How to use a key, Biology

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Q. How to Use a Key?

The use of a key is analogous to travelling a high way, that forks repeatedly, each fork having roadside directions. If a traveller follows the proper directions, the destination will be reached

The first step in identification of an unknown plant involves the use. of keys to determine the family, next is the key to genera which will provide the generic name. After the genus is determined the keying process is repeated within the genus for a determination of the species.

If a number of plants ABCDEFG is given to you for identification, you have to place them in two group viz. Dicots and Monocots with the aid of keys already given to you. The characters that you have to study for their grouping are that of a) Leaves - their venation, b) flower - the number of floral parts, c) embryos - the number of colyledons.

Carry out the study of these characters in the plants provided to you and record these. Suppose in case of plant ACEF the answer given to three characters given in the key is identical to those mentioned in lead, these belong to dicots i, e. their leaves have a reticulate venation, their flowers are pentamerous or tetramerous and the number of cotyledons is 2 while in plant BD and G characters are identical to those mentioned in lead 1 i.e. leaves have a parallel venation, flowers are trimerous and the embryos,
have only one cotyledon, these belong to monocots.

Further classification of plants into three series of Dicots viz. Monochlamydeae, Polypetalae and Gamopetalae is possible by ascertaining the presence or absence of characters mentioned in leads 2 and 3 in the key 2 para 3.

While using a key

i) understand the terms clearly and use proper terms.

ii) Read both the leads (clues) of a couplet carefully. When the answer to one lead is positive and that of the alternative lead is negative. You are on correct lines, If the answer is positive or negative in both the cases there is some mistake.

iii) If the alternatives in the couplets are not clear and contrasting but these overlap, make the conclusion after checking the description matching with identified species,

iv) While checking the measurements of organs mentioned in the key, measure more than one such parts preferably in 3 replicates and take an average. You should understand that there is a variation in size in-fresh and dried specimens.

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