The Class 9 is an important year in a student’s life and Science is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 9 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete NCERT Class 9 Science Book syllabus.
Q1. Why do we classify organisms?
Ans:
By classifying organisms, it is easier and more convenient to study their characteristics. Similarities exhibited by various entities allow us to categorise different entities into a class and hence, study the group as a whole.
Q2. Give three examples of the range of variations that you see in life forms around you.
Ans:
Listed below are a few ranges of variations observed in life forms:
(a) Small frog to big whale
(b) Creeper to the eucalyptus tree
(c) Black cuckoo to colourful peacock
Q3. Which of the following 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 most basic classification of organisms should be established on the kind of cells they are made up of. This is because the habitat can have species with different characteristics living harmoniously, whereas the entities with similar cell arrangements will exhibit equivalent characteristics.
Q4. What is the primary characteristic on which the broad division of organisms is made?
Ans:
The basic characteristic on which organisms are primarily divided is the nature of cells. It is broadly classified as prokaryotic cells and eukaryotic cells, which furthermore is classified into subclasses.
Q5. On what basis are plants and animals put into different categories?
Ans:
The following is the basis for the categorisation of plants and animals:
(a) The most fundamental consideration of classification is the presence and absence of a cell wall.
(b) The next important criterion is the mode of nutrition. The mechanism through which entities acquire their nutrients is used as the base for classification.
Q6. Which organisms are called primitive, and how are they different from the so-called advanced organisms?
Ans:
Primitive organisms are the organisms that exhibit a very simple and basic cell arrangement, mechanism and structure and no division of labour is observed. Advanced organisms, on the other hand, are organisms possessing millions of cells that are grouped into various organs performing different functions, such as mammals.
Q7. Will advanced organisms be the same as complex organisms? Why?
Ans:
Yes, complex organisms are the same as advanced organisms. The consequence of advancement leads to multiple cell arrangements that operate uniquely.
Q8. What is the criterion for the classification of organisms as belonging to the kingdom Monera or Protista?
Ans:
One of the most significant differences in classification is the development of the nucleus. The ones with no nuclear membranes are defined to be Monera, while the ones that have well-defined nuclei walls are Protista.
Q9. In which kingdom will you place an organism which is single-celled, eukaryotic and photosynthetic?
Ans:
Since the cell is photosynthetic, it must have a well-defined nucleus wall. Therefore, it needs to be placed in the Protista kingdom.
Q10. 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?
Ans:
(a) The organisms belonging to the Kingdom Monera will have the smallest number of organisms and with maximum characteristics in common.
(b) The organisms belonging to the Kingdom Animalia will have the largest number of organisms.
Q11. Which division among plants has the simplest organisms?
Ans:
Algae or Thallophyta has the simplest organism among plants.
Q12. How are pteridophytes different from phanerogams?
Ans:
The following are the differences between pteridophytes and phanerogams:
| Pteridophytes | Phanerogams |
| They possess a naked embryo | They possess a covered embryo |
| Exhibit unclear reproductive organ | Exhibit well-defined reproductive organ |
Q13. How do gymnosperms and angiosperms differ from each other?
Ans:
In gymnosperms, the seeds are naked, while in angiosperms, the seeds are covered.
Q14. How do poriferan animals differ from coelenterate animals?
Ans:
Listed below are the differences between poriferan and coelenterate animals:
| Porifera | Coelenterata |
| Division of labour is not noticed | Division of labour is observed |
| The cellular level of the organisation exhibited | The tissue level of the organisation exhibited |
| Coelom absent | Coelom present |
Q15. How do annelid animals differ from arthropods?
Ans:
Listed below are the differences between annelid and arthropods:
| Annelida | Arthropoda |
| The entire body is segmented into rings | Segmentation of the body into the head, abdomen and the thorax region |
| Skeleton is absent | Presence of exoskeleton |
| Hermaphrodites | Presence of different sexes, bisexuals present |
Q16. What are the differences between amphibians and reptiles?
Ans:
Listed below are the differences between amphibians and reptiles:
| Amphibia | Reptilia |
| Skin is moist and soft | Skin is hardened |
| In water, they breathe through their skin | They can exist in water. They come to land to intake oxygen |
| Respire through lungs or gills | Respire through lungs |
| Capable of jumping | They crawl |
| Indirect development is noticed | Direct development observed |
Q17. What are the differences between animals belonging to the Aves group and those in the mammalian group?
Ans:
Listed below are the differences between animals belonging to the Aves group and the mammalian group:
| Aves | Mammalia |
| Body is covered with feathers | Body is covered with hairs |
| Teeth absent | Teeth present |
| They possess a beak | Beak absent |
| Forelimbs are present and modified to take a flight | Forelimbs are present and used for multiple activities |
| Bones are hollow | Bones are solid |
| Body is streamlined | Streamlining of the body is not observed (except for whales) |
Q1. What are the advantages of classifying organisms?
Ans:
Listed below are the advantages of the classification of organisms:
Q2. How would you choose between two characteristics to be used for developing a hierarchy in classification?
Ans:
The basis of the start of the hierarchy will be formed by the gross character, while the basis of further steps will be taken care of by the fine character.
For instance:
Q3. Explain the basis for grouping organisms into five kingdoms.
Ans:
The following factors govern the basis of grouping organisms into five kingdoms
Q4. What are the major divisions in the Plantae? What is the basis of these divisions?
Ans:
The following table depicts plant division and the basis of classification for each division.
| Division | Basis of Classification |
| Thallophyta or Algae | Like body |
| Bryophyta | The body is divided into leaf and stem |
| Pteridophyta | The body is separated into root, stem and leaf |
| Gymnosperm | Seed-bearing, naked seeds |
| Angiosperm | Seed bearings covered seeds |
Q5. How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals?
Ans:
Hence, morphological characteristics play a key role in plant classification. In animal classification, cytology is considered primarily as more minute structural variations are taken into account.
Q6. Explain how animals in Vertebrata are classified into further subgroups.
Ans:
Vertebrata has two subclasses, namely
Wherein organisms belonging to the Pisces subclass have streamlined bodies with tails and fins, which help them in their movement (swimming), whereas the Tetrapoda species have four limbs for their movement.
Furthermore, the Tetrapod animals are classified as:
1. Amphibia: The animals belonging to this group are adaptive in nature. They dwell both on the land as well as in water. They show the presence of specialised organs, which allows them to breathe underwater.
2. Reptilia: The animals belonging to this class crawl. Their skin is very thick and withstands extreme temperatures.
3. Aves: The forelimbs of these organisms are modified, which helps them in their flight. They lack teeth and instead have a beak and feathers that cover up their body.
4. Mammalia: The animals belonging to this group show nurturing skills as they contain mammary glands to support them. Their skin is covered with hair, and most of them are viviparous in nature.
Diversity of Living Organisms refers to the variety of living organisms present on earth. These organisms classified by H. Whittaker into five-kingdom classifications are as follows:
Monera is a unicellular, prokaryotic, heterotrophic or autotrophic organism.
Protista is a unicellular, autotrophic or heterotrophic eukaryotic organism.
Fungi are multicellular, eukaryotic organisms with plant and animal-like features. They may be saprophytic or parasitic.
Plantae is multicellular, eukaryotic autotrophs which are further classified as follows:
Animalia is eukaryotic, multicellular, heterotrophs which are classified as follows:
(a) Whether they are made of prokaryotic or eukaryotic cells
(b) Whether the cells are living singly or organised into multi-cellular and, thus complex organisms
(c) Whether the cells have a cell wall and whether they prepare their own food.