In AQA, each science is split into three modules- P1, P2, P3; B1, B2, B3; and C1, C2, C3. The number of modules that you do depends on which qualification that you study- Core Science, Additional Science or Triple Science.
For Core Science, you study P1, B1 and C1, taking three exams at the end of two years. At the end you attain one grade in core science.
For Additional Science, you study the Core Science modules (P1, B1, C1) as well as three more: P2, B2 and C2. In this qualification, six exams are taken. You obtain two GCSEs through this: core science & additional science.
In triple science, all three modules are studied: P1, P2, P3; B1, B2, B3; and C1, C2, C3, with nine exams taken at the end of two years. Each science is treated individually, so three separate science GCSEs are obtained: Physics, Biology and Chemistry.
Triple science is treated the hardest out of the three options, as three modules are taken in each science, getting progressively harder.
*The letter at the start of the module name (e.g. P1) refers to the name of the science: Physics, Biology or Chemistry.