Question

Two plants belongs to same species if they
a. Have more than 90% similar genes.
b. Look similar and possess identical secondary metabolites.
c. Have a similar number of chromosomes.
d. Can reproduce freely with each other and form seeds.

Answer 1

Hint: As we all know that there are seven obligate taxonomic categories named as Kingdom, Division, Class, Order, Family, Genus and Species. When we move from Species to Kingdom number of common characters and complexity in organisms increase.

Complete answer:
> We already know that in taxonomy, Kingdom is the highest category followed by Division, Class, Order, Family, Genus and Species. Also, the number of organisms increases when going from lowest to highest category, number of common characters also increases and complexity in organism increases as well whereas the specificity increases when we move from the highest category to the lowest category.

> Let us talk about Species which are the lowest category of classification. It is defined as the closely related individuals with similar morphological, anatomical, biochemical and cytological characters. We can also define species as a group of naturally interbreeding populations with the ability to produce fertile offsprings. Individuals belonging to the same Species share a common gene pool.

> Different species possess different numbers of chromosomes therefore this cannot be used as a determining factor. Similarly, species do not have 90% of similar genes and species do look similar to some extent only and they do not have identical secondary metabolites as same species can have different strains which produce different metabolites.

So we can say that the characteristic feature in determining the closely related species is their freely interbreeding nature and offspring production.
Hence, the correct answer is option (D).

Note: In higher plants, determination of species is mainly based on floral morphology because reproductive characters are more conservative as compared to vegetative characters. Also when species is determined on the basis of interbreeding then they are known as Biological species.