What are Dichotomous Keys?
Dichotomous keys are used to identify objects or living things based on their characteristics or features.
A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item, by narrowing done the features into smaller groups.
"Dichotomous" is a greek word that means "divided into two parts".
There are two main types of Dichotomous keys:
There are also keys that group with more than two possible choices at each step such as:
Many keys rely on detailed observations and clever descriptions to paint a picture in the reader's mind and allow them to distinguish between each choice. Other keys include pictures, diagrams or photos to aid the reader to make better choices.
Task 1:
Have a look at each of the diagrams of keys below. Use the clues above to decide which type of key it is. What features helped you decide this?
A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item, by narrowing done the features into smaller groups.
"Dichotomous" is a greek word that means "divided into two parts".
There are two main types of Dichotomous keys:
- Branching dichotomous
- Stepped or tabular keys
There are also keys that group with more than two possible choices at each step such as:
- Circular keys
- Branching keys
Many keys rely on detailed observations and clever descriptions to paint a picture in the reader's mind and allow them to distinguish between each choice. Other keys include pictures, diagrams or photos to aid the reader to make better choices.
Task 1:
Have a look at each of the diagrams of keys below. Use the clues above to decide which type of key it is. What features helped you decide this?
Task 2
Activity using a Step Dichotomous Key: Shark Identification
students.ga.desire2learn.com/d2l/lor/viewer/viewFile.d2lfile/1798/12579/taxonomy10.html
Task 3
Use the key data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf
to identify the following macroinvertebrates from the images supplied.
You will need to practice your observation and description skills to complete this task. Complete the table in your book. Your teacher may provide this table as a photocopy.
Activity using a Step Dichotomous Key: Shark Identification
students.ga.desire2learn.com/d2l/lor/viewer/viewFile.d2lfile/1798/12579/taxonomy10.html
Task 3
Use the key data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf
to identify the following macroinvertebrates from the images supplied.
You will need to practice your observation and description skills to complete this task. Complete the table in your book. Your teacher may provide this table as a photocopy.
What can the presence of waterbugs tell us about the health of the wetland ecosystem?
Some waterbugs are really tolerant to pollution and will survive in a wide range of conditions. You will find these waterbugs in almost any ponding survey.
Some waterbugs are really sensitive to pollution and will only survive when there is little to no pollution in the wetland. Other waterbugs are somewhat tolerant to pollution and can survive in a slightly higher, but not too high, pollution levels.
Finding these species gives a good indication of the pollution levels in the wetland ecosystem. We call these species indicator species.
Task 4
This table shows many of the species you may find in your ponding survey of the freshwater ecosystem.
Have a look at the table.
Some waterbugs are really sensitive to pollution and will only survive when there is little to no pollution in the wetland. Other waterbugs are somewhat tolerant to pollution and can survive in a slightly higher, but not too high, pollution levels.
Finding these species gives a good indication of the pollution levels in the wetland ecosystem. We call these species indicator species.
Task 4
This table shows many of the species you may find in your ponding survey of the freshwater ecosystem.
Have a look at the table.
- Which species would be really useful to find?
- Which species would not provide useful information about pollution levels?
- If you found the species in the Aquatic Macroinvertebrate Identification table above, what could you say about the health of the wetlands?
Teacher Resources
Victorian Curriculum Links
This Essential Question links to the Victorian Curriculum Standards for Science Level 7 and 8
Biological Science
Questioning and predicting
Teacher notes:
These notes are helping students create an awareness of the tools scientists use to identify and order the natural world around them. For the Field Investigation, students will need to know how to make great observations and descriptions of their aquatic macroinvertebrates that they find by ponding. They will use the key: https://data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf to identify the waterbugs at the wetlands. They do not need to be able to make a key for this task. Spending too much time on this one skill may rob time from the development of the remaining skills. Spending time on making observations and descriptions will be more valuable to the students being able to complete the CAT to a high standard.
