Sec __
Name:
_
Experiment: Leaf Structure And Function
(B. Science 10-P-36)
Purpose: To observe how external and internal leaf
i structures makes a leaf the primary photosynthetic organ.
Materials:
microscope
prepared slide of leaf x.s. (Ligustrum)
Methods: As you answer the questions also label the
diagram with the parts printed in bold.
1. Examine the picture of a typical leaf in the results section.
The flat portion of the leaf is referred to as the blade. The
I,contain
veins ofxylem
the leaf
as What
lines on
the function
blade. The
veins
andappear
phloem.
is the
of the
,I veins?
iI 2. The petiole is the stalk of the leaf that attaches the leaf
I to the branch. The petiole connects the xylem and the
phloem of the branch to the xylem and the phloem of the
'veins in the leaf. What two tissues must be in the petiole so
------------- ..it can connect the leaf to the branch.
3. Examine a prepared slide of a leaf cross section under low power of your microscope. Be sure to
observe the top to the lower surface and from one margin to the other. Observe that the leaf is
-')mposed of three main types of tissues: epidermis. mesophyll. and conducting tissue. Study the
.pper epidermis. How many cells thick is it?
4. Are any chloroplasts present in the upper epidermis (not the cuticle layer)?
5. The cells of the epidermis are covered by a waxy layer called cuticle. Record its function.
6. The mesophyll is the largest area of the leaf and is composed of two regions. The first of these
is made up of palisade cells which lie just below the upper epidermis. Study this area under high
power. Describe the cells and their orientation to the upper epidermis.
7. Locate some chloroplasts
in the palisade cells. Record the function of the palisade CBlIs.
8. How is the shape and orientation of the palisade cells important for effective photosynthesis?
9. Study the lower region of the mesophyll. Locate the spongy layer of cells below the palisC1de
cells. Of the two, which layer is more compact?
10. Are chloroplasts as numerous in the spongy cells region as they are in the palisade cells?
11. Account for any difference you find.
12. Note the numerous spaces among the spongy cells. These are the air spaces. On the basis
of their relationship to other tissues in the leaf, what do you think their function is?
13. The spongy layer is penetrated by numerous circular veins. Move the slide until you are able
to locate a vein. How can you tell a vein from other structures in a leaf?
. 14. Examine the vein closely. Locate empty cells with thick walls in the upper parts of the section.
These are the xylem cells. Record the two functions of the xylem cells.
15. The thin - walled cells that form a cluster below.the xylem cells are the phloem cells. What is
the function of the phloem cells?
16. Find a small vein in your section near the leaf margin. Which kind of cell composes the small
'ein?
.7.- Examine the lower epidermis. How many cell layers compose it?
18. Closely examine the lower epidermis. Try to find tiny pores with small, rounded cells on either
side. The pores are the stomata and the rounded cells are the guard cells. Determine the
j
Sec:__
Name:
relationship between the stomata and the air spaces of the spongy tissue.
19. Describe the function of the stomata.
_
Results:
Cross section of a leaf
1. function:
3. thicJc
5. function:
7. function:
9. layer:
11.. why:
13. unique:
15. function: _
17. number of layers:
19. function:
2. two tissues:
4. present:
6. describe:
8. important:
1D. spongy is:
12. function:
14. functions (2):
16. kind of cell:
18. relationship:
Conclusions: Fill in the blank
1. The layer of leaf cells which lacks chloroplasts is the
_
2. The
is the largest volume of a leaf.
3. The
layer is composed of cells which are oriented at right angles to the
epidermis.
4. The presence of
is typical of the spongy layer.
5. The
is a waxy layer which prevents the loss of water from the leaf.
6. The
is composed of tissues which carry materials to and from leaf.
7. Pores found on the underside of leaves are known as
_
8. Conducting tissues in a leaf are
and
_
9. The only cells that contain chloroplasts in the epidermis layer are the
10. The three basic tissues of the leaf are
,
• and
11. Read Proverbs 11: 27 - 30. Why is "the righteous flourishing", compared to green leaves?
12. Read Mark 13: 24 - 29. Why is the analogy of the "tender branch putting forth its leaves," used
to predict the closeness of the second coming?
(