CBSE Class 9 Science Chapter 7: Diversity in Living Organisms NCERT Solutions

We classify organisms because there are millions of different species on Earth. It is impossible for any individual to study each species in detail during their lifetime. Classification helps us organize these diverse life forms into groups based on certain common characteristics, making the study of biology more manageable and systematic.

The range of variations in life forms around us is immense. Here are three examples:

• Insects and Arthropods: Ants, cockroaches, spiders, and houseflies might all inhabit the same building. Although they live in close proximity and share some basic characteristics placing them in the phylum Arthropoda, they exhibit significant differences in their appearance, size, and specific features.
• Mammals: Humans, monkeys, cats, and dogs can be found living in the same neighborhood. Despite sharing the class Mammalia due to characteristics like having hair and being warm-blooded, they display a wide array of physical forms and behaviors.
• Plants: A local park can showcase a remarkable variety of plant life, from small, low-growing grasses to large, towering trees like the banyan. This illustrates the significant variations in size, structure, and life cycles within the plant kingdom.

The kind of cells an organism is made of is a more basic and fundamental characteristic for classification than the place where it lives. This is because cell structure provides a scientific and evolutionary basis for grouping organisms. For instance, organisms with prokaryotic cells form one major group, while those with eukaryotic cells form another. In contrast, a particular habitat, like a pond or a forest, can be home to a vast diversity of organisms belonging to completely different classification groups (e.g., plants, animals, bacteria, fungi).

The primary characteristic on which the first division of organisms is made is the organization of the nucleus within their cells. This distinction leads to two major groups: prokaryotes, which lack a well-defined nucleus and other membrane-bound organelles, and eukaryotes, which possess a true nucleus and membrane-bound organelles.

Plants and animals are placed into different categories based on several fundamental differences:

• Mode of Nutrition: Plants are primarily autotrophs, meaning they produce their own food through photosynthesis. Animals, on the other hand, are heterotrophs; they obtain their food by consuming other organisms.
• Cell Wall: Plant cells are characterized by the presence of a rigid cell wall made of cellulose, which provides structural support. Animal cells lack a cell wall.
• Mobility: Most animals are capable of movement, actively seeking food, shelter, or mates. Plants are generally stationary and do not move from one place to another, although parts of them may grow or respond to stimuli.