Some propreties about $ \mathfrak{Coh}_X $ and $ \mathfrak{QCoh}_X $.

Question

I would like to know :

• why is the category $ \mathfrak{Coh}_X $ of coherent scheaves the smallest abelian category containing line bundles ?
• Why is the category $ \mathfrak{QCoh}_X $ of quasi coherent scheaves the smallest abelian category containing locally free scheaves ?

Thanks a lot for your help.