Teaching enzymes to pre-service science teachers through POE (predict, observe, explain) method: The case of catalase

The students took part in predict stage in all of the activities carried out in this study. It was seen in the predict stage that the pre-service teachers had imperfect or incorrect knowledge and misconceptions on some subjects (Tekkaya et al., 2000a; 2000b; Sungur et al., 2000; Dikmenli et al, 2002; Tekkaya and Balcı, 2003; Yıldırım et al., 2004; Konuk and Kılıç, 2002; Çepni et al., 2006; Köse, 2007).

In the predict stage of the activities based on the POE method, the students realized that their prior knowledge was not enough to explain new events. They corrected such imperfect knowledge in the explain stage following the observe stage. Consistently with the results of this study, previous experimental research shows that the POE method is effective in creating a conceptual change (Kearney, 2002a; 2002b; Kearney and Treagust, 2000a; 2000b; Köseoğlu et al. 2002; Wandersee et al., 1994; McGregor and Hargrave, 2008; Liew and Treagust, 1995; 1998).

The following conflicts indicate the existence of an inconsistency between their predictions and their observations: prediction was that enzyme had run out in the liver while the observation result was that reaction took place in both tubes and thus enzymes could be used again and again as long as substrate was available in the environment; prediction was that the gas to come out as a result of reaction was CO₂ while the observation result was O₂; prediction was that reaction would take place in all of the test tubes because the potato had protein structure and the apple was acidic, but the reason was different though the observation result was the same as the prediction; prediction was that reaction would take place only in the tubes containing the liver and the chicken because the others did not contain catalase, but the observation result was that reaction took place in all of them, and indeed all of them contained catalase; prediction was that reaction would take place only in the tube containing the liver as the others did not contain enzyme, but the observation result was that reaction took place in all of them; prediction was that catalase was unique only to the liver and did not exist in the others and thus reaction would not take place in the tubes containing the others, but the observation result did not prove that to be true; prediction was that as the contact surface decreased, reaction rate would increase, and the fastest reaction would take place in the 2nd tube, but the observation result was that the fastest reaction took place in the 3rd tube. It can be said that this improved learning in a different dimension. Thus, it is thought that the method has self-control within itself and thus reduces the amount of mistakes made by students and provides permanent learning through doing, observing, and reinforcing with explanations.Though the students had difficulty in predicting in the present study, it is thought that the observe stage of the POE method helped students reconstruct their prior knowledge. Some previous studies (Mthembu, 2001; Liew and Treagust, 1995; 1998) explored the effect of the POEmethod on understanding science subjects and concluded that it improves students’ levels of understanding subjects and enriches the process of using knowledge. It is also possible to say that the POE method makes a positive contribution to students’ levels of understanding experiments (Tekin,2006; 2008b; Wu and Tsai, 2005; Bilen, 2009).

Literature does not contain any other study dealing with the use of the POE method in teaching enzymes. There is no general attempt in which each stage of the method is evaluated separately and then its success is explored as a whole. The related studies in literature generally report that activities carried out by use of the POE method improve success (Tao and Gunstone 1997; Windschitl and Andre, 1998; Kearney and Treagust, 2001; Kearney, Treagust, Yeo and Zadnik, 2001; Kearney, 2004; Küçüközer, 2008; Bilen and Aydoğdu, 2010; Bilen and Köse, 2012a; 2012b; Akgün, Tokur and Özkara, 2013; Yavuz and Çelik, 2013; Harman, 2014; 2015). Likewise; it is reported that the method improves student success (Karatekin and Öztürk, 2012; Mısır and Saka, 2012a; 2012b) and has a positive effect on understanding subjects (Tekin, 2008a; 2008b) and opinions about scientific knowledge (Akgün, Tokur and Özkara, 2013).

The overall success rate of the POE was found to be 79.16% for the activity entitled, “The Effect of Catalase”, 73.86% for the activity entitled, “Catalase Concentration”, 96.64% for the activity entitled, “Relationship between Catalase Concentration and Surface Increases in a Liver Piece”, and 86.55% for the activity entitled, “Can Catalase Be Reused?”.

The method was seen to have a lower overall success rate for the activity entitled, “Catalase Concentration” in comparison to the other activities. The problems resulting from the prior knowledge of the students about enzyme concentration still continued. Literature contains no study about enzyme concentration in living being pieces but involves studies dealing with general misconceptions about enzymes (Atav et al., 2004; Selvi and Yakışan, 2004; Marini, 2005; Emre and Yılayaz, 2006; Sinan, 2007; Orgill and Bodner, 2007; Linenberger and Bretz, 2012). It was also determined in the present study that the students had learning difficulties on the subject of enzymes and some students had misconceptions in this matter.

The high success rate achieved in the activity entitled, “Relationship between Catalase Concentration and Surface Increases in a Liver Piece” is supported by research reporting that experiments carried out based on the POE method have positive effects on understanding a subject (Tekin, 2008a; 2008b); the POE method supports the experiments carried out for proving purposes in terms of conceptual understanding (Tekin, 2008b); the method increases students’ interest in and willingness and curiosity about experiments (Karaer, 2007) as well as their motivation; the method is interesting (Tekin, 2008b; Mısır and Saka, 2012a; 2012b); and the method ensures active participation in lessons and has positive effects on socialization (Mısır and Saka, 2012a; 2012b).

Literature contains studies whose results are in line with the results of the present study. Such studies report that the POE method is an effective method for construction of concepts and for meaningful and permanent learning (Bilen and Aydoğdu, 2010; Özdemir, Köse and Bilen, 2012; Yavuz and Çelik, 2013); allows teaching a lesson effectively and makes students notice their mistakes personally (Bilen and Köse, 2012b); improves problem-solving, conceptual understanding, and application skills (Mısır and Saka, 2012a; 2012b); and contributes to the elimination of misconceptions (Bilen and Köse, 2012a; Mısır and Saka, 2012a; Özdemir, Köse and Bilen, 2012; Öner-Sünkür, İlhan and Sünkür, 2013; Yavuz and Çelik, 2013).

All in all, it is thought that the POE method is quite appropriate for teaching experimental activities in science lessons. The POE method is not appropriate for teaching all subjects and concepts in the curriculum, which is also true for other teaching methods, but is very effective for covering experimental and practical subjects. Though it activates students’ prior knowledge, leaves the resolution of conflicts to students, makes students implement its stages without skipping any, and can be defined as a more constructive method in comparison to other concept teaching strategies, certain difficulties are confronted during its implementation. Especially in crowded classroom environments, problems are faced in monitoring students, class management, making correct observations during the experiment, evaluating student performance, making a proper use of prior knowledge, ensuring students’ active participation, reaching the information, and interpreting the events correctly. Researchers should take into consideration these difficulties or problems before implementing the method and take necessary measures for more effective educational activities.