Why can some ions move across membranes but others cannot

What is the importance of having the us forest service, the bureau of land management, the us fish and wildlife service, and the national park service? to manage land resources for conservation and the development of natural resources to manage land resources for conservation and the development of urban areas to preserve historical landmarks and manage the development of urban areas to preserve historical landmarks and manage the development of rural areas

The activity of the modern sample is 1.10 bq . how long does that measurement take?

What will happen if two of the base pairs of the stand of the dna are switched