Get expert help for Emath, Amath, Physics and Chemistry at Eton Tuition Centre (next to Hougang Mall). Tel: 63853133 A friends Centre, where I tutor O-level Chemistry. Note that for a 5 mark question, there are at least 6 marking points. Important terms such as stimulus and receptor/nerve endings typically score a mark each for the O-levels, but are typically one mark total for school exams.