- The seed is a remarkable structure that enables seed plants to survive unfavorable conditions. Each seed contains an embryo that can grow into a mature plant. In addition, the seeds of flowering plants have structures called cotyledons. The cotyledons store food for use by the embryo in the form of starch. Starch is long chains of glucose molecules. The embryo needs to break these chains, forming sugars it can use for energy. It does this by releasing the enzymes alpha-amylase and beta-amylase.
- Alpha-amylase works by dividing the long starches across the middle of their chains. It keeps dividing the chains until they are one, two, or three glucose molecules long. Glucose being the smallest molecule, Maltose is a chain of two glucose molecules, and Maltriose is a chain of three glucose molecules.
- Beta-amylase works by nibbling at the ends of the starch chains to make them into chains of one, two, or three glucose molecules.
- In this lab, you will investigate this enzyme action, by first testing a dry bean seed for the presence of glucose, then testing a been seed that has germinated.
MATERIALS:
*Bean seeds (or other kinds of seeds)
Zip-lock bag
Mortar and pestle
2 test tubes
Test tube rack
Test tube holder
10-mL graduated cylinder
400-ml beaker
Hot plate
Distilled water
**Benedict's solution-
*Use beans intended for growing in garden or for sprouts, not dry beans from the grocery store.
My students used Kitchen Crop seeds for sprouting, produced by NK Lawn & Garden Co.: Mung bean, Lentil, and Alfalfa. Both the beans did well, but alfalfa gives a very strong positive for both un-germinated and germinated.This lab is very sensitive to concentrations, so follow the instructions carefully.
**You can obtain Benedict's solution from a science supply company.
1. Place some beans in a zip-lock bag and cover them with water (don't use to much water). Place the bag, standing up, in a dark warm place. The next day, empty out any extra water, and rinse the seeds with fresh water. Pour off the excess water and laying the bag on its side, return the seeds to the dark warm place being used for germination. Rinse the seeds once or twice a day, pouring off the excess. Leave the seeds there for approximately 3 days to germinate.
After the seeds in step 1 have germinated:
2. Fill a 400-ml beaker to about 300 ml with water and heat on the hot plate.
3. Take a dry (un-germinated) bean and crush it in the mortar. If using smaller beans like mung, use two. If using a very small seed, use a small pinch. Place the crushed bean in an appropriately marked test tube.
4. After cleaning the mortar and pestle, crush the same size sample of the germinated beans. Place the crushed, germinated bean, in an appropriately marked test tube.
5. Add 5.0 ml of distilled water and 10 drops of Benedict's solution to each test tube. Mix with a stirring rod, or holding the tube between the thumb and index finger of one hand, thump it with the middle finger of the other hand to mix.
REMEMBER: If you use a stirring rod, wash it after every use, so you won't contaminate one solution with another.
6. When the water boils, place the test tubes in the water bath. Leave the test tubes in the water bath for 10 minutes.
REMEMBER: Do not let the water bath boil hard. Control the boiling by turning the hot plate on and off as needed.
7. Remove the test tubes with tongs and place the tubes in a test tube rack. Unplug the hot plate to cool. When the tubes cool, an orange or red precipitate will form if large amounts of glucose are present. Small amounts of glucose will form a yellow or green precipitate. The intermediate between these will appear brown.
8. Record the color of each sample
Color of dry bean sample = _________________
Color of germinated bean sample = _________________
Question: What can you infer about germination and amylase production, based on your test results?
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Back to Lab Dad's Laboratory
- Alpha-amylase works by dividing the long starches across the middle of their chains. It keeps dividing the chains until they are one, two, or three glucose molecules long. Glucose being the smallest molecule, Maltose is a chain of two glucose molecules, and Maltriose is a chain of three glucose molecules.
ENZYME ACTION IN
GERMINATING SEEDS
(Amylase)
INTRODUCTION: