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NCERT Solutions for Class 9 Science chapter 7 – Diversity in Living Organisms

Back Exercise

Question 1.
What are the advantages of classifying organisms ? (CCE 2012, 2013, 2014)
Answer:

1. Identification is not possible without any system of classification.
2. Classification helps in bringing out similarities and dissimilarities amongst organisms.
3. Relationships are built up with the help of classification. They indicate the evolutionary pathways.
4. Organisms of other localities and fossils can be studied only with the help of a system of classification.
5. It is not possible to study every organism. Study of one or two organisms gives sufficient idea about other members of the group.
6. Other branches of biology depend upon proper identification of the organism which is possible only through a system of classification.

Question 2.
How would you choose between two characteristics to be used for developing a hierarchy in classification ?
Answer:
The character which is of fundamental importance, generally present in larger number of organisms, as a change in body design, is used in raising a higher category. The character of lesser importance, generally present in smaller number of individuals is used for raising lower category.

Question 3.
Explain the basis for grouping of organisms into five kingdoms. (CCE 2012, 2013)
Answer:
Four criteria have been used for grouping of organisms into five kingdoms—

1. Procaryotic and eukaryotic nature
2. Unicellular and multicellular nature
3. Nutrition

Question 4.
How are criteria for deciding divisions in plants different from the criteria for deciding subgroups amongst animals ?
Answer:
Body design of plants is quite different from that of animals. Plants are anchored. They require organs for fixation and absorption. Plants are autotrophic. Reproductive organs, mechanical tissues and conducting tissues have evolved in higher plants. In animals the requirement is mobility for obtaining food and other necessities. Their evolution has occurred towards greater mobility, protection, increased efficiency in obtaining food and care of young ones. Therefore, criteria for deciding divisions or subgroups are different for plants and animals.

Question 5.
What are the major divisions in the plantae ? What is the basis for these divisions ? ( CCE 2015)
Answer:

1. Multicellularity. Plantae includes multicellular organisms except for some primitive relatives of algae.
2. They are eukaryotes, that is, with a nucleus and membrane bound cell organelles.
3. Cell Wall. A cell wall generally containing cellulose occurs around cells.
4. Central Vacuole. A mature cell commonly possesses a single large central vacuole.
5. Food Reserve. It is starch and fat.
6. They are double membrane covered cell organelles found in all plants. Some plastids possess photosynthesis pigments. They are called chloroplasts.

Kingdom plantae has three levels of classification:

1. The first level of classification deals with presence or absence of well differentiated distinct parts. Undifferentiated plants are included amongst thallophyta.
   
2. The second level of classification deals with presence or absence of vascular tissues.
   
3. The third level of classification is based on the presence or absence of seeds and whether the seeds are exposed or enclosed inside fruits.

Question 6.
Explain how animals in vertebrata are classified into further subgroups.
Answer:
Vertebrata is divided into five classes—pisces, amphibia, reptilia, aves and mammalia on the basis of following characteristics :

1. It consists of scales in fishes and reptiles, feathers in birds and hair in mammals. Skin is smooth and moist in amphibians.
2. It is cartilaginous in chondrichthyes and bony in others.
3. It occurs through gills in all fishes and larvae of amphibians. Other have lungs for breathing.
4. Fishes and amphibians lay eggs in water. Reptiles and birds do so outside water.
5. They occur in birds. Wings are used for flight.
6. External Ears. They occur in mammals.
7. Mammals generally show vivipary or give birth to young ones.

In-Text Questions

Question 1.
Why do we classify organisms ? (CCE 2012)
Answer:

1. Identification is not possible without any system of classification.
2. Classification helps in bringing out similarities and dissimilarities amongst organisms.
3. Relationships are built up with the help of classification. They indicate the evolutionary pathways.
4. Organisms of other localities and fossils can be studied only with the help of a system of classification.
5. It is not possible to study every organism. Study of one or two organisms gives sufficient idea about other members of the group.
6. Other branches of biology depend upon proper identification of the organism which is possible only through a system of classification.

