The main source of energy for all life comes from

the sun

Explanation:

The Sun is the major source of energy for organisms and the ecosystems of which they are a part. Producers, such as plants and algae, use energy from sunlight to make food energy by combining carbon dioxide and water to form organic matter. This process begins the flow of energy through almost all food webs.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.