This article provides ideas for a laboratory investigation into the role of the plant hormone ethylene in seed germination. The role of ethylene is explored from various perspectives, namely from an indigenous knowledge perspective, but also from a botany and economic angle. This article shows how students could test indigenous knowledge claims related to ethylene in the school laboratory.

I'm calling on our nation's governors and state education chiefs to develop standards and assessments that don't simply measure whether students can fill in a bubble on a test, but whether they possess 21st century skills like problem-solving and critical thinking and entrepreneurship and creativity.

President Barack Obama
Address to the Hispanic Chamber of Commerce, March 10, 2009

Introduction: Vision & Change

Hailman (1975) argued four decades ago that the approach to the “scientific method” in schools was often just as detached from how an Einstein functioned as color-by-number sets are removed from Michelangelo's painting technique. This metaphor is very applicable in the era of the Vision and Change document (AAAS, 2011). Have we succeeded in catapulting inquiry learning in the science classroom, and using science–technology–society approaches that will result in the achievement of affective outcomes?

The Vision and Change initiative envisages graduates with a well-defined level of functional biological literacy and critical-thinking skills. Another initiative, A New Biology for the 21st Century (National Research Council, 2009), is a collaborative, interdisciplinary approach to biological research, tasked to find solutions to a myriad of societal challenges. This suggests that biology teachers need to design learning experiences in which students can be exposed to interdisciplinary thinking, and not just slavishly follow the curriculum. This would also include indigenous knowledge perspectives in biology. If teachers want to foster 21st-century skills and cultivate biological literacy within students, students need to be actively involved and cognitively stimulated in their learning processes.

Here, we explore the possibilities of an interdisciplinary activity on the plant hormone ethylene, in the way that Kober (2015) envisages the transformed biology classroom as a space where students are challenged to think critically, make connections across disciplines, and work in teams. Among other things, we show how indigenous knowledge could be incorporated in the biology curriculum. The main learning objective for this activity is to plan and execute an experiment to investigate two indigenous knowledge claims, namely the influence of incense on the release of ethylene during germination of seeds, and secondly how scarred tissue could result in increased ethylene production. This activity will contribute to at least two objectives of the Vision and Change approach/initiative:

  • It will integrate core concepts and competencies as students define their own learning goals while planning and executing the experiment. In addition, their biological literacy will be developed while practicing the tenets of the nature of science, thereby developing their science-learning competencies. It may further stimulate their curiosity and make the content relevant by associating it to students’ real-life experiences.

  • It will focus on student-centered learning because the students will be actively involved in this inquiry-driven, cooperative teaching–learning activity.

Ethylene

Indigenous Knowledge Perspectives, Current Research & Implications in Modern Society

Ethylene (C2H4) is a gaseous plant hormone and forms part of the alkene group. When discussing ethylene in the biology classroom, we suggest a threefold approach, namely (1) focusing on indigenous knowledge, which seems to have become increasingly important in science education research recently; (2) taking cognizance of current research being done on ethylene; and (3) exploring the role of ethylene in modern society.

Indigenous Knowledge Perspectives: The Influence of Burning Incense on Seed Germination

One of the tenets of science is that it is a human endeavor and thus socially and culturally influenced. Students do not enter the biology classroom as “blank slates,” and indigenous knowledge could serve as a very good entry point into the abstract world of science. Researchers like Wilson (2002) and De Beer (2015) have called for the inclusion in school science curricula of indigenous knowledge from an embodied, situated, and distributed cognition perspective. The viewpoint of “embodied cognition” is that cognitive processes are deeply rooted in the body's interactions with the world (Wilson, 2002). Learners develop their worldviews on the basis of their (situated) engagement with people and the environment. Such cultural knowledge is co-constructed (and, therefore, distributed in the community). In this laboratory activity, the investigation is approached from an indigenous knowledge perspective. There is an ancient Chinese practice of burning incense in closed rooms with stored pears. Burning incense releases (among other things) ethylene gas (Yang et al., 2007), which results in the ripening of the fruit. One of the aspects that students can investigate in this activity is the influence of burning incense on seed germination. An interesting discussion could also follow on the health hazards of burning incense. In many (especially Eastern) cultures, the burning of incense in temples and in homes is common practice. However, epidemiological studies have demonstrated a relationship between burning of incense and lung cancer, brain tumors, and childhood leukemia (Yang et al., 2007).

