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. Pay careful attention to your instructor on the use of Petri dishes.
A. Observation. Seeds do not germinate inside their fruits even though it is moist and warm inside the fruit.B. Question. Do the juices surrounding seeds inhibit their germination?
C. Hypothesis. The juices surrounding seeds inhibit their germination.
D. Prediction. If the hypothesis is true, then seeds placed in fruit juice will not germinate as well as seeds placed in water.
E. 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 four days and eight days, count out the number of seeds germinating and express as percent germination.
After ______ Days After Eight Days Treatment Total
GerminatedGermination
(% of 50)Newly
GerminatedTotal
GerminatedGermination
(% of 50)Water + light % % Tomato Juice + light % % Abscisic Acid + light % % Other observations:
F. Analysis.
More seeds germinated in: water tomato juice abscisic acid G. Decision.
The hypothesis: "The juices surrounding seeds inhibit their germination" is: rejected not rejected
A. 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.B. Question. Do species requiring light to germinate use the phytochrome pigment to determine if they are in the light or darkness?
C. Hypothesis. Light-sensitive seeds do use the phytochrome pigment.
D. 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.
E. 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 ÒdarkÓ 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 ÒdarkÓ dishes under red and blue cellophane with incandescent lighting.
After four days and eight days, 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
GerminatedGermination
(% of 50)Newly
GerminatedTotal
GerminatedGermination
(% of 50)Water in red light % % Water in far-red light % % Water in darkness % % F. Analysis.
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-simulating form of phytochrome is: Pr Pfr G. Decision.
The hypothesis: "Light-sensitive seeds do use the phytochrome pigment" is: rejected not rejected
A. 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.B. Question. Can lettuce seeds or pea seeds germinate better if planted deeply in soil?
C. Hypothesis. Lettuce seeds germinate poorly when planted deeply compared to peas.
D. 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.
E. 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 first observations. One week from now you will take your second set of observations.
Record the number of seedlings appearing above the soil and calculate the percent germination:
Lettuce Seeds After One Week After the Second Week Planting Depth Number
GerminatingGermination
(% of 20)Total
GerminatedGermination
(% of 20)0 cm % % 1.5 cm % % 3 cm % % 6 cm % %
Pea Seeds After One Week After the Second Week Planting Depth Number
GerminatingGermination
(% of 10)Total
GerminatedGermination
(% of 10)0 cm % % 1.5 cm % % 3 cm % % 6 cm % % Other observations: Peas planted at 0 cm were unusually:_______________
F. Analysis.
The seeds germinating better when planted shallow: lettuce pea The seeds germinating better when planted deep: lettuce pea G. Decision.
The hypothesis: "Lettuce seeds germinate poorly when planted deeply compared to peas." is: rejected not rejected
Is there good evidence that the active hormone in tomato juice is abscisic acid? yes no Defend/condemn the statement: "Lettuce seeds need light to germinate" using the data you obtained in laboratory.
Lettuce seeds do need light to germinate
do not need light to germinatebecause seeds in the dark because seeds in red light because seeds in far-red light Explain how you can tell whether far-red light had any effect (Hint: what was the control?)
Seed germination in far-red light was greater less than seed germination in the control seeds which were in What was the purpose of exposing the seeds treated with far-red light to white light for an additional time and observing germination again?
What conclusion do you draw from the results of the second exposure?
What is the optimum planting depth for lettuce seeds? 0 1.5 3 6 cm What plant characteristics did you use to base your conclusion upon?
What is the optimum planting depth for pea seeds? 0 1.5 3 6 cm What plant characteristics did you use to base your conclusion upon?
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