Branched keys and statement keys! - Whalsay

Branched keys and statement keys! A key is used in biology t help us identify a certain type of species. There are two types of branching keys and a statement key. This diagram above is an Branched keys! This is a branched key diagram which helps us identify and name an organism by looking at the

organism closely and following the key. Statement keys! A paired statement key is another simple way of identifying a species. Branched keys:continued! Branched key is a way of identifying a species using diagrams and questions unlike a statement key which only uses questions. I find this technique of identifying species helpful

especially for children. More information!! This task is quite easy when it involves telling the difference between major groups.For instance, there is little difficulty in distinguishing between beetles and butterflies.In detailed studies, however, there remains the problem of identifying organisms all way to genus or species level.Having found a beetle, for example how is it to be identified from the 300,000 different species in the world?! First, it is almost certain that the beetles country of origin will be known, which reduces

the range of possibilities a little, there are about 3700 British beetles. Second, there is the possibility of making an identification by looking through books with accurate illustrations of living things from various countries, but in the case of organisms which look very much alike it is difficult to know where to begin.Therefore we use keys. These devices called keys take advantage of structural differences between organisms.Statement describing these differences are listed, and by a process of elimination the class, order, family, etc.,of a particular organism are eventually found.Often these structural differences are difficult or even impossible to see or understand unless the user of the key has a fair knowledge of the organisms involved.Key designers have to make us of many technical

words in order to avoid lengthy and complex descriptions within the key. How do they work? Table 3 is a very simple key leading only to class level of indetification.First it assumes that the reader is familiar with the term phylum Chordata. Second it assumes a knowledge of familiar structures such as hair, feathers, and fins. Third, it assumes a knowledge of less familiar anatomical details such as bone, cartilage, and fish scales of the cycloid and placoid type.The user of this and any other key starts at the first anatomical features described.Where necessary the second and subsequent pairs of statementa are consulted. If it is correctly used the key leads automatically to indentification.

Table 3 key to the classes of the phylum Chordata 1a hair present..Class mammalia 1b hair absent.Go to 2 2a feathers present.Class Aves 2b feathers absentGo to 3 3a Dry scaly skin.Class Reptilla 3b Other type of skinGo to 4

4a Four limbs, moist scale less skin..Class Amphibia 4b LimblessGo to 5 5a Fins, cycloid scales and bony skeletonOsteichthyes (bony fish) 5b Fins, placoid scales and cartilage skeleton..Chondrichthyes (cartilage fish) More information!! After samples have been taken each organism found must be identified.This is done

using a biological key.The key is often in the form of a series of questions about the organism and the questions are answered by looking at the organism closely.The questions lead finally to the name of the organism being identified. Question 1 Are the leaves like needles? Yes ? go to question 2 No ? go to question 3 Question 2 Are the needles in pairs? Yes ? go to question 4 No ? go to question 5 Question 3 Are the leaves simple or compound (several leaflets)? Yes ? go to question 6

No ? go to question 7 Question 4 It could be a Scots Pine. [Start again.] Question 5 Are the needles in circular clusters? ... Question 6 Is the leaf heartshaped? ... etc. etc. This power point was brought to you by Zo Irvine!