Another indigenous knowledge practice that students could investigate is the ancient Egyptian practice of wounding figs to enhance ripening responses. The ethylene produced by the injured fruit tissue triggers a broader ripening response. The experimental procedure could therefore include the use of a whole fruit, as well as a wounded fruit (e.g., cutting an apple into smaller pieces), so that students could test whether a wounded fruit releases more ethylene.

Scientists first noticed the effect of ethylene on plant growth in 1864. Girardin reported premature shedding of leaves near street lights. In those days, coal gas was used for street illumination, and this practice resulted in the release of ethylene. The recognition of ethylene as a plant hormone, however, is credited to Dimitry Neljubow, a graduate student at the Botanical Institute of St. Petersburg in Russia (Arshad & Frankenberger, 2002). In 1901, he was trying to grow peas in the laboratory. He noticed irregular growth: the germinating pea seedlings were very short, and the stems were large in diameter and bent sideways. This was later called the “triple response” of peas to ethylene. Neljubow discovered that this was caused by the air in the laboratory. The lab had gas lamps that produced ethylene gas.

When discussing indigenous knowledge in the classroom, it is advisable to focus students’ attention on the tenets of the nature of science, and on how these correspond to the tenets of the nature of indigenous knowledge. For example, both science and indigenous knowledge are empirical in nature, tentative (subject to change), and inferential (Cronje et al., 2015; also see Table 2). A pedagogy that could be used effectively in exploring the relationship between indigenous knowledge and Western science is de Bono's “thinking hats,” as described in De Beer & Whitlock (2009).

Current Research on Ethylene

Recent research has shown that ethylene has an important role in many plant development processes, including stimulation of seed germination (Nascimento, 2003; Cervantes, 2006), fruit ripening (Burg & Burg, 1962), leaf abscission, and senescence (biological aging; Rudman & Whitehead, 2015). Here, we focus specifically on the role of ethylene in seed germination, and students could do desktop research on the Internet and work on a group presentation on recent plant physiological studies on seed germination and ethylene. Recent research shows that ethylene can assist in overcoming seed dormancy in many species. Nascimento (2003) has shown that ethylene could induce seed germination in lettuce seed under high temperatures. High temperatures (35°C) inhibit seed germination in most lettuce cultivars, but ethylene has been shown to alleviate the inhibitory effects of high temperatures. Students could also be asked to design an experiment to test this in the lab.

Exploring the Role of Ethylene in Modern Society

There are many commercial applications of ethylene in modern society. Industrial reactions of ethylene include polymerization that results in polyethylene (or polythene), the world's most widely used plastic. Another commercial reaction includes the oxidation of ethylene to produce ethylene oxide, a key raw material in the production of surfactants and detergents. Another interesting area of research that students could explore is senescence, which is stimulated by the presence of ethylene. Ethylene binds to a membrane-bound receptor that then produces a signal that accelerates the rate of senescence in plant tissues (Rudman & Whitehead, 2015). In the florist industry, research is done to see how the postharvest lifetime of flowers could be improved, to inhibit the senescence triggered by ethylene. One product that is being used is 1-methylcyclopropene.

