In this deck, we'll explore the required practical for sampling organisms. It's often impossible to count every single plant or animal in an area, so ecologists use sampling to estimate population sizes and see how species are distributed. We'll cover the two main techniques you need to know for your GCSE exam: random sampling with quadrats, and systematic sampling with transects.

Let's start with random sampling. You use this method when you want to estimate the population of a species in a large, fairly uniform area, like a school field. The key to random sampling is avoiding bias, which means you can't just throw your quadrat wherever you like. Instead, you need to be systematic about being random.

To carry out random sampling, you first create a grid of the area. An easy way to do this is to lay two tape measures at right angles along two sides of the field. Then, you use a random number generator to create pairs of coordinates. You walk to these coordinates and place your quadrat down. You then carefully count the number of your target species inside the quadrat. You must repeat this process many times to get a reliable estimate.