Biology



Honors Biology Name ______________________________

Stomata Lab Date ___________

Introduction

Plants and animals both have a layer of tissue called the epidermal layer. Plants have special pores called stomata to allow passage of material. The stomata pores are surrounded on both sides by jellybean shaped cells called guard cells. 

[pic]

Unlike other plant epidermal cells, the guard cells contain chlorophyll to do photosynthesis.  This allows the cells to expand/contract  to open or close the stomata.  Guard cells also close when dehydrated.  This keeps water in the plant from escaping.  The number of stomata on the epidermal surface can tell you a lot about a plant.  Usually, a high concentration of stomata indicates fast growth and wet climate.  Lower concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather.

Materials:

1 leaf, compound light microscope, microscope slides, and tweezers

Procedure:

1. Get the materials from the front bench and bring them to your lab station.

2. Determine the ventral side (bottom) of the leaf. It will be less shiny than the dorsal surface (top).

3. Carefully peal back the thin layer of the ventral side of the leaf the size of your pinky fingernail. Tweezers will work but I find fingernails work best.

4. Set up a wet mount and examine the ventral side of the leaf.

5. Examine the leaf under a microscope at 400X.

6. Find 1 stomata and draw what you see.

7. Count all the stomata in the field of view under low Power. Record the number on your data table.

8. Repeat counts for at least three other distinct microscope fields. Record all the counts.

9. Repeat steps 1-10 for the dorsal surface of the leaf.

10. When finished, clean and return all the materials to the front bench. Wipe down your lab station. Work with your lab partner on the data table and post lab questions.

Drawings (label the dorsal and ventral side)

Data Table (2 points)

|Leaf Surface |Count 1 |Count 2 |Count 3 |Average |

|Ventral | | | | |

|Dorsal | | | | |

 Post Lab Questions

1. Which leaf surface had the most stomata? Why do you think this was so?

2. Under what conditions would the stomata be closed? Why?

3. Define transpiration.

 4. What three molecules move in and out of the leaf stomata? What is the purpose of each?

5.  Write the photosynthetic summary equation. Underline the reactants.

6. What is the ultimate purpose of photosynthesis?

7. What pigment in plants makes them green? Where is this pigment located in a leaf cell?

8. From #7, what other pigments are in plants? What is their purpose?

9. How are the stomata different in C3, C4 and CAM plants? Why?

10. If tree leaves are green most of the year, when can you see the other pigments naturally?

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