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1. How do different conditions affect the speed at which fruit and vegetables ripen?
Temperature, light, placement in sealed bags, exposure to other ripe fruit--all have different effects on different fruits and vegetables. Design an experiment to test two or more of these variables.
Background Info: Ethylene gas is the ripening agent that many fruits and vegetables produce naturally. Ethylene causes them to ripen--and then overripen. While refrigeration and humidity slow the effects of ripening, they don't stop the production of ethylene gas. The more the fruit ripens, the more ethylene gas it makes. This has a big effect on how--and when--farmers harvest their fruits and vegetables for market. Most commercial tomatoes are picked before ripening is completed, so the fruit won't spoil before it gets to your market. But picking early also means the tomato spends less time on the vine, where ethylene would help build more of the sugars and acids that create tip-top tomato flavor.
2. How do different types of fertilizers affect plant growth?
Fertilizers differ in their amounts of the nutrients nitrogen, phosphorus and potassium. Get different fertilizers from a garden shop or nursery and apply them to groups of the same plant. Do the different fertilizers change how the plants grow? You could measure height, width, number of leaves, how fast the plants grow, number of flowers or yield.
3. What happens when you grow sweet potatoes next to other plants?
Compare how fast the other plants grow at different distances from sweet potatoes. Remember to grow some control plants nowhere near the sweet potato.
Background Info: Allelopathy is a chemical process that a plant uses to keep other plants from growing too close to it. Some plants that use allelopathy are black walnut trees, sunflowers, wormwoods, sagebrushes, and trees of heaven.
There are several ways in which an allelopathic plant can release its protective chemicals:
- Volatilization - Allelopathic trees release a chemical in the form of a gas through small openings in their leaves. Other plants absorb the toxic chemical and die.
- Leaching - Some plants store protective chemicals in the leaves they drop. When the leaves fall to the ground, they decompose, giving off chemicals that protect the plant.
- Exudation - Some plants release defensive chemicals into the soil through their roots. Those chemicals are absorbed by the roots of other nearby plants, which are damaged.
4. How do different treatments change how fast seeds sprout?
You can find out how quickly seeds sprout under different temperatures, or after being soaked for different times or in different liquids. Or, see how one kind of treatment affects different types of seeds.
5. How close does a pesticide have to be to protect a plant?
Grow a number of groups of the same plant. Apply a Bt-based insecticide directly to the plant according to the directions on the package and at various distances from the plants. Compare the amount of insect damage to each group of plants. You might also look at how big or fast each group of plants grows.
6. How does soil pH affect the pH of water that touches the soil?
Gather different types of soil. Put some of each type in a cup and check out the pH. Then add water to the cups, and mix. Wait for the soil to settle and measure the pH of the water. Be sure you use water from the same source for each soil. Find out more about soil.
Background Info: A pH meter can be found at almost any garden shop or nursery.
The pH scale - Just about every substance is acidic, basic or neutral. The acid or base nature of a substance is measured by a pH scale that runs from 0 to 14. Substances from 0 to 7 are considered acid; substances from 7 to 14 are basic. Seven, the pH of pure water, is considered "neutral." The pH of your blood is about 7.35. Most plants grow best around pH 7.0. Some--like blueberries, azaleas and rhododendrons--like acid soil with a pH from about 5 to 6.
7. Which way is up?
Many seeds and bulbs have a definite top and bottom. What happens if you plant them upside down or sideways? Will the seeds still grow; will it take longer for leaves to start showing up?
What happens if you change a seed's direction once it starts to sprout? Many seeds like beans can be sprouted in moist cotton or paper towels. What happens if you turn the seed 90 or 180 degrees from right side up every few days after it sprouts?
You can take it a step further by using a record player turntable to simulate changing gravity's pull on seeds. You'll want to know more about the chemical auxin, which affects where roots and stems grow.
Sprout bean seeds for 3 days in moist paper towels inside pieces of folded aluminum foil.
Then tape one or more packets on the turntable and set it for 78 RPM. Allow the machine to rotate continuously for 5 days. After the 5 days are up, turn off the record player and without changing the position of the foil, open them up and observe the beans.
The rotating turntable creates a gravity with an outward force instead of the normal down.
8. Roots Restrictions
Does the amount of room a plant has for roots make a difference in how big a plant will grow, regardless of how much fertilizer the plant is given? Plant seeds in a variety of different-sized containers using vermiculite or other soil-less material, so you will be able to give each plant a measured amount of fertilizer. Or plant a number of plants in the same size containers and vary the amount of fertilizer and see what happens. Be sure to use small enough containers so that root growth really will be constricted.
9. Can different colors and types of cloth attract or repel insects from plants?
Plant a number of groups of the same type of plant near each other, but far enough apart to surround each set with several feet of fabric. Or select several of the same kind of bush in one yard. You want to use the same type of plant in the same place, so all of the plants will have the same potential for insect damage.
Surround each group of plants with a different color fabric. Be sure water can penetrate the fabrics. At set intervals, record all the insects you can find on each plants and any signs of insect damage on the plant. It is a good idea to check reference sources for common insect problems of the type of plants you are using.
10. The effects of light on seedlings germination
How do light and dark conditions affect the germination and growth of seedlings?
