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The first signs of life emerged nearly 3.5 billion years ago. Since that time, life has evolved into a multitude of organisms that have come and gone over the aeons. It tells us how varied life is. This topic is elaborated in detail in NCERT Solutions For Class 9 Science Chapter 7 - Diversity in Living Organisms. Of the billions of species on earth, birds are rather unique vertebrates - accomplishment of true flight.

Birds are now considered as the living relatives of dinosaurs, especially the therapods (meat-eating, bipedal dinosaurs). And just like their ancestors, they have pneumatic bones. It means that the bones are hollow and have dense struts to provide strength without the excess weight. And also, there are air sacs present in their body to support the structure.


Most birds have to work against gravity and weight is one of the biggest factors that limit their ability to fly. Evolution and natural selection have resulted in birds having bones that are hollowed out and filled with struts to increase strength. This adaptation has resulted in them having a lighter, but a stronger structure that helps during flight. However, most diving birds like penguins do not have hollow bones as they do not fly.


Besides having hollow bones, birds have air sacs that are present in these hollow spaces. To put it in the simplest way possbile, these air sacs help in respiration by allowing the birds to take in oxygen while inhaling or exhaling. Basically, humans and most other mammals have bi-directional airflow. This means fresh air is mixed with the existing air in the lungs which has lower oxygen content. Birds, on the other hand, have unidirectional airflow, that is, air flows in one direction, and as a result, have higher oxygen content. This enables them to fly quickly and more efficiently.

In conclusion, visit My NCERT Solutions website to learn more about birds or other related topics. Also explore the best resources for CBSE exams on our website.

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