Laboratory Investigation

Students Formulate Hypotheses & Develop Experimental Designs to Explore the Role of Ethylene in Seed Germination

We suggest making use of both cooperative learning and problem-based learning. Johnson et al. (2008) define cooperative learning as group work that happens when students work cooperatively in small groups (three or four) to achieve a common goal. During problem-based learning, students use “triggers” from the problem, case, or scenario to define their own learning objectives (Wood, 2003). In the process, they use their critical-thinking and problem-solving skills to offer solutions to the problem. In this regard, the usefulness of ethylene in society can be portrayed as a problem to students. This problem can serve as a starting point where students must formulate a hypothesis and then design and execute an experiment in small groups. This topic fits well into high school Life Sciences (HS-LS 2 & 3) according to the Next Generation Science Standards (NGSS Lead States, 2013).

Learning Objectives

  1. Students should formulate a hypothesis on the role of ethylene in seed germination.

  2. Students should develop an experimental design, identifying the dependent and independent variables.

  3. Students should make valid conclusions based on the data obtained.

Questions to Ask

The following questions are useful to guide the students during their investigations (based on Lawson, 2010; De Beer, 2012):

  • What is puzzling about what you read?

  • What are possible explanations (hypotheses)

  • How might these explanations be tested? (Design an experiment to test your hypothesis.)

  • What are the expected results of the planned test(s)?

  • Following your test, what are the observed results?

Methods

In our own investigation, we wanted to see what the role of external ethylene is on seed germination. We decided to test the influence on seed germination of (1) burning incense (to determine the merit of the ancient Chinese custom of burning incense to help fruit ripen) and (2) ethylene released by scarred fruit tissue (to determine the merit of the Egyptian practice with wounded figs).

Our control consisted of three types of seed (beans, watermelon, and lettuce), and these seeds were placed between layers of wet cotton wool (see Figure 1), without any exposure to external ethylene. Seeds should be examined every day. It is essential to change the cotton wool every second day, or alternatively to use a fungicide, to prevent fungal growth (in Figure 2 we show the result if this does not happen).

Figure 1.

Setup on day 1. Testing the influence of ethylene on seed germination.

Figure 1.

Setup on day 1. Testing the influence of ethylene on seed germination.

Figure 2.

The cotton wool should be regularly inspected for fungal growth.

Figure 2.

The cotton wool should be regularly inspected for fungal growth.

We had five sets of experimental treatments. We exposed one set of seeds (for beans, watermelon, and lettuce) to burning incense (see Figure 1). The seeds were daily exposed to burning incense (in a bell jar) for 10 minutes. In the other four treatments (again for beans, watermelon, and lettuce) we used different types of fruit. Cutting a fruit stimulates ethylene production and release. We also wanted to see whether there are differences between so-called climacteric fruits (apple, pear, and banana) and a non-climacteric fruit (blueberry). Students can do desktop research on climacteric and non-climacteric fruits. Some fruits show a significant variation in the pattern of declining respiration rate during their ripening. They exhibit a distinct increase in respiration rate – a respirator climacteric – and are described as climacteric fruits (Frontline Services, 2015).

The results are shown in Figures 26. The apple treatment consistently provided the best results. Of the three types of seeds, beans provided the best results.

Figure 3.

Bean seeds after 48 hours. Germination started in the seeds treated with incense, and in all of the fruit (ethylene) treatments (except banana). The control seeds do not show signs of germination yet.

Figure 3.

Bean seeds after 48 hours. Germination started in the seeds treated with incense, and in all of the fruit (ethylene) treatments (except banana). The control seeds do not show signs of germination yet.

Figure 4.

Bean seeds on day 7.

Figure 4.

Bean seeds on day 7.

Figure 5.

Comparison of the control and experimental apple exposure on day 7.

Figure 5.

Comparison of the control and experimental apple exposure on day 7.

Figure 6.

Watermelon seeds on day 7. Germination has just started in the control seeds; the experimental apple-treatment seeds are showing advanced germination already.

Figure 6.

Watermelon seeds on day 7. Germination has just started in the control seeds; the experimental apple-treatment seeds are showing advanced germination already.

Figure 7.

Lettuce seeds on day 7. Germination occurs earlier in lettuce seeds (compared to watermelon), but again the experimental apple-treatment seeds show advanced germination.

Figure 7.

