacteria are the sole member of the Kingdom Monera. They are the most abundant organism on the planet Earth. They are everywhere.
02. KINGDOM PROTISTA
Kingdom Protista consists of single-celled organisms which have a well-developed nucleus bound by a nuclear membrane. Some are animal-like since they do not make their own food. For example, Amoeba, and paramecium. Some are plant-like since they have chlorophyll and can make their own food using solar energy. For example, Euglena. To know more about amoeba and paramecium, have a look at this great video prepared by MooMoo Math and Science.
03. KINGDOM FUNGI
Kingdom Fungi includes organisms which can be unicellular, multicellular or filamentous.Saprotrophs – Living things which cannot prepare their own food and mostly live on the dead, decaying organic matter. Like bacteria, their nuclei are distributed throughout inside the cell. They lack chlorophyll, thus they cannot prepare their own food. They depend on dead or decaying organic matter for their food. For example, mushroom, yeast, and bread mold.
04. KINGDOM PLANTAE
Kingdom Plantae included living things called plants. Plants are mostly multicellular organisms with a cell wall made of cellulose.Autotrophs – Living things which can prepare their own food.They show a great diversity from single-celled microscopic ones to huge trees. They contain chlorophyll and can prepare their own food. Broadly we divide plants into two main groups – non-flowering plants, and flowering plants.
Non-flowering plants do not bear flowers, thus they reproduce by other methods such as vegetative propagation. They include – algae, mosses, and fern. Flowering plants as the name suggests, bear flowers and produce seed. For example – mango, neem, rose, sunflower, apple, maize, etc.
05. KINGDOM ANIMALIA
Kingdom Animalia includes all multicellular animals with a heterotrophic mode of nutrition and they feed on plants or other animals. The most important feature of this group is that they possess a nervous system with sense organs.Heterotrophs – Living things which cannot prepare their food by themselves, they feed either on plants or on other animals.
Animals are classified into two groups, that is, invertebrates and vertebrates, based on the presence or absence of a backbone. Invertebrates are animals without a backbone or a bony skeleton. For example – insects, sea sponge, tapeworm, butterfly, cockroach, etc. Vertebrates are those which have a backbone or a bony skeleton. For example – fish, frog, birds, lizard, man, etc.