Name the standard method used for collecting and preserving biological evidence.

The standard method for collecting and preserving biological evidence involves air-drying the samples and packaging them in breathable containers. This approach is critical because biological materials, such as blood, saliva, or other bodily fluids, can be highly susceptible to degradation due to moisture. By allowing these samples to air-dry, the risk of mold growth and bacterial contamination is minimized, thereby preserving the integrity of the evidence for analysis.

Using breathable containers, such as paper bags or envelopes, ensures that air can circulate around the samples, preventing moisture accumulation that could compromise the evidence. This method is widely accepted and recommended in forensic protocols for handling biological evidence in order to maintain its viability for future examination and testing.

Other methods listed, such as freezing and sealing in plastic or direct storage in liquid nitrogen, can actually be harmful to most types of biological evidence because they can cause cellular damage or degradation. Heating is also not a suitable method for preserving biological samples, as high temperatures can lead to the breakdown of crucial biological components. Therefore, the air-drying and breathable container technique is the most effective and scientifically sound approach for preserving biological evidence at crime scenes.