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1. Introduction  
The development of the 21
st
century requires everyone to have a variety of skills in order to live in a 
global society. Asrari states that one of the skills that is needed is critical thinking skills [1]. Partnership 
for 21
th
Century Skills (P21) also emphasized that 21
st
century learning must be able to create students 
who have the ability to think critically, solve problems, communicate, and collaborate [2]. As a 
developing country, progressing toward more democratic society and economically, Indonesia has 
realized its role in world matter. To play more role in this manner, Indonesia require qualified human 
resource. Education is one of the potential fields to produce human resources who could bring the 
country to a greater prosperity. Through education, young Indonesian are expected to be critical, 
creative, innovative, confident, tolerant, socially sensitive, democratic, and responsible [3]. These are 
some of the qualities clearly stated in the Regulation of the Republic of Indonesia Number 17 Year 2010. 
The Government through the Ministry of Education and Culture in Indonesia applies the 2013 
curriculum with various improvements, one of which is intended to improve critical thinking skills so 
that it can encourage students to think broadly and deeply about learning material [4]. 
When it comes to educational management and administration as educational objectives, however, 
there seem to be some constraints on achieving these stated objectives. In fact, the ability of students in 
Indonesia is still very low. Based on the results of Program for International Students Assessment (PISA) 
2015, it was found that out of the 6 levels of ability formulated in the PISA, only 31% of Indonesian 
students mastered the lesson to 4th level. Indonesia ranked 62nd out of 70 countries that participating in

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The International Seminar on Bioscience and Biological Education
IOP Conf. Series: Journal of Physics: Conf. Series 1241 (2019) 012020
IOP Publishing
doi:10.1088/1742-6596/1241/1/012020
2
PISA 2015 [5]. As stated in the PISA analysis, students in Indonesia have a low ability in: (1) linking 
science to everyday life; (2) interpret data; (3) analyze and solve problems; (4) conducting 
investigations; (5) concluding based on logical reasons; and (6) understanding complex information [3]. 
It may not be easy to produce people with the aforementioned qualites and to make people aware of 
the importance of them if practicioners in education are not clearly directed toward those goals. The 
development of critical thinking skills does not appear to have been seriously support in secondary 
education throughout the country. This idea supported by Alfianti which states that learning in Indonesia 
has not included the content of critical thinking. Teachers have not encouraged critical thinking skills in 
learning, so students are not challenged to think critically [6]. Most teachers in Indonesia have not clearly 
understood what critical thinking is and how to incorporate critical thinking into their teaching [7]. 
Aside form failing to encourage critical thinking, Indonesian school teacher still utilize traditional 
teaching methods, for example, teachers read from textbook, dictate, or write on the whiteboard while 
student listen and copy [8]. Education in Indonesia requires a new paradigm in the learning process, 
including learning biology. Biology as a science is not just knowing and memorizing about biological 
concepts, but the process of learning biology is expected to foster the skills of critical thinking, work, 
and scientific attitude [9].
The result of the observations conducted in November 2017 on SMA Negeri 2 Sleman showed that 
biology learning activities in the classroom mostly use expository method. The teacher explain and 
demonstrates, then the students hear, take notes, and do the task according to what the teacher instructs. 
Learning activity mostly oriented to remembering information contained in the textbooks without 
connecting in to real life. Learning methods applied by the teacher do not get an active response from 
students. This condition seen during the learning process, most students are less involved in learning 
and choose to do other activities such as chatting with friends. 
The topic in this research, immune system, is choosen because the charateristic of immune system 
material required the student to think critically in order to understand the material. Immune system 
contain complex physical and chemical mechanisms. Immune system also has a causal mechanism and 
physiological processes, so that in learning the material, students need critical thinking skill in order to 
mastering abstract consept [10]. Learners in studying immune system need the ability to understand the 
mechanism of physiology and link it causally to the phenomena of the immune system. Accurate 
conception and critical thinking about the immune system are important for the development of 
reasoning skills. Such material characteristics became a challenge for the student because it is hard to 
understand the concept with memorization [11].
Suhartono states that problems related to immune system learning include learning strategies. 
Teachers find difficulty to design learning strategies because of the short time to teaching immune 
system material, so that teachers tend to use the lecture method. Lecture learning strategies have the 
potential to cause student’s low critical thinking skills [10]. One of the effective learning approach to 
improving critical thinking skills is problem based learning. Problem based learning is a learning 
approach that uses problem as a context for students to learn through critical thinking and problem 
solving processes. Learners who learn to solve problem problems will make them apply the knowledge 
they have or try to know the knowledge they need. Learning can be more meaningful and expanded 
when students are faced with situation where the concept is applied. Learners integrate knowledge and 
skills well and continously, and can apply them in relevant contexts. Problem based learning can also
improve critical thinking skills, foster initiative in work, internal motivation to learn, and can develop 
interpersonal relationship through working in group [12].
Several previous studies have proven that through problem based learning implementation, student’s 
critical thinking skills can be developed. Problem based learning is used to improve critical thinking 
skills by using human physiology cases into nursing learning [13]. The results of the Experimental 
Biology workshop in Washington DC states that to improve critical thinking skills in learning 
physiology, problem based learning is used by using real-life cases that contain basic physiological 
concepts [14]. Abraham states that learning physiology can be done by linking physiological research 
to real life problems so it can produce enthusiasm and motivation to learn and to show the relevance of 

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The International Seminar on Bioscience and Biological Education
IOP Conf. Series: Journal of Physics: Conf. Series 1241 (2019) 012020
IOP Publishing
doi:10.1088/1742-6596/1241/1/012020
3
the basic concepts of physiology in the real life of students. The basic elements of integrating basic 
physiological concepts can be put in the form of critical thinking questions and case studies on the topics 
taught [15].