Problem-solving skills are the skills essential for students to have. This research aimed to analyze the problem-solving skills of senior high school students in biology learning of excretory system topics. The method used was descriptive-quantitative. The data were collected using a problem-solving essay test. The subjects were the eleventh-grade students of senior high schools in Surakarta, who were divided into A category (upper class) and B category (low level). Based on the analysis result, it can be seen that the problem-solving skill achievement of the eleventh grade of A group includes: defining the problem (50.78%), examining the problem (40.62%), planning a solution (19.53%), implementing the solution (37.50%), and evaluating (40.62%); while that of B category includes: Defining the problem (46.35%), examining the issue (34.67%), planning a solution (18.54%), implementing the solution (20.96%), and evaluating (32.25%). The lowest percentage in both categories was found in planning the solution and evaluating. Based on the result, the average problem-solving skills in A group is 37.81% and B Category 32,26%. Based on the data, it can be concluded that students' problem-solving skills in A and B categories are still low. The skills can be improved by conducting problem-solving based learning and familiarizing students to solve problems according to problem-solving stages.

Analytical thinking is a complex skill because it uses element of knowledge, understanding thinking. The skill is essential in learning excretory system which demands them to understand the concept, principle and application in life. This research was carried out to investigate the students' analytical thinking in doing excretory system concept. Method used was quantitative descriptive with 120 students as the subject. The instrument used was test based on total score in every indicator. The result showed that students' error percentage in doing the items in every indicator of analytical thinking was: 10.5 % Examining Ideas, 14% Identifying Argument, and 25.5% Analyzing Argument. Therefore, it can be concluded that students' analytical thinking skill was relatively low. Therefore, teachers must train students to do analytical questions or use appropriate strategy.