A Tree of Life Activity

Authors: Nicole VanderSal

Overview: This lesson first introduces a large diagram of the Tree of Life that will be a reference for the evolutionary relationships of California organisms for the rest of the year. Then there is a class-participation activity using traits of organisms on the tree to determine the identity of a mystery organism.

Lesson Concepts:

• Everything living is related.

• The Tree of Life shows how living things are related to each other.

• Morphological features can be used to put organisms into different groups.

• Scientists classify organisms.

Grade Span: 9–12 (can be simplified for younger classes)

Materials:

• Poster of the Tree of Life (download pdf)

• Pictures (or specimens if possible) of organisms that have some life stage that can be found in the air: Mammal (bat), Bird, Reptile (gliding snake or lizard), Fish (flying fish), Spider (ballooning spiderlings), Insect (dragonfly or butterfly), Fungus (spores), Conifer (cone), Flowering Plant (Maple seed, Dandelion seed)

• Picture (or specimen) of the "Mystery Organism" — A Flying Squirrel

• Something to cover the list of characters for the mystery organism activity

• Small copies of the Tree of Life for each student to follow along (and put on characters if you want)

Time: 50 minutes

Procedure:

Begin by putting up the Tree of Life poster and pass out small copies of the Tree of Life for students to follow along with. Go over organism groups on the tree that the students do not know. Explain that all living things have a place on the tree of life. Organisms are grouped by their similarities and differences. In addition, the branches show how groups of organisms are evolutionarily related to each other.

Explain the concept of "Character" as a trait of an organism that we use to identify the organism and group it with other organisms that are similar. You should emphasize that certain characters of an organism are not useful for grouping things together on a large scale (i.e., bird, bat and insect wings, or red flowers, insects and birds) but can be useful to separate organisms into small groups (species). Starting at the bottom of the tree, work as a class to determine what characters all organisms beyond a branch have in common (see list at bottom of lesson). Remind the students that these are just some of the characters that scientists use to group organisms based upon their evolutionary relationships. Other characters that we cannot directly see are also used to construct the tree of life: DNA sequences, development of embryos, and bone structure.

Give an introduction to the mystery organism activity:
You are outside and you look up to see something in the sky above you. As you watch, you see the object fall down right in front of you. You can see that it is something that is living (not a man-made object), but you are unsure what it is exactly. You decide to use characters that you remember from your class lesson to place the organism on the Tree of Life.

First have the class make a list of organisms or parts of organisms that might be found in the air at some point (naturally). Pass out pictures (or specimens) of the organisms as they are listed and have the students tape the picture where those organisms should be on the tree of life and what characters the organisms have (based upon characters you established from the beginning of the lesson). This activity reaffirms the idea that organisms, though they may look similar or act similarly, are more closely related to other organisms with more similar characters.

Once students have come up with all of the organisms, say that you will start at the bottom of the tree for the mystery organism. You should have the following list covered so that you can show one character at a time:

Character	Does the organism have it?
	Yes	No
Multicellular?	X
Photosynthesis?		X
Vertebrae?	X
Eggs that can be laid on land?	X
Warm-blooded?	X
Feathers?		X
Modified fingers?		X

With each answer, have the students determine which branch on the tree of life you should follow (this helps the students understand that all organisms beyond a branch will share that characteristic). In the end, have the students guess the identity of the mystery organism. Show the picture or specimen. If there is time, you can bring up the concept of body specializations that the flying squirrel has for its nocturnal, gliding lifestyle: skin flaps, long, flattened tail, large eyes and ears.

Throughout the year, you can return to the tree of life to tape photos of animals and plants collected from the school yard and field trips. If the class learns about a group in more detail (i.e., insect orders), the branches of the tree be expanded out to show this new information. In this way, the tree can tie the year's activities together.

Characters on the Tree of Life
These can be talked about with the entire class and/or directly written on the tree. Some characters may be skipped depending on the background biology level of students.

After:	Character:
Viruses	Replicate their own DNA
Unicellular Prokaryotes	Organelles in the cell
Protists	Multicellular
Red & Brown Algae	Towards plants: Photosynthesis Towards animals: Consume other organisms for energy
Green Algae	Land plants
Moss	Vascular system
Ferns	No spores
Conifers	Cones
Flowering Plants	Flowers and fruits
Fungi	Circular symmetry
Sponges	Bilateral symmetry
Jellyfish	Centralized nervous system
Worms	More specialization of body areas
Mollusks	Towards insects: Exoskeleton **Towards vertebrates: ?
Millipedes & Centipedes	Many legs
Arachnids	Two body parts and chelicerate mouthparts
Insects	Three body segments
Crustaceans	Two pairs of antennae
Sea Stars & Urchins	Vertebrae
Fish	Ability to be out of water for extended time
Salamanders & Frogs	Eggs do not have to be in water
Mammals	Fur, mammary glands, and warm-blooded
Turtles	Backbone fused to form external shell
Lizards	Teeth on shelves
Snakes	No limbs
Crocodiles	Teeth in sockets, larger than lizards
Birds	Feathers and warm-blooded

Reflections:

This lesson really emphasized characters used for making the Tree of Life, but as with any whole class activity/discussion, some students were more involved than others. From this activity it was difficult to assess whether every student understood the concepts of characters and how/why the animals are related. We used pictures of the animals, and I think the activity would be better if the students could see specimens to really see the characters that are on the Tree of Life. I think that slight modifications of the lesson could make it very salient for the students: perhaps by breaking them up in groups for more discussion, but I am not sure how to incorporate that in the current lesson.