CELL MEMBRANE

What is osmosis?

Osmosis is the net movement of water across a semipermeable membrane from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration).

What is the cell membrane?

The cell membrane (also known as the plasma membrane) is a biological membrane that separates the interior of all cells from the outside environment. It regulates the passage of substances into and out of the cell.

Describe endocytosis.

Endocytosis is a cellular process in which substances are brought into the cell by engulfing them in a vesicle formed from the cell membrane. This includes processes like phagocytosis and pinocytosis.

Describe exocytosis.

Exocytosis is a cellular process in which vesicles containing substances fuse with the cell membrane and release their contents to the outside of the cell.

What is facilitated diffusion?

Facilitated diffusion is a type of passive transport where substances move across the cell membrane with the help of transport proteins (channel proteins or carrier proteins) down their concentration gradient, without the expenditure of cellular energy.

What is simple diffusion?

Simple diffusion is a type of passive transport where substances move directly across the lipid bilayer of the cell membrane from an area of higher concentration to an area of lower concentration, without the assistance of membrane proteins or energy.

What are phospholipids?

Phospholipids are a class of lipids that are a major component of all cell membranes, forming a lipid bilayer. Each molecule has a hydrophilic (water-loving) head and two hydrophobic (water-fearing) tails.

What does "hydrophobic" mean in the context of cell membranes?

Hydrophobic means "water-fearing." In the cell membrane, the fatty acid tails of phospholipids are hydrophobic and face inward, forming the core of the lipid bilayer, repelling water.

What does "hydrophilic" mean in the context of cell membranes?

Hydrophilic means "water-loving." In the cell membrane, the phosphate heads of phospholipids are hydrophilic and face outward towards the aqueous environment (both inside and outside the cell).

What is the key difference between active transport and passive transport?

Passive transport moves substances down their concentration gradient without cellular energy (e.g., simple diffusion, facilitated diffusion, osmosis), while active transport moves substances against their concentration gradient, requiring cellular energy (ATP).

What are membrane-spanning proteins?

Membrane-spanning proteins (also known as transmembrane proteins) are integral membrane proteins that extend completely through the lipid bilayer, with parts exposed to both the intracellular and extracellular environments. They often function as channels, transporters, or receptors.

What is a hypertonic solution?

A hypertonic solution has a higher solute concentration than the cell's cytoplasm. When a cell is placed in a hypertonic solution, water moves out of the cell, causing it to shrink.

What is a hypotonic solution?

A hypotonic solution has a lower solute concentration than the cell's cytoplasm. When a cell is placed in a hypotonic solution, water moves into the cell, causing it to swell or burst.

What is an isotonic solution?

An isotonic solution has a solute concentration equal to that of the cell's cytoplasm. When a cell is placed in an isotonic solution, there is no net movement of water, and the cell maintains its normal size and shape.

How do ions transport through the cell membrane?

Ions, being charged, cannot cross the lipid bilayer directly. They typically transport through the cell membrane via specific ion channels or protein pumps (membrane-spanning proteins) through facilitated diffusion or active transport.

How does glucose transport through the cell membrane?

Glucose, a polar molecule, transports through the cell membrane primarily via facilitated diffusion using specific carrier proteins (such as GLUT transporters). In some specialized cells (e.g., intestinal cells), it can be transported via secondary active transport.

How do large proteins transport through the cell membrane?

Large proteins generally do not 'transport' directly across the cell membrane in a simple manner. Instead, they are typically internalized by endocytosis (e.g., receptor-mediated endocytosis) or secreted by exocytosis, processes that involve vesicle formation.

How does CO2 transport through the cell membrane?

CO2 (carbon dioxide) is a small, nonpolar molecule that can easily pass directly through the lipid bilayer

What is a semipermeable membrane (or selectively permeable membrane)?

A semipermeable membrane is a biological or synthetic membrane that allows certain molecules or ions to pass through it by diffusion or facilitated diffusion, but not others. The cell membrane is an example, regulating what enters and exits the cell.

What are three ways to demonstrate the semipermeable nature of a membrane?

The semipermeable nature of a membrane can be demonstrated by:

1. Osmosis Experiments: Observing the movement of water across the membrane in response to solute concentration differences, while larger solute molecules are retained.

2. Selective Passage of Molecules: Showing that small, uncharged molecules (e.g.,O2, CO2) can diffuse freely, while larger, polar, or charged molecules (e.g., glucose, ions) require specific transport mechanisms or are impermeable.

3. Impermeability to Macromolecules: Observing that very large molecules like proteins and polysaccharides are generally unable to cross the membrane without specific vesicular transport processes (endocytosis/exocytosis).