SEBA Class 9 Science: Diversity in Living Organisms
IN–TEXT QUESTIONS
1. Why do we classify organisms?
Answer: Organisms are classified to make the study of the great variety of life forms easier. Since millions of organisms exist on earth, studying each one separately is difficult. By grouping them on the basis of similarities, we can study the whole group together. Classification also helps us understand the diversity of life and their evolutionary relationships.
2. Give three examples of the range of variations that you see in life-forms around you.
Answer: Three examples of variations in life-forms are:
1. Some organisms, like bacteria, are only a few micrometres in size, while blue whales and redwood trees are extremely large.
2. Some pine trees live for thousands of years, but insects like mosquitoes survive only for a few days.
3. Life-forms range from colourless or transparent worms to brightly coloured birds and flowers.
IN–TEXT QUESTIONS
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?
Answer: The kind of cells organisms are made of is a more basic characteristic. This is because having prokaryotic or eukaryotic cells affects all aspects of the body design and functions. On the other hand, the place where organisms live does not show major differences in their body structure, so it is less important for classification.
2. What is the primary characteristic on which the broad division of organisms is made?
Answer: The broad division of organisms is mainly made on the basis of the kind of cells they have, that is, whether the cells are prokaryotic or eukaryotic. This difference affects the entire body design and is used as the primary characteristic for classification.
3. On what bases are plants and animals put into different categories?
Answer: Plants and animals are put into different categories mainly on the basis of their body design. Plants make their own food by photosynthesis and have different structural features, while animals cannot make their own food and have a different way of organising their body parts. These differences in body design place them in separate groups.
IN–TEXT QUESTIONS
1. Which organisms are called primitive and how are they different from the so-called advanced organisms?
Answer: Organisms that have ancient and simple body designs are called primitive. Their body structure has not changed much over time. Advanced organisms are those that have acquired their body designs more recently and are usually more complex. Primitive organisms are older and simpler, while advanced organisms are younger and show greater complexity in their body design.
2. Will advanced organisms be the same as complex organisms? Why?
Answer: Yes, advanced organisms are generally the same as complex organisms. This is because organisms that appeared later usually have more developed and complicated body designs. Older organisms are simpler, while the newer or advanced ones show greater complexity in their structure.
IN–TEXT QUESTIONS
1. What is the criterion for the classification of organisms as belonging to the kingdom Monera or Protista?
Answer: The criterion for classifying organisms into Monera or Protista is based on the type of cells and organization.
Organisms of Monera are prokaryotic and unicellular, without a defined nucleus.
Organisms of Protista are eukaryotic and unicellular, having a true nucleus.
2. In which kingdom will you place an organism which is single-celled, eukaryotic, and photosynthetic?
Answer: An organism that is single-celled, eukaryotic, and photosynthetic will be placed in the Protista kingdom.
3. In the hierarchy of classification, which grouping will have the smallest number of organisms with maximum common characteristics, and which will have the largest number of organisms?
Answer: In the hierarchy of classification, the species has the smallest number of organisms because only those organisms that are similar enough to breed and continue their kind belong to the same species.
The kingdom has the largest number of organisms, as it includes many different types of living beings with fewer common characteristics.
IN–TEXT QUESTIONS
1. Which division among plants has the simplest organisms?
Answer: The division that has the simplest organisms among plants is Thallophyta, because their plant body is not well-differentiated.
2. How are pteridophytes different from the phanerogams?
Answer: Pteridophytes have a plant body with roots, stem and leaves, but their reproductive organs are inconspicuous, so they do not produce seeds.
Phanerogams, on the other hand, have well-developed reproductive parts that form seeds, which may be naked or enclosed in fruits.
3. How do gymnosperms and angiosperms differ from each other?
Answer: Gymnosperms and angiosperms differ mainly in the way their seeds are formed. Gymnosperms have naked seeds, which remain exposed because they are not protected by any fruit. In angiosperms, the seeds are enclosed inside an ovary, and this ovary later develops into a fruit, giving the seeds proper protection.
