Theory:

Our country is home to various species and rich flora and fauna. Some of the species doesn't exist any longer.
The species that no longer exists on the earth are called extinct species.
Extinct species can be plants or animals, and an animal that no longer exists on earth are called extinct animals.
Example:
Dinosaur and Dodo are extinct species that lived on earth. Other examples include Caspian tiger, Irish deer, Passenger pigeon, Giant ground sloth and Cave lion.
FotoJet (8).png
Clockwise from top: Dinosaur, Mammoth elephant, Dodo, Passenger pigeon, Cave lion, Caspian tiger, Giant ground sloth
The species of animals or plants which are facing the risk of extinction are called endangered species.
They exist in a small number and there are only a very few of them left on the planet and soon that they might get extinct.
Important!
In India \(172\) species of animals are globally threatened which is \(2.9%\) of world's threatened species.
Causes for endangerment of species:
  1. Disturbances or loss of the natural habitat.
  2. Hunting and poaching of animals.
  3. Pollution (air and water pollution).
  4. Due to usage of chemicals like pesticides and other chemicals which harm desired animals and plants.
  5. Introduction of new species or invasive species.
  6. Natural calamities like flood, fire etc.
Endangered plant species in India:
 
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Clockwise from top: Umbrella tree, Malabar lily, Indian mallow, Rafflesia flower
  
Endangered animals in India:
  
Indian animals that are endangered includes Indian one-horned rhinoceros, Asiatic lion, Himalayan snow leopard, Desert cat, Lion tailed macaque, Bengal fox, Marbled cat, Asiatic wild ass, gaur, Asiatic water buffalo etc.
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Clockwise from top: Indian rhinoceros, Asiatic lion, Snow leopard, Desert cat, Lion tailed macaque
 
Small animals like lizards, frogs, and snakes are more in danger of becoming extinct than larger animals. Whether small or large, each organism has a unique place in the food chain that contributes to the ecosystem.
 
Small animals form part of the food chain and food webs essential for maintaining balance in the ecosystem. By killing them, there is a disturbance in the ecosystem. Animals are endangered mainly due to human activity. We need to take specific strict measures to protect them and preserve them.
Reference:
https://upload.wikimedia.org/wikipedia/commons/thumb/5/50/Oxford_Dodo_display.jpg/1024px-Oxford_Dodo_display.jpg
https://en.wikipedia.org/wiki/Revival_of_the_woolly_mammoth#/media/File:Woolly_mammoth_model_Royal_BC_Museum_in_Victoria.jpg
https://www.flickr.com/photos/nostri-imago/3425837302
https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Ectopistes_migratorius_%28passenger_pigeon%29.jpg/1024px-Ectopistes_migratorius_%28passenger_pigeon%29.jpg
https://www.flickr.com/photos/edenpictures/28881076915
https://upload.wikimedia.org/wikipedia/commons/thumb/8/81/Cave_lion_at_the_Ice_Age_Centre.jpg/1024px-Cave_lion_at_the_Ice_Age_Centre.jpg
https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Gloriosa_superba_L._%281391264465%29.jpg/1024px-Gloriosa_superba_L._%281391264465%29.jpg
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Abutilon_indicum_-_Indian_Mallow_from_Theni_%284%29.jpg/1024px-Abutilon_indicum_-_Indian_Mallow_from_Theni_%284%29.jpg
https://www.flickr.com/photos/axelrd/15433888479
https://www.flickr.com/photos/gaurika/38805167805
https://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Gangtok_Bulbuley_Himalayan_Zoological_Park_Captive_Snow_Leopard_Walk_and_Stare.jpg/1024px-Gangtok_Bulbuley_Himalayan_Zoological_Park_Captive_Snow_Leopard_Walk_and_Stare.jpg
https://upload.wikimedia.org/wikipedia/commons/7/77/Great-Indian-one-horned-rhinoceros-at-Kaziranga-national-park-in-Assam-India.jpg
https://www.flickr.com/photos/tariquesani/6779024740/
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/THE_LION-TAILED_MACAQUE.jpg/1024px-THE_LION-TAILED_MACAQUE.jpg