Core Practical: Investigate the relationship between organisms and their…

The idea

This core practical asks you to carry out real fieldwork, not just describe it. Choose a site where an environmental factor changes, such as light intensity from a woodland edge into open field, or trampling pressure across a footpath. Place a quadrat randomly by using random numbers to pick coordinates, then record the organisms inside and measure the abiotic factor at the same spot. For a belt transect, run a tape across the gradient and place quadrats at regular intervals along it, recording organisms and the changing factor at each station. Repeat readings to improve reliability, keep sampling the same quadrat size, and identify species consistently. You then look for a relationship between the distribution or abundance of organisms and the environment.

What earns the marks

• States that a quadrat samples a known area and is placed randomly, for example using random number coordinates, to avoid bias.
• Describes a belt transect as a line across a gradient with quadrats placed at regular intervals, recording organisms at each position.
• Identifies that an abiotic factor such as light intensity, soil moisture or trampling is measured at each sampling point alongside the organisms.
• Explains that repeats or multiple quadrats improve reliability and that consistent quadrat size and identification keep results comparable.
• Recognises that the investigation looks for a relationship or correlation between organism distribution and the environmental factor.

Common mistakes and how to put them right

• Thinking quadrats are placed wherever the learner chooses.

  Put it right: Is that random placement using random numbers reduces bias.

• Confusing a belt transect with a single quadrat.

  Put it right: Is that a belt transect samples along a line at regular intervals across a gradient.

• Recording only organisms and ignoring the environmental factor.

  Put it right: Is that the abiotic factor must be measured at each point to reveal a relationship.

Exam tips

• Link each technique to its purpose: quadrats estimate abundance in an area, belt transects show change along a gradient.
• Name a specific abiotic factor and say how it is measured at each sampling point.
• Explain why repeats and random placement matter, using the words reliability and bias correctly.