AIM: SWBAT describe the different layers in a cross section of a tree trunk

1. AIM: SWBAT describe the different layers in a cross section of a tree trunk Please Do Now: What molecule does woody plant tissue have, that green plant tissue like leaves does not?

2. Agenda • Do Now • Tree Notes • Video • Tree ring activity • Quiz

3. Why does lignin make wood woody? • Lignin is a large complex molecule • It has lots of strength in compression (it resists squeezing) where cellulose has lots of strength in tension (pulling)

4. Why does lignin make wood woody? • Lignin is even harder to digest than cellulose • So, not only does lignin give wood its rigidity, it also protects the tree from things that would like to eat it • Different species of trees have wood with different qualities because they have different amount of cellulose, hemicellulose and lignin in them

5. What is bark?

6. Lignin • Bark cells also have lignified secondary cell walls, which is what gives bark its tough qualities

7. Tree Trunks • Taking a cross section of a tree will show you multiple layers • Each of these layers has a different function, and a different structure to match that function

8. What does the bark do? • It serves to protect the more valuable parts inside the tree from drying out, insects, disease, fire etc… • In most trees, it is made of very tough cells with lots of lignin in their secondary cell walls

9. Bark

10. What does the phloem do? • It is what sugars move through when they are transported from the leaves where they are made down to the roots • It is a thin layer with lots of tube-like structures responsible for transport

11. Phloem

12. What is the cambium? • The cambium is where all the outward growth takes place • If the cambium gets damaged, the tree will die

13. What is the sapwood? • The next layer in is the sapwood, the first layer that seems truly woody • It is still alive (unlike the heartwood) • It contains the xylem, which water is transported through • The cell walls here have lots of lignin, as well as lots of tube structures for water transport

14. Sapwood

15. What is the heartwood? • The heartwood is the center of the tree • The cells here are dead, and the material is basically all highly lignified cell walls • It provides structural support to the tree

16. Tree rings

17. Tree rings • Every year, a tree has periods when it is growing very fast (summer) and when it hardly grows at all (winter). • The periods when the cambium is dividing rapidly will produce a slightly different color of wood then when it is growing slowly • In this way “rings” form in the trunk, each representing a year of growth