Chapter 3
Organization at the Cellular Level
By Boundless
![Thumbnail](../../../../../figures.boundless-cdn.com/31416/raw/embrane-detailed-diagram-4.jpg)
The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
![Thumbnail](../../../../../figures.boundless-cdn.com/18618/square/figure-05-01-03.jpeg)
The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates.
![Thumbnail](../../../../../figures.boundless-cdn.com/20157/square/figure-05-01-01.jpeg)
The mosaic nature of the membrane, its phospholipid chemistry, and the presence of cholesterol contribute to membrane fluidity.
![Thumbnail](../../../../../figures.boundless-cdn.com/18631/square/figure-05-02-02.jpeg)
Diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration.
![Thumbnail](../../../../../figures.boundless-cdn.com/18634/square/figure-05-02-06.jpeg)
Osmosis is the movement of water across a membrane from an area of low solute concentration to an area of high solute concentration.
![Thumbnail](../../../../../figures.boundless-cdn.com/18635/square/figure-05-02-07.jpg)
Tonicity, which is directly related to the osmolarity of a solution, affects osmosis by determining the direction of water flow.
![Thumbnail](../../../../../figures.boundless-cdn.com/18632/square/figure-05-02-04.jpeg)
Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
![Thumbnail](../../../../../figures.boundless-cdn.com/18622/square/figure-05-02-02.jpeg)
Passive transport, such as diffusion and osmosis, moves materials of small molecular weight across membranes.
![Thumbnail](../../../../../figures.boundless-cdn.com/18641/square/figure-05-03-03.jpeg)
The sodium-potassium pump maintains the electrochemical gradient of living cells by moving sodium in and potassium out of the cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/18639/square/figure-05-03-01.jpeg)
To move substances against the membrane's electrochemical gradient, the cell utilizes active transport, which requires energy from ATP.
![Thumbnail](../../../../../figures.boundless-cdn.com/18642/square/figure-05-03-04.jpg)
In secondary active transport, a molecule is moved down its electrochemical gradient as another is moved up its concentration gradient.
![Thumbnail](../../../../../figures.boundless-cdn.com/18643/square/figure-05-04-01.jpeg)
Endocytosis takes up particles into the cell by invaginating the cell membrane, resulting in the release of the material inside of the cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/20009/square/0318-nucleus.jpeg)
Found within eukaryotic cells, the nucleus contains the genetic material that determines the entire structure and function of that cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/18589/square/figure-04-03-04.jpeg)
A eukaryotic cell has a true membrane-bound nucleus and has other membranous organelles that allow for compartmentalization of functions.
![Thumbnail](../../../../../figures.boundless-cdn.com/18595/square/figure-04-03-02.jpeg)
The plasma membrane is made up of a phospholipid bilayer that regulates the concentration of substances that can permeate a cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/18603/square/figure-04-04-02-new.jpeg)
The endoplasmic reticulum is an organelle that is responsible for the synthesis of lipids and the modification of proteins.
![Thumbnail](../../../../../figures.boundless-cdn.com/18604/square/figure-04-04-03.jpeg)
The Golgi apparatus sorts and packages materials before they leave the cell to ensure they arrive at the proper destination.
![Thumbnail](../../../../../figures.boundless-cdn.com/18605/square/figure-04-04-04.jpeg)
Lysosomes are organelles that digest macromolecules, repair cell membranes, and respond to foreign substances entering the cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/19992/square/0316-peroxisome.jpeg)
Peroxisomes neutralize harmful toxins and carry out lipid metabolism and oxidation reactions that break down fatty acids and amino acids.
![Thumbnail](../../../../../figures.boundless-cdn.com/18599/square/figure-04-03-07.jpeg)
Mitochondria are organelles that are responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule.
![Thumbnail](../../../../../figures.boundless-cdn.com/18608/square/figure-04-05-04ab.jpeg)
Microtubules are part of the cell's cytoskeleton, helping the cell resist compression, move vesicles, and separate chromosomes at mitosis.
![Thumbnail](../../../../../figures.boundless-cdn.com/18606/square/figure-04-05-02.jpeg)
Microfilaments, which are the thinnest part of the cytoskeleton, are used to give shape to the cell and support all of its internal parts.
![Thumbnail](../../../../../figures.boundless-cdn.com/18610/square/figure-04-06-01.jpeg)
The extracellular matrix of animal cells holds cells together to form a tissue and allow tissues to communicate with each other.
![Thumbnail](../../../../../figures.boundless-cdn.com/18613/square/figure-04-06-04.jpeg)
Intercellular junctions provide plant and animal cells with the ability to communicate through direct contact.