Final answer:
The cellular membrane manages entry and exit of substances through passive transport, requiring no energy, and active transport, which requires energy.
Step-by-step explanation:
The cellular membrane controls what goes into and comes out of a cell, maintaining a state of semi-permeability. This is integral to the cell's ability to sustain life. There are multiple modes of transport across a cellular membrane:
- Passive Transport: This includes processes that do not require energy, such as diffusion, osmosis, and facilitated diffusion.
- Active Transport: This type of transport requires energy, often in the form of ATP, to move substances against their concentration gradient via transport proteins or pumps.
Passive transport is efficient for small, nonpolar molecules like O2 or CO2, which can diffuse directly through the phospholipid bilayer.
In contrast, facilitated diffusion requires specific transport proteins to move substances like glucose or ions across the membrane.
Substances that are vital to the function of a cell, like sodium (Na+) or potassium (K+), often necessitate active transport mechanisms to maintain necessary concentrations inside the cell.