Page No. 80
Q.1. Why do we classify organisms?
Ans: Classification of living organisms has the following advantages:
(a) It makes the study of a wide variety of organisms convenient and easy.
(b) It projects before us a picture of all life forms at a glance.
(c) It helps us to understand the interrelationships among different categories of organisms and thus, provides us information about their evolution.
(d) All biological sciences depend upon a system of classification for the study of organisms, e.g.; biogeography, ecology, pathology, forestry.
(e) Classification gives a system for identification of known and unknown organisms.
Q.2. 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:
(a) 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 blue whale is about 30 metres and height of redwood trees of California is about 100 metres.
(b) Life span: There is a lot of variation in the life span of organisms. The life span of insects like mosquito is only a few days whereas, the life span of a pine tree is thousands of years.
(c) Colour: There is a lot of variation seen in colour. Worms are colourless or transparent whereas, flowers and birds are brightly coloured.
Page No. 82
Q.1. 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.
Q.2. 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.
Q.3. On what basis are plants and animals put into different categories?
Ans: Plants and animals are put into different categories on the following basis:
(a) Plants are stationary, whereas animals are not stationary.
(b) Plants make their own food, whereas animals eat plants or animals as food.
(c) Plants grow indefinitely, whereas animals stop growing after attaining a certain size.
(d) Plant cells are surrounded by a cell wall, whereas animal cells are not surrounded by a cell wall.
(e) Plant cells contain chlorophyll, whereas animal cells do not contain chlorophyll.
Page No. 83
Q.1. 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.
Q.2. 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 evolutionary time to compete and survive in the changing environment.
Page No. 85
Q.1. What is the criterion for 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 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.
Q.2. 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.
Q.3. 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, Kingdom has largest number of organisms.
Page No. 88
Q.1. Which division among plants has the simplest organisms?
Ans: Thallophyta has the simplest organisms among plants.
Q.2. How are pteridophytes different from the phanerogams?
|(a) Plant body is differentiated into root, stem and leaves.||(a) Plants are more developed and advanced.|
|(b) They are seedless plants.||(b) They are seed-bearing plants.|
|(c) Reproductive organs are inconspicuous, i.e. with hidden reproductive organs.||(c) Reproductive organs are well developed.|
|(d) They have specialised tissue for the conduction of water, etc. The vascular system is primitive.||(d) They have advanced vascular system.|
Q.3. How do gymnosperms and angiosperms differ from each other?
|1. The plants bear naked seeds.||1. Seeds are enclosed in fruits.|
|2. They produce cones formed of sporophyte. The sporophyte carries the male and female sex organs.||2. Reproductive organs are flowers, carrying male and female sex organs.|
|3. Ovules are not enclosed in ovary.||3. Ovules are enclosed in ovary.|
|4. Plants of this group are usually evergreen, perennial and woody.||4. Plants of this group may be annual, biennial or perennial. They may be woody or non-woody.|
|5. Xylem lack vessel.||5. Xylem contains vessels.|
|6. Phloem does not contain companion cells.||6. Phloem contains companion cells.|
Page No. 94
Q.1. How do poriferan animals differ from coelenterate animals?
|Sr. No.||Poriferan Animals||Coelenterate Animals|
|1||They possess cellular level organisation.||They possess tissue level organisation.|
|2||The body has several pores, ostia and osculum.||The body has a single opening.|
|3||The body design of these animals involves minimal differentiation.||The body design of these animals shows more I differentiation.|
|4||Appendages are absent.||Appendages occur in the form of tentacles.|
|5||Digestion is intracellular.||Digestion is both intracellular and intercellular.|
|6||Muscles and nerve cells are absent.||Muscles and nerve cells appear for the first time in coelenterates.|
Q.2. How do annelid animals differ from arthropods?
List three distinguishing features between Annelids and Arthropods animals.
|1||They have true body cavity.||They have a false body cavity with blood.|
|2||They do not have jointed legs.||They have jointed legs.|
|3||A chitinous exoskeleton is absent.||A chitinous exoskeleton is present,|
|4||Excretory organs are nephridia.||Excretory organs are green glands and malpighian tubules|
|5||Sensory system is less developed.||Sensory system is well developed.|
|6||Respiration is mostly through skin.||Respiration is by gills or lungs or tracheae.|
Q.3. What are the differences between amphibians and reptiles?
|1.||They do not have scales.||They have scales.|
|2.||Skin is smooth and moist.||Skin is dry and cornified.|
|3.||Respiration either through gills or lungs.||Respiration through lungs.|
|4.||Fertilisation is external.||Fertilisation is internal.|
|5.||Digits do not possess claws.||Digits end in claws.|
|6.||They lay eggs in water.||They lay eggs with tough coverings and do not need water for laying eggs.|
Q.4. What are the differences between animals belonging to the Aves group and those in the mammalia group?
List in the tabular form any three differences between the Aves and the Mammalia group.
|a||They lay eggs.||They give birth to young ones.|
|b||They do not have mammary glands.||They have mammary glands for production of milk to nourish their young ones.|
|c||They can fly.||They cannot fly except bat.|
|d||Body is covered with feathers.||Feathers are absent.|
|e||Forelimbs are modified into wings.||Wings are absent except in bats.|
|f||Bones are hollow or pneumatic.||Bones do not possess air cavities.|
|g||Birds are oviparous.||Mammals are viviparous with a few exceptions like platypus and echidna.|
Page No. 97
Q.1.What are the advantages of classifying organisms?
Ans: Following are the advantages of classifying organisms:
(i) It makes us aware of and gives us information regarding the diversity of plants and animals.
(ii) It makes the study of different kinds of organisms much easier.
(iii) It tells us about the inter relationship among the various organisms.
(iv) It helps us to understand the evolution of organisms.
(v) It helps in the development of other life sciences.
Q.2. 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.
Q.3. Explain the basis for grouping organisms into five kingdoms.
Ans: The basis for grouping organisms into five kingdoms is:
(i) Nature of the cells, i.e., either prokaryotic or eukaryotic cells.
(ii) Number of cells, i.e., unicellular (a cell living singly) or multicellular (complex organisms).
(iii) Presence or absence of cell wall.
(iv) Mode of nutrition, i.e., whether they prepare their own food or get their food from outside.
Q.4. What are the major divisions in the Plantae? What is the basis for these divisions?
Ans: The major divisions in Kingdom Plantae are:
The following points constitute the basis of these divisions:
(i) Presence or absence of distinct organelles.
(ii) Presence or absence of distinct and differentiated tissues, which can carry food and water.
(iii) Presence or absence of seeds.
(iv) Whether the seeds are enclosed within fruits or not.
Q.5. 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
(i) differentiation of the plant body;
(ii) distinct vascular (conduction) tissues;
(iii) seed producing ability; and
(iv) 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.
Q.6. 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:
|Characteristics||Exoskeleton of scales, endoskeleton of bone/ cartilage, breathing through gills||Gills in larva, lungs in most- adults, slimy skin||Exoskeleton of scales laying eggs outside water||Exoskeleton of feathers, lay eggs outside water, flight possible||Exoskeleton of hair, external ears, mostly giving birth to live young ones|