Tag Archives: leaf epidermis

OS14 Pumpkin Leaves Have Layers

A pumpkin leaf is so thin, how can it have even thinner layers? How could we even see those very thin layers, if they are there? Those layers would be stuck together tightly and be hard to pull apart. Let’s take a look at a pumpkin leaf.

 Note: I brought the wrong pictures. They were in the right folder but it must have been mislabeled. I will try to get the right ones here on Saturday.

Question: Do pumpkin leaves have layers?

Materials:

Big young leaf from a pumpkin plant

Microscope

4 Slides

Paper towel (Not all paper towels will do this. I used Viva Towels.)

Scissors

Penny

Rubbing alcohol

Pint glass jar

Procedure:

Step 1: Open your Science Journal, write “Investigation 14” and the date.

Part 1:

Step 2: Slowly tear off a piece of leaf between major veins. Try to do it at an angle to tear the top and bottom of the leaf apart.

torn leaf

A small triangle of leaf tore apart this time. This small bit of leaf layer will give lots to see under a microscope.

Note: This is difficult to do but you need only a small area, just a square mm or two. It may take tearing more than one leaf into small pieces to get a small area. Younger, thicker, moister leaves are easier to do. I pinch bits of the leaf between a thumbnail and finger then pull. It can take 20 or 30 tries and more than one leaf. Remember that the torn piece has a top on one leaf piece and a bottom on the other piece. Make two slides.

Step 3: Take areas where the leaf surfaces are torn apart and make slides with them. This requires only a very small piece of leaf on a drop of water

Step 4: Examine these slides with the microscope. Try to see the cells from the inside of the leaf.

Part 2: Chromatography

Step 5: Cut a piece of paper towel about 3cm wide and 3cm longer than your jar is tall.

Step 6: Draw a line across the piece of paper about 3cm from the end.

chromatography spot

Rubbing a leaf with a penny crushes the cells and grinds the chlorophyll onto the paper towel.

Step 7: Put a piece of leaf over the line and rub it with the penny to leave a dark green spot on the paper.

Step 8: Attach the other end of the paper to the center of a pencil with some tape.

Step 9: Pour about 2cm alcohol in the jar

The mark on the paper is to make sure the spot is above the alcohol layer. Otherwise the chlorophyll will dissolve into the alcohol instead of go up the paper towel.

The mark on the paper is to make sure the spot is above the alcohol layer. Otherwise the chlorophyll will dissolve into the alcohol instead of go up the paper towel.

Step 10: Dangle the spotted end of filter paper in the alcohol making sure the spot does NOT touch the alcohol rolling up extra paper on the pencil.

Step 11: Watch the alcohol travel up the filter paper. When it is almost up to the pencil, take it out and examine what happened to the spot. The line will be faint and when the alcohol evaporates, everything will disappear. Draw what you see.

Observations:

Describe and draw the cells from the torn piece of leaf

microscope slide of leaf layer

The bottom layer of a leaf shows the clear epidermal cells and the stomates each surrounded by two green guard cells.

Describe what you see on the paper towel

Conclusions:

Does a leaf have layers? Why do you think so?

Where are most of the green cells containing chlorophyll found in a leaf?

Why do you think the cells on the top and bottom [called the epidermis] of the leaf are clear?

There are pairs of green cells called guard cells in the epidermis. Where are most of these cells found?

These cells surround openings called stomates into the leaf. Leaves need carbon dioxide from the air. Think back to Investigation 13. What does a stomate do?

Why do you think there are more stomates on the bottom of a leaf than on the top?

Compare the shapes of the epidermis cells and the cells inside the leaf.

The green coloring in the inside cells is chlorophyll. Why does this make it hard to see the cells?

chromatography results

The alcohol has spread the original spot but the marks are faint. They disappear once the towel dries.

Alcohol going up the paper towel holds onto the chlorophyll molecules and carries them up as it goes up. Each different kind of molecule is carried differently. Are all the chlorophyll molecules in a leaf the same? Are they all green? Why do you think so?