These experiments will teach you a few different things about plants...
Erosion is what happens to soil on the ground when it is moved by a natural force (not people). Soil is made up of very small pieces of organic matter and particles of rock. These can easily be blown away by wind, washed away by rain or flooding or fall downwards from a hillside.
What do you think might happen if all the soil became eroded, or disappeared from the ground? There would be nowhere for plants to grow, or worms to live and the animals that depend on plants (including people) would no longer have a source of food or habitat.
Plants are an excellent way to keep soil in its place. Their roots anchor the soil and prevent it from washing or blowing away. If there were no plants on a hillside, the soil would tumble down and fall on anything below, even houses!
Here is an experiment you can do at home that will show you how plants and their roots keep soil together.
You need: a packet of radish or mustard seed from the garden shop, 2 paper cups and 2 cups of garden soil.
Soak six seeds in water for 2 or 3 days until they begin to sprout (leafy bits stick out). Put the seedlings in a paper cup that is 3/4 filled with soil. Let the seedlings grow for 2 weeks and water them, but not too much. If plants are overwatered their roots 'drown' because they can't draw in enough oxygen.
After 2 weeks, try to pull out one of the stems. You'll notice that most of the soil comes up with the plant. This shows how good plants are at holding onto soil.
Plants are called primary producers because they are the only living things on earth (except for a few types of algae) that can take energy from the sun's rays and convert it into food energy. All other living things on earth either eat plants or eat something that eats plants.
When plants are making their own food using sunlight, water and carbon dioxide (a gas in our atmosphere), they produce sugar molecules (their food) and oxygen. We all know that people and animals need oxygen in the air to breathe. We use oxygen in each of our cells and without it we would die.
Here is an experiment to help you see that plants really do make oxygen! This one is for advanced botanists-in-training, or you could convince Mom or Dad to help you out.
You need: 2 small elodea plants (from your fish tank or aquarium supply store), 2 wide-mouthed jars, 2 test tubes, 2 glass funnels, several toothpicks.
Place one elodea in each jar. Invert (put upside down) a glass funnel over each plant. Now fill each test tube with water. Holding your thumb over the opening of the test tube, invert it. Lower it under water in the jar; take your thumb away and place the test tube over the inverted funnel. Do the same with the second jar. Click here for a picture.
Now comes the waiting: Place 1 jar in sunlight for a day. Place the other in a closet (we in science call this the control! It proves that the results are valid, and not a fluke. If the same results happen to the tube that wasn't tested with the plant, then whatever happened is not because of the plant.). At the end of the day remove the test tube very carefully from the jar that was in sunlight. Keep your thumb over the test tube opening. Now light a toothpick (or have Mom of Dad do this) so that it flames. Blow out the flame and immediately (still glowing) put it in the test tube. Do the same thing with the test tube from the dark jar.
You should notice that when you put the glowing toothpick in the sunlight test tube, it burst into flame. This is because the test tube contained the oxygen that the plant produced while photosynthesizing in the sunlight. The dark test tube did not flame, and therefore did not have any oxygen, meaning the plant did not produce oxygen without the sun.
A scientist called Priestley first proved in 1773 that plants produce oxygen in his experiments using plants and mice in jars. Those mice which lived in jars with plants survived because the plants made oxygen!
Leaves on many trees change colour according to the season. You may have noticed that maple leaves are green, but can be red, orange or dark purple in the fall. (Except for "evergreen" trees like pines!)
The reason behind this is simple: plants produce their own food from sunlight using a molecule called chlorophyll. Chlorophyll absorbs red light and reflects back green light. The light from the sun contains all colours, so we see the reflected green colour.
Plants also have different molecules that are red, orange and purple. During the warm months when there is a lot of sunshine, there is lots of chlorophyll so the other colours are hidden by all this green pigment. When the fall comes, the nights get longer and the tree gets ready to become dormant for the winter (sort of like hibernating bears do) they stop photosynthesizing. This means that there is less green to hide the other colour.
