Question

What are the differences between diffusion, osmosis, facilitated diffusion, and active transport? How are these processes related to transport across the cell membrane?

Answer 1

- The power of the cell membrane to control the concentration of substances within the cell is one of its greatest achievements.
- These compounds contain ions like Ca, Na, K, and Cl, as well as nutrients like carbohydrates, fatty acids, and amino acids, as well as waste materials including carbon dioxide $(CO_2)$.
- The lipid bilayer arrangement of the membrane provides the first degree of regulation by allowing the entry and exit of the gaseous and ionic particles.

Complete answer:
The phospholipids are closely packed, and the membrane's interior is hydrophobic. The membrane is narrowly permeable as a result of this arrangement. Only substances that satisfy certain requirements will move through a membrane that has selective permeability. Only comparatively thin, nonpolar materials can pass through the lipid bilayer of the cell membrane (remember, the lipid tails of the membrane are nonpolar).

Other lipids, oxygen and carbon dioxide gases, and alcohol are examples of these. Water-soluble compounds, such as oxygen, amino acids, and electrolytes, need some help to cross the membrane since the hydrophobic tails of the phospholipid bilayer repel them. Both substances passing through the membrane do so in one of two ways, which are classified according to whether or not energy is needed.

The passage of substances through the membrane without the use of cellular energy is known as passive transport. Active transport, on the other hand, is the passage of compounds through a membrane using adenosine triphosphate as a source of energy (ATP).

i) Diffusion is the passage of molecules or ions from one concentration area to another. It may or may not happen when a semipermeable membrane is crossed. There is no difficulty in diffusion since it occurs over a concentration gradient, but in, active transport, molecules migrate in the opposite direction of the concentration gradient, from lower to higher concentration.
ii) Energy is required for active transport; in this case, protein molecules serve as molecular pumps, allowing the cell to absorb glucose/ions against a concentration gradient. Adenosine triphosphate (ATP) is needed here as a source of metabolic energy.
iii) Facilitated a diffusion is a form of passive transport in which ions/molecules are transported across a semipermeable membrane with the help of permeases. Facilitated diffusion, like simple diffusion, requires no metabolic energy and happens simply over a concentration gradient.
iv) Osmosis is the process of moving water from a hypotonic (lower concentration) to a hypertonic (higher concentration) solution across a semipermeable membrane. Since the cell membrane is permeable to water, water molecules can travel back and forth along the concentration gradient.

Note:
- Most cell (plasma) membranes include the sodium-potassium pump.
- The pump is powered by ATP and pushes sodium and potassium ions in opposing directions toward their concentration gradients.
- Three sodium ions are extruded from the cell and two potassium ions are imported in a single pump loop.
- Substances disperse according to their concentration gradient; different substances in the medium can diffuse at different concentrations based on their gradients within a structure.