Lettuce seeds on day 7. Germination occurs earlier in lettuce seeds (compared to watermelon), but again the experimental apple-treatment seeds show advanced germination.

Investigating Variables

Students might decide to study the amount of ethylene released by whole fruit, or by fruit cut into smaller pieces (damaged plant tissue). There are several other investigations that students can engage in, such as designing an experiment to demonstrate the “triple response” of plants to ethylene; or the role of ethylene in overcoming seed dormancy under high temperatures. In each of these cases, students should formulate hypotheses and design laboratory procedures to investigate these variables.

Observations & Findings

All the experimental designs resulted in better germination of seeds, with the apple treatment providing the best results in bean, watermelon, and lettuce seeds. In watermelon seeds, the first signs of germination are visible in the control seeds on day 7, whereas the apple treatment already shows remarkable germination. The incense treatment also yielded positive results.

Assessment: Writing a Lab Report

It might be a good idea to include items such as the following, which students should also reflect upon in their laboratory reports. Figure 8 illustrates ethylene production, respiration rate, and the firmness of tomato fruit, during the fruit development stage. Students should study the graph and answer these questions:

  1. What do you observe regarding the production of ethylene and the firmness of the fruit?

  2. Carbon dioxide production is an indication of respiration. Explain how ethylene influences plant respiration.

Another graphing exercise is the following. Table 1 illustrates the changes in the internal ethylene concentration of apples during maturation on the tree.

  1. Draw a line graph to illustrate ethylene concentrations over the 30 days of this study. Provide an explanation for the big rise in ethylene concentration between day 22 and day 30.

  2. How can scientists determine ethylene concentrations? (Answer: through gas chromatography, using commercial equipment such as a Pye gas chromatogram. Ethylene can also be measured with a hydrogen flame ionization detector.)

Figure 8.

Ethylene and fruit development (based on data published by the Australian Society of Plant Scientists, 2010). Units: firmness = kg cm−2; CO2 = μmol/h/kg; ethylene = nmol/h/kg.

Figure 8.

Ethylene and fruit development (based on data published by the Australian Society of Plant Scientists, 2010). Units: firmness = kg cm−2; CO2 = μmol/h/kg; ethylene = nmol/h/kg.

Table 1.
Ethylene concentration of apples during maturation on the tree (based on Reid et al., 1973).
DayEthylene Concentration (parts per million)
0.026 
0.086 
0.082 
10 0.035 
14 0.058 
17 0.095 
19 0.098 
22 0.683 
30 2.32 
DayEthylene Concentration (parts per million)
0.026 
0.086 
0.082 
10 0.035 
14 0.058 
17 0.095 
19 0.098 
22 0.683 
30 2.32 

Conclusion

An interesting class discussion that could emerge is, for instance, the claim that the burning of incense is linked to the higher occurrence of lung cancer, brain tumors, and childhood leukemia. Students could also discuss the commercial use of ethylene in the fruit industry. These discussions and investigation will highlight for students the role and application of science in modern society.

The investigation described here can assist students in epistemological border-crossing as they consider the role of indigenous knowledge in modern-day science. Indigenous knowledge systems are receiving considerable worldwide attention, and this activity introduces indigenous knowledge in a manner that links it with the tenets of science. This also addresses the Vision and Change call for more interdisciplinary approaches in science teaching and learning.

Finally, these laboratory investigations provide empirical evidence for indigenous knowledge claims. You could facilitate a rich discussion in the classroom, utilizing the tenets of the nature of science and of indigenous knowledge, as pointed out in Table 2.

