IB Biology SL Extended Essay Example

The student communicates the biological context clearly and shows why eutrophication and algal growth are relevant.

The student's research question is specific, measurable, and time-bound, which gives the investigation a clear experimental direction.

The student justifies key methodological choices, including the use of preliminary testing to select a counting method.

The student's independent variable is not kept consistent throughout the report, as the method uses fertiliser mixtures rather than nitrogen alone.

Several controls are described too vaguely, especially light and temperature.

The method does not fully isolate the effect the student claims to test, which weakens the precision of the investigation.

The student uses biological terminology accurately in many places, including eutrophication, nutrient assimilation, and growth-related concepts.

The student applies a range of relevant source material from scientific and institutional sources.

The student connects background biology to the investigation in a way that supports understanding of the topic.

Some source material is transferred too directly across different species or nutrient contexts.

The report alternates between nitrogen concentration and fertiliser concentration, which weakens conceptual precision.

Some chemical notation and statistical language are not always used accurately.