Here is an experiment to help you see how colours change in leaves.
You need: a tree with leaves that turn red in autumn, aluminum foil or heavy paper and masking tape.
Before the leaves turn colors in the fall, find a maple tree, flowering dogwood, sweet gum, or other tree or shrub that you know will turn bright red or purple. Find several leaves that receive bright sunlight, and cover part of them with foil or heavy paper and tape.
After
the leaves have changed color, remove the covering and observe the different
colors underneath. These are the colors that were in the leaf all summer. The
bright reds and purples are only made in the fall, with exposure to light.
Plants
and
gravity
Did you ever wonder how plants know to grow with their leaves climbing up towards the sky and their roots pushing down into the soil? What would happen if you put a plant in soil upside down?
Here is an experiment to test what will happen.
You need: ten radish or bean seeds, 2 jam jars, blotting paper, paper towels, string, tap water.
Soak 8 seeds in water overnight. Line the inside of your jars with blotting paper that you or your parents have cut to fit. Fill the middle of each jar with crumpled paper towel. Saturate the blotting paper and the paper towel with water and pour off any extra water that didn't soak in. Be sure to keep the paper moist or your seeds will not grow. Put four soaked seeds between the glass and the blotting paper at the top of each jar. (you don't have to feed the seeds because they already contain food) Place the seeds in all different positions - horizontal, vertical and diagonal.
After they have grown 2.5 cm above the top of the jars, set one jar on its side. Have a look at your sideways plant a few days later. Are the stems growing upwards? They should be.
Stems and leaves grow in the direction of light and away from the force of gravity. This is called negative geotropism because the plant is growing away from the force of gravity.
Can you think of an example of positive geotropism? What about the roots of the plant? They are growing towards the force of gravity. How does it work? Plants have hormones that respond to the pull of gravity and tell the plant which way to build cells and grow. So now you know that you can't plant a seed upside down.
Click here for an experiment on phototropism (Can you guess what that is?)
How does water reach the top of a plant or a tree? Try this experiment.
You need: a cup half-filled with water, blue or red food colouring, a stalk of celery with some leaves on it.
Mix a teaspoon of the food colouring with water. Cut the celery stalk about 2 cm from the bottom to expose a fresh end. Stand the stalk in the water. Leave the celery in the water for an hour or two and you'll notice the dye gradually colouring the tips of the leaves.
Take the celery out and cut the stalk through the middle. You'll see a row of tiny circles outlined in colour, like rings. They are the ends of fine long tubes that travel the length of the stalk. The coloured water travelled up the tubes to reach the leaves.
How do plants move water up? They don't have muscles, but they still move water. This is kind of tricky, so you may want to read this more than once. Water from the leaves is evaporated into the air by the heat from the sun (just like sweat evaporates from your skin on a hot day). Water molecules inside the plant hold very tightly together almost like a chain, so when some are taken from the top, others move up like they are next in line. Because they are squished into such narrow tubes (like you saw in the celery) they have enough strength to pull all the water molecules behind them. This only works if the tubes are full with water to begin with, so trees and plants have liquid-filled tubes from their days as seedlings.
Plants are an important resource for medicines people use to cure illnesses. Here are a few medicines that come from plants:
American
Ginseng - used for general health
Ginkgo biloba
- an ancient tree that contains chemicals
that can increase energy
Willow
- contains a compound called ASA (acetasalicylic acid) that is used in Aspirin
to cure headaches
Witch Hazel
- used in skin ointment
Cedar
- contains Vitamin C, used by native Americans to cure scurvy (disease where if
you don't have enough Vitamin C your teeth and gums begin to hurt and your teeth
can fall out!)
Red Elm
- bark contains an ingredient used in cough syrups
You too can explore and record plant biology!
Make your own Herbarium!
A herbarium is not a place for herbs! It's a collection of dried plants and leaves that scientists use to identify species and study the biology of trees and other plants.
Click here to make your own Herbarium
