a: Diffusion ~
b: coasting your bike down a hill
What: "If diffusion is like coasting your bike down a hill, then active transport is like using energy to pedal your bike up a hill. Cells need large amounts of glucose to be used as energy. The cells need to move the glucose from an area of low concentration (outside the cell) to an area of high concentration (inside the cytoplasm). This is the opposite of diffusion. This controlled movement (active transport) of glucose through the cell membrane take energy and is controlled by proteins embedded in the membrane. The proteins are called carrier proteins. The carrier proteins act like the guards in front of the castle gates -- they only allow certain things through the gate."
Writer: Robert Geary
Where: Reference Link Has Evaporated
Date: Dec 30 2013 6:25 PM
# 4529 Critique Analogy