The Living World Question Answers: NCERT Class 11 Biology

A large variety of plants, animals, and microbes found on earth and they differ in size, shape, colour, habitat, and many other characteristics. So, studying each of them is impossible. Therefore, scientists have devised mechanisms to classify all living organisms on certain rules and principles that allow identification, nomenclature, and finally classification of an organism.

For example, based on presence of three pairs of legs and 2 pairs of wings, an organism is identified as an insect, it will be given a scientific name and then grouped with other similar organisms. Thus, various groups or taxon include organisms based on their similarity and differences.

Therefore, the biological classification helps in revealing the relationship between various organisms. It also helps in making study of organisms easy and organized.

Key is a taxonomical aid that helps in identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called couplet.

Each statement in a taxonomic key is referred to as a lead. For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used. It is also useful in identification of unknown organisms.

Keys are of two types- indented and bracketed keys. Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters are used.

(i) Indented key to identify different species of Rhododendron.

1. Leaves evergreen

2. leaves densely hairy below, orange or white hair; flower

appears to have separate petals

………………………. Rhododendron groenlandicum

2. hair absent on leaves, flower has five petals fused in a shallow

tube

………………………. Rhododendron maximus

1. Leaves deciduous

2. pink flowers with two free petals and three fused petals

………………………. Rhododendron canadense

3. white to pink flowers with all petals fused together

(ii) Bracketed key to identify different species of Rhododendron.

1.      Leaves evergreen-----------------------------------------------2

1. Leaves deciduous-----------------------------------------------3

2. Leaves densely hairy below, orange or white hair; flower

appears to have separate petals

……….………………………. Rhododendron groenlandicum

2. Hair absent on leaves, flower has five petals fused in shallow

tube

………………………………..Rhododendron maximus

3. Pink flowers with two free petals and three fused petals

……………………………… Rhododendron canadense

3. White to pink flowers with all petals fused together-----4

The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy.

In this hierarchy, species is present at the lowest level whereas kingdom is present at the highest level.

Classification of a plant

As an example, let us classify Solanum melongen a (Brinjal).

Kingdom – Plantae

Division – Angiospermae

Class – Dicotyledonae

Order – Solanales

Family – Solanaceae

Genus – Solanum

Species – melongen a

Classification of an animal

As an example, let us classify MAN

Kingdom – Animalia

Phylum – Chordata

Class – Mammalia

Order – Primate

Family – Hominidae

Genus – Homo

Species – Sapiens

Millions of plants, animals, and microorganisms found on earth, have been identified by the scientists while many new species are still being discovered around the world. Therefore, to classify these newly discovered species, with new characters, new systems of classification have to be devised every now and then. This creates the requirement to change the existing systems of classification.

To classify a class of forty students, let us start the classification on the basis of sexes of the students. This classification will result in the formation of two major groups- boys and girls. Each of these two groups can be further classified on the basis of the names of the students falling in these groups.

Since it is possible that more than one student can have a particular name, these names can be further suffixed with the surnames.

Since there is still some chance that more than one student can have the same surname, the final level of classification will be based on the roll numbers of each student.

The knowledge of characteristics of an individual or its entire population helps in the identification of similarities and dissimilarities among the individuals of same kind or between different types of organisms. It helps the scientists to classify organisms in various categories depending upon these similarities and dissimilarities.

In binomial system of nomenclature, the generic name of a species always starts with a capital letter whereas the specific name starts with a small letter. Therefore, the correct scientific name of Mango is Mangifera indica.

Each unit or category of classification is termed as a taxon. It represents a rank. For example, the basic level of classification is species, followed by genus, family, order, class, phylum or division, in ascending order. The highest level of classification is known as kingdom. So each of these categories can be called as a taxon.

Both (a) and (c) represent correct sequences of taxonomic categories as the correct hierarchical arrangement of taxonomic categories in ascending order is

Species → Genus → Family → Order → Class → Phylum → Kingdom

In sequence (b), species should have been followed by genus. Therefore, it does not represent the correct sequence.

In biological terms, species is the basic unit of taxonomy. It can be defined as a group of similar organisms capable of interbreeding freely among themselves under natural conditions to produce fertile off springs.

Therefore, a group of similar individuals that are reproductively isolated from other group of individuals form a species.

