Which type of mutation results in a base pair within a dna sequence being replaced with a different pair?

Which type of organism is missing from the food web seen in the illustration? primary consumers decomposers primary producers secondary consumers

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?

Which layer will become saturated first when rain falls?