Question of Exercise-3

Evidences of Evolution of Class 12

An important evidence in favour of organic evolution is the occurrence of:


Option 1 Homologous and vestigial organs

Option 2 Analogous and vestigial organs

Option 3 Homologous organs only         

Option 4 Homologous and analogous organs

Frequently Asked Questions

What are the components of a nucleotide?



  • Nucleotides are the building blocks of DNA that comprise a nucleoside associated or linked to a phosphate group.
  • A nucleoside further comprises a nucleobase and five-carbon sugars. The five-carbon sugars in a nucleotide are ‌ribose or deoxyribose.
  • A nucleotide is a nitrogen-containing molecule and includes adenine (A), Guanine (G), and cytosine (C), common to both DNA and RNA. Thymine (T) is present only in DNA and Uracil (U) is present only in RNA in place of thymine.
  • Thus, the components of a nucleotide include a sugar molecule (ribose sugar in RNA or deoxyribose in DNA), a phosphate molecule, and a nitrogen base.

Nucleotide= Nucleoside (base and sugar) + phosphate molecule


Final Answer

The main components of a nucleotide are pentose sugar, a nitrogenous base and a phosphate group

What are the advantages of sexual over asexual reproduction



Reproduction is the process by which production of new offspring takes place. 

It is mainly of two types:- Asexual and sexual reproduction.

Asexual reproduction is a type of reproduction in which offsprings produced are identical to their parents and only one parent is involved.

Sexual reprpdouction is a type of reproduction in which offsprings produced are similar to their parents and two parents are involved.

Advantages of sexual reproduction over asexual reproduction are following:- 

  • In sexual reproduction more variations are produced. Hence, it provides better chances of survival of species in a population.
  • The newly formed offspring has characteristics of both the parents.
  • During sexual reproduction, diversity of characters are produced. 
  • In sexual reproduction, there is a chance of evolution to occur with the flow of time.

Final answer:- 

Hence, these are the advantages of sexual over asexual reproduction. 

Lactobacilli are harmful bacteria

A: True

B: False



  • Lactobacilli are also friendly bacteria that normally live in the gastrointestinal tract, urinary, and genital system without any adverse effects.
  • They are probiotic bacteria that reside in our body and also improve digestion and prevent some diseases such as traveler’s diarrhea and rotaviral diarrhea.
  • They are quite helpful in fermented food such as dietary supplements and yogurt. 
  • Hence, it is wrong to state that Lactobacilli are harmful bacteria.

Final Answer: Hence, it is a false statement that Lactobacilli are harmful bacteria.

Which of the following restriction enzymes produces blunt ends

A: Sal I

B: Eco RV

C: Xho

D: Hind III



Sal I is a restriction endonuclease enzyme obtained from Streptomyces albus.

It produces sticky ends.

Eco RV is a restriction endonuclease enzyme obtained from Escherichia coli. 

It produces blunt ends.

Xho is a restriction endonuclease enzyme obtained from Xanthomonas campestris.

It produces sticky ends.

HindIII is a restriction endonuclease enzyme obtained from Haemophilus influenzae.

It produces sticky ends.

Final answer:

The correct answer is Eco RV, i.e option (B).

'The origin of life' book was written by

A: Darwin

B: Oparin

C: Gray

D: Smith



Oparin proposed his theory of evolution along with Haldane and said that the first form of life developed from the pre-existing simple inorganic and organic compounds. They said that when life arose the atmosphere of earth was reducing. 

Oparin explained his theory in his book ‘The origin of life’, in 1936.

Charles Darwin wrote ‘the origin of species’, in 1859.

Charles Darwin is also known as the father of evolution.

Final answer:

The correct answer is oparin, i.e option (B).

Talk to Our counsellor