The cell membrane is a selectively permeable barrier that controls the movement of substances into and out of the cell. It allows certain substances to pass through while blocking others.

Membrane lipids are amphipathic molecules, meaning they have both hydrophilic (water-loving) and hydrophobic (water-hating) regions. Phospholipids are the most abundant type of membrane lipid and consist of a glycerol backbone, two fatty acid chains, and a phosphate group. Glycolipids are similar to phospholipids, but they have a sugar molecule attached to the glycerol backbone.

Membrane proteins are embedded in the lipid bilayer and perform a variety of important functions. They can transport substances across the membrane, act as receptors for signaling molecules, generate energy for the cell, and provide structural support to the membrane.

Active transport requires energy to move substances against their concentration gradient, while passive transport does not. Active transport is carried out by membrane proteins, while passive transport can be carried out by both proteins and lipids. Active transport moves substances against their concentration gradient, while passive transport moves substances down their concentration gradient.

The sodium-potassium pump is an active transport protein that maintains the resting membrane potential by pumping three sodium ions out of the cell for every two potassium ions it pumps in. This creates a concentration gradient for both sodium and potassium ions, which drives the passive movement of these ions across the membrane.

The endoplasmic reticulum is a network of membranes that plays a key role in membrane biogenesis. It synthesizes membrane lipids, assembles membrane proteins, and transports membrane components to their final destination.

The Golgi apparatus is a stack of flattened membranes that plays a key role in membrane biogenesis. It modifies membrane proteins, packages membrane proteins into vesicles, and transports membrane vesicles to their final destination.

The lysosome is a membrane-bound organelle that plays a key role in membrane biogenesis. It degrades membrane lipids, degrades membrane proteins, and recycles membrane components.

The plasma membrane is the outermost membrane of the cell and plays a key role in cell signaling. It receives signals from the extracellular environment, transmits signals to the inside of the cell, and integrates signals from different sources.

The nuclear membrane is a double membrane that separates the nuclear DNA from the cytoplasm. It regulates the entry of transcription factors into the nucleus, controls the export of mRNA from the nucleus, and plays a role in gene expression.

The mitochondrial membrane is a double membrane that plays a key role in energy production. It generates ATP through oxidative phosphorylation, transports electrons along the electron transport chain, and pumps protons across the membrane, creating a proton gradient.

The chloroplast membrane is a double membrane that plays a key role in photosynthesis. It captures light energy from the sun, converts light energy into chemical energy, and transports electrons along the electron transport chain.

The vacuolar membrane is a single membrane that surrounds the vacuole, a large organelle found in plant cells. It stores water and nutrients, maintains turgor pressure, and helps to detoxify the cell.

The lysosomal membrane is a single membrane that surrounds the lysosome, a membrane-bound organelle that contains digestive enzymes. It protects the cell from the digestive enzymes inside the lysosome, transports digestive enzymes into the lysosome, and helps to fuse lysosomes with other organelles.

The peroxisomal membrane is a single membrane that surrounds the peroxisome, a membrane-bound organelle that contains enzymes that produce reactive oxygen species. It protects the cell from the reactive oxygen species produced inside the peroxisome, transports substrates into the peroxisome, and helps to fuse peroxisomes with other organelles.