Mr. Chapman Biology 20

Extracting chlorophyll from leaves and making it glow.

If you remove chlorophyll molecules from their cells and expose them to bright light, the chlorophyll will absorb the light energy. Recall that chlorophyll is the pigment found in leaves that absorbs light energy from the sun. The absorbed energy will be lost as heat or released as dull-coloured light, known as fluorescence. This is what we are hoping to see.

1. Use the mortar and pestle to crush a handful of spinach leaves. 2. Add enough methanol to make approximately 10 mL of extract. Use a graduated cylinder to collect and measure the extract. 3. Place the filter paper in the funnel, and hold the funnel over a beaker. A second person should pour the extract through the funnel to filter the extract.

5. Carefully transfer the extract to a test tube, and hold it in front of a light in the classroom for about one minute. 6. Quickly take the test tube and go to the storage room, closing the door so it is pitch black. Can you see any fluorescence from the test tube? 7. Clean up all of the materials you used for the lab. Wash all of the materials with soap and dry them with paper towel.

1. What color does the fluorescence appear? 2. Why did the chlorophyll have to be extracted before the fluorescence could be observed? 3. Why do plants have pigments that can absorb light? What are the three things a plant requires in order to perform photosynthesis? 4. Name one way in which you could have improved the experiment.

Structure of Leaves, and Various Types

Leaves grow out of a plant’s stem, and are composed of a few basic parts: Blade: usually broad and flat, but not always. Collects sunlight for the plant. Petiole: the blade connects to the stem by a thin stalk called the petiole. Auxiliary bud: grows between the petiole and the stem of the plant, marking where leaf ends.

Like all plant parts, leaves have an outer layer of dermal tissue. Inside the dermal tissue is an internal system of vascular tissue, surrounded by ground tissue. Remember that the dermal tissue is often covered by cuticle, a waxy substance that prevents water from escaping the leaves.

Between both layers of the dermal tissue (the top and bottom of the leaf) is mesophyll, which is composed of parenchyma tissue. Xylem and phloem is the vascular tissue that runs through the mesophyll.

In most plants, the tops and bottoms of the leaves have different functions. The top of the leaf is where the mesophyll has the most chloroplasts, allowing it to absorb the most light and perform photosynthesis. The bottom of the leaf contains the stomata and is where transpiration and gas exchange occur.

During the day, the stomata of most plants are open, which allows the plant to acquire the carbon dioxide it requires for photosynthesis. The stomata must be open in order for the plant to get carbon dioxide. Guard cells plump up when the plant is full of water, opening up the stoma.

When the stomata are open and absorbing carbon dioxide, the plant is losing water. If the plant loses water faster than it absorbs it in its roots, the guard cells deflate and then close. The guard cells are always closed at night, and other factors have an affect on whether or not the stomata will open.

Some leaves are simple, with just one blade connected to the petiole. Other leaves are compound, with many blades connected to the petiole. Multiple blades are called leaflets. All of the leaflets and their petiole together are known as one leaf, because auxiliary bud is at the base of the petiole attached to the stem.

Not all leaves are leafy. Leaves are adapted depending on their particular environment. Cactus leaves are sharp spines, protecting them from predators and preventing excess water loss. Some plants store water in their leaves, and have very thick cuticles in order to prevent water loss.

Some plants that rest on water, like water lilies, have stomata on the upper part of the leaf instead of underneath, to allow gas exchange. Many tropical plants have huge, broad leaves. This is due to the challenge the plants have to absorb light with all of the other plants blocking the way. Some plants are predators, with leaves that attract and trap small insects, digesting them to get to their sweet, sweet nitrogen.