Biology Lessons Part 2: Population Biology

   
 
Lesson 2.1 Teachers' Guide: How Does a Green Plant Grow?

Time
To Ponder
Supplies
Objectives
Introduction and Background
Resources

AAAS Benchmarks
Exercise 1: Define a Question
Exercise 2: Design an Experiment
Exercise 3: Predict the Outcome
Exercise 4: Gather the Materials
Exercise 5: Conduct the Experiment
Exercise 6: Interpret the Results

Grade Level

Prospective and Practicing K-8 Teachers; may be adapted for use in K-12 classes

 

Below we propose that each student group design its own experiment involving growing beans. That is, we want to give students the freedom to design an experiment. In order to improve the odds that the experiments will be successful, and also to provide some answers to frequent questions, we include two sample experiments that we have used many times. A teacher may simply prefer to use the 'canned' experiments.

As preparation for this lab, you can review the experiments on the web or download them as printed Word 5.1 for the Macintosh or Word 6 for Windows documents.

Link-out to web sites displaying:

Experiment 1: Growing Beans in Baggies

Teachers' Guide Experiment 1: Growing Beans in Baggies

Experiment 2: Growing Beans in Soil

Teachers' Guide Experiment 2: Growing Beans in Soil

Download Macintosh Word 5.1 Documents containing Experiment 1 (Growing Beans in Baggies) and Experiment 2 (Growing Beans in Soil):

 

 

Download Word 6 for Windows Documents containing '2.1aExp. 1' ( Growing Beans in Soil) and '2.1a Exp 2' (Growing Beans in Baggies):

 

For your reference, we are also including the following brief summary describing kidney bean characteristics and growth:

1. The kidney bean is prototypical of an Angiosperm.

2. The kidney bean can lay dormant (and alive) for years. It will grow when exposed to favorable conditions.

3. The triggering condition for growth is moisture.

4. Other essential conditions for bean growth include appropriate temperatures, light, nutrients, space, and freedom from toxins, parasites, and consumers.

5. Bean growth is initially supported by nutrients stored in the endosperm inside the cotyledons (as shown by beans in baggies).

6. Once the endosperm is used up, the bean needs another source of nutrients (especially usable nitrogen) to survive, typically obtained from soil.

7. Plants with a more robust supply of nutrients will be more green and grow more robustly than plants deprived of nutrients.

8. The kidney bean is a seed. It contains a diploid embryo (capable of growing into a new progeny plant) as well as endosperm.

9. A plant seed is formed by sexual reproduction via the union of haploid pollen and egg.

10. The reproductive structure in an Angiosperm is the flower. Eggs located in the ovary at the base of the flower are fertilized by pollen which is often delivered by insects, birds, and wind.


 

Time

The initial set-up of these experiments takes no more than an hour. After they set up their experiment in this lesson, students will need to make observations during the following 3 weeks .

To Ponder

1.

What is a seed? What are some examples?

A seed may be defined as the product of fertilization of the egg of a seed plant. It is analogous to a zygote in animals. It usually consists of an embryo with its food reserves enclosed in a protective coat. Seeds are an important adaptation, making life on land possible because they resist desiccation (drying out).

2.

Where do seeds come from?

A seed is produced when pollen from the same or a different plant of the same type fertilizes an egg. In flowering plants or angiosperms, the egg and the pollen are located in the ovary of the flower. Both sexes are combined in most plants (about 95%), but in some plants each individual is one sex or the other. Gymnosperms (conifers) are also seed plants.

3.

Do all plants produce seeds? At what point in the life cycle of a plant are they produced?

All Gymnosperms (conifers) and Angiosperms (flowering plants) produce seeds. Seeds mark the transition from the haploid condition of pollen and egg (which were produced by meiosis or reductive cell division) to the diploid stage. Diploid seeds are produced by the fusion of male and female nuclei during fertilization. Some parts of the seed, especially the nutrient supply, may be triploid (3N).

  4.

Are seeds alive? (They can exist for a long time - dozens, hundreds, even thousands of years - without changing.)

