Question

How is a key helpful in the identification and classification of an organism?

Answer 1

Hint: Key or taxonomic key is another aid used for the identification of different plants and animals on the basis of similarities and differences between them. These keys are based on the contrasting (opposite) pairs of characters named as couplets.

Complete answer:
Keys (Taxonomic keys) are artificial devices in the form of dichotomic table of alternative characteristics which are used in identification of -
-Class
-Order
-Family
-Genus
-Species
Separate taxonomic keys are required for identification and classification of each category. The keys are contrasting pairs called couplets that make choices between two opposite characters that means either acceptance or rejection of one only.
These are of two types indented (Yoked) and bracketed.
Indented or Yoked Key- Here there is a sequence of two or more alternate characteristics from which selection or choice is to be made through selection and elimination.
Bracketed Key- The key does not separate contrasting characters by subdividing them but instead gives them numbers in brackets.
Six vertebrates (fish, frog, snake, bird,bat and cat) are to be identified. The two types of keys are used as follows.

Bracketed Key	Indented Key
External ears absent -2	External ears absent
Wings present - BirdWings absent-3	Wings present - BirdWings absent.
Gills present - Fish Gills absent - 4	Gills present - FishGills absent
Limbs present - Frog Limbs absent - Snake	Limbs absent - Snake Limbs present - Frog

Five genera of family ranunculaceae are to be identified - Clematis, Naravelia, Anemone, Nigella and Aconitum.

Bracketed Key	Indented Key
1. Carpel single ovuled, fruit achene - 2	1. Carpels single ovulated, fruit achene
1. Carpel many ovulated, fruit follicle - 4
2. Leaves opposite, compound - 3	2. Leaves alternate, radical - Anemone
2. Leaves alternate, radical - Anemone	2. Leaves opposite, compound
3. Petals absent, leaves without distinct tendrils - Clematis	3. Petals present, terminal leaflet modified into tendril- Naraveila
3. Petals present, terminal leaflet modified into tendril - Naravelia	3.Petals absent, leave without distinct tendrils - Clematis

Note:
Keys are used for identification and classification of different plants and animals on the basis of similarities and differences in characters. These are used in identification of class, order, family, genus and species. It is divided into pairs of opposite characters that are either present or absent. Bracketed and Indented are the two types of taxonomic Key.