Construction and Use of Dichotomous Keys

A dichotomous key is a method for determining the identity of something (like the name of a butterfly, a plant, a lichen, or a rock) by going through a series of choices that leads the user to the correct name of the item. Dichotomous means 'divided in two parts'. At each step of the process of using the key, the user is given two choices; each alternative leads to another question until the item is identified. In this project, you will be creating a dichotomous key. Dichotomous keys are tools used by scientists to identify unknown organisms. Use the animals listed to create a dichotomous key. Decide upon a way to divide the items into two groups. Think of identifying characteristics such as shape, size, position, colour, texture, etc.

Dichotomous Key Worksheet Pdf

• Biological keys are sets of statements that act as clues leading to the identification of an organism.

Dichotomous Key: This is a re-drawing of one of the given keys that pertains to your OU. Make sure that the end of each branch terminates with an organism’s name. (See next chapter “Constructing an Identification Key”). However, there may be one or two empty slots in each key. Dichotomous keys are often used in the sciences, such as biology and geology. To make your own dichotomous key, first, select the characteristics you can use to contrast your specimens, then formulate these as a series of statements or questions you can use to narrow them down. Dichotomous Key; Dichotomous Keys (Printable Version. This link will take you to a printable form of the dichotomous keys. It is in PDF format, if you do not have Acrobat Reader please go to www.adobe.com).

• By following the keys we can be able to place an organism in its group.
• The most common key is the dichotomous key.
• This is a biological tool for identification of unknown organisms.
• The word dichotomous means branching into two.
• A single characteristic is considered at a time.
• Two contrasting statements are put forward to describe the characteristics in such a way as to separate the organisms.
• This continues until all the organisms have been identified.
Rules Used to Construct a Dichotomous Key
• Use morphological characteristics as far as possible e.g. type of leaf - simple or compound.
• Select a single characteristic at a time and identify it by number. 1. Type of leaf. .
• Use identical forms of words for two contrasting statements e.g.:
a) Flowers scented.
b) Flowers not scented.
• Start with a major characteristic that divide the organisms into two large groups then proceed to lesser variations that would separate the organisms further into smaller groups.

• Use positive statements especially the first one.
• Avoid generalizations e.g. short plants. Be specific in your description e.g.:

Make A Dichotomous Key Generator

a) Plants above 1m tall.
b) Plants below 1m tall.
Some Common Features Used for Identification
In Plants
Leaves
1. Type of leaf Leaf
Compound leaves.
• Simple leaf
• Trifoliate
• Pinnate
• Type ofleaf margin.
Type of venation.
• Type ofleaf arrangement on stem.
• The colour of leaf.
• The texture ofleaf; whether hairy or smooth.
• Shape of the leaf e.g. palmate.
Stem
• Type of stem - woody or herbaceous.
• Shape of stem - cylindrical or rectangular.
• Texture of stem smooth or spiny.
Infloresence
• Are flowers terminal or lateral
• For each flower:
• Is the flower regular or irregular?

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• Number of floral parts for each whorl.
• Are floral parts free or fused?
Roots
• Type of root system- Taproot or fibrous?
• Function of the root.
In Animals
Features used to identify animals:

Online Dichotomous Key

• Type of mouthparts.
• Type of skeleton.

Create Your Own Dichotomous Key

• Presence or absence of antennae.
• Body segmentation.

Dichotomous Key Template Pdf

• Body covering: scales, fur, hair or feathers.
• Number of body parts.
• Locomotory structures: legs, wings and fins.

Dichotomous Key Activity

• Presence or absence of vertebral column.
• Presence and type of eves.