Seeds are alive but are dormant. Dormancy is a state of reduced physiological activity. Seeds typically remain dormant over the winter, but dormancy may last dozens, hundreds, or in rare recorded cases, thousands of years. Normal physiological activity is resumed when certain conditions for growth are met.

 

  5.

What stimulates a seed to begin growing, to germinate?

Seeds will germinate (begin to grow) under conditions conducive to growth, especially good moisture and temperature levels. In addition, some plants have special triggering requirements. For example, in many non-tropical plant species a very cold period (winter) is required for germination in the spring. Seeds from some fire-adapted plant species need to be exposed to fire to allow germination. Seeds from the tomato plant on the Galapagos Islands must be passed through the digestive system of a Galapagos tortoise in order to germinate.

 

6.

What does a seed require to grow?

Initially, adequate moisture and favorable temperatures are required. The seed can draw nutrients from its own reserves. Some seedlings can continue growth without additional requirements even after using up their food reserves. Others will require the nutrients in soil once their reserves are consumed.

 

7.

What is the difference between a seed and a bean? A seed and a nut?

A bean is a kind of edible seed. It may be found in a pod which is a kind of fruit. A fruit is a ripened ovary or ovaries of a seed-bearing plant, and it contains the seeds. An apple or pear is a prototypical fruit. Grains are also fruits. A true nut, such as an acorn, walnut, or pistachio, is a dry fruit with a hard shell (fruit wall) and only one seed. The popular meanings of the word nut often are in contradiction to the scientific meanings; from the biological perspective, for example, the peanut is not a nut - a peanut is a seed.

 

Supplies

These are some materials you may want for the sample experiments supplied with this lesson.

  • kidney beans from grocery store
  • ziploc baggies
  • paper towels
  • elastic bands
  • masking tape
  • bottled water
  • forceps
  • cardboard
  • spray bottle
  • water
  • stapler
  • scissors
  • soil
  • 1/2 gal. milk or juice carton, well rinsed

Objectives

1.

Define a question to explore how seeds grow.

2.

Design an experiment to answer your question.

3.

Predict the outcome of the experiment.

4.

Conduct the experiment.

5.

Interpret the results of your experiment.

6.

Compare predictions with results and explain similarities or differences.
Introduction

The theme of populations ties all the lessons in Part II together. We begin with producers because they are at the bottom of every food web, they support every community. Their wondrous ability to make sugars out of thin air and to generate excess oxygen makes possible all higher forms of life. This lesson provides an opportunity to review such ideas as plant cell structure, chloroplasts, photosynthesis, and transpiration, and the alternation of generations (haploid egg and pollen to diploid fertilized egg, seed, seedling and plant).

 

 To Do   1. 

 Working with your group, define your own question about plant seed growth and then design an experiment to answer your question. To help you get started, some questions are suggested below. You can modify or elaborate these questions if you wish, or generate a new question about this topic.

 

    2.

It often helps to read about the kinds of experiments that have been done in the past. Many different approaches to plant seed growth can be found in the curriculum materials in the library and in children's books found in stores like the Nature Company. It is also a good idea to read about plants and their seeds in a college biology book. A scientist does not operate in a vacuum, but learns as much as she can about what has already been discovered.

 

    3.  After you design your experiment, predict the outcome, conduct it, and prepare a report on your results. You may have an opportunity to post your report including question, experiment, results, interpretation, etc. on the World Wide Web.

Background
Information

   

Green Plants

 

   4. Living things naturally exist in communities composed of some similar and some different kinds of organisms. Every community of living things depends upon its producers to convert inorganic carbon (from the carbon dioxide in the air) into organic molecules (such as sugar) through the process of photosynthesis. That is, plants and other photosynthesizers make food out of thin air. To repeat, photosynthesizers use inorganic carbon dioxide from the air to make sugars, and the sugars are then used to construct larger organic molecules.
     5. No other living things have this capability. All the rest of the organisms in the world rely on plants to capture the sun's energy and convert it into usable organic form. Animals, fungi and bacteria cannot synthesize organic molecules from inorganic sources and light energy. On the other hand, plants wouldn't do very well without nitrogen-fixing bacteria and the decomposer organisms, so there is a high level of interdependence among the organisms in a community.
     6. The photosynthesizers or producers provide the foundation for the entire food web. Without them, no living things could survive. This seems like a simple idea, but it is one whose significance is often lost. Can you think of an analogy that would help clarify the importance and uniqueness of the conversion of inorganic CO2 to organic sugars by green plants during photosynthesis? For example, one analogy might be: "A green plant is like a magician - it creates itself out of thin air." Can you think of others? 
     7. In summary, in this lab, we will examine the growth of a producer, specifically a terrestrial green flowering plant, the kidney bean. Each group will design their own experiment and will report first what they plan to do and later on their results to the others.

