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

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?

Agenda

• Do Now• Tree Notes• Video• Tree ring activity• Quiz

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)

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

What is bark?

Lignin

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

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

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

Bark

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

Phloem

What is the cambium?

• The cambium is where all the outward growth takes place

• If the cambium gets damaged, the tree will die

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

Sapwood

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

Tree rings

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