IN-TEXT QUESTION
1. How do poriferan animals differ from coelenterate animals?
Answer: Poriferan animals have pores all over the body and a canal system that circulates water to bring in food and oxygen. Their bodies show very little tissue differentiation, and they are non-motile, remaining attached to solid surfaces.
Coelenterate animals, on the other hand, have a body cavity and their body is made of two layers of cells. They show more body design differentiation and may live solitarily or in colonies.
2. How do annelid animals differ from arthropods?
Answer: Annelid animals have a true body cavity, and their body is segmented internally and externally with organs arranged in each segment. They show extensive organ differentiation, and examples include earthworms and leeches.
Arthropods also have a segmented body, but they possess jointed legs and have an open circulatory system where blood does not flow in proper vessels. Their coelomic cavity is filled with blood, and this group includes prawns, spiders, insects, and scorpions.
3. What are the differences between amphibians and reptiles?
Answer: Amphibians do not have scales, and their skin contains mucus glands. They have a three-chambered heart and breathe through gills or lungs. They lay eggs in water and live both on land and in water.
Reptiles are cold-blooded, have scales, and breathe only through lungs. Most have a three-chambered heart, but crocodiles have four chambers. They lay eggs with tough coverings, and their eggs do not need to be laid in water.
4. What are the differences between animals belonging to the Aves group and those in the Mammalia group?
Answer: Animals of the Aves group are warm-blooded, have a four-chambered heart, and their body is covered with feathers. They lay eggs, and their forelimbs are modified for flight. All birds belong to this group.
Animals of the Mammalia group are also warm-blooded and have a four-chambered heart, but they possess mammary glands to produce milk for their young. Their skin has hair, sweat glands, and oil glands. Most mammals give birth to live young ones, while a few lay eggs.
EXERCISE QUESTIONS
1. What are the advantages of classifying organisms?
Answer: The advantages of classifying organisms are:
Classification helps us to study the huge variety of life forms more easily. It allows us to group organisms based on their similarities, so we can study a whole group instead of each organism separately. It also helps us understand the diversity of life and the evolutionary relationships among different organisms.
2. How would you choose between two characteristics to be used for developing a hierarchy in classification?
Answer: To choose between two characteristics for developing a hierarchy in classification, we select the one that is more basic and important for creating broad groups. A basic characteristic is one that affects the entire body design of an organism and does not depend on other features. Less important characteristics are used only for making smaller sub-groups within the main groups.
3. Explain the basis for grouping organisms into five kingdoms.
Answer: Organisms are grouped into five kingdoms on the basis of three main characteristics. The first is the cell structure, whether the organisms have prokaryotic or eukaryotic cells. The second is whether the cells exist singly or form multicellular bodies with complex organisation. The third is whether the organisms have a cell wall and whether they can prepare their own food or depend on others. Using these characteristics, the five kingdoms are formed.
4. What are the major divisions in the Plantae? What is the basis for these divisions?
Answer: The major divisions in the Plantae are Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms. These divisions are made on the basis of three main features. The first is whether the plant body is well-differentiated into roots, stem and leaves. The second is whether the plant has special tissues for the conduction of water and other substances. The third is whether the plants can bear seeds, and if they do, whether the seeds are naked or enclosed in fruits.
5. How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals?
Answer: The criteria for deciding divisions in plants are based on features like whether the plant body is differentiated, whether it has special conducting tissues, and whether it forms seeds or not. In animals, the criteria for deciding subgroups depend on the body design, such as the type of symmetry, the presence of a body cavity, the segmentation, and the organisation of organs and tissues. Thus, plants are divided mainly on structural and reproductive features, while animals are grouped based on their body design and complexity.
6. Explain how animals in Vertebrata are classified into further subgroups.
Answer: Animals in Vertebrata are classified into further subgroups based on the features of their body structure. All vertebrates have a vertebral column, but they differ in characters like the type of skin, the kind of heart, the method of respiration, and the way they reproduce. Based on these differences, vertebrates are divided into six classes: Cyclostomata, Pisces, Amphibia, Reptilia, Aves, and Mammalia. Each group has its own special characteristics, such as jaws, presence of scales or feathers, heart chambers, and mode of life.