The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring an input of energy (often as ATP).
Can be used to "pump" against the concentration gradient.
Moves bulky materials.
Located on one of the lipid layers versus the other and they can freely move in and out.
Takes place in stroma. The 2nd of 2 stages of photosynthesis; a cyclic series of chemical reactions that occur in the stroma of a chloroplast, using the carbon in CO₂ and the ATP and NAPH produced by the light reactions to make the energy-rich sugar molecule G3P.