Random sampling means selecting samples by chance, with each sample having an equal likelihood of selection.

Non-random sampling involves selection based on specific criteria or patterns and the sample is not chosen at random.

Systematic sampling is a non-random sampling method where different areas within a habitat are sampled at regular intervals to avoid bias.

It is often carried out using a line or a belt transect.

The advantage of systematic sampling is that it allows for the study of how species' distributions change across different areas within a habitat.

Transect sampling is a method of studying the distribution of organisms in a specific area. It involves marking a line (transect) and taking samples along this line at regular intervals.

A belt transect uses a quadrat to take samples along one marked line, or by marking two parallel lines and sampling the area between them. Belt transects provide more information than line transects. 

A line transect does not use a quadrat, but involves marking a single line and taking samples along it.

A way to remember this is that a quadrat on a tape measure line looks like the buckle on a belt, so quadrats are only used in belt transects.

Abiotic factors, like light intensity, pH and water availability, directly impact the living organisms in a habitat.