NCERT Solutions for Class 11 Biology Chapter 1
The Living World Class 11
Chapter 1 The Living World Exercise Solutions
Exercise : Solutions of Questions on Page Number : 15
Why are living organisms classified?
A large variety of plants, animals, and microbes are found on earth. All these living organisms differ in size, shape, colour, habitat, and many other characteristics. As there are millions of living organisms on earth, studying each of them is impossible. Therefore, scientists have devised mechanisms to classify all living organisms. These methods of classification are based on rules and principles that allow identification, nomenclature, and finally classification of an organism.
For example, based on certain principles, once 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.
Why are the classification systems changing every now and then?
What different criteria would you choose to classify people that you meet often?
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 divided based on the surnames.
What do we learn from identification of individuals and populations?
Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica Mangifera indica
Define a taxon. Give some examples of taxa at different hierarchical levels.
Can you identify the correct sequence of taxonomical categories?
(b) Genus → Species → Order → Kingdom
Answer :
The correct hierarchical arrangement of taxonomic categories in ascending order is Species → Genus → Family → Order → Class → Phylum → Kingdom
Therefore, both (a) and (c) represent correct sequences of taxonomic categories.
Try to collect all the currently accepted meanings for the word 'species'. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand and bacteria on the other hand.
In biological terms, species is the basic taxonomical rank. It can be defined as a group of similar organisms that are capable of interbreeding under natural conditions to produce fertile offsprings.
Therefore, a group of similar individuals that are respectively isolated form a species. Species can also be defined as group of individuals that share the same gene pool.
Define and understand the following terms:
Answer :
Phylum is the primary division of kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term 'division' is used.
Class is a taxonomic group consisting of one or more related orders. For example, the class, Mammalia, includes many orders.
Family is a taxonomic group containing one or more related genera. In plants, families are categorized on the basis of vegetative and reproductive features.
Order is a taxonomic group containing one or more families. For example, the order, carnivore, includes many families.
How is a key helpful in the identification and classification of an organism?
Key is another 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
3. 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
Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy.
As an example, let us classify Solanum melongena (Brinjal). Kingdom โ Plantae
Division โ Angiospermae Class โ Dicotyledonae
Order โ Solanales Family โ Solanaceae Genus โ Solanum Species โ melongena
As an example, let us classify Columba livia (Blue rock Dove). Kingdom โ Animalia
Phylum โ Chordata Class โ Aves
Order โ Columbiformes Family โ Columbidae Genus โ Columba Species โ livia