Weathering: Plant Roots

 

Plants, specifically plant roots, are one source of weathering.  Cracks in driveways and sidewalks often provide evidence of this, but it's simple to watch it take place within your classroom. 

You'll need some Plaster of Paris*, seeds** and a small disposable cup or cupcake paper.

Mix the plaster according to the package instructions (usually 2 parts plaster to 1 part water).  Pour the plaster into your vessel. 

Poke two or three seeds into the plaster.  Place in a spot where it won't be disturbed while the plaster sets and the seeds germinate (there's enough moisture in the plaster for the seeds to begin germinating, no need to add anything). 

Within a day my seeds had swollen and begun to germinate.  The force the seed exerted was enough to crack the plaster. 

Now think about what happens in a driveway or sidewalk... a crack forms in the surface, seeds blow or fall into the crack, a bit of rain falls and the seeds begin to germinate.  The force of the seed germinating and the roots taking hold forces the more cracking.  Now there's a larger crack into which more seeds can gather and cause further cracking.  If nothing is done to curb the problem, eventually the sidewalk or driveway will be dessimated. 

*FYI Plaster of Paris does have a limited shelf life.  If it gets too old, it won't set up properly and you'll have a crumbly mess.

**I've mentioned it before, but dried beans (like you'd use to make soup or baked beans) will germinate.  They're cheaper to buy in a large quantity than garden seeds and they can be found easily year-round.

Let Us Weigh Lettuce

An easy lesson in measuring mass, collecting data, graphing (if you wish), percentages and plants. And a great experiment to start at the beginning of the school year.

You'll need a leaf of lettuce and a balance.  The precision of an electronic balance is nice for this particular activity, if you have one available.

If you have a balance that can remain dedicated to this activity, you can place the lettuce leaf right on it.  Record the mass.  Each day when the students come to class, they should record the mass of the lettuce.  Continue recording the mass every day for a month.

[If you cannot dedicate a balance to the activity, you'll need to first find the mass of a weighing paper.  Record that, then place the lettuce on the weighing paper and record that mass.  Lift the paper with the lettuce on top and keep in a safe place while the balance is being used elsewhere.  Return the paper and lettuce to the balance each day to find the mass.  You'll have to subtract the mass of the weighing paper from each measurement to get the mass of the lettuce.]

Once you've collected all the data, you can graph it if you wish.  Is the water lost at the same rate throughout the month or does it change?

You can also determine how much of lettuce (by mass) is water.

Mass of lettuce at start - Mass of lettuce at end = Mass of water

(Mass of water / Mass of lettuce at start) * 100 = % of lettuce mass that was water

If you've caught your students' attention with this one, you can proceed to follow the same procedure to find the water content in other items.  Maybe your students will want to compare the water content in different types of lettuces or different types of leaves or different types of fruits or vegetables.  Lots of possibilities - you could have something going every month of the school year!

Dandelion Curls

It's spring in the northeast and that means (at least in my yard): Dandelions!

Did you know you can use dandelion stems to teach a simple (and pretty fun) lesson in osmosis as well as introducing the terms hydrophilic and hydrophobic?

Separate the stem from the flower and pull the stem into long strings.

Drop the strings into a tub of water and watch the stems curl up into all kinds of fun shapes! 

 If you drop the stem pieces one at a time, you can actually watch the curling process take place within just a minute or two.  Or you can dump a whole bunch in and have fun sorting through the results!

 What's happening?

The inside of the stem is hydrophilic, which is sometimes referred to as water-loving.  It's the part of the plant that absorbs the water.  And when it's placed into a tub of water, there's a whole lot of water to absorb!  The water moves into the cells through the process of osmosis. 

The outside of the stem is hydrophobic - it repels water.

The cells that make up the inside of the stem absorb so much water that they swell up.  The cells on the outside of the stem stay the same size.  The increasing size of the cells on the one side of the stem forces the stem into curls of various shapes.  

There's definitely something fun about sitting outside on a warm day and watching the curls form!  And if you can't be outside, grab some dandelions on your way to school and bring a bit of the outdoors in for your students.   

PS The idea of one side expanding more than the other side is similar to the way a bimetallic strip in a thermostat works.  The expansion is caused by temperature instead of water movement and it isn't as drastic as this, but it's conceptually similar. 

It's Pumpkin Time!/The Apple Pie Tree: Seed Germination

It's Pumpkin Time! follows the growth of a pumpkin - from seed to large, orange orb.