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Exercise 1

Define a Question to Explore

In this lab you have an opportunity to define your own question. To help you get started, here are some possible questions and hypotheses about red kidney beans and the seedlings they produce.

One of the surprising things about scientific research is how narrow a question must be in order to be studied. As a teacher, you will spend a lot of time helping students narrow their questions into 'doable' hypotheses of manageable proportions.

To Do 1. Question: What do red kidney beans need to begin growing? (some considerations: temperature, light, soil, moisture, other?)

Hypothesis: Red kidney beans require soil, moisture (damp but not inundated), at least four hours of light, and temperatures in the range of 50o F. to 100o F. for germination.
2. Question: What kinds of changes occur as a bean germinates and develops into a seedling?

Hypothesis: The beans will develop a good root system first and then a stem will grow and finally some leaves.
3. Question: Can a kidney bean seedling grow in a damp environment in a baggy or flask, without soil, and if so, for how long?

Hypothesis: Without the nutrients in the soil, the kidney beans will not be able to germinate.
Data
Collection
4. Question: If kidney beans can grow in water, will their growth be more robust, less robust, or about the same as in soil?

Hypothesis: Kidney bean seedlings will grow better in water than in soil.
5. Question: Can kidney beans grow when immersed in water?

Hypothesis: Kidney bean seedlings will germinate when immersed in water.
Your questions and hypotheses are limited to flowering plants, specifically to the red kidney bean, and more specifically to bean and bean seedlings, so that we are all working "in the same ballpark." There is precedence for this in science -- for example, when viruses were first being studied, scientists around the world agreed to concentrate their efforts on just a few viruses so as to study them thoroughly.

Notice that the question is more general and the hypothesis is more specific. Specificity and narrow focus are necessary in order for you to design an experiment that can be performed. Please adapt one of the questions/hypotheses above or preferably create another of your own choosing.
To Do When you have decided upon a hypothesis, talk with your instructor about it and post it for comments by other class members.
 

Exercise 2

Design a Simple Experiment to Answer Your Question

Below we discuss the hypotheses above, providing some hints to help you get started in designing an experiment to answer the question you have posed. You can adapt the discussions below as needed to your own questions.

1.

Hypothesis 1: Red kidney beans require soil, moisture (damp but not inundated), at least four hours of light, and temperatures in the range of 50oF. to 100oF. for germination.

This requires an experimental design. What conditions do you think are necessary for germination? You may want to do research (reading) about growing kidney beans. One approach would be to grow kidney beans under your hypothesized "ideal" conditions, and to grow them in several other conditions in which one condition at a time is changed. For example, if you think light, soil, water, and temperature are important, you may want in addition to your ideal condition, conditions where you a) remove the light, b) remove the soil, c) remove the water, and d) change the temperature to a temperature you think would be unfavorable for growth.

2.

Hypothesis 2: The beans will develop a good root system first and then a stem will grow and finally some leaves.

This question requires careful observation. You may want to use a digital camera to record the changes. You could begin by dissecting the bean and identifying its parts. Then you can grow several beans in soil and "sacrifice" one each day you come into lab, recording the changes that have occurred (in writing and with the digital camera) and the time period in which they occurred. Note what happens to the different parts of the seed over time.

3.

Hypothesis 3: Without the nutrients in the soil, the kidney beans will not be able to germinate.

