Multiple Choice
How is active transport different from diffusion?
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6. The Membrane
Passive vs. Active Transport
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How is active transport different from simple diffusion and facilitated diffusion?
A
Active transport moves substances down their concentration gradient, unlike simple diffusion and facilitated diffusion.
B
Active transport involves the movement of water molecules, unlike simple diffusion and facilitated diffusion.
C
Active transport requires energy input, while simple diffusion and facilitated diffusion do not.
D
Active transport only occurs in plant cells, whereas simple diffusion and facilitated diffusion occur in all cell types.
Verified step by step guidance1
Understand the concept of concentration gradient: In biology, a concentration gradient refers to the difference in the concentration of a substance between two areas. Substances tend to move from an area of higher concentration to an area of lower concentration, which is known as moving 'down' the concentration gradient.
Define simple diffusion: Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy or assistance from transport proteins. It occurs directly across the phospholipid bilayer of the cell membrane.
Define facilitated diffusion: Facilitated diffusion is similar to simple diffusion in that it moves substances down their concentration gradient. However, it requires the assistance of transport proteins embedded in the cell membrane to help certain molecules, such as ions or larger polar molecules, cross the membrane.
Define active transport: Active transport is the movement of molecules across a cell membrane from an area of lower concentration to an area of higher concentration, which is 'against' the concentration gradient. This process requires energy, usually in the form of ATP, because it is moving substances against their natural flow.
Compare the processes: Active transport differs from both simple and facilitated diffusion in that it requires energy input to move substances against their concentration gradient, whereas simple and facilitated diffusion do not require energy and move substances down their concentration gradient.
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