Species can also be defined as group of individuals that share the same gene pool.

(i) Phylum

Phylum is second highest unit of classification after Kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term ‘division’ is used.

(ii) Class

Class is a taxonomic group consisting of one or more related orders. For example, the class, Mammalia, includes many orders like Primata (Man), Carnivora(Lim, tiger) etc.

(iii) Family

Family is a taxonomic group containing one or more related genera eg. Family hominidae contains Apes, Monkeys and Man. In plants, families are categorized on the basis of vegetative and reproductive features.

(iv) Order

Order is a taxonomic group containing one or more families. For example, the order, carnivora, includes many families.

(v) Genus

Genus is a taxonomic group including closely related species. For example, the genus, Solanum, includes many species such as nigrum, melongen a, tuberosum, etc.

The ability of an object which can self- replicate and self- regulate is known as Living. The four defining characteristics are:

1. Growth and development
2. Reproduction
3. Metabolism
4. Consciousness

Growth: This is a permanent and the irreversible change in the size of the cell, organ and the whole organism that is usually accompanied by the increase in dry weight, mass and number of individuals. Growth of living organisms occurs by the cell division, enlargement and its differentiation.

Reproduction: It is a biological process by which new individuals are produced from both their parents (maternal or paternal). Every organism have the characteristic to produce more of its own kind by the process called reproduction.

Metabolism: It is the total of all chemical and biological reactions occurring inside the cells. It is also defined as the exchange of materials and energy within the organisms and between the organism and its environment.

Consciousness (Response and Irritability): Ability of the body to sense to respond to the external or environmental stimuli. And, as an response, the change or reaction which is shown by the organism as a result of applied stimulus is known as response.

Following are the examples of this statement:

1. Blood is a connective tissue that is made up of RBCs, WBCs and Platelets. Its function is to transport different parts of body whereas blood cells do not play this role.
2. Bone is a specialized connective tissue which acts as a supporter. It is made up of osteocytes. These osteocytes does not provide any mechanical support.
3. A muscle tissue is capable of contraction but its all constituents cell may not capable of doing so.

Taxonomic aids can easily identify species and classify them which is very useful in agriculture, forestry and in various industries. Newly discovered plant can be identified with the help of herbaria, monographs and preserved plant specimen. The scientist has to study morphological characters of the plants, plant parts, compare the characteristic features with similar information availability in the scientific literature. After that he can name it according to the rules of binomial nomenclature and fix its systematic position.

1. Mustard
2. The first name represents genus and second name denote species.
3. To indicate their Latin origin.
4. It refers to Linnaeus, who was the first discoverer of this plant.

1. Collection of information, techniques, procedures which helps to identify and classify an individual is called Taxonomic aids which are useful in agriculture, forestry and in various industries.
2. Herbarium is an collection of pressed, dried and preserved plants which are mounted on paper sheets, properly labelled, systematically arranged and available for reference or study. These are used to study the morphology of plants, identification of unknown plants and provide information about flora.
3. Museum is a building which is used for the preservation, storage and exhibition of inanimate objects which illustrate the human or natural history. It consist of a collection of preserved plants and animals used for study and references.
4. Botanical gardens helps in conservation of plants by growing important local plant species and keeping record of them whereas Zoological parks also contribute in conserving biodiversity by providing natural environment and open space to animals, i.e. wildlife species.

The grouping of organisms at any level is known as taxon.

Taxonomic hierarchy refers to the sequence of categories in increasing or decreasing order. Organism classification rank from the lowest to the highest category for a plant and an animal is:

As we move from species to kingdom there will be decrease in the number of common characteristics occurs.

A key is a set of alternate characters in such a manner that is used to identify plants and animals based on their similarities and dissimilarities and here that key is taxonomic keys. The keys are based on the contrasting character generally occur in couplet.

Metabolism is the chemical reaction that happens in the body’s cells which converts the food into energy. Isolated metabolic reaction are performed in laboratories, thus they cannot be considered as metabolism because they are conducted in the controlled environment. But these reactions are taking inside a living system so are considered as living reaction.

A coma is defined as a state of long term of unconsciousness. This is a state of mind which keep the person sleep even though he is alive. A lot of many metabolic activities still take place and people often come out from their state, so they are living.