Lab Topic 26
Investigating Leaf Structure and Photosynthesis



Types of Leaves
Palmately compound
Pinnateley compound

Arrangement Pattern


Venation Patterns
Pinnate venation
Palmate venation
Parallel venation


Leaf Variety


New Pic A
New Pic B
New Pic C

What type of leaf arrangements and venation do these various plants have?
Which of the above has pinnately compound leaves? Which has palmately compound?
Do you suspect that any of the above leaves are monocots? Which ones? Why do you say so?
Can stems be photosynthetic?
Are needles leaves?
Why are leaves important?
Through what structures in leaves do gas exchanges take place?
How is this gas exchange regulated in the stoma?
What is a petiole and what function does it serve?
Is a monocot or dicot leaf more likely to have parallel veins?
Is a monocot or dicot leaf more likely to have netted venation?
Why are leaves important in water transport?



Internal Leaf Anatomy
Structure of a Dicot Leaf
In the photo above, identify the epidermis, columnar mesophyll cells, spongey mesophyll cells, and the vascular bundle. Discuss the function of each.  Names the layers seen in this cross section of a dicot leaf. Give the functions of each layer. 
How many cells thick is this leaf? 
What is the function of the waxy layer located outside of the epidermis in this photo? 
Beneath the epidermis is a layer of columnar cells. What are they called? What is their function? 
While pointing to the appropriate structures and regions in the photo above,  indicate how water vapor, carbon dioxide, and oxygen enter and exit the leaf. 

In he vascular bundle of a  dicot leaf, is the xylem nearest the lower or upper epidermis and what purpose does it serve?
In a dicot leaf, is the phloem nearest the lower or upper epidermis and what purpose does it serve?
The photosynthetic region of the leaf is located in the  ______________.
What is the difference between the palisade and spongy mesophyll regions?
When parenchyma cells contain chloroplasts they are called ________________. ( Must be spelled correctly)
Which of the mesophyll layers contains more chloroplasts?
In which layer, the upper or lower, are stomata generally found in a dicot leaf?


Structure of a Monocot Leaf
 Is this a slide of a dicot or monocot leaf?  How do you know this?
Give the name and function for this layer of cells.
What is the name given to the cells indicated by the pointer? Function?
Name one characteristic in leaves that separates dicots from monocots.
What does the layer of bundle sheath cells surround?
What is the role of "bulliform" cells?
 Would you expect to see a palisade layer in a monocot leaf? If so, point to it in the above photo. 
Does this leaf have an epidermis? Point to it.
Where are the vascular bundles in this photo? What is their function? 
Recalling the structure of a dicot and monocot leaf, what leaf is this? Why do you think so?
Is the xylem toward the lower or upper epidermis?
What is the function of the cells surrounding the vascular bundle?
What structures in this leaf allows it to curl to reduce transpiration?


Which cells are xylem and which are phloem? 
Point to the guard cells in this photo. What is their function?
What is the name of the pore in this leaf?  What is its function? 
In which layer, the upper or lower, are stomata generally found in a monocot leaf?
True or false: In a monocot leaf, the mesophyll is not in layers but exists outside the vascular bundles.
On a really hot day, one might see corn leaves in a field fold in on itself. What causes this?
Why are leaves coated with wax?


Guard-cell Response to Osmotic Stress
Guard Cell "before" pic
Guard Cell "after" pic



Photosynthetic Pigments
Extraction Procedure
Weighing Spinach pic

Steps in the isolation procedure described in the lab manual.


Safety note: Volatile solvents in closed containers must be vented to avoid pressure build-up.

Absorption Spectrum

First a solvent only tube is used to zero spectrophotometer and then second tube with sample is inserted.

Explain why a spectrophotometer is a useful analytical device.

Briefly describe the basic principles of a spectrophotometer's design.

Why must a spectrophotometer be blanked with a solvent first before reading a colored sample?

Given this solution, determine its maximum absorbance.

Plotted sample results of absorption readings.

At what wavelengths of light does chlorophyll have its maximum absorption?
Use this graph to explain why chlorophyll is green.
What wavelengths of light would you expect to be most active in "driving" photosynthesis?
What is the product of the light reaction? The dark reaction?
Explain the two major peaks found on this graph.
In general what does the chlorophyll molecule look like and why is this structure advantageous to the plant?
Briefly describe how to extract and measure the absorbance of chlorophyll in plant tissue?
Why is chlorophyll important?
In what organelles do you find chlorophyll?

Light Intensity and Photosynthetic Rate

The apparatus below can be used to measure photosynthesis. Explain the purpose of each piece of equipment and how oxygen is produced and measured.
Why is an empty tube used in the experiment measuring photosynthesis?

Explain how you relate photosynthetic rate to light intensity and distance from light source.

If you did not reach the light compensation point in your experimental set up, how might you calculate a theoretical value for this point? 

What is photosynthesis?
In photosynthesis, plants get what two chemicals from the environment  to produce carbohydrates?
In general what is the difference between the light and dark reactions in photosynthesis?
Why do plants need carbohydrates?
Oxygen produced in photosynthesis is a measure of ______________________. (Use the diagram for photosynthesis)
Explain what the light compensation point is and how might you measure it?


Starch Accumulation in Leaves
Demonstration pic
Leaf from Dark


General and Comparative Questions

Explain why plants are green, relate your answer to the information you know in regards to chloropyll's absorbance curve.
  (An absorption spectrum will be provided) Which wavelength (color) of light does chlorophyll absorb? If you exposed a plant to blue light and then green light while measuring its rate of photosynthesis, which color light should give the highest rate?
(A graph of an example light compensation point will be provided)  What is occurring at this point? What is the light compensation point?
Where would you expect to find chlorophyll  in plants? Why is it important?
What would you expect to happen to photosynthetic rate as light intensity increased?
Using your data, how could you determine the light intensity that resulted in oxygen production just equal to the amount of oxygen consumed in respiration?
What is the advantage of guard cells being able to close the stomatal openings?
How many cells thick are leaves? Does this form in any way reflect a leaf''s function?
Compare structure of a monocot and a dicot leaf.
Draw the anatomy of either a monocot or dicot leaf in cross section. Indicate the function of the different cell layers found in the leaf.



Photos and Layout by Linda Westgate, Warren D. Dolphin, and Mark A. Mangum