The Validity and Readability Test for the Development of PBLBased UKBM Teaching Materials on the Physics of the Human Circulatory System is Oriented Towards Students' Critical Thinking

The scientific literacy ability of Indonesian students is still low (Zahara & Atun, 2018). Indonesia ranks 74th out of 79 countries with an average scientific literacy score of 389 (Schleicher, 2018). PISA's scientific literacy scores can show the critical thinking skills of junior high school students (Pratiwi, 2019). Students' critical thinking ability is one of the high-level skills that are needed in the teaching and learning process (Bustami et al., 2019). According to Piaget's theory of development, the age of junior high school children is a transition from the concrete thinking stage to the formal thinking stage (Santrock, 2008). Armed with critical thinking skills, students can connect abstract learning materials with phenomena in everyday life (Yustiqvar, 2019). Several indicators can be used to assess students' critical thinking activities, namely classifying, assuming, predicting, designing investigations, minimizing errors in investigations, observing, making graphs, interpreting data, analyzing, making conclusions, and evaluating (Carin, 1998). Critical thinking skills can train students to decide solutions to a problem, so they can optimize learning outcomes (Rusdi et al., 2016). To improve students' literacy skills, it is necessary to make improvements in classroom learning (Hewi & Shaleh, 2020). Improvements can be made through the development of lesson plans (Depdiknas, 2008). Planning in learning includes lesson plans, syllabus, teaching materials, learning media, learning resources, assessment tools, and learning scenarios (Per