The purpose of this study is to explore an experienced science teacher’s pedagogical content knowledge (PCK) about circulatory system by using framework developed by Magnusson, Krajcik and Borko (1999). One of the important characteristics that effective teachers have is pedagogical content knowledge (Magnusson et al., 1999). PCK, differentiates teacher from subject specialist, is presented by Shulman (1986). Teachers’ PCK represents that how teacher planned and enacted lesson according to students’ level and their learning difficulties and diverse interest of students at specific-topic (Shulman, 1987). This is a kind of transformation of teachers’ subject-matter knowledge into instruction to access student (Geddis, 1993). Although there are many PCK frameworks (i.e., Grossman, 1990; Cochran, DeRuiter, & King, 1993; Veal & MaKinster, 1998), the ones proposed by Magnusson et al., is the comprehensive one and includes orientations toward teaching science, knowledge of science curricula, knowledge of students’ understanding of science, knowledge of instructional strategies, and knowledge of assessment in science. Teachers’ orientation toward science shapes other components while teacher planning and enacting lesson. Knowledge of science curricula is examined into two aspects which are specific science curricula and science goals and objectives. Knowledge of instructional strategies includes domain specific strategies which is teachers’ knowledge for any science topic and topic specific strategies like representations and activities. In respect of teachers’ knowledge of students’ understanding of science, teachers’ knowledge about students’ learning difficulties such as misconceptions and their learning needs are examined. Knowledge of assessment strategies represents both teachers’ methods to asses students and what the teacher evaluates.

Considering the topic specific nature of PCK, current study exploresscience teachers’ PCK (knowledge of science curriculum, knowledge of students, knowledge of instructional strategies, knowledge of assessment strategies) regarding circulatory systems. Understanding of circulatory system is crucial for students to comprehend homeostasis because circulation of blood is important to support working conditions in our body (Sungur, Tekkaya, & Geban, 2001). Moreover, the human body systems play an important role in the elementary and secondary school curriculum and are taught first at the 6^th grade in the elementary science curriculum thus they have curriculum significance. However, students have misconceptions such as “Contraction of heart is one of the factors that help blood return to the heart.”(Alkhawaldeh, 2007, p. 215), and “Circulatory system is an open system.” (Sungur et al., 2001). Not only students but also teachers have misconceptions such as “The reason for the low velocity of the blood in the capillaries is that the capillaries have high resistance due to the narrow diameter of the vessel.” (Yip, 1998).

Case study (Merriam, 2009) which is one of the common qualitative methodology design was selected in the current study. Semi-structured interviews include Content Representation (CoRe) questions (Loughran, Mulhall, & Berry, 2004), researcher’s field-notes, observations during instruction were used to gather data. Interviews helped teachers to reveal their rationale for teaching decisions. After classroom observations, post-interview was conducted whether there are differences between teacher’s planned and enacted instruction. Audio was recorded during interview and classroom observation under favor of teacher’s permission. Data were analyzed by using inductive method. To increase internal validity, member checking was used to control results whether there is misinterpretation or not (Stake, 2010). In addition to this, triangulation which increases internal validity (Merriam & Tisdell, 2016) was supported by using both observation and interview to gather data. We employed a purposeful sampling strategy (Merriam & Tisdell, 2016). The teacher has 20 years of experience and working at one of the private schools in Ankara, capital of Turkey. Although graduated from chemistry department, she enrolled in a graduate science teacher certification program. She has been teaching science for 18 years.

The teacher defines the purpose of teaching science in elementary school as to educate students as scientifically literate and enable them to make sense of nature and events in nature. She explains student needs by saying “they learn better when they are a part of the process by observing, and experimenting.”. She knows that the circulatory system is taught in the 6th grade as a 2nd unit, and defines the course objectives correctly as “to know the structure and organs in the circulatory system, to know the function of each of them, and also pulmonary circulation, systemic circulation, blood groups, blood transfusion”. She appears to be aware of students’ difficulties and misconceptions and stated that students especially had difficulty in understanding the path of blood flow in both pulmonary and systemic circulation. She seems to be informed about knowledge of instructional strategies and mentioned that she uses 5E learning cycle model to plan all instructions, including circulatory system. She told that she uses heart dissection as one of the activities in the classroom to make vessels, chambers and valves of heart more visible to students besides showing animations related to blood circulation (topic-specific strategy). As an assessment strategy, she focuses on assessment of objectives given in the curriculum. She evaluates students’ understanding by using questioning, open-ended questions and multiple choice examination. Although limited to only one teacher, this study offers important implication for teacher researcher in the field of pedagogical content knowledge regarding complex body systems.

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