Curriculum Links:
Grade 10 Life Science--Sustainability of Ecosystems
Biology 20 –Diversity of Life
Outcomes:
Students will utilize a dichotomous key to identifying plants.
Students will create their own key to help others identify a selected person.
Materials:
Sample key and leaf sketches (included in the lesson)
Explore: Ask the students if they have ever heard of people using plants for medicines? Have them
elaborate on what they have understood. Explain that before the days Europeans explored North
America the First Nations people had viable communities that survived using all the natural resources
surrounding them. Through trial and error they learned to use different parts of plants for different
aliments. For example Willow bark contains salicin, which works as a pain killer. They discovered
that leaves of the White Birch can be chewed and plastered on insect stings to extract the poison.
Muskeg tea, as it was locally called, was brewed to treat colds and coughs. Much of the knowledge of
these traditional plant uses are being lost today. Young aboriginals are being drawn away from the old
traditions as modern culture influences their lives.
Sometimes it may be tempting to go out and experiment ourselves in trying to utilize plants in different
ways. Unless we have thoroughly researched it this could be dangerous as many plants not used
properly can be poisonous or harmful to humans.
Today students have very little knowledge of plants of any type. We are so use to getting our food
from groceries stores that we have trouble identifying edible plants unless they are packaged for us.
Even gardening has become a dying art. Just a generation or so ago most people had family gardens
where the majority of the vegetables they consumed where grown. Now it seems easier to go to the
local farmers market than try to grow your own food.
Today we are going to learn how to use a key to help us identify different types of trees. Scientist that
study plants create these dichotomous keys to help others identify the plants they have studied.
Learning to use these keys and creating them ourselves will be a first valuable step in our study of
plants.
Activity: Hand out a copy of the Dichotomous Key and the sheet of leaf drawing to each student.
(given below) Have them use the key to identify which tree or shrub the leaves belong to. They can
write the name of the tree near its leaf.
Dichotomous Keys can be set up in different ways. Some use lines leading one to different choices,
others use questions such as the example one. Tell the students that to ensure that they grasp what a
dichotomous key is they will now create one. They are to choose five students in the class. They will
make a key up using the five students they choose to help others identify the students by reading about
their physical characteristics. The students must be kind in the choices they make in describing the
students. Put this simplified example on the board.
Male
blond hair
dark hair
Female
blond hair
dark hair
mustache
no mustache
round face
oval face
tall
short
tall
short
David
Jill
Explain to the students that once they understand how to use dichotomous keys they will be able to use
any reference key and go out and find the specific plants they are looking for. Keys exist for
mushroom pickers, berry pickers, and many other different types of plant life. They are often found in
reference books. A search of the local library may be the best place in finding a key for the plant types
you are interested in.
Closure: This class we explored the concept of how to identify specific plants. We learned about
dichotomous keys and how to use them. We discussed why it is important to be able to identify
different plants and some of the uses these plants had in the past. During the next class we can select
different students come to the front of the class. We will then read out the characteristics of one of the
dichotomous keys you created. We will see if we can identify which person is being described.
(The teacher must be careful to screen the descriptions so that no student will be hurt by insensitive
choices.)
Plants to be identified using the Dichotomous Key:
Dichotomous Key Use this key to determine what the plants are according to the
characteristics of their leaves.
1.
Trees with needle-like leaves ..................................................... ……………………..go to2
Trees with broad, blade-like leaves ............................................. ……………………..go to5
2.
Leaves are arranged singly on the stem………………………………………………….…..3
Leaves are arranged in clusters of two on the stem………………………….…….………..4
3.
Irregularly-placed leaves which give the stem a "hairy" appearance…………..Black Spruce
Leaves tend to extend more regularly straight out from the stem………….......White Spruce
4.
The needle-like leaves often spiral and end in a sharp point ……………... Lodgepole Pine
The needle-like leaves extend straight without twisting……………...…………..…..Jack Pine
5.
The leaves have an opposite arrangement on the stem………………..……………………..6
The stem is characterized by alternately-arranged leaves…………………….…………….7
6.
Leaves are simple with notches giving them three to five lobes………….….Mountain Maple
Leaves are compound, with three to seven leaflets………………………..….Manitoba Maple
7.
Stems have thorns……………………………………………………………………Hawthorn
Stems are without thorns……………………………………………………………..………8
8.
The narrow leaves have margins which are relatively even, with possibly a few, rounded
teeth……………………………………………………………………………………..Willow
Leaves have many, tiny teeth along the margins……………………………………...………9
9.
The stalk of the-leaf is usually longer than the blade, allowing the leaf to
"tremble" or flutter easily in a breeze……………………………………………Aspen (Poplar)
The leaf stalk is usually shorter than the leaf blade………………………………....White Birch