There are two properties of the cell necessary to maintain nonequilibrium cellular composition; the first is selectivity and the second is energy conversion. Which of the following statement(s) is/are true concerning energy converting transport?

c. In some systems, energy inherent in the transmembrane ion gradient can be used to drive transport of a second species

d. Examples of species transported via secondary active transport include hydrogen ions, calcium, amino acids and glucose

The selectivity of the plasma membrane, although impressive, cannot account for the nonequilibrium composition of living cells. A cell can be maintained in a nonequilibrium state only by continual expenditure of energy. The maintenance of a steady-state, nonequilibrium cellular composition is possible because the plasma membrane is the site of energy converters, membrane proteins that function as biologic transport machines using energy derived from metabolic processes to perform transport work. The archetype for the biologic transport machine is the Na+-K+-ATPase, a membrane protein that hydrolyses cytosolic ATP and couples the resulting free energy to transport of Na+ and K+. A second equally important  type of energy-converting transporter is one in which the energy inherent in a transmembrane ion gradient, usually that of Na+ can be used to drive the transport of a second species such as protons, calcium, amino acids, or glucose.