Table 2.
The tenets of the nature of indigenous knowledge (NOIK) in relation to the tenets of the nature of science (NOS) (based on Cronje et al., 2015, p. 323).
Tenet no.Tenets of NOIKTenets of NOS
1 Empirical and metaphysical
The universe is orderly, metaphysical, and partly predictable. 
Empirical
Nature is real, observable, and testable. The universe is orderly and predictable. 
2 Resilient yet tentative
Indigenous knowledge has withstood the test of time but is constantly changing as tradition also does. 
Tentative
Science is subject to change and is not absolute and certain. 
3 Inferential yet intuitive
Facts are tested and experimental observations are made. However, metaphysical dimensions are also included. 
Inferential
There is a clear distinction between observations made of nature and deductions or conclusions (inferences) made from observations to explain the causes. 
4 Creative and mythical
Observations and experimenting are not the only sources of ways of knowing. Human creativity, imagination, and metaphors also play a role. 
Creative
Observations and experiments are not the only sources of scientific knowledge. Human creativity and imagination also play a role. 
5 Subjective
Indigenous ways of knowing are based on cosmology and are interwoven with culture and the spiritual. 
Subjective (theory-laden)
Scientists strive to be objective and culture free, but as human beings they are often subjective and influenced by prior knowledge and beliefs. 
6 Social, collaborative, and cultural
Indigenous ways of knowing are situated in cultural tradition; it is locally rooted and ecologically based. 
Social and cultural
Although science is objective, it is a human endeavor and is therefore affected by a social and cultural milieu. 
7 Wisdom in action
Indigenous knowledge is generated by practical engagement in everyday life through trial-and-error experiences. 
Methods
Scientists use a variety of methods to solve problems and test theories. 
8 Functional application
Indigenous knowledge is concerned with the everyday lives of people rather than facts, theories, and laws. 
Theories and laws
Scientists use theories and laws to explain what, why, and how things happen in nature. 
9 Holistic approach
Problems are solved in a holistic manner, addressing all the smaller parts with no boundaries with the metaphysical world. 
Reductionist approach
Complex phenomena can be broken down into small parts and analyzed. 
Tenet no.Tenets of NOIKTenets of NOS
1 Empirical and metaphysical
The universe is orderly, metaphysical, and partly predictable. 
Empirical
Nature is real, observable, and testable. The universe is orderly and predictable. 
2 Resilient yet tentative
Indigenous knowledge has withstood the test of time but is constantly changing as tradition also does. 
Tentative
Science is subject to change and is not absolute and certain. 
3 Inferential yet intuitive
Facts are tested and experimental observations are made. However, metaphysical dimensions are also included. 
Inferential
There is a clear distinction between observations made of nature and deductions or conclusions (inferences) made from observations to explain the causes. 
4 Creative and mythical
Observations and experimenting are not the only sources of ways of knowing. Human creativity, imagination, and metaphors also play a role. 
Creative
Observations and experiments are not the only sources of scientific knowledge. Human creativity and imagination also play a role. 
5 Subjective
Indigenous ways of knowing are based on cosmology and are interwoven with culture and the spiritual. 
Subjective (theory-laden)
Scientists strive to be objective and culture free, but as human beings they are often subjective and influenced by prior knowledge and beliefs. 
6 Social, collaborative, and cultural
Indigenous ways of knowing are situated in cultural tradition; it is locally rooted and ecologically based. 
Social and cultural
Although science is objective, it is a human endeavor and is therefore affected by a social and cultural milieu. 
7 Wisdom in action
Indigenous knowledge is generated by practical engagement in everyday life through trial-and-error experiences. 
Methods
Scientists use a variety of methods to solve problems and test theories. 
8 Functional application
Indigenous knowledge is concerned with the everyday lives of people rather than facts, theories, and laws. 
Theories and laws
Scientists use theories and laws to explain what, why, and how things happen in nature. 
9 Holistic approach
Problems are solved in a holistic manner, addressing all the smaller parts with no boundaries with the metaphysical world. 
Reductionist approach
Complex phenomena can be broken down into small parts and analyzed. 

Assessment tasks that require students to compare the tenets of the nature of science and those of indigenous knowledge require the kind of critical and creative thinking expected in the 21st century. In a world that faces economic problems and high unemployment figures, indigenous knowledge systems also hold promise of developing entrepreneurship and job opportunities.

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