| wrong | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | Group Name: | |
| right | 70 | 69 | 68 | 67 | 66 | 65 | 64 | 63 | 62 | 61 | 60 | 59 | 58 | 57 | 56 | 55 | 54 | 53 | ||
| score | 100 | 98.6 | 97.1 | 95.7 | 94.3 | 92.9 | 91.4 | 90.0 | 88.6 | 87.1 | 85.7 | 84.3 | 82.9 | 81.4 | 80.0 | 78.6 | 77.1 | 75.7 | . |
| Seed Germination | Name________________________ |
In this exercise you will learn about propagating plants sexually (from seeds). It is expected that you have read the appropriate sections in the textbook prior to coming to class.
Observation. Seed companies recommend different planting depths for seeds. Lettuce seeds are small and need light to germinate. Pea seeds are quite a bit larger.
Question. Can lettuce seeds or pea seeds germinate better if planted deeply in soil?
Hypothesis. Lettuce seeds germinate poorly when planted deeply compared to peas.
Prediction. If the hypothesis is true, then pea seeds planted deeply will germinate much better than lettuce seeds planted at the same depth. Moreover, pea seeds may be light-inhibited and germinate poorly when planted shallowly.
Experiment. Earlier in the semester, you planted four pots with lettuce and pea seeds at various depths in the soil. You should locate your pots and make your observations. Record the number of seedlings appearing above the soil and calculate the percent germination:
| Lettuce Seeds | Pea Seeds | |||
|---|---|---|---|---|
| Planting Depth | Number Germinating | Germination (% of 20) | Total Germinated | Germination (% of 10) |
| 0 cm | % | % | ||
| 1.5 cm | % | % | ||
| 3 cm | % | % | ||
| 6 cm | % | % | ||
| Other observations: Peas planted at 0 cm were unusually: |
| The optimum depth for lettuce seeds is: | 0 1.5 3 6 | cm. |
| The optimum depth for pea seeds is: | 0 1.5 3 6 | cm. |
| The plants growing taller when planted at 6 cm than at 0 cm: | lettuce pea |
Decision.The hypothesis: "Lettuce seeds germinate poorly when planted deeply compared to peas." is:
| rejected not rejected |
| - /20 |
Observation. Seeds do not germinate inside their fruits even though it is moist and warm inside the fruit.
Question. Do the juices surrounding seeds inhibit their germination?
Hypothesis. The juices surrounding seeds inhibit their germination.
Prediction. If the hypothesis is true, then seeds placed in fruit juice will not germinate as well as seeds placed in water.
Experiment. Obtain three Petri Dishes from the supply and put one disc of filter paper in the bottom of each dish. The bottom is the smaller of the two dishes and fits inside the cover. Label the dish covers (and bottoms!) with the marking pen. The labels should be:
Water in light Tomato Juice in light Abscisic Acid in light
Put 5 mL of distilled water in the first dish, 5 mL of tomato juice in the second dish, and 5 mL of 1 mM Abscisic Acid in the third dish.
With your partner, carefully count out three groups of 50 'Salad Bowl' lettuce seeds. Of course the counts must be accurate, but WORK QUICKLY! Place one group of 50 seeds into each dish on top of the moist paper.
Place the three dishes under the lights to allow the seeds to germinate.
After a few days and after a week, count out the number of seeds germinating and express as percent germination.
| After ______ Days | After Eight Days | ||||
|---|---|---|---|---|---|
| Treatment | Total Germinated | Germination (% of 50) | Newly Germinated | Total Germinated | Germination (% of 50) |
| Water + light | % | % | |||
| Tomato Juice + light | % | % | |||
| Abscisic Acid + light | % | % | |||
| Other observations: |
| More seeds germinated in: | water tomato juice abscisic acid |
| Is there good evidence that the active hormone in tomato juice is abscisic acid? | yes no |
| rejected not rejected |
| - /20 |
Observation. Seeds of some species germinate in the light but do not do so well in the dark. The pigment phytochrome has two forms, Pr and Pfr which absorb red and far-red light, respectively. Perhaps this pigment helps seeds detect the light.
Question. Do species requiring light to germinate use the phytochrome pigment to determine if they are in the light or darkness?
Hypothesis. Light-sensitive seeds do use the phytochrome pigment.
Prediction. If the hypothesis is true, then lettuce seeds placed in red light will germinate much better than seeds placed in darkness or far-red light. Moreover, seeds in far-red light should be particularly inhibited.
Experiment. Obtain three Petri Dishes from the supply and put one disc of filter paper in the bottom of each dish. Label the dish covers (and bottoms!) with the marking pen. The labels should be:
Water in red light Water in far-red light Water in dark
Put 5 mL of distilled water in each dish, and obtain a square of aluminum foil so that you are ready to wrap the "dark dish immediately. BE READY!
With your partner, carefully count out three groups of 50 lettuce seeds. Of course the counts must be accurate, but WORK QUICKLY! Place one group of 50 seeds into each dish on top of the moist paper.
IMMEDIATELY wrap the "dark" dish in aluminum foil so that it is completely enshrouded. Place the "red light" dish under red cellophane with fluorescent lighting. Place the "far-red light" and the "dark" dishes under red and blue cellophane with incandescent lighting.
After a few days and one week, count out the number of seeds germinating and express as percent germination. After 2-5 days, move all the seeds into white light.
| After ______ Days | After Eight Days | ||||
|---|---|---|---|---|---|
| Treatment | Total Germinated | Germination (% of 50) | Newly Germinated | Total Germinated | Germination (% of 50) |
| Water in red light | % | % | |||
| Water in far-red light | % | % | |||
| Water in darkness | % | % | |||
| The most seeds germinated in ______ days of: | red light far-red light darkness |
| The fewest seeds germinated in ______ days of: | red light far-red light darkness |
| The germination-stimulating form of phytochrome is: | Pr Pfr |
| The hypothesis: "Light-sensitive seeds do use the phytochrome pigment" is: | rejected not rejected |
| - /21 |
Defend the statement: "Lettuce seeds need light to germinate" using the data you obtained in laboratory.
Lettuce seeds do need light to germinate, because germination of seeds was greater less in the dark than in white light. Moreover, after ___ days of darkness, the ungerminated seeds were exposed to white light and more no more germinated.
Condemn the statement: "Lettuce seeds need light to germinate" using the data you obtained in the laboratory.
Lettuce seeds do not need light to germinate, because germination of seeds in the darkness was more than 0 5% in white light control .
Explain how you can tell whether far-red light had any effect.
Seed germination after ___ days in far-red light was greater equal to less than seed germination in the control seeds. These control seeds were in __________________________.
The failure of a seed to sprout could be due to the fact that its germination is indeed inhibited. But there is also a second possibility: perhaps the treatment does not inhibit seed germination directly, but simply kills the embryo. Such a situation would certainly not produce a germinating seed! In this exercise you exposed the seeds treated with far-red light to white light for an additional time and observed germination again. Present arguments for both possibilities!
Far-red light inhibits germination--My evidence is that germination after the white light exposure was:
Far-red light kills the embryo--My evidence is that germination after the white light exposure was:
| - /9 |
This page © Ross E. Koning 1994.
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