What is the process called when molecules move across the membrane without requiring energy?
What is the process called when molecules move across the membrane without requiring energy?
Active transport
Simple diffusion
Facilitated diffusion
Osmosis
Solution
To solve the question of identifying the process by which molecules move across a membrane without requiring energy, let's analyze each option:
1. **Active Transport:**
- Active transport involves the movement of molecules across a membrane from a region of lower concentration to a region of higher concentration.
- This process requires energy, usually in the form of ATP, because it is against the concentration gradient.
2. **Simple Diffusion:**
- Simple diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
- This process does not require energy as it occurs along the concentration gradient.
- It typically involves small and nonpolar molecules that can easily pass through the lipid bilayer of the cell membrane.
3. **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.
- Like simple diffusion, it does not require energy.
4. **Osmosis:**
- Osmosis is a specific type of diffusion that involves the movement of water molecules through a selectively permeable membrane.
- It occurs from a region of lower solute concentration to a region of higher solute concentration.
- Osmosis does not require energy.
Given these explanations, the process described in the question is **Simple Diffusion**, as it involves the passive movement of molecules across the membrane without the need for energy input. Therefore, the correct option is:
**Option B: Simple Diffusion**