Ask you lab assistant to produce A3 laminated macroinvertebrate charts in colour for use by pairs in this task. If you can get live samples of these organisms, students will have first hand experience with their size and movements. Explain to students the limitations of this table in this activity. Which columns can we not complete now, with only photos? Why is this additional data useful in the field?
Other useful teaching resources include:
Sources for images of keys
www.thinksciencemaurer.com/dichotomous-key-of-scientific-equipment/ Leaf Dichotomous Key example
http://ib.bioninja.com.au/_Media/dichotomous3_med.jpeg Invertebrate branching key example
http://wps.pearsoned.com.au/wps/media/objects/8335/8535831/_images_/ch4b.jpg
https://data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf
http://s3.amazonaws.com/engrade-myfiles/4089544937923278/Screen_Shot_2012-10-16_at_7.47.01_PM.png
This is the macroinvertebrate chart to use for Task 3 above
Biological Science
- There are differences within and between groups of organisms; classification helps organise this diversity(VCSSU091)
Questioning and predicting
- Identify questions, problems and claims that can be investigated scientifically and make predictions based on scientific knowledge (VCSIS107)
- Collaboratively and individually plan and conduct a range of investigation types, including fieldwork and experiments, ensuring safety and ethical guidelines are followed (VCSIS108)
- In fair tests, measure and control variables, and select equipment to collect data with accuracy appropriate to the task (VCSIS109)
- Construct and use a range of representations including graphs, keys and models to record and summarise data from students’ own investigations and secondary sources, and to represent and analyse patterns and relationships (VCSIS110)
- Use scientific knowledge and findings from investigations to identify relationships, evaluate claims and draw conclusions (VCSIS111)
- Reflect on the method used to investigate a question or solve a problem, including evaluating the quality of the data collected, and identify improvements to the method (VCSIS112)
- Communicate ideas, findings and solutions to problems including identifying impacts and limitations of conclusions and using appropriate scientific language and representations (VCSIS113)
Teacher notes:
These notes are helping students create an awareness of the tools scientists use to identify and order the natural world around them. For the Field Investigation, students will need to know how to make great observations and descriptions of their aquatic macroinvertebrates that they find by ponding. They will use the key: https://data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf to identify the waterbugs at the wetlands. They do not need to be able to make a key for this task. Spending too much time on this one skill may rob time from the development of the remaining skills. Spending time on making observations and descriptions will be more valuable to the students being able to complete the CAT to a high standard.
Ask you lab assistant to produce A3 laminated macroinvertebrate charts in colour for use by pairs in this task. If you can get live samples of these organisms, students will have first hand experience with their size and movements. Explain to students the limitations of this table in this activity. Which columns can we not complete now, with only photos? Why is this additional data useful in the field?
Other useful teaching resources include:
- 5 lesson unit on Classification by ASTA: scienceweb.asta.edu.au/years-7-8/unit2/overview/yr78-unit2-overview.html
- The CSIRO invertebrates website includes lots of information for the detailed study of an organism, including a computer based dichotomous key http://www.ento.csiro.au/education/index.html
- A handout for the dichotomous key video above can be found at http://www.amoebasisters.com/uploads/2/1/9/0/21902384/video_recap_of_dichotomous_keys_by_amoeba_sisters.pdf
Sources for images of keys
www.thinksciencemaurer.com/dichotomous-key-of-scientific-equipment/ Leaf Dichotomous Key example
http://ib.bioninja.com.au/_Media/dichotomous3_med.jpeg Invertebrate branching key example
http://wps.pearsoned.com.au/wps/media/objects/8335/8535831/_images_/ch4b.jpg
https://data.environment.sa.gov.au/Content/Publications/macroinvertebrate_chart.pdf
http://s3.amazonaws.com/engrade-myfiles/4089544937923278/Screen_Shot_2012-10-16_at_7.47.01_PM.png
This is the macroinvertebrate chart to use for Task 3 above
aquatic_macroinvertebrate_identification.pdf | |
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aquatic_macroinvertebrate_identification_answers.docx | |
File Size: | 84 kb |
File Type: | docx |