What Trees Really Do
Water does get all the way up to the top of tall trees. This process is known as the Vascular system. Plants have a special type of tissue called vascular tissue. This vascular tissue is how plants including trees transport water and nutrients to different parts of the plant. The vascular tissue is made up of a network of tubes that are located inside the plant.
"Water gets all the
way up there?"
Remember? The formation of vascular bundles is one of the ways we know if a tree is a dicot or a monocot! (Image 3.3)
This is a cross section of a stem from the St John's Wort plant viewed on a light micograph. Though the St John's is not a tree is does have a similar structure to tree stems. The red outlined circles are the vascular bundles or tissue. It would be those red outlined circles that would have water and other nutients traveling through them. (Image 3.2)
There is a special tissue within the vasular bundles known as xylem. It is the xylem tissue that is actually responsible for transporting water in trees and other plants. Xylem is made up of small long mostly hollow tubes. These tubes are formed by cells known as tracheids or vessel elements. (Image 3.4) These cells start out as living cells in immature stems, but when they mature the living componients of the cells die. Only the walls of the cells remain. These walls create the hollow tubes that form the xylem tissue. The xylem of gymnosperms only has tracheids but the xylem of angiosperms has both tracheids and vessel elements.
Quick Question
How are vessel elements and tracheids similar and different?
Quick Quest
Take some time to go outside. Find a tree that you have not yet encountered on a Quick Quest. Using a pair of scissors cut a stem from the tree. See if you are able to squeeze or push out any water. Take a photo of the stem and use the #QuickQuest. Be sure to include if you were or weren't suprised by the amount of water in the stem.
What Trees Really Do Continued
Another part of the vascular tissue is known as phloem. Phloem is similar to xylem because it too is made of cells that form long tubes. Phloem is different from xylem in several ways. First phloem cells are living unlike xylem cells. Xylem cells only carry water whereas phloem cells transport nutrients throughout the tree. Xylem cells use osmosis to carry water from the roots of a tree to the leaves. This means that xylem tubes can only carry water in one direction from root to leaf. Phloem tubes are able to transport nutrients in any direction. This process of moving nutrients is known as translocation. Phloem cells actually use oxygen and water to move nutrients. Phloem tissue has three main parts: sieve-tube member, companion cell, and sieve plate. (Image 4.1)
Cinema Central
Watch this video to learn even more about Xylem and Phloem!
Cinema Central Take a ride up a Xylem Tube!
The nutrients that the phloem is carrying will eventually end up at the roots of the tree in the form of starch. Starch is not able to pass through the phloem tissue so it is desolved by water to form sucrose which is smaller and able to move through pholem cells. (Image 4.2)
Quick Question
Quick Quest
Take some time to go outside. Find a tree you have not yet studied on a Quick Quest. Cut a stem from the tree and squeeze or push out as much liquid as you are able. Smell the liquid, rub it in your figures. It is not just water like we may have thought before, there is sucrose in there as well. Snap a picture and use the #QuickQuest. Be sure to include what the liquid smelt and felt like.
What two things is phloem tissue able to do that xylem tissue is not able to do?
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The Leaf and it's Function
All vasular plants have leaves, but they varry in color, shape, size, and formation. What all vasular plant leaves do have in common is the function they preform. Not matter if the tree or plant is a gymnosperm or angiosperm, monocot or dictot the leaves' primary function is to convert Sun light into nutrients for the plant. This process is know as photosynthesis. (image 5.1)
Parts of a Leaf
5.1
The epidermis is an outer layer of living tissue on all types of leaves. It's purpose is to protect the inner tissue of a leaf from fungi and bacteria. The epidermis is not fully waterproof. Cuticle is a waxy, non-living that is outside the epidermis layer of a leaf that makes it waterproof. Not only does the cuticle stop water from passing through epidermis cells it also stops gases. (Image 5.2)
5.2
Stoma or stomata (plural) are similar to skin pores. Stomata tend to be more present on the underside of a leaf. The function and the purpose of stomata is to allow gas pass into the interior of the leaf. (Image 5.3- Apple tree stomata) (Image 5.4- English Oak stomata) (Image 5.5- Stoma diagram) The stomata are inbetween two guard cells. These guard cells control how much gas the stomata allow into the leaf by changing the size of the stomata. The guard cells do this through compressing or releasing pressure on the stomata. The less pressure the gurad cells put on the stomata the larger the stamata becomes and larger amounts of gases can pass into the leaf.
Cinema Central
Look IN the Leaf
Quick Quest
Take a quick trip outside. Find three different leaves and drip small amounts of water on them. Note how the cuticle repels the water. (Image 5.6) Take a photo and use the #QuickQuest. Be sure that you include any classification details you may know about the leaves.
Quick Question
What does cuticle stop from entering a leaf that stomata allows to enter the leaf?
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