Cell Membranes- Dhaani Patel

Cell Membrane

A thin, flexible barrier that surrounds all cells, controls what enters and leaves the cell, and maintains homeostasis.

Fluid Mosaic Model

Structure of the cell membrane made of a phospholipid bilayer with parts that move around and is composed of many pieces including lipids, proteins, and carbohydrates.

Phospholipids

Form the basic structure of the cell membrane; have hydrophilic heads (water-loving) and hydrophobic tails (water-fearing).

Proteins

Help with transport (channels, pumps) and cell signaling in the cell membrane.

Carbohydrates

Act like ID tags for cell recognition in the cell membrane.

Cholesterol

Keeps the membrane flexible and stable.

Selectively Permeable

Describes a membrane that allows only certain molecules to pass through while blocking others without help.

Surface Area to Volume Ratio (SV:ratio)

SV:ratio = surface area ÷ volume; cells need enough surface area to efficiently exchange materials.

Passive Transport

Movement of molecules from high to low concentration without the need for energy (ATP).

Active Transport

Movement of molecules from low to high concentration that requires energy (ATP).

Simple Diffusion

Molecules move from high to low concentration directly through the membrane, e.g., O₂, CO₂.

Facilitated Diffusion

Molecules move from high to low concentration but require a protein channel, e.g., glucose, ions.

Osmosis

Water movement across a membrane to balance concentrations of solute.

Hypotonic Solution

Solution has less solute (more water) than the cell, causing water to enter and the cell to swell.

Hypertonic Solution

Solution has more solute (less water) than the cell, causing water to leave and the cell to shrink.

Isotonic Solution

Solution has the same solute concentration as the cell, resulting in water moving in and out equally, keeping the cell size the same.

Endocytosis

Process where a cell engulfs large materials into vesicles, e.g., white blood cells eating bacteria.

Exocytosis

Process where a cell releases large materials, e.g., cells releasing hormones or waste.

Osmosis & Tonicity

Osmosis is about where water goes, moving toward areas with more solute (less water).

Phospholipid Bilayer

Double layer of fats forming the membrane.

Selective Permeability

Some substances can pass through the membrane while others cannot.

SV:ratio

Smaller cells have better exchange efficiency.