Materials: 20 bean seeds, 2 Ziploc bags, 2 damp paper towels, desk lamp.
Procedure: Separate bean seeds into two different piles with equal number of seeds (10 seeds in each pile). Wet the paper towels until completely dampened. Place the dampened paper towels in the Ziploc bags, and then place 10 seeds on top of the paper towels in each bag. Make sure the seeds are on the paper towel in the bag and close the bag, but not completely (about 3/4 way closed). Wrap one of the Ziploc bags completely in aluminum foil. Leave the other one uncovered. Place both Ziploc bags under a desk lamp. After 7 days, check the bag that has been in the light as well as the bag that has been wrapped in aluminum foil. Compare the germinated seeds. You should definitely see a difference between the two. You should note mainly the color and stem length differences between the seedlings that germinated in light and those that germinated in darkness.
What differences did you observe between seedlings that germinated in the light and in the dark? (color of leaves, length of stems, etc.) What caused those differences?
11. What affect does the brightness of light have on the growth rate of a plant?
How do light and dark conditions affect the germination and growth of seedlings?
Materials: Greenhouse or sunny window sill, 10 bean seeds, 10 small pots, water, ruler, potting soil, pencil.
Procedure: Fill the 10 small pots with equal amounts of dampened potting soil. With a pencil, make holes about 2 centimeters deep in each pot. Place the 10 bean seeds, one per pot, and cover the seeds with some of the soil. Place 5 of the pots in the greenhouse or on a window sill on the sunny side of the house. Place the other 5 on a window sill that does not receive bright sunlight. Seeds will germinate within 7 days, and you can begin making stem measurements. Take stem measurements for 14 days. Be sure to water the plants as needed. Note the difference in stem length for each set of plants, and write down your observations.
What differences did you observe between seedlings that grew in the bright sunlight compared to less bright light? (color of leaves, length of stems, etc.) What caused those differences?
12. Does crowding affect plant growth?
Determine the effects of growing plants close together vs. growing plants farther apart.
Materials: 6 medium-sized pots, 10 bean seeds, potting soil, water, ruler, large measuring cup, desk lamp, pencil.
Procedure: Fill all pots with an equal amount of potting soil. Be sure that the soil has been dampened with water. Using a pencil, make 5 holes about 2 centimeters (cm) deep in the soil of one pot. Place seeds in each hole making sure that they are spaced relatively close but equal distance from each other within the pot. Place the remaining 5 seeds, 1 in each of the remaining 5 pots, about 2 cm deep. Cover the seeds with soil. Place all the pots underneath a large desk lamp so that each pot receives full light. Be sure to water each plant as needed. The seeds will germinate in about 7 days, and you will be able to begin making stem measurements. Take measurements for 14 days. Note the difference in stem length for each plant and write down your observations.
What differences did you observe between seedlings that were crowded and those that were not? (color of leaves, length of stems, etc.) What caused those differences?
13. Does Colored Mulch Affect Soil Temperature?
To determine if different colored plastic (or mulch) on the soil surface affects the temperature of soil.
Materials: Digital thermometer; potting soil; 8 pots; colored mulch in black, white, and red; window sill with full sun; tape.
For the colored mulch, you can use different paint colors to paint black plastic, or you might use different colored plastic bags or mulch from the store.
Procedure: Fill pots with equal amounts of soil. Place 2 uncovered pots on the window sill where there is full sun. Cover 2 pots with black plastic, 2 pots with white plastic, and 2 pots with red plastic. Make sure the plastic covers the top of the pot, and tape it to the pot. Place these pots on the window sill. In 24 hours, record your first temperature measurements. You can do this by sticking the temperature probe in the drainage hole of the pot. For 10 days, record the temperatures for each pot in the morning and afternoon. Note the differences in temperature among the colors, and record observations.
Which pot had the highest soil temperature? What color kept the soil the coolest? Why do you think that some mulch colors make the soil hotter or cooler? How does this affect plant growth (see project 14)?
14. Does Colored Mulch Affect the Growth Rate of a Plant?
To determine if colored plastic (mulch) will affect the stem length of plants.
Materials: 8 pots; 8 bean seeds; colored plastic in red, black, and white; ruler; water; toothpicks; greenhouse or window that receives full sun; tape; potting soil; pencil; small cup.
Procedure: Fill pots with equal amounts of potting soil. Make a hole about 2 cm long in each pot using a pencil, and place 1 seed in each pot. Cover seed with loose soil. Mark where you planted the seed with a toothpick. Cut plastic in pieces large enough to cover each pot. Cut a smaller hole in the center of the plastic and cover pot with the plastic. Be sure the smaller hole in the center is where your toothpick is so the seed is exposed to light. Take the toothpicks out after you have taped the plastic to the pot. Do this twice for each of the colors. You will have 2 red, 2 black, 2 white, and 2 uncovered. After the seeds have emerged through the soil (about 5 days), take stem measurements. Measure the stems in each pot for 14 days. Do not forget to water your plants during the experiment. About every other day, use a small cup and pour a small amount of water in each hole where the plant is growing. Note the differences in height among the plants grown over different colored plastic.
Which plastic helped produce the longest stem length? Which plant had the shortest stem length? What do you think this tells us about how a plant uses reflected light?
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