General science is usually given in years S1 and S2 to give pupils a "taster" of each of the three sciences (biology, chemistry and physics) so that they can get an idea what they would like to go on to study in further years at school.
Every school is different in how they teach science; some may work on a rotation where the pupils move to a chemistry teacher for this part of the course then to the other subjects in turn. Other schools may settle with the class having one science teacher for the whole year and that's why a biology/ chemistry/ physics teacher must also function as a science teacher.
A pupil will be graded in general science and this will be carried out to find out what level of standard grade/ intermediate that student will go on to take in S3 and S4, or to determine how many sciences the child will do. If a child does very well in S2 then they could be recommended to do all three sciences.
The content of the science course includes: processes of life, biotechnology, metals, chemical reactions, forces, electricity and many more.