NCERT Solutions for Class 11 Biology Chapter 1 The Living World

Q1. Why are living organisms classified?

Answer:

Living organisms are classified for the following reasons:

There are numerous different species of living beings on our planet. It is hard to study each one separately. Scientists unite similar species to make it more convenient to research them. Studying one group, we learn about the properties of all the species in the group.

Classification also helps us in learning how various species relate to one another in terms of evolution.

Q2. Why are the classification systems changing every now and then?

Answer:

Earth is inhabited by numerous plants, animals, and microorganisms. The total number of species is not known yet. A lot of species have already been discovered and classified by scientists, but there are many more still to be discovered. When a new species is found, the system of classification is revised to accommodate it. That is why classification continues to change with time.

Q3. What different criteria would you choose to classify people that you meet often?

Answer:

The people that we often meet can be classified on the basis of their sex or gender, the age group in which they fall, profession, education, hobbies, etc.

Q4. What do we learn from the identification of individuals and populations?

Answer:

The identification of individuals helps us to know how they differ from or are similar to others within the same population. It also helps establish relationships between individuals from various populations. Researching populations enables us to know about their characteristics and how they compare to other populations. This process also helps in classifying organisms properly and knowing their evolutionary relationships.

Q5. Given below is the scientific name of Mango. Identify the correctly written name.

• Mangifera Indica
• Mangifera indica

Answer:

The correct scientific name of mango is Mangifera indica. As per the binomial system of nomenclature, the first name in a scientific name is the genus name while the second name is specific. The scientific name is always written in italics. The first letter of the genus name is written in capitals while that of the specific name is written in small letters.

Answer:

Taxon refers to a particular level of hierarchy in the classification of living beings. Examples of taxa at different hierarchical levels are species, genus, order, family, phylum and kingdom.

Q7. Can you identify the correct sequence of taxonomical categories:

(A) Species → Order → Phylum → Kingdom

(B) Genus → Species → Order → Kingdom

(C) Species → Genus → Order → Phylum

Answer:

The correct sequence of taxonomic categories from lowest to highest is species, genus, family, order, class, phylum, kingdom. Thus, A and C represent the correct sequence of taxonomic categories with some categories missing in between, while B is incorrect as the genus is given before species.

Q8. Try to collect all the currently accepted meanings for the word species. Discuss with your teacher the meaning of species in the case of higher plants and animals on the one hand, and bacteria on the other hand.

Answer:

The word "species" is explained as:

• A collection of organisms with common traits that can reproduce within themselves.
• The most basic unit of classification brings together people with a common genetic makeup.
• A naturally occurring group of organisms that are similar in form, function, structure, and cellular composition.

For plants and animals at the higher levels, the first definition is the most precise since they reproduce sexually. For bacteria, the second and third definitions hold since bacteria are asexually reproduced and categorised according to genetic and structural similarities.

Q9. Define and understand the following terms:

(i) Phylum

Answer:

Phylum - A phylum is a large group of animals. which is formed of one or more classes. The term phylum is replaced by division in the case of plants. For example, the phylum chordate of animals contains mammals, aves, reptiles, amphibians, etc.

(ii) Class

Answer:

Class - It is a taxonomic group higher than order and lower than phylum. A class is made of one or more related orders. For example, the class dicotyledoneae of flowering plants contains all dicots, which are grouped into several orders, like Rosales, Polemoniales, etc.

Q9. Define and understand the following terms:

(iii) Family

Answer:

Family refers to that taxonomic category which contains one or more related genera. For example, the family Solanaceae contains a number of genera like Solanum, Withania, Datura etc. All genera of a family are related through some common features or correlated characters.

Q9. Define and understand the following terms:

(iv) Order

Answer:

Order is the taxonomic category higher than family and lower than class. An order consists of one or more groups of families which share certain common characteristics. For example, the families Felidae and Canidae are included in the same order of carnivores.

Q9. Define and understand the following terms:

(v) Genus

Answer:

Genus - A genus is a group of related species which resemble one another in certain correlated characteristics. All species of the genus are presumed to have evolved from a common ancestor. Lion, Tiger, and Leopard are closely related species and placed in the same genus, Panther.

Q10. How is a key helpful in the identification and classification of an organism?

Answer:

A taxonomic key refers to an artificial analytical device used for identifying organisms. Usually, in a key, two contrasting characters are used. The one present in the organism is chosen while the other is rejected. Each statement of a key is called a lead. Separate taxonomic keys are used for each taxonomic category like species, genus, family, etc. Keys are generally analytical in nature.

Q11. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.

Answer:

Taxonomical hierarchy refers to the classification of organisms into a definite sequence of taxonomic categories starting from the kingdom and going up to species. An illustration of the taxonomic hierarchy is given below.