The pieces you discarded represented the oceans, deserts, and mountains. Tundra could be illustrated by ice and snow covered land - small vegetation such as mosses and lichens. After the murals are completed each group will present their mural to the entire class explaining the biome. They will need to explain the biome along with the plant type and animal they were assigned. Each student will do an individual report on one of the animals present in their biome.
Biomes are large geographic areas that have the same climate and life forms.
Abiotic factors include temperature, light intensity, patterns of rainfall and availability of water. I suggest that Tundra not be offered as a choice to the students. At this site you will find a interactive endangered species map, the site also takes on several other conservation issues. There is too much here to try and describe, you just have to see it for yourself. I will tell you that the first screen offers some lesson plans and activities that can be done using the site.