The next four Investigations look at the parts of a growing pumpkin plant so I have left all four in a row here but am only adding pictures for 11 today and will do 12 next week.
Although you can do each one separately, all of them can be done using the same side branch listed in the Materials part of Investigation 12. Most side branches have at least one adventitious root for Investigation 11. The stem is used for Investigation 12. The leaves can be used for Investigations 13 and 14. The vine will wilt overnight so all the Investigations would have to be done one after the other which will take several hours.
In Investigation 9 you examined a pumpkin sprout root. This time you will examine a root from a pumpkin plant to find out if it is the same or if it has changed as the plant grew big. Of course, once you dig a plant up by the roots, the plant will die. So you can examine the roots of a plant you are thinning out because a hill can only have so many plants growing in it or you can use an adventitious root, one that has grown from a pumpkin plant vine node. The best is to do both kinds to find out if they are the same. Let’s look at some roots.
Question: What are the parts of a root?
A root from a pumpkin plant with the dirt carefully rinsed off
Step 1: Dig up a pumpkin plant root. If you pull it up, you will damage the roots.
Step 2: Rinse the dirt off the roots. Shake the roots gently in a pail of water but don’t scrub them or you will damage the roots. Not all of the dirt will rinse off.
Step 3: Spread the roots on a damp paper towel. Examine them by looking and with the magnifying glass.
Step 4: Cut off a piece of root and examine the cross section of the root
Step 5: Cut a section of root 3cm to 4cm long and try to cut it lengthwise. Examine the pieces.
Step 6: Cut off a tiny root off the main root, about 1cm long, place one or two on a drop of water on a slide and examine the pieces with a microscope.
Draw the root.
Draw the very tips of the roots on the slide.
Move up the roots on the slide until you can see little hair-like roots sticking out. Draw these.
A taproot has a main root with side roots branching off. A fibrous root has many roots that look alike coming from the end of the stem. Which kind of root does a pumpkin have?
The very end of a root has a root cap, a bunch of cells on the end that rub off as the root grows. Why would a root need a root cap?
All but the very ends of the root have a thick layer of protective cells on them and can not absorb this water. Why do roots need this protective layer?
A plant uses a lot of water. The tips of the roots must supply all of the water. How would having lots of root hairs, the little stick out parts, help the root tips absorb more water?
What Are the Parts of a Stem?
Not all plants have stems. Some plants like dandelions just have leaves. These plants can’t get very big. Stems come between the roots and the leaves letting a plant get big. Let’s see how a stem does this.
Question: How does a stem let a plant get big?
1 pumpkin side vine about 1.5 m long
Jar of water with lots of food coloring (red or blue) in it
Step 1: Open your Science Journal, write “Investigation 12” and the date.
Step 2: Cut a side vine off a pumpkin vine
Step 2: Cut off a section of the stem with a leaf on the top end. Put the stem in the jar of water and set it aside overnight.
Step 3: Examine the rest of the side vine. What does it feel like? How long are the stem pieces (internodes) between leaf petioles? What shape is the stem?
Step 4: Cut off a piece of stem from between two petioles to examine. Is it solid? Is it the same diameter at both ends? Is it the same all the way around? Try to tear it across. Try to tear it lengthwise. Does the inside feel the same as the outside? What else do you see?
Step 5: Examine the strings and soft parts with the magnifying glass. How many strings are there? Are they all the same? Try to cut some strings lengthwise to examine. [Be very careful not to cut yourself.]
Step 6: Cut open a section of vine so you can see how a leaf petiole joins the stem. Examine how the strings go from the stem into the leaf.
Step 7: Carefully cut off a tendril and examine it. What does it feel like? Is it hollow? Try to cut it lengthwise and see what is inside it. [Do this carefully.]
Step 8: Carefully cut off a white area from the stem below a leaf (the adventitious root) and examine it. How is it different from the stem?
Step 9: Examine the 5cm at the tip of the vine. Is it like the rest of the vine? What is found at the tip? Carefully cut the parts of the tip open to see what is inside.
Step 10: Examine flower buds on the vine by a leaf. Are the stalks like the vine? Do the cords go into the flower stems? Carefully cut open the flower buds. What is inside the buds?
Step 11: Take the piece of vine out of the food coloring. Cut across the end of the stem above where it was in the water. Can you find food coloring inside the vine?
Use this section to write down and draw what you see.
Petiole, Tendril and Stem:
Root and Stem:
Stem cross section plain (top) and food coloring:
Leaves from the very tip to 5cm back:
Tendrils from the very tip and 5cm back:
Male Flower from tip whole (top) then cross section:
Female Flower from tip whole (top) then cross section:
Compare tearing the stem across and lengthwise. Which way was easier? Why is this way easier?
What do you think the cords in the vine stems do?
How does the cord pattern change around the petiole? Why do you think the pattern does this?
How do the cords affect how the stem crushes?
What are the advantages of a hollow stem to the plant?
What are the disadvantages of a hollow stem to the plant?
Where are the spines found on the stem? What do the spines do for the plant?
Why are the parts so small at the tip of the vine?
How do you think they get bigger? How can you test your idea?
Compare the growing tips of the sprout [from Investigation 10] and the vine. Why do you think a plant only grows longer at the tips?
How does a pumpkin plant use tendrils? Why is this important to the plant? [You can go out and look at the tendrils on your pumpkin plant.]
Look back at Investigation 10. How has the stem changed from that of a sprout?
What’s In a Leaf?
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?
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.
Question: Do pumpkin leaves have layers?
Big young leaf from a pumpkin plant
Paper towel (Not all paper towels will do this. I used Viva Towels.)
Pint glass jar
Step 1: Open your Science Journal, write “Investigation 14” and the date.
Step 2: Put a small piece of tape [about 1.5cm long] on the top of the pumpkin leaf between the major veins. Press all but one corner down firmly on the leaf.
Step 3: Starting with the loose corner, pull off the piece of tape, attach it to the center of a slide and label the slide.
Step 4: Put another piece of tape on the same spot, press all but one corner down firmly, remove it and put it on a slide. Label the slide.
Step 4: Turn the leaf over and do two more pieces of tape putting them on slides. Label the slides.
Step 5: Examine the slides with the microscope. The first pieces of tape on top and bottom may just have leaf hairs and debris on them. The second pieces should have cells from the top and bottom layers of the leaf. Draw what you see.
Step 6: 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. 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 leaves are easier to do.
Step 7: 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 8: Examine these slides with the microscope. Try to see the cells from the inside of the leaf.
Part 3: Chromatography
Step 9: Cut a piece of paper towel about 3cm wide and 3cm longer than your jar is tall.
Step 10: Draw a line across the piece of paper about 3cm from the end.
Step 11: Put a piece of leaf over the line and rub it with the penny to leave a dark green spot on the paper.
Step 12: Attach the other end of the paper to the center of a pencil with some tape.
Step 13: Pour about 2cm alcohol in the jar
Step 14: 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 15: 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.
Describe and draw the cells from each piece of tape
Describe and draw the cells from the torn piece of leaf
Describe what you see on the paper towel
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?
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?