B11 LAB ­ Cross Section of a Leaf modified.notebook
October 29, 2013
CROSS­SECTION OF A LEAF INTRODUCTION
The leaf is an organ in a plant consisting of many different tissues. The primary function of a leaf is to make (synthesize) food through a chemical reaction called ___________________________. The "photo" part to this name refers to the role the sun has in the reaction. The chemical reactants must be "mixed" in the presence of the sun to drive the reaction. The two reactants in this reaction are __________________ and ___________________.
To obtain light the leaf _________________________________________________
To obtain carbon dioxide the leaf _________________________________________
To obtain water the leaf
1. ________________________________________________________________
2. ________________________________________________________________
The products in this reaction are _____________________ and _______________
Write the word equation for this reaction.
Write the skeletal equation for this reaction.
http://harvardforest.fas.harvard.edu/research/leaves/leaf_structure.html
epidermis, which produces a waxy The general structure of a leaf has an outer layer, the guard cells, which swell and waterproof coating. The epidermis of the undersurface produces shrink to close and open the pores (stomata) which control the loss of water vapor (transpiration) and the entry of carbon dioxide. The internal tissues consist of the mesophyll, the photosynthetic cells of the leaf. These are typically the long columnar cells nearer the surface (palisade parenchyma) and the looser irregular cells beneath (the spongy mesophyll parenchyma). These cells are loaded with chloroplasts in the cytoplasm. Each of these cells has a large vacuole, bound by a membrane, which takes up some 90 % of the cell volume. xylem tissue in the veins, and the sugar Water and nutrients move into these tissues via the phloem tissue. products of photosynthesis are translocated to other parts of the plant via the The importance of the movement of carbon dioxide and water into the plant are seen in the summary equation for photosynthesis. 1
B11 LAB ­ Cross Section of a Leaf modified.notebook
October 29, 2013
Label this diagram using the names from the other diagram. PARTS OF A LEAF Fill in the blanks using the word bank below ­ some words can be used more than once.
Function of the Leaf Tissues
The cuticle is a __________ coating which helps the leaf retain ___________.
Epidermal cells protect the internal tissues in a leaf from invasion of organisms but they also must allow for the exchange of ___________________ and they must allow ___________ to pass through for the purpose of _____________________________.
The palisade cells contain a greater concentration of _____________ than most plant cells for the purpose of performing _____________________.
The spongy mesophyll cells are more ________________ in shape and are spread farther apart. The spaces between these cells can fill with ____________ and ____________. The main function of these cells is to temporarily store the __________ made during ________________________.
The guard cells found on the lower epidermis open and close to allow for the exchange of _______________ and __________________. The opening in the guard cells is called the _____________.
The vein contains two specialized cells called _______________ and ______________. The ____________ cells transports _________________ up from the root. The ______________ cells transport ________________ to any location for cells to use as an energy source during _________________________.
Word Bank
chloroplast
gases
photosynthesis
phloem
waxy
xylem
irregular
O2 respiration
sunlight
CO2
water
stomata
sugars
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B11 LAB ­ Cross Section of a Leaf modified.notebook
October 29, 2013
http://www.sites.ext.vt.edu/virtualforest/modules/photo.html http://www.kscience.co.uk/animations/transpiration.htm https://download.elearningontario.ca/repository/13/1300700000/UsingTheMicroscope.html http://content.bfwpub.com/webroot_pubcontent/Content/BCS_3/Sadava_9e/Animated%20Tutorials/life9e_3501_xylem_trans.html http://wps.prenhall.com/wps/media/objects/2688/2752944/Web_Tutorials/30_A01.swf http://www.sciencemag.org/site/feature/misc/webfeat/vis2005/show/transpiration.swf 3
B11 LAB ­ Cross Section of a Leaf modified.notebook
October 29, 2013
Procedure
1. Obtain a microscope and bring it to your working station holding the arm and base of the microscope. 2. Obtain a prepared slide of a cross section of a leaf. Focus the microscope under low power before proceeding.
3. In this activity you will have to create 2 biological drawings. The first drawing will require a detailed drawing of a large section cells under medium power, so that the various tissues of a leaf can be easily identifiable. The second drawing will consist of the detail in a single cell of any specific tissue in a leaf. Select high magnification and the appropriate lighting to create these two drawings. 4. Clean up your work station and return all equipment.
Observations
Table 1: Field of View for Microscope Magnification
40 ×
100 × 400 × Field of View (μm)
Complete the 2 biological drawings on the attached page with appropriate labels. Include a size estimate of the thickness of the leaf and the length of the single cell you chose to draw.
Discussion Questions Answer the following questions on the back of your biological drawing sheet for this activity or on a separate sheet of lined paper.
1. For each of the different tissues in the cross section of the leaf (epidermal cells, palisade cells, spongy cells, guard cells) describe how their location helps them perform their primary function.
2. Both the spongy cells and the palisade cells perform photosynthesis. Which set of cells do you think contains more chloroplasts and why?
3. Why are there no guard cells on the upper epidermis?
4. What is the most important function of a leaf and why does the shape of this organ aid in this function?
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B11 LAB ­ Cross Section of a Leaf modified.notebook
October 29, 2013
Size Estimate of a leaf
Size Estimate of a leaf
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