Background:

The leaves, roots, and/or other plant organs of some ferns, gymnosperms, and angiosperms produce chemicals that inhibit the growth and/or germination of other plants. These chemicals could be a good survival strategy. Can the inhibitory effects of these chemicals be demonstrated?

Procedures Overview:

Working in a group, you will extract water-soluble chemicals from the leaves of one plant species. You will test for the presence of possible allelopathic chemicals by comparing the germination percentage of two different plant seeds as influenced by either your leaf extract or a control (deionized water).

1. Wear gloves whenever handling the plant leaves. Some people are allergic to chemicals in some plant leaves.
2. Obtain 20 g of your assigned leaves: eucalyptus, buckeye, sweet gum, or other plant species. Do not use stems and petioles, just the leaf blades. What is the name of the plant your group is working with?
3. Tear the leaves into smaller pieces, no larger than 1 cm (½ inch).
4. Place the torn leaves into a blender with 120 ml of deionized water.
5. Cover the blender and blend until the leaves are finely ground and the mixture is a uniform slurry (pourable like a milkshake). If your leaves are not readily ground, you may need to divide your leaves and water into smaller batches.
6. If your mixture is too thick to easily pour, add limited amounts of additional deionized water. Keep track of how much water you add. Do not add any more water than is necessary.

BiOL. 4 to Lab 24 Allelopathy 260 Procedures (continued):

7. While the leaves are being blended, place two layers of cheesecloth into a funnel that is on top of a 250 ml beaker.
8. After blending has been completed, filter the slurry through the cheesecloth to remove the larger pieces, which you can throw into the trash. Keep the filtered, liquid extract.
9. Line the bottom halves of eight Petri dishes with three layers of paper towels. Cut the paper towels to fit tightly in the bottom of each dish, so that seeds will not move underneath layers of paper when you add a liquid.
10. Use tape and a marker to label the tops of your eight Petri dishes as listed below:
- group number, date, control-1, carrot
- group number, date, control-2, carrot
- group number, date, control-1, radish
- group number, date, control-2, radish
- group number, date, extract-1, carrot
- group number, date, extract-2, carrot
- group number, date, extract-1, radish
- group number, date, extract-2, radish
11. Saturate the paper in each of the bottoms of your four control Petri dishes with 10 ml of deionized water. You should have some unabsorbed water in each dish.
12. Saturate the paper in each of the bottoms of your four extract (experimental group) Petri dishes with 10 ml of your liquid leaf extract (excluding foam). You should have some unabsorbed extract in each dish.
13. Obtain your two assigned species of plant seeds. Place ten (10) seeds of the appropriate species onto the wet paper towels of each dish. Place only one species of plant seed in each dish. Try to spread the seeds evenly. Move the dishes carefully so that your seeds are not moved around.
14. Place your two stacks of Petri dishes into the container designated by the instructor. Move the dishes carefully so that your seeds are not moved around. Keep your plates upright and horizontal; these are not cultures of bacteria!
15. You should have a total of 20 carrot seeds in your control group, 20 carrot seeds in your experimental (extract) group, 20 radish seeds in your control group, and 20 radish seeds in your experimental (extract) group.

Question:

The experimental procedures you followed have been used as a quick way to determine the presence of any potentially allelopathic chemicals in leaves. However, these experimental procedures have been criticized for not being an accurate way to determine if allelopathic effects actually occur in nature. Explain several limitations to the experimental procedures, and explain how they could be improved to more accurately determine any allelopathic effects that may (or may not) occur in nature. What would be challenges of conducting these revised experiments? [Think. Apply course concepts.]

Question

11-01-2024
Biology

High School

We appreciate your visit to Background The leaves roots and or other plant organs of some ferns gymnosperms and angiosperms produce chemicals that inhibit the growth and or germination of. This page offers clear insights and highlights the essential aspects of the topic. Our goal is to provide a helpful and engaging learning experience. Explore the content and find the answers you need!

Background:

The leaves, roots, and/or other plant organs of some ferns, gymnosperms, and angiosperms produce chemicals that inhibit the growth and/or germination of other plants. These chemicals could be a good survival strategy. Can the inhibitory effects of these chemicals be demonstrated?

Procedures Overview:

Working in a group, you will extract water-soluble chemicals from the leaves of one plant species. You will test for the presence of possible allelopathic chemicals by comparing the germination percentage of two different plant seeds as influenced by either your leaf extract or a control (deionized water).

1. Wear gloves whenever handling the plant leaves. Some people are allergic to chemicals in some plant leaves.
2. Obtain 20 g of your assigned leaves: eucalyptus, buckeye, sweet gum, or other plant species. Do not use stems and petioles, just the leaf blades. What is the name of the plant your group is working with?
3. Tear the leaves into smaller pieces, no larger than 1 cm (½ inch).
4. Place the torn leaves into a blender with 120 ml of deionized water.
5. Cover the blender and blend until the leaves are finely ground and the mixture is a uniform slurry (pourable like a milkshake). If your leaves are not readily ground, you may need to divide your leaves and water into smaller batches.
6. If your mixture is too thick to easily pour, add limited amounts of additional deionized water. Keep track of how much water you add. Do not add any more water than is necessary.

BiOL. 4 to Lab 24 Allelopathy 260 Procedures (continued):

7. While the leaves are being blended, place two layers of cheesecloth into a funnel that is on top of a 250 ml beaker.
8. After blending has been completed, filter the slurry through the cheesecloth to remove the larger pieces, which you can throw into the trash. Keep the filtered, liquid extract.
9. Line the bottom halves of eight Petri dishes with three layers of paper towels. Cut the paper towels to fit tightly in the bottom of each dish, so that seeds will not move underneath layers of paper when you add a liquid.
10. Use tape and a marker to label the tops of your eight Petri dishes as listed below:
- group number, date, control-1, carrot
- group number, date, control-2, carrot
- group number, date, control-1, radish
- group number, date, control-2, radish
- group number, date, extract-1, carrot
- group number, date, extract-2, carrot
- group number, date, extract-1, radish
- group number, date, extract-2, radish
11. Saturate the paper in each of the bottoms of your four control Petri dishes with 10 ml of deionized water. You should have some unabsorbed water in each dish.
12. Saturate the paper in each of the bottoms of your four extract (experimental group) Petri dishes with 10 ml of your liquid leaf extract (excluding foam). You should have some unabsorbed extract in each dish.
13. Obtain your two assigned species of plant seeds. Place ten (10) seeds of the appropriate species onto the wet paper towels of each dish. Place only one species of plant seed in each dish. Try to spread the seeds evenly. Move the dishes carefully so that your seeds are not moved around.
14. Place your two stacks of Petri dishes into the container designated by the instructor. Move the dishes carefully so that your seeds are not moved around. Keep your plates upright and horizontal; these are not cultures of bacteria!
15. You should have a total of 20 carrot seeds in your control group, 20 carrot seeds in your experimental (extract) group, 20 radish seeds in your control group, and 20 radish seeds in your experimental (extract) group.

Question:

The experimental procedures you followed have been used as a quick way to determine the presence of any potentially allelopathic chemicals in leaves. However, these experimental procedures have been criticized for not being an accurate way to determine if allelopathic effects actually occur in nature. Explain several limitations to the experimental procedures, and explain how they could be improved to more accurately determine any allelopathic effects that may (or may not) occur in nature. What would be challenges of conducting these revised experiments? [Think. Apply course concepts.]

Answer :

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