![A molecular view of the cell membrane[Credits : Encyclopædia Britannica, Inc.]](http://media-2.web.britannica.com/eb-media/74/53074-003-48875193.gif){kind=small}
A thin membrane surrounds every living cell, delimiting the cell from the environment around it. Enclosed by this cell membrane (also known as the plasma membrane) are the cell’s constituents, often large, water-soluble, highly charged molecules such as proteins, nucleic acids, carbohydrates, and substances involved in cellular metabolism. Outside the cell, in the surrounding water-based environment, are ions, acids, and alkalis that are toxic to the cell, as well as nutrients that the cell must absorb in order to live and grow. The cell membrane, therefore, has two functions: first, to be a barrier keeping the constituents of the cell in and unwanted substances out and, second, to be a gate allowing transport into the cell of essential nutrients and movement from the cell of waste products.
Principal-structures-of-an-animal-cell-Cytoplasm-surrounds-the-cellsPrincipal structures of an animal cell[Credits : © Merriam-Webster Inc.]
Animal-cells-and-plant-cells-contain-membrane-bound-organelles-includingAnimal cells and plant cells contain membrane-bound organelles, including a distinct nucleus. In …[Credits : Encyclopædia Britannica, Inc.]
Cutaway-drawing-of-a-eukaryotic-cellCutaway drawing of a eukaryotic cell.[Credits : Encyclopædia Britannica, Inc.]
The-eight-step-tricarboxylic-acid-cycleThe eight-step tricarboxylic acid cycle.[Credits : Encyclopædia Britannica, Inc.]
The-initial-proposal-of-the-structure-of-DNA-by-JamesThe initial proposal of the structure of DNA by James Watson and Francis Crick was accompanied by a …[Credits : Encyclopædia Britannica, Inc.]
Molecular-genetics-emerged-from-the-realization-that-DNA-and-RNAMolecular genetics emerged from the realization that DNA and RNA constitute the genetic material of …
The-ovum-contains-a-small-collection-of-cells-in-theThe ovum contains a small collection of cells in the early stages of human development. As cells …[Credits : Encyclopædia Britannica, Inc.]
A-molecular-view-of-the-cell-membrane-Intrinsic-proteins-penetrateA molecular view of the cell membrane[Credits : Encyclopædia Britannica, Inc.]
Cells are the basic units of life.[Credits : Encyclopædia Britannica, Inc.]
Cells ingest molecules through their plasma membranes.[Credits : Encyclopædia Britannica, Inc.]
The carbon atom is essential to all organic compounds. Every carbon atom can bond with four other …[Credits : Acquired from Vast Video]
Most enzymes are proteins. Enzymes regulate nearly all chemical reactions that occur in living …[Credits : Acquired from Vast Video]
The location, importance, and mechanisms of photosynthesis.[Credits : Encyclopædia Britannica, Inc.]
ATP is the key source of energy in the cells of the body. The water-mediated reaction known as …[Credits : Acquired from Vast Video]
James Watson and Francis Crick revolutionized the study of genetics when they discovered the …[Credits : Acquired from Vast Video]
The structure and movement of cilia and flagella.[Credits : Encyclopædia Britannica, Inc.]
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