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what does the difference in charges across the membrane provide energy to do?

answer:

the difference in charges across the membrane provides the energy to make atp. however, the membrane contains a protein called atp synthase (sin-thays) that allows h+ ions to pass through it. as h+ ions pass through this protein, the protein rotates like a turbine being spun by water in a hydroelectric power plant.

explanation: google

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.