Lesson 4, Spring 2014 – Plants & Water
Introduction (group):
Q: What are we learning about this quarter?
A: Water (may also get bubbles, soap, boats, etc.)
Q: What have we learned about water?
A: That it has special properties – like surface tension, which is caused by all the molecules of the water
sticking tightly to each other.
Q: Is water important for living things? What would happen to you without water?
A: Yes, water is important! Living things, like people, need water to survive.
Q: Do plants need water? What happens if you forget to water a plant?
A: Yes, plants need water. This is why we have to water our gardens and lawns in California in the
summertime. If you forget to water a plant, it will wilt, dry out, and die.
Q: How does water get into a plant? Can plants drink?
A: Water is taken up by the roots of the plant, where it is absorbed.
Q: What happens to the water inside of the plant? Do plants have blood and veins like people?
A: Plants don’t have blood, exactly, but they do have veins that they use to carry water and nutrients to
the stems and leaves.
Q: Why do plants dry out when it is hot? How do they lose water?
A: Water evaporates (leaves the plant as a gas) through tiny holes in the leaves.
Q: Why would the plant want this? Why would it have holes in its leaves?
A: Losing water from the leaf surface helps the plant cool down, like you sweating on a hot day. But for a
plant, it is even more important. Losing water through the leaves pulls new water and nutrients up
through the veins, in a process called transpiration. If this didn’t happen, water would stop moving
through the plant – sort of as if your heart stopped pumping blood through your body.
Q: Why does losing water from leaves pull water up from the roots and stems?
A: For the same reason that we saw surface tension in other lessons – because water molecules like to
stick together. When some of them are lost from the leaf, they tug on others further down in the stem,
pulling them up in a long “chain.”
We will watch a short (1-minute) video that illustrates how water molecules stick to each other to move
through the plant: https://www.youtube.com/watch?v=At1BJJDcXhk.
Part 1: Celery and Food Dye (small groups)
Introduction: We will use food dye to trace the path of water through a celery stalk. The dye will be
sucked up from the base of the celery to the top through the xylem elements (veins of the plant). This
allows students to see transpiration in action, and also colors the vein system so it is easily seen.
The basic procedure is to place a celery stalk in water colored with food dye, then let it sit for awhile (at
least 15 minutes) to allow the dye to move up through the veins. Most students will have already seen
this experiment at some point, or be able to predict what will happen (the celery will turn colors). We
will do two variations on this today:
Leafy or Leafless? Students will make a prediction about whether dye is going to move faster up a celery
stalk with leaves, or one that is leafless. (We would expect the one with leaves to go faster, because
there is more surface area for evaporation to occur over.)
1. Get two celery stalks of the same approximate length, one with leaves and one without. These
should be 3-4 inches long (in the interests of the dye reaching the top by the end of the class).
2. Fill a cup with about an inch of water each.
3. Add food coloring (~5 drops). Blue works best, red is also okay.
4. Place the leafy and leafless celery stalks in the cup. Note the time, and how the stalks look (no
color yet).
5. Check the stalks at 5-10 minute intervals to see if color is visible at the top yet. The stalk with
leaves should show faint color in 10 or 15 minutes, and clear color in 30-45 minutes. The stalk
without leaves may or may not show detectable color during the class period.
Two-Tone Celery. What would happen if we split the bottom of the stalk on a leafy piece of celery and
put each side into a different color dye? Ask students to make predictions (half red, half blue? purple?
blue and red patches?), and think about what the prediction would mean for the path of water in the
stem. I.e., does it just move straight up? Does it cross over between sides?
1. Get a leafy celery stalk (again 3-4 inches long) and carefully cut the bottom 2” in half with a
plastic knife.
2. Get two cups and fill them both close to the brim with water.
3. Add food coloring (~10 drops) to each cup, using blue and red.
4. Place the celery so that each half of the stalk bottom is in one of the cups. Note the time and
how the stalk looks.
5. Check the stalk at 5-10 minute intervals to see if color is visible at the top yet. The leaves should
come out half red and half blue, corresponding to the sides on which the two cups are placed,
indicating that water just moves straight up (and does not cross over much within the stem).
Once the leafy celery has clearly turned color, if time allows, students can cut it up and examine the
veins. If they cut sections across the stem, they should be able to see the veins as small, bright dots in a
semi-circle. If they cut sections the long way, they should be able to see the veins as long, tough threads.
Students can also look leaves and/or sections on the microscope if they are interested. Sections need to
be very thin to work well, ideally cut with a razor, and should be mounted on a slide with a coverslip and
some water. I will have razors that tutors can use to cut sections (not to be used by students!).
 Microscope image of celery leaf with blue food dye in veins
Part 2: Leaf Pigment Chromatography
This part is not really about how water moves in a plant, but instead takes advantage of the properties
of water (and rubbing alcohol) to look at the different pigments, or color compounds, in a leaf. Based on
http://www.education.com/science-fair/article/leaf-pigment-comparison/.
Intro: Ask students what color a leaf is. They’ll probably say “green.” Ask if all leaves are exactly the
same green, and whether leaves are still green in the fall. Hopefully, these questions will make them
consider that leaves may have more than one color in them. Tell them that we are going to use water
and rubbing alcohol to see the different pigments that are in a leaf.
Procedure:
1. Have students collect leaves from three different plants. (Some leaves will be provided, but they
can also get ones from the garden). Try to pick leaves that are different colors – brighter/darker
green, reddish, etc.
2. Get two strips of chromatography paper for each leaf. Wrap the leaf around the edge of a coin,
and use it to “press” a stripe of green across the chromatography paper, about half an inch from
the bottom. Get the stripe as dark as possible. Do this for two strips of paper for each leaf.
3. Using pencil, label the strips (e.g., with the initials of the student who collected the leaf.)
4. Fill one plastic cup with about 1 cm of water, and another with about 1 cm of rubbing alcohol.
Place three chromatography paper strips in each cup (one for each leaf), with the pigment line
above the liquid surface.
5. Leave the samples for 10-30 minutes (go on to part 3), then check back to see what has
happened to them. Ask the students:

Did the “green” of the leaf separate into different colors?
It should separate, at least some. Orange and yellow colors (carotenes and
xanthophylls) should run fastest, then greens (chlorophylls), then reddish-purples
(anthocyanin). Explain that these different-colored things are called pigments and
help the plant capture light.

Did all three leaves have the same colors in them, or were they different?
This will depend on the plants the kids pick. The sample leaves from daisies should
show definite chlorophyll and anthocyanin bands.

Did water or rubbing alcohol work better to separate the colors?
Rubbing alcohol will generally work better. Explain that the reason the colors move
different speeds is because of how well they “stick” to the liquid that is moving up
the paper. The colors that stick to the liquid best will move fastest, while the ones
that stick to it worst will move slowest. In general, plant pigments stick to (dissolve
in) isopropanol better than in water.
Part 3: Leaf Stomata Peels (small groups)
Introduction: Water evaporates through tiny holes in the leaf surface. These are actually not just plain
holes. They are pairs of cells with a hole in the middle, which can open and close depending on
conditions (e.g., allowing the plant to lose less water if it is very dry/hot). These are called stomata. We
will use nail polish peels to look at stomata in different plants from the garden.
Procedure: Instructions are modified from http://www.biologyjunction.com/leaf_stomata_lab.htm.
1. Obtain three leaves from different types of plants in the garden. Remember or write down what
kind of plant each leaf came from. Hint: leaves that are not very fuzzy will work best.
2. Paint a patch (~1 cm2) of clear nail polish on the underside of the leaf surface being studied.
3. Allow the nail polish to dry completely. Takes 3-4 minutes or so.
4. Tape a piece of clear cellophane tape to the dried nail polish patch.
5. Gently peel the nail polish patch from the leaf by pulling on a corner of the tape and "peeling"
the fingernail polish off the leaf. This is the leaf impression you will examine.
6. Tape your peeled impression to a microscope slide.
7. Examine the leaf impression under a light microscope at 400X. Make an entry in the chart to
describe what you see.
8. Repeat for your other leaves.
The nail polish impressions seem to work pretty well, but there will also be some example slides in case
the groups are having trouble getting clear impressions.
If you have extra time: try the same process with other types of plants, or with other parts of the plant
(that aren’t the undersides of leaves). Can you find stomata on the other side of the leaf? The stems?
Flower petals?
Examples (using the method above, a few stomata circled):
Carnation
Tree
Part 4: Leaf Rubbings (small groups, minimal guidance needed)
Background: You don’t need a microscope to see the veins in plant leaves; in fact, for many species you
can see the major veins with your eyes, and capture the vein pattern nicely by doing a leaf rubbing with
crayon or chalk.
Procedure: This is an activity that the kids will probably enjoy, and which does not need a lot of tutor
guidance. Basically, kids should collect leaves from different plants in the garden and bring them back to
the classroom. Then, they will place the leaf under a sheet of thin paper (e.g., printer paper) and rub a
crayon over the top. This should capture an image of the leaf where the veins stand out clearly. This
works most nicely for big tree leaves, but the kids can try different kinds and see which are better or
worse for making rubbings.
Some questions to ask the kids:



What pattern do the veins form? Are they organized?
Do all plants have the same pattern of veins, or are they different?
If you look at two leaves from the same plant, do they have the same vein pattern?
Example of how the rubbings can look (http://www.filthwizardry.com/2009/11/leaf-rubbing-and-paintmural.html, for a tree leaf):
Leaf Stomata Chart
Type of plant
Picture of the leaf under the microscope
Stomata big or small?
How many stomata?
(Count, or none/some/lots)