This question requires careful observation and optimum conditions for growth in water. Perhaps the first question you must determine is whether you begin with the seed under water or in a moist environment above a supply of water (so the roots can grow down to it). You might learn this by reviewing some literature. Then design your set-up. Use a number of beans so you will obtain results even if several die. Observe the seedling growth and closely watch what happens to the seed itself.

4.

Hypothesis 4: Kidney bean seedlings will grow better in water than in soil.

This suggests a comparative study. Kidney beans may be grown under optimum conditions in both cases. You can perhaps find out what those optimum conditions are by reviewing the literature. A digital or other camera would allow you to record changes under both conditions and to compare size, color, etc. Keep a careful record of the date of each picture (one way to do this is by writing the date on a card and including it in the photograph). In addition, you can draw and describe your observations from time to time.

5.

Hypothesis 5: Kidney bean seedlings will germinate when immersed in water.

This question could be answered in a comparative study. You may want to determine if kidney beans will germinate when immersed in water, as well as or better than when they are dry or simply damp. You could set up 3 baggies with paper towels at the bottom, with beans on top of each paper towel. You could then immerse the first set of beans in water, keep the second set of beans dry, and in the third set, keep the towel moist to wet but do not cover the beans with water. The baggies should be kept in a warm place with open tops for air circulation and monitored to make sure appropriate water/moisture levels are maintained. Germination will probably take about a week.

All these experiments will take 2 to 4 weeks to complete. Observe them carefully each class period, taking notes, drawing images, and perhaps taking photographs. Monitor the conditions of each environment and water or otherwise modify as needed, recording what you do.

Use all the resources at your disposal to design your experiment: read books, ask questions at the plant nursery, explore the web, etc. Design your experiment in careful detail, checking with the instructor as you do so. Also, post your question and your experimental design for review and comment by class members.

If you make changes, post your revised experimental plan for any additional comments and suggestions. Identify all the variables you will monitor and design one or more tables or charts for recording all pertinent data.

 

Exercise 3

Predict the Outcome

To Do

Talk about what you expect will happen in the experiment and why. Try to reach a consensus in your prediction and be sure to write it down. If you can't agree, write down the various predictions made by your group members. In each case, explain why you think this is what will happen and why you disagree with the other theory(s) being proposed. Understand that predictions which are not supported by observations are just as valid/successful as ones that yield expected results. Often we learn more from experiments that don't turn out the way we think they will!

Students - even college students - think that to be a successful scientist they must predict the correct outcome. In fact, they often try to change their predictions once they see the outcome. This is to be strongly discouraged. If we knew the outcome for sure, there would be no need to perform the experiment! It is OK to have your prediction falsified. The important things are a) that the experiment and its results are reproducible and b) that you can find a satisfactory explanation for why the results are as they are.

 

Exercise 4

Gather Materials Needed for Experiment

Figure out everything you need to do the experiment and talk with your instructor to see what the school can provide and what you need to obtain.
 

Exercise 5

Conduct the Experiment

Start a journal. Record the date and the way in which you set up the experiment. Keep track of progress and changes. Determine if you need to create any additional charts for systematic recording of data.
 

Exercise 6

Interpret the Results

When the experiment is completed, review your data and interpret it. What does it mean? Do your observations match your prediction? If so, do you think your initial reasoning for the prediction remains valid, or would you change it now? If not, why not? How do you explain your observations?

Compare your observations with those made by other groups. Are they consistent? Can the same reasoning (explanation, model) account for all the results?

Post your results, interpretation and explanation for review by the class. Include a pictorial record where appropriate. Also post any questions you may have at this point.

Sense-making is a very important part of doing an experiment. So is convergence. If seven out of eight groups get the same result, and one group gets a different result, it is as important to understand why the different result occurred as it is to be able to explain why the main result occurred. The teacher has an important role to play in guiding these discussions.

Supplementary
Resources

Ardley, N. (1991). The Science Book Of Things That Grow. San Diego, Ca.: Gulliver Books, Harcourt Brace Jovanovich, Publishers.

Overbeck, C. (1981). Sunflowers. Text and photographs describe the growth of a sunflower from a seed to a full-grown plant. Minneapolis, MN.: Lerner Publications Co.

