In geology say, a gross sample would be a representative sample of the whole rock. A lab sample would be a fraction of that, refined such that measurements are able to be made on a single mineral.

for example, a piece of basalt would be a convenient field (gross) sample, from which say, mica is extracted after grinding and separation, to enable the 'date' of the basalt to be determined.

Similar concepts would apply in other fields, such as biology, botany, water sampling and so on.

That sample which consists of several portions.It may be pure or impure.It may be heterogeneous or homogeneous.

It ensures that all the heat must enter the water, which in turn raises its temperature.

if there was not enough water to completely cover the sample, then some of the heat could be lost directly to the air, resulting in a (potentially gross) underestimate of the heating value of the sample.

random sample is a big sample and convenience sample is small sample

a sample is a sample sized piece given... a sample size is the amount given in one sample