Not all plants have leaves (think about cactus) but most do. The leaves are many shapes and sizes. Pumpkin leaves are big and flat. So leaves must be important to a plant. Lots of insects and animals eat leaves so plants try to find ways to protect their leaves. You have seen that a plant collects water with its roots and sends that water to the leaves. Let’s find out ways pumpkin plants protect their leaves and use water.
Question: Why can leaves be thin but strong?
Leaf with petiole from a pumpkin plant
2 Leaves on a pumpkin plant
Clear plastic bag, rubber band
Dark construction paper (brown or black), paperclip
Tincture of iodine
Step 1: Open your Science Journal, write “Investigation 13” and the date.
Step 2: Cut a 5cm x 12cm piece of dark construction paper.
Step 3: Fold the paper in half and place it around a pumpkin leaf on a pumpkin plant. Use the paperclip to hold it in place
Step 4: At least 24 hours later cut the leaf off the pumpkin plant and take it to where you do your Investigations.
Step 5: Take the paper off the leaf. Examine the leaf for any differences between where the paper was and where it was not. Do not leave the leaf in the light very long before the next step.
Step 6: Put drops of Tincture of Iodine on the leaf both where the paper was and on another similar piece of leaf.
Step 7: Put the clear plastic bag over a pumpkin leaf in the sun on a vine
Step 8: Use the rubber band or a paper clip to fasten the bottom of the bag around the petiole
Step 9: Wait 2 hours and take the bag off the leaf examining what is in the bag
Step 10: Cut a leaf and petiole off a pumpkin plant.
Step 11: Examine both sides of the leaf and petiole with the magnifying glass. Describe and draw what you see.
Step 12: Cut the petiole open flat where it joins the leaf and examine the area with the magnifying glass. Describe and draw what you see.
Step 13: Cut lengthwise down the petiole into the main leaf vein and examine how the petiole joins the vein with the magnifying glass. Describe and draw what you see.
Step 14: Tear across one piece of leaf. Does it tear in a straight line? Describe and draw what you see.
Describe the leaf where it was covered by the paper
Describe what happens when you put iodine on the leaf
Describe what you find in the plastic bag
Describe the leaf and petiole.
Describe how a petiole joins a leaf
Describe how the petiole veins and the leaf veins join
Describe tearing a leaf
Why does the leaf change color when sunlight can’t get to it?
Iodine turns dark purple when it touches starch. Starch is made of many sugar molecules joined together. Where did you find starch in the pumpkin leaf? Why is it there?
What do you think the liquid in the plastic bag is?
Where do you think the liquid came from?
Why do you think the leaf loses the liquid?
What do you think would happen to a leaf if it couldn’t replace this liquid?
How is the petiole like a stem?
How is a petiole unlike a stem?
What happens to all the cords in the petiole when they get to the leaf?
Why does a pumpkin leaf need so many veins? Try to think of at least two things a leaf uses veins for.
How do the veins affect how a leaf tears?
Why do you think pumpkin leaves have spines?
Why do you think some parts of a leaf are thin?