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nucleotide : a monomer of nucleic acids; contains a pentose sugar, a phosphate group, and a nitrogenous base | https://openstax.org/books/concepts-biology/pages/2-key-terms |
nucleus : (chemistry) the dense center of an atom made up of protons and (except in the case of a hydrogen atom) neutrons | https://openstax.org/books/concepts-biology/pages/2-key-terms |
octet rule : states that the outermost shell of an element with a low atomic number can hold eight electrons | https://openstax.org/books/concepts-biology/pages/2-key-terms |
oil : an unsaturated fat that is a liquid at room temperature | https://openstax.org/books/concepts-biology/pages/2-key-terms |
periodic table of elements : an organizational chart of elements, indicating the atomic number and mass number of each element; also provides key information about the properties of elements | https://openstax.org/books/concepts-biology/pages/2-key-terms |
pH scale : a scale ranging from 0 to 14 that measures the approximate concentration of hydrogen ions of a substance | https://openstax.org/books/concepts-biology/pages/2-key-terms |
phospholipid : a major constituent of the membranes of cells; composed of two fatty acids and a phosphate group attached to the glycerol backbone | https://openstax.org/books/concepts-biology/pages/2-key-terms |
polar covalent bond : a type of covalent bond in which electrons are pulled toward one atom and away from another, resulting in slightly positive and slightly negative charged regions of the molecule | https://openstax.org/books/concepts-biology/pages/2-key-terms |
polypeptide : a long chain of amino acids linked by peptide bonds | https://openstax.org/books/concepts-biology/pages/2-key-terms |
polysaccharide : a long chain of monosaccharides; may be branched or unbranched | https://openstax.org/books/concepts-biology/pages/2-key-terms |
protein : a biological macromolecule composed of one or more chains of amino acids | https://openstax.org/books/concepts-biology/pages/2-key-terms |
proton : a positively charged particle that resides in the nucleus of an atom; has a mass of 1 and a charge of +1 | https://openstax.org/books/concepts-biology/pages/2-key-terms |
radioactive isotope : an isotope that spontaneously emits particles or energy to form a more stable element | https://openstax.org/books/concepts-biology/pages/2-key-terms |
ribonucleic acid (RNA) : a single-stranded polymer of nucleotides that is involved in protein synthesis | https://openstax.org/books/concepts-biology/pages/2-key-terms |
saturated fatty acid : a long-chain hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized | https://openstax.org/books/concepts-biology/pages/2-key-terms |
solvent : a substance capable of dissolving another substance | https://openstax.org/books/concepts-biology/pages/2-key-terms |
starch : a storage carbohydrate in plants | https://openstax.org/books/concepts-biology/pages/2-key-terms |
steroid : a type of lipid composed of four fused hydrocarbon rings | https://openstax.org/books/concepts-biology/pages/2-key-terms |
surface tension : the cohesive force at the surface of a body of liquid that prevents the molecules from separating | https://openstax.org/books/concepts-biology/pages/2-key-terms |
temperature : a measure of molecular motion | https://openstax.org/books/concepts-biology/pages/2-key-terms |
trans-fat : a form of unsaturated fat with the hydrogen atoms neighboring the double bond across from each other rather than on the same side of the double bond | https://openstax.org/books/concepts-biology/pages/2-key-terms |
triglyceride : a fat molecule; consists of three fatty acids linked to a glycerol molecule | https://openstax.org/books/concepts-biology/pages/2-key-terms |
unsaturated fatty acid : a long-chain hydrocarbon that has one or more than one double bonds in the hydrocarbon chain | https://openstax.org/books/concepts-biology/pages/2-key-terms |
van der Waals interaction : a weak attraction or interaction between molecules caused by slightly positively charged or slightly negatively charged atoms | https://openstax.org/books/concepts-biology/pages/2-key-terms |
A cell is the smallest unit of life. Most cells are so small that they cannot be viewed with the naked eye. Therefore, scientists must use microscopes to study cells. Electron microscopes provide higher magnification, higher resolution, and more detail than light microscopes. The unified cell theory states that all org... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1â5.0 µm. | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. Eukar... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. The p... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Animal cells also have a centrosome and lysosomes. The centrosome