NCERT Solutions for Class 9 Science - Diversity In Living Organisms

Page No. 80

Q1. Why do we classify organisms?
Ans: Classification of living organisms has the following advantages:

• It makes the study of a wide variety of organisms convenient and easy.
• It projects before us a picture of all life forms at a glance.
• It helps us to understand the interrelationships among different categories of organisms and thus, provides us with information about their evolution.
• All biological sciences depend upon a system of classification for the study of organisms, e.g.; biogeography, ecology, pathology, forestry.
• Classification gives a system for the identification of known and unknown organisms.

Q2. Give three examples of the range of variations that you see in life-forms around you.
Ans: The range of variations that we see in life-forms around us are:

• Size: There is a lot of variation in the size of organisms that we see. The size of microscopic bacteria is few micrometres while the size of a blue whale is about 30 metres and the height of redwood trees of California is about 100 metres.
• Life span: There is a lot of variation in the life span of organisms. The life span of insects like mosquitoes is only a few days whereas, the life span of a pine tree is thousands of years.
• Colour: There is a lot of variation seen in colour. Worms are colourless or transparent whereas, flowers and birds are brightly coloured.
  Birds and Flowers

Page No. 82

Q1. Which do you think is a more basic characteristic for classifying organisms?
(a) The place where they live.
(b) The kind of cells they are made of. Why?
Ans: The kind of cells they are made of is a more basic characteristic for classifying organisms.
When organisms are classified on the basis of the kind of cells they are made of, then there are two groups of organisms - prokaryotes and eukaryotes. It is used in a hierarchical classification.

Q2. What is the primary characteristic on which the first division of organisms is made?
Ans: The characteristic that some organisms have cells with membrane-bound organelles, including a nucleus and some organisms do not have a nucleus is the primary characteristic on which the division of organisms is made.

Q3. On what basis are plants and animals put into different categories?
Ans: Plants and animals are put into different categories on the following basis:

• Plants are stationary, whereas animals are not stationary.
• Plants make their own food, whereas animals eat plants or animals as food.
• Plants grow indefinitely, whereas animals stop growing after attaining a certain size.
• Plant cells are surrounded by a cell wall, whereas animal cells are not surrounded by a cell wall.
• Plant cells contain chlorophyll, whereas animal cells do not contain chlorophyll.

Page No. 83

Q1. Which organisms are called primitive and how are they different from the so-called advanced organisms?
Ans: Primitive organisms are those which have ancient body designs and have not changed much. They have simpler body designs and are also called lower organisms.
On the other hand, the organisms that have acquired more complex structures and body designs relatively recently are called advanced organisms.

Q2. Will advanced organisms be the same as complex organisms? Why?
Ans: Yes. It is because the ‘advanced’ organisms were also like the primitive ones once. They have acquired their complexity relatively recently. There is a possibility that these advanced or ‘younger organisms acquire more complex structures during the evolutionary time to compete and survive in the changing environment.

Page No. 85

Q1. What is the criterion for the classification of organisms as belonging to kingdom Monera or Protista?
Ans: The organisms belonging to Kingdom Monera are prokaryotic. It means that they do not have a defined nucleus and cell organelles are absent. They do not have a multicellular body design.
The organisms belonging to Kingdom Protista are unicellular eukaryotic. Some of them have appendages such as hair-like cilia or whip-like flagella for moving around.

Q2. In which kingdom will you place an organism which is single-celled, eukaryotic and photosynthetic?
Ans: Organisms of kingdom Protista are single-celled, eukaryotic and photosynthetic.

Q3. In the hierarchy of classification, which grouping will have the smallest number of organisms with a maximum of characteristics in common and which will have the largest number of organisms?
Ans: Species will have the smallest number of organisms with a maximum of characteristics in common in the hierarchy of classification whereas, the Kingdom has the largest number of organisms.

Page No. 88

Q1. Which division among plants has the simplest organisms?

Ans: Thallophyta has the simplest organism among plants.

Q2. How are pteridophytes different from the phanerogams?
Ans: Differences:

Q3. How do gymnosperms and angiosperms differ from each other?
Ans:

Page No. 94

Q1. How do poriferan animals differ from coelenterate animals?
Ans: 

Q2. How do annelid animals differ from arthropods?
OR
List three distinguishing features between Annelids and Arthropods animals.
Ans: 

Q3. What are the differences between amphibians and reptiles?
Ans: Differences:

Q4. What are the differences between animals belonging to the Aves group and those in the mammalian group?
OR
List in the tabular form any three differences between the Aves and the Mammalia group.
Ans: 

Page No. 97

Q1.What are the advantages of classifying organisms?
Ans: Following are the advantages of classifying organisms:

• It makes us aware of and gives us information regarding the diversity of plants and animals.
• It makes the study of different kinds of organisms much easier.
• It tells us about the inter-relationship among the various organisms.
• It helps us to understand the evolution of organisms.
• It helps in the development of other life sciences.

Q2. How would you choose between two characteristics to be used for developing a hierarchy in classification?
Ans: For developing a hierarchy of classification that characteristics out of the two would be chosen which decides more fundamental differences among organisms. This would create the main broad groups of organisms. Within these groups, smaller sub-groups will be decided by less important characteristics.

Q3. Explain the basis for grouping organisms into five kingdoms.
Ans:  The basis for grouping organisms into five kingdoms is:

• Nature of the cells, i.e., either prokaryotic or eukaryotic cells.
• Number of cells, i.e., unicellular (a cell living singly) or multicellular (complex organisms).
• Presence or absence of cell wall.
• Mode of nutrition, i.e., whether they prepare their own food or get their food from outside.

Q4. What are the major divisions in the Plantae? What is the basis for these divisions?
Ans: The major divisions in Kingdom Plantae are:

• Thallophyta
• Bryophyta
• Pteridophyta
• Gymnosperms
• Angiosperms 

The following points constitute the basis of these divisions:

• Presence or absence of distinct organelles.
• Presence or absence of distinct and differentiated tissues, which can carry food and water.
• Presence or absence of seeds.
• Whether the seeds are enclosed within fruits or not.

Q5. How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals?
Ans: The criteria for dividing the plants include

• differentiation of the plant body;
• distinct vascular (conduction) tissues;
• seed producing ability; and
• the seeds enclosed within fruits.

But the animals can’t be divided into groups on these criteria. It is because the basic designs of animals are very different from plants. They are divided on the basis of their body structure.

Q6. Explain how animals in Vertebrata are classified into further subgroups.
Ans: Vertebrates can be further classified into subgroups on the basis of simple or complex body structures and their functions. For example, fishes have two-chambered hearts, amphibians have three-chambered hearts while birds and mammals have four-chambered hearts to keep the oxygenated and deoxygenated blood separate.
The following characteristic features are considered for classifying Vertebrata into the further subgroups: