Glossary
Aquaporins
Specific channel proteins that greatly increase the rate of water movement across cell membranes.
Example:
Plant roots use aquaporins to rapidly absorb large amounts of water from the soil.
Cell membrane
The outer boundary of an animal cell and the inner boundary of a plant cell, regulating the passage of substances into and out of the cell.
Example:
The cell membrane acts like a security guard, deciding which nutrients can enter a hungry cell.
Cell wall
A rigid outer layer found in plant, fungal, and bacterial cells that provides structural support and protection.
Example:
The sturdy cell wall of a tree allows it to stand tall against strong winds.
Cellulose
A complex carbohydrate that is the primary component of plant cell walls, providing strength and rigidity.
Example:
The tough fibers in celery are largely made of cellulose, which is indigestible for humans.
Chitin
A structural polysaccharide that forms the cell walls of fungi and the exoskeletons of arthropods.
Example:
The crunchy texture of a mushroom's stem comes from its chitin cell walls.
Diffusion
The net movement of molecules from an area of higher concentration to an area of lower concentration, driven by random molecular motion.
Example:
When you spray air freshener, its scent spreads throughout the room by diffusion.
Hydrophilic heads
The water-loving, phosphate-containing regions of phospholipids that face the aqueous environments inside and outside the cell.
Example:
The hydrophilic heads of the phospholipids are attracted to the watery cytoplasm, orienting themselves towards it.
Hydrophobic tails
The water-fearing, fatty acid chains of phospholipids that form the interior core of the cell membrane, acting as a barrier to polar molecules.
Example:
The hydrophobic tails create a nonpolar barrier in the middle of the membrane, making it difficult for charged ions to pass through.
Passive transport
The movement of substances across a cell membrane without the expenditure of cellular energy, typically following a concentration gradient.
Example:
Oxygen entering red blood cells is an example of passive transport, as it moves from a high concentration in the lungs to a lower concentration in the blood.
Peptidoglycan
A polymer consisting of sugars and amino acids that forms the cell wall of most bacteria.
Example:
Antibiotics like penicillin target the synthesis of peptidoglycan, weakening bacterial cell walls.
Phospholipid bilayer
The fundamental structure of the cell membrane, composed of two layers of phospholipid molecules arranged tail-to-tail.
Example:
The phospholipid bilayer forms the basic framework of all cellular membranes, creating a fluid mosaic.
Selectively permeable
A property of the cell membrane that allows certain substances to pass through while restricting others.
Example:
Because the cell membrane is selectively permeable, only specific ions can cross it to generate a nerve impulse.
Transport proteins
Integral membrane proteins that facilitate the movement of specific molecules or ions across the cell membrane.
Example:
Glucose needs transport proteins to enter cells because it's a large, polar molecule.