Postlethwait, J. H. & Hopson, J. L. (1995). The Nature of Life, Third Edition. San Francisco: McGraw-Hill, Inc.

Sidwell Friends School Virtual Lab; The Plant Lab http://www.sidwell.edu/sidwell.resources/bio/VirtualLB/plant/plant.html.

Wilkins, M. B. (1988). Plantwatching. How plants remember, tell time, form partnerships, and more. New York, NY. : Facts on File Publications.

Related
AAAS
Benchmarks

Chapter 1: THE NATURE OF SCIENCE

Section A: The Scientific World View

Grade K-2 Benchmark 1 of 2

When a science investigation is done the way it was done before, we expect to get a very similar result.

Grade K-2 Benchmark 2 of 2

Science investigations generally work the same way in different places.

Grade 3-5 Benchmark 1 of 1

Results of similar scientific investigations seldom turn out exactly the same. Sometimes this is because of unexpected differences in the things being investigated, sometimes because of unrealized differences in the methods used or in the circumstances in which the investigation is carried out, and sometimes just because of uncertainties in observations. It is not always easy to tell which.

 

Grade 6-8 Benchmark 1 of 4

When similar investigations give different results, the scientific challenge is to judge whether the differences are trivial or sign ificant, and it often takes further studies to decide. Even with similar results, scientists may wait until an investigation has bee n repeated many times before accepting the results as correct.

Section B: Scientific Inquiry

Grade K-2 Benchmark 1 of 4

People can often learn about things around them by just observing those things carefully, but sometimes they can learn more by doing something to the things and noting what happens.

Grade K-2 Benchmark 2 of 4

Tools such as thermometers, magnifiers, rulers, or balances often give more information about things than can be obtained by just observing things without their help.

Grade K-2 Benchmark 3 of 4

Describing things as accurately as possible is important in science because it enables people to compare their observations with tho se of others.

Grade 3-5 Benchmark 1 of 4

Scientific investigations may take many different forms, including observing what things are like or what is happening somewhere, collecting specimens for analysis, and doing experiments. Investigations can focus on physical, biological, and social questions.

Grade 3-5 Benchmark 2 of 4

Results of scientific investigations are seldom exactly the same, but if the differences are large, it is important to try to figure out why. One reason for following directions carefully and for keeping records of one's work is to provide information on what might have caused the differences.

Grade 6-8 Benchmark 1 of 4

Scientists differ greatly in what phenomena they study and how they go about their work. Although there is no fixed set of steps that all scientists follow, scientific investigations usually involve the collection of relevant evidence, the use of logical reasoning , and the application of imagination in devising hypotheses and explanations to make sense of the collected evidence.

Grade K-2 Benchmark 1 of 3

Everybody can do science and invent things and ideas.

Grade K-2 Benchmark 2 of 3

In doing science, it is often helpful to work with a team and to share findings with others. All team members should reach their own individual conclusions, however, about what the findings mean.

Grade K-2 Benchmark 3 of 3

A lot can be learned about plants and animals by observing them closely, but care must be taken to know the needs of living things and how to provide for them in the classroom.

Chapter 5: THE LIVING ENVIRONMENT

Section D: Interdependence of Life

Grades 3-5 Benchmark 1 of 5

For any particular environment, some kinds of plants and animals survive well, some survive less well, and some cannot survive at all.

Section E: Flow of Matter and Energy

Grades K-2 Benchmark 1 of 2

Plants and animals both need to take in water, and animals need to take in food. In addition, plants need light.

Grades 3-5 Benchmark 2 of 3

Some source of "energy" is needed for all organisms to stay alive and grow.

Grades 6-8 Benchmark 1 of 3

Food provides molecules that serve as fuel and building material for all organisms. Plants use the energy from light to make sugars from carbon dioxide and water. This food can be used immediately or stored for later use. Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. Then they are consumed by other organisms.

Grades 6-8 Benchmark 3 of 3

Energy can change from one form to another in living things. Animals get energy from oxidizing their food, releasing some of its energy as heat. Almost all food energy comes originally from sunlight.

Grades 9-12 Benchmark 3 of 3

The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.