Question 2.
Give three examples of the range of variations that you see in life forms around you.
Answer:

1. Size: It varies from microscopic organisms (e.g., bacteria, size 0-5-5-0 pm) to very large sized animals (e.g, Blue whale, 30 metres long) and trees (e.g, Redwood tree, height 100 metres).
2. Life Span: May fly lives for one day, most mosquitoes for a few days while some Pine trees live for thousands of years.
3. Colour: Jelly fish and many worms are colourless. Birds, butterflies and flowers are variously coloured brightly.

Question 3.
Which do you think is a more basic characteristic for classifying organisms ?
(a) The place they live
(b) The kind of cells they are made of Why ? (CCE 2012)
Answer:
The kind of cells: Habitat is a place where diverse types of organisms live together. It cannot be used for classifying organisms. Cells have specific structure, prokaryotic in monerans and eukaryotic in the remaining organisms.
Organisms are unicellular in protista and multicellular in others. A cell wall is absent in animals. Cell wall contains chitin in fungi and cellulose in plants. Plastids occur in plant cells. They are absent in animal cells.

Question 4.
What is the primary characteristic on which the first division of organisms is made ? (CCE 2012)
Answer:
Type of cell, prokaryotic (genetic material or nucleoid free in cytoplasm) and eukaryotic (genetic material enclosed in nucleus).

Question 5.
On what basis are plants and animals put into different categories ? (CCE 2012)
Answer:
Plants and animals are placed in different categories because they differ in several characteristics.

1. Shape: Animals have a definite shape while plants have less definite shape.
2. Branching: Animals are unbranched (exception sponges), while plants are generally branched.
3. Growth: Animals stop growing after reaching a certain size. Plants continue to grow till death.
4. Locomotion: Animals can move from place to place (exception corals, sponges) while plants are fixed.
5. Nutrition: Animals eat ready made food while plants manufacture their own food.
6. Reserve Food: It is glycogen in animals and starch in plants.
7. Cell Wall: Animal cells do not have a covering of wall while individual plant cells are surrounded by cell walls.
8. Excretory Organs: They are present in animals but absent in plants.
9. Sense Organs and Nervous System: They are found in animals but not in plants.

Question 6.
Which organisms are called primitive and how are they different from the so called advanced organisms ?
(CCE 2011, 2012)
Answer:
Primitive organisms are those organisms which have simple ancient body design with only basic characteristics of the group. There has been little change over a long period of time. Specialisations are fewer.
Advanced organisms are more recent organisms. They are also called higher organisms because they possess several specialisations. They have more complex structure and some new characteristics alongwith the basic ones.

Question 7.
Will advanced organisms be the same as complex organisms ? Why ? (CCE 2012, 2015)
Answer:
Yes. Advancement is based on development of specializations. Specialisation occurs where there is more elaboration and hence more complexity. However, there is likelihood of specialisation to lead to overspecialisation which becomes a hindrance to competitive nature of existence in the biosphere. Dinosaurs, giant crocodiles and mammoth have died down due to this reason. Therefore, advancement is possible only if specialisation leads to greater elaboration and efficiency.

Question 8.
What is the criterion for classification of organisms as belonging to kingdom Monera or Protista ?
(CCE 2012, 2014)
Answer:
Cell structure is used as a criterion for placing an organism in monera or protista. In monera the cells are prokaryotic. Membrane bound cell organelles are absent. In protista the cells are eukaryotic.
Membrane bound cell organelles are present. Protista contains only unicellular eukaryotes. Monera may have unicellular or multicellular forms.

Question 9.
In which kingdom will you place an organism which is single-belled, eukaryotic and photosynthetic ?
(CCE 2012, 2013)
Answer:
Protista.

Question 10.
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.
(CCE 2011, 2012)
Answer:

1. Small number (one) with maximum common characteristics— Species
2. Largest number— Kingdom.

Question 11.
Which division among plants has the simplest organisms ?
Answer:
Thallophyta.

Question 12.
How are pteridophytes different from phanerogams ? (CCE 2012)
Answer:

Question 13.
How do gymnosperms and angiosperms differ from each other ? (CCE 2012)
Answer:

Question 14.
How do poriferan animals differ from coelenterate animals ?
Answer:

Question 15.
How do annelid animals differ from arthropods ? (CCE 2012)
Answer:

Question 16.
What are the differences between amphibians and Pisces? (CCE 2012)
Answer:

Question 17.
What are the differences between animals belonging to the aves group and those in mammalia group ? (CCE 2012)
Answer: