Chromatography & Leaf Structure

Experiment 8:

Chromatography & Leaf Structure

Part A: Chromatography

Purpose: To determine if the green material in a leaf is a single substance or a mixture of many substances.

Materials:

Leaves (spinach)

Filter Paper

Coin

Test Tube

Solvent Mixture

Rubber Stopper

Procedure:

1. Obtain a piece of filter paper and cut the ends to make a triangular tip

2. Place a spinach leaf near the triangular tip side of the paper

3. Rub a line of pigment off the leaf onto the filter paper with the edge of the coin about 3-4 cm from the bottom edge

4. Add solvent to the test tube to about 1 cm deep

5. Place the filter paper into the test tube until the end is in the solvent but the pigment line is above the solvent – make sure not to bend the paper, tip the test tube, or splash solvent onto the upper filter paper

6. Stopper the test tube and stand it upright for 10–15 minutes – make sure that solvent is not allowed to run through the top of the paper

7. While waiting for the solvent to absorb, go to part B of the lab.

8. SKETCH and LABEL your chromatogram using the pigment key to identify the substances

Data/Observations:

Draw a picture of the chromatogram and the bands of pigment that are produced. COLOR and LABEL the chromatogram. Staple your drawing to the lab.

Analysis:

1. Is the green pigment seen in leaves a single pigment or a mixture of pigments? Explain.

2. Chlorophyll is green. Is all of the pigment in the leaves you tested chlorophyll? Explain.

3. How many color bands can you see on your chromatogram?

4. Compare your chromatogram with the other groups at your lab table. How do they compare? Do all groups have the same number of bands in the same order?

Conclusions:

1. In the fall, most leaves on broad-leafed trees die and drop off. How do the observations of this investigation help to explain the various color changes that the leaves go through as they die?

2. Which color wavelengths of light do the chlorophylls absorb? Which color(s) are reflected?

3. What is the main type of chlorophyll involved in photosynthesis? What are accessory pigments?

Part B: Leaf Structure

Purpose: To examine the internal structure of a leaf and determine how it functions.

Materials:

Microscope

Prepared slide: Cross section of dicot leaf

Prepared slide: Leaf epidermis

Procedure:

1. Observe the dicot leaf cross section under medium power and compare what you are looking at to the cross section diagram on p. 596 of your text.

2. Draw the cross section and label the following structures:

a. upper epidermis

b. lower epidermis

c. palisade mesophyll

d. spongy mesophyll

e. vascular bundle (vein)

3. Observe and draw the epidermis slides under medium power.

4. Using the information from your text on p. 597 identify and label:

a. epidermal cells

b. guard cells

c. stoma

Data/Observations:
Attach your drawings of the leaf cross section and the epidermis to your lab report.

Analysis:

Using your textbook (pg. 596-597), describe the function of the following structures:

1. Palisade mesophyll

2. Vascular bundle (Vein)

3. Spongy mesophyll

4. Guard cells

5. Stoma

6. The surface of some leaves has a waxy cuticle. What do you think is its purpose?

7. Explain the process of transpiration.

8. Describe how gases are exchanged through leaves of plants.

Conclusion:

On a separate sheet of paper, write a paragraph (5-6 sentences) that explains how leaf STRUCTURE contributes to leaf FUNCTION.