The Apple Pie Tree follows the growth of an apple tree through a season - from a bare-branched tree to one loaded with heavy fruit.

Either one, or both, make a nice accompaniment to the seed germination activity we've done before. 

This time, use seeds straight from an apple or pumpkin.  That can provide an added lesson for students - we regularly refer to that part of apples (and other fruit) as the seed, but there are students (young and old) out there who don't truly understand that those seeds will sprout and grow into a new plant. 

Following the same procedure as before...

Fold a paper towel in quarters.

Wet the towel and wring out as much water as possible.

Slide the towel into a zip-top bag.

Place the seeds in a row, about an inch from the bottom of the bag. 

Push the air out of the bag and seal the top. 

Put the bag in a safe location (you can even hang it) and observe.

After completing this activity, you and your students might want to see what other seeds, taken directly from food you eat, you can get to germinate.  Be forewarned - seeds that have been cooked in some way won't germinate, and some seeds need to go through extra steps before they'll germinate, like tomatoes, but you should find quite a few that you can get to grow.

Tops & Bottoms: What Parts of Plants Do We Eat?

Tops & Bottoms is a cute story of a bear and a hare.  Bear is lazy and finds hare's offer to share the harvest of his garden with him a good deal.  When deciding how to split the harvest, hare asks bear if he prefers "tops or bottoms".  Bear chooses the tops, and is quite dismayed when hare's half of the harvest yields carrots, radishes, and beets while his half is a pile green stems and leaves.  The silliness continues for two more harvest seasons.  Will bear get some food out of this deal by the end? 

It's a fun story that points out the different parts of plants that we eat.  Challenge your students to plan a meal that includes the following plant parts:

• Root
• Stem
• Leaf
• Flower
• Fruit
• Seed

 Or, if you're feeling ambitious, you can assign each student to bring in one item and you can have a lunchtime plant salad bar, in which students have to build and eat a salad that contains all of the plant parts. 

Here are some items that could be used for each of the plant parts.

Roots

beet

carrot

radish

Stems

celery
potato (tubers are considered a modified stem, not a root)
onions (bulbs are considered a modified stem, not a root)

paper plates and napkins (for serving)

Leaves

lettuce

spinach

Flower

artichoke heart
broccoli (this could also count in the stem category)

edible flowers

Seeds

sunflower seeds

lima beans

corn

soybean (edamame)

peas

Fruit (these are broken down by different classifications of fruit, as might be discussed with older students, with younger students you'd just stick with "fruit")

pepo - cucumber, pumpkin, melon

drupe - peach, olive, cherry

berry - tomato, grape
pome - apple, pear

Others (if you're interested)

ferns - fiddleheads

gymnosperms - pine nuts

sprouts - bean sprouts, alfalfa sprouts

grasses - rice, wheat, oats

Plants: Does it Matter Which Direction you Plant a Seed?

Take the basic procedure used for observing seed germination one step further.

Prepare two bags.  This time, across the bottom of each bag, mark 4 arrows, one up, one down, one to the left and one to the right.

Place a bean above each arrow, so that the concave part of the seed is pointing in the direction of the arrow.

Hang the bag on the refrigerator (or on another vertical surface) and leave the other on a flat surface and observe.

Observe what happens with the seeds in the different bags. 

Seeds rely on gravity to help them grow the "appropriate" way.  When the bag is hanging vertically, the seeds will orient their roots so they all go down.  Because the roots can't go "down" while the bag is laying flat, the roots in that bag will grow in whatever direction they can.

Microscopes: Elodea Lab

Elodea is an aquatic plant that can be found at most fish stores. It is great for looking at under the microscope because the leaves are so thin, only a couple of cell layers thick and light can pass through the leaf.

Place an elodea leaf on a clean slide. Place a drop of water on the leaf and then the cover slip. View under the microscope. You will note the regular, retangular shape of the plant cells, the cell wall, the chloroplasts, and the nucleus.

Plants: Grow a Carrot Top

Sometime, when you cut up some fresh carrots, try this activity.

Place the cut off carrot top on a small plate.  Pour some water on the plate.

Leave the plate in a warm, bright spot for a few weeks and observe - a new carrot starts to sprout!

Microscopes: Onion Skin Lab

One variety of plant cells…

Cut some onion into small pieces and separate each layer. Each layer of the onion contains a thin layer of cells that can easily (usually!) be peeled off the rest of the onion. Place the layer of cells onto a clean slide, make sure not to fold the onion skin over on itself. Place a drop of iodine on top of the onion skin and then a cover slip. View under the microscope. You will note regular, rectangular shape of the plant cells, the cell wall and the nucleus.

One question to ask your students…. They are plant cells, why are there no chloroplasts? [Think about where onions grow…]

Chromatography: Spinach

Is spinach colored by purely chlorophyll (green pigment)? Or are there other pigments hiding in there, masked by the presence of chlorophyll?

Before beginning, if you aren't familiar with chromatography, you may want to review the basics, here.  

Use a quarter to rub spinach into a piece of filter paper, a couple of centimeters from the end of the paper. (If you’re doing this at home and don’t have lab grade filter paper, have no worries! A coffee filter works beautifully (that’s actually what I used with my students – why spend the money on expensive filter paper!) and even paper towels can be made to work).

 Put about a centimeter or so of rubbing alcohol in a cup.  Place the filter paper in the cup, so the end is in the alcohol, but the spinach transfer is above the liquid.  Allow it to sit.

Now, here's where it would be nice to have a picture of the finished chromatograph.  But, milk spilled on mine before I snapped a picture and I haven't had the opportunity (or spinach) to recreate it.  It's subtle, but you can find both green and yellow pigments on the paper, if you look carefully. 

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Presented at the 2003 New Jersey Science Convention.

Plants: Roots: Radish Seedlings

Radishes are perfect for this... they sprout and develop roots SO quickly!

About 3 or 4 days before you'll need them, sprinkle some radish seeds on a damp paper towel.  Keep the towel moist (a spray bottle with a fine mist is good for this) in the interim.

  

On lab day, have students observe the radish roots.

What is the fuzz on the root?
What does it do for the plant?
Draw the seed and developing root - label the first leaves, devleoping root, and root hairs.


A few notes, from personal experience
--Keep the radish seeds covered with another damp paper towel.
--Keep the seeds in a place where you will see them so you will keep them moist - they will need water a couple times a day - they dry out super quick!
--Be very careful when removing the seedlings from the paper towel - it doesn't take much for the root to break off. 

Starches in Plants

We previously tested a variety of food products for starch and hopefully you reached the conclusion that starch is found in food that is derived from plants.

Unfortunately, it can be hard to test for starch in a lot of plants because of their natural pigments.

Here’s one technique:

Soak a piece of spinach in rubbing alcohol overnight.  You can speed up this process by heating the rubbing alcohol.  Just be careful - alcohol is flammable. 

Pat dry. (Don’t rinse it).

Test with a drop of iodine. Remember black indicates the presence of starch.

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Presented at the 2003 New Jersey Science Convention.

Plants: Seed Germination

Each student will need a sandwich-size zip-top bag, a paper towel, and several seeds (dried beans from the grocery store will work, as well as regular garden seeds).

Get the paper towel wet and then wring out all the excess water. Flatten the towel and fold in half and then in half again (in the opposite direction this time). Slide the towel into the bag. Place the seeds in a line about an inch from the bottom of the bag (about an inch between the seeds). With the bag lying flat on the table, squeeze out as much air as possible and seal the bag. Now observe. You may wish to have students make observations in a journal. With a good seal, the bag should have enough moisture and not require any additional water.

I prefer this method over planting seeds in dirt for two reasons:

1 - No dirt=much easier clean-up.

2 - You can actually wantch the seed germinate.... which part emerges first, where does it emerge from, etc.

Plants: Celery in Colored Water

You may have done this as a kid!

Cut about an inch off the end of a stalk of celery, so you have a fresh end. Place the celery in a cup of colored water and allow to sit for a few days while you observe.

Because the water is carrying food dye with it, you will be able to see the path the water takes as it moves up the stem and into the leaves. This provides a great visualization of the vascular system contained in most plants.


It’s also fun to place white daisies (or other white flowers) in colored water and watch the petals change color. I’d recommend doing the celery first, because you can see the xylem in the celery stem and therefore see how the water travels up the stem.

Plants: Dissect a Seed

So simple, but brings the textbook picture to life…
Soak dried beans (from the grocery store) in water overnight.

Provide each student with a seed. They can identify and remove the seed coat.

Then, split the seed open and identify the cotyledon (seed leaf) and stored food (the bulk of the seed).