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Microbiology

Define a dichotomous key.

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Dichotomous Key
Objectives:
Define a dichotomous key.
Learn how to use a key.
Create a key to household items.
Background:
Scientists use dichotomous keys to describe or identify what they are studying.A dichotomous key is a tool that gives you steps that should lead you to a proper solution.Each step in the key has two (di) mutually exclusive choices (couplets) to lead you to the next step in the key.Below is an example of a dichotomous key you might use to fix something on your car.
Dichotomous keys are also useful as taxonomic tools.They can be used to differentiate and identify things.In many of our labs for this course, we will learn tests and techniques that are used to identifying different species of bacteria. And we will create a dichotomous key based on the results of these tests (positive or negative, for example) that should be able to identify your species for the bacteria unknown lab practical that occurs later this semester.
Instructions:
For this assignment you will be creating a simple dichotomous key to identify some household objects.Creating a dichotomous key can be tricky because you must ensure that everyone will follow it the same way. It should be foolproof, so some planning and forethought are necessary.For this dichotomous key you can choose almost any six objects, but it’s helpful to consider items that have some similarities and differences that are easy to describe.When making the dichotomous key, you’ll need five couplets to differentiate and identify 6 different items.Follow the steps below to create a dichotomous key. When you are ready to create your dichotomous key, here is a helpful Download MS Word Dichotomous Key Template that you can use if you’d like. It simply provides fillable and moveable textboxes that you can manipulate to meet your needs for your dichotomous key.
Step 1: Choose six objects.
Example:
1. Carrot
2. Pineapple
3. Tomato
4. Beet
5. Ginger
6. Avocado
Step 2: Describe each item and then group these items to help you construct a key. Think about similarities and differences between your objects as you describe them.
Example:
1. Carrots: Edible portion does not originate from a flower; Edible portion grows underground; Edible portion is longer than it is wide; Surface texture is rough; Not juicy; Peel not consumed
2. Pineapple: Edible portion originates from a flower; Edible portion grows above ground; Edible portion is longer than it is wide; Surface texture is rough; Juicy; Peel not consumed; Feathery leaves
3. Tomato: Edible portion originates from a flower; Edible portion grows above ground, Edible portion is round; Surface texture is smooth; Juicy; Peel consumed; Singular leaves
4. Beets: Edible portion does not originate from a flower; Edible portion grows underground; Edible portion is round; Surface texture is rough; Juicy; Peel not consumed; Singular leaves
5. Ginger: Edible portion does not originate from a flower; Edible portion underground; Edible portion is longer than it is wide; Surface texture is smooth; Not juicy; Peel not consumed; Singular leaves
6. Avocado: Edible portion originates from a flower; Edible portion grows above ground; Edible portion is round; Surface is rough; Not juicy; Peel not consumed; Singular leaves
Step 3:Group your descriptions together and organize them into groups with two mutually exclusive subgroups.You can have as many groups as you feel necessary to help you construct your key. I made 10 groups in my example.
Example:
Group 1: Origin of edible Portion
Subgroup 1: Edible portion originates from a flower
Subgroup 2: Edible portion does not originate from a flower
Group 2: Types of leaves
Subgroup 1: Plant has feathery leaves
Subgroup 2: Plant has large leaves
Group 3: Shape of edible portion
Subgroup 1: Edible portion is longer than it is wide
Subgroup 2: Edible portion is bulbous
Group 4: Surface Texture of edible portion
Subgroup 1: Surface texture of edible portion is smooth
Subgroup 2: Surface texture of edible portion is rough
Group 5: Symmetry
Subgroup 1: Edible portion has radial symmetry
Subgroup 2: Edible portion is asymmetric
Group 6: Number of Seeds
Subgroup 1: Multiple seeds
Subgroup 2: Single seeds
Group 7: Edible Peels
Subgroup 1: Peels are edible
Subgroup 2: Peels are inedible
Group 8: How many times it can be harvested
Subgroup 1: Can be harvest more than once
Subgroup 2: Can only be harvested once
Group 9: Juiciness of Edible Portion
Subgroup 1: Edible portion is juicy
Subgroup 2: Edible portion is not juicy
Group 10: Type of root
Subgroup 1: Has a taproot
Subgroup 2: No taproot
Step 4: Combine your groups into pairs to create five couplets that will differentiate and identify your six items.
Example:
Couplet 1
Group 1: Origin of Edible Portion + Group 8: How many times it can be harvested
a. edible portion originates from a flower and can be harvested multiple times
b. edible portion does not orientate from a flower and cannot be harvested multiple times
Couplet 2
Group 4: Surface Texture of edible portion + Group 7: Edible Peels
a. surface texture is rough and peel is not consumed
b. surface texture is smooth and peel is consumed
Couplet 3
Group 9: Juiciness of Edible Portion + Group 6: Number of Seeds
a. edible portion is juicy and has a multiple seeds
b. edible portion is not juicy and has a single seed
Couplet 4
Group 5: Symmetry + Group 10: Type of Root
a. edible portion is has radial symmetry and has a taproot
b. edible portion is asymmetric and does not have a taproot
Couplet 5
Group 2: Types of leaves + Group 3: Shape of edible portion
a. plant has large leaves and edible portion is bulbous
b. plant has feathery leaves and edible portion is longer than it is wide
Step 5: Create your Dichotomous Key
Example:

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