AGRISCIENCE EXERCISE

University of Arkansas - AgriScience Project

AGRISCIENCE EXERCISE

PLANT SCIENCE & BIOTECHNOLOGY

Key Concept: Sexual Reproduction in Plants

Sub-Concept: Germination

Agricultural Context: The germination of various agricultural crop plants is very important financially to producers; therefore, it is important for all phases of the germination process to proceed efficiently.

Exercise: Examine Factors Affecting Seed Imbibition

Applied Principle: The first step in the germination of a seed is the uptake of water by the dry seed, known as imbibition. This activates the necessary hormones and enzymes for the embryo to grow and for the food stored in the cotyledons to break down.

Goals:

Define imbibition.
Explain the importance of imbibition in seed germination.
Discuss the effects of various environmental factors on seed imbibition.

Materials:

3 clear film canisters with lids
bean seeds
water

Materials for group experiments will vary. Each group should compile a list of needed materials as a part of its experiment design.

References: Lamb, E. (1994). "Plant Science Component of the FFA Teachers Course." Fayetteville, AR: University of Arkansas, College of Agricultural, Food, and Life Sciences, Department of Horticulture.

Osborne, E.W. (1994). Biological Science Applications in Agriculture. Danville, IL: Interstate Publishers, Inc.

Teacher Preparation Notes:

Step one of the procedures for this activity is to demonstrate the imbibition of water by seeds. The object of the demonstration is for the students to see the lid of the film canister pop off due to the swelling of the seeds. To accomplish this, you will need to experiment with some seeds a few days in advance. Fill a film canister about 3/4 full of undamaged bean seeds and fill with water. Place the lid securely on the canister. Then keep careful track of how long it takes for the lid to pop. This way, you will know how far in advance to begin preparations for the classroom demonstration. [If you have more than one class, you will need to time additional demonstration set-ups accordingly.]
Prepare a complete demonstration for step one of the procedures. Set up one canister 3/4 full of dry beans, another 3/4 full of beans and filled with water, and the canister about to pop top so that students may see all steps of imbibition.

Procedures for Conducting the Activity:

1. Allow the students to observe the film canisters previously prepared. They should be able to see the top pop off of the canister, due to the imbibition of water by the seeds.

2. Explain that imbibition is the first step in the germination of a seed, and what this means. [Note: Refer to the "Teacher Background Sheet" for more information.]

3. Lead the students in a discussion of what factors might affect this process. Write possibilities on the board (or have a student write them). Answers could include, but are not limited to: temperature, type of seed, salinity of water, and mechanical damage.

As a part of the discussion, encourage the students to hypothesize about each factor, and why they arrived at their answers.

4. Divide the class into 4 groups.

5. Provide each group with a different instruction sheet. There will be four different imbibition experiments, one conducted by each group.

Lead the class in a review of the steps in the scientific process. Emphasize that these steps must be included in their experiment designs.

6. Allow groups time to carefully read over their instruction sheets and to write up their experiment designs.

Below are some ideas you may wish to offer to the students in designing their experiments:

Temperature Effects: May test imbibition at room temperature, in a refrigerator, under a lamp, etc. Can it be too cold or too hot for seeds to imbibe? What does that mean about the seed? Are there different temperature limits for different types of seeds?

Water Salinity Effects: Weigh 20 seeds for each treatment to be tested. Treatments could be: 30 ml distilled water, 30 ml tap water, 30 ml distilled water plus 1/4 teaspoon salt, 30 ml distilled water plus ½ teaspoon salt, 30 ml distilled water plus ½ tablespoon salt. Cap the canisters. Weigh the seeds every hour for 4-5 hours and overnight. Which seeds take up more water? What are the implications of this finding?

Seed Variation Effects: Do different types of seeds imbibe differently? What about different varieties of the same seeds? How long before seeds start to imbibe (the seed coats look wrinkled)? How long before imbibition is finished (there is no change in weight or appearance)?

Seed Damage Effects: Mechanical damage to seeds during cleaning and packaging may have some effect on imbibition, and therefore on germination. What if the seeds have cracks in their seed coats? (If there are no cracked seeds, mechanical damage may be simulated by dropping them from about 5 feet onto a hard metal surface.)

7. Instruct groups to gather materials and set up their experiments. Be sure to carefully supervise each group.

8. After all data has been gathered from the experiments, each group will present their findings to the class.

Oral reports should include all steps in scientific process. Students should especially emphasize the implications of their results.

AGRISCIENCE EXERCISE

- Seed Imbibition -

Student Data/Instruction Sheet

GROUP 1: TEMPERATURE EFFECTS

Objective: Determine how long imbibition takes at different temperatures.

Instructions:

Design an experiment which will allow you to test the effects of various temperatures on seed imbibition. Be sure to include all steps in the scientific process in your design.

Once you have completed your experiment design, ask your instructor to review it before proceeding.

Experiment design:

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AGRISCIENCE EXERCISE

- Seed Imbibition -

Student Data/Instruction Sheet

GROUP 2: WATER SALINITY EFFECTS

Objective: Determine whether the salinity of water affects seed imbibition.

Instructions:

Design an experiment which will allow you to test the effects of water salinity on imbibition. Be sure to include all steps in the scientific process in your design.

Once you have completed your experiment design, have your instructor review it before proceeding.

Experiment Design:

AGRISCIENCE EXERCISE

- Seed Imbibition -

Student Data/Instruction Sheet

GROUP 3: SEED VARIATION EFFECTS

Objective: Determine whether different types of seeds imbibe differently.

Instructions:

Design an experiment which will allow you to test the effects of seed variation on imbibition. Be sure to include all steps in the scientific process in your design.

Once you have completed your experiment design, have your instructor review it before proceeding.

Experiment Design:

AGRISCIENCE EXERCISE

- Seed Imbibition -

Student Data/Instruction Sheet

GROUP 4: DAMAGED SEED EFFECTS

Objective: Determine whether mechanical damage affects seed imbibition.

Instructions:

Design an experiment which will allow you to test the effects of mechanical seed damage on imbibition. Be sure to include all steps in the scientific process in your design.

Once you have completed your experiment design, have your instructor review it before proceeding.

Experiment Design:

TEACHER BACKGROUND SHEET

- Seed Imbibition -

During storage, seeds contain only 5 to 10% moisture; respiration is occurring, but at a very inhibited rate. The first step in the germination of a seed is imbibition, or water uptake. Seeds absorb water primarily through the micropyle. During the first 12 hours of the imbibition process, seeds may raise in water content to between 30 and 40%.

The hydration of large molecules within the seed causes water uptake; this occurs until the molecules are restored to full turgor. The pressure exerted against the cell wall by the increased water content causes the cells to become more turgid (rigid).

Respiration within the seed also increases with water intake. Since respiration is essential for cell division to occur, oxygen must be present for seeds to germinate.

After seeds imbibe water, their reserve substances (proteins, fats, carbohydrates, etc.) are changed to simple sugars and amino acids through enzymatic action. These are transported to the embryo, where some are respired to provide energy and others are used in the synthesis of protein, starch, and cellulose. Water and oxygen are necessary for the enzymes to break down the seed's reserves.

Thus the steps in seed germination are as follows:

1. Water is absorbed by the seed through the micropyle and/or seed coat.

2. The seed cells enlarge.

3. Seed respiration increases.

4. The seed metabolic rate increases.

5. Protein synthesis increases.

6. Gibberellins cause enzymatic activity.

7. Enzymes change starch in the seed's reserves to sugar.

8. The embryo breaks through the seed coat.

9. The root and shoot elongate.

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