Among other physical seed factors, some seeds (e.g. bean seeds) have softer shells and others (e.g. Coconut) have harder shells, which has an impact on the time, water, oxygen, pH level and temperature required for germination. Generally, weaker seeds require more specific, and smaller quantities, whereas stronger seeds have much larger tolerable ranges for factors that affect seed germination. Stronger seeds can be considered as 'easier' to grow, as there would be less room for error, and thus would be a wiser option to conduct a practical with.