Class 12 Biology


NCERT Exercise

Question 1: Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

Answer: Doctors use various antibiotics to control infections. Over a period of time, bacteria develop resistance against an antibiotic. Individual bacteria which are better fit to survive the changed conditions due to antibiotic are able to outbreed other bacteria. Thus, such resistant bacteria survive in the long run. This supports the Darwinian selection theory.

Question 2: Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

Answer: Recently, a fossil of human was discovered in Israel. This fossil has been named as Misliya-1; after the cave in which it was found. Previously scientists believed that Homo sapiens left Africa around 100,000 years ago. But this fossil makes the scientists estimate that Homo sapiens may have left Africa about 175,000 to 200,000 years ago.

Question 3: Attempt giving a clear definition of the term species.

Answer: A group of organisms which have the capacity to interbreed is called species.

Question 4: Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)

Answer: Following are some of the components of human evolution:

Question 5: Find out through internet and popular science articles whether animals other than man have self-consciousness.

Answer: Go to this link: Wikipedia

Question 6: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.

Answer: Modern man can be linked to fossils of ancient Homo sapiens or of Neanderthals. Elephants can be linked to fossils of mammoth. Crocodiles and lizards can be linked to fossils of dinosaurs. Birds can be linked to fossils of Archaeopteryx.

Question 7: Practise drawing various animals and plants.

Answer: Do It Yourself

Question 8: Describe one example of adaptive radiation.

Answer: Evolution of different types of beaks in finches of Galapagos islands.

Question 9: Can we call human evolution as adaptive radiation?

Answer: Human evolution did not take place in a confined geographical area and not in a short time span. It took thousands of years for evolution of modern man. So, human evolution cannot be termed as adaptive radiation.

Question 10: Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal say horse.

Answer: Following table shows evolution of horse

Period60 mya40 mya
height0.4 m0.6 m
Salient feature4 toed hoof; well adapted for walking on soft ground.Toe lost for moving faster over dry ground.
MerychippusPilohippusEquus (modern horse)
Period30 mya10 mya1 mya
height1.0 m1.0 m1.6 m
Salient featureMiddle toe developed into a hoof, helped in running fasterOther toes lost as only middle hoof used.Single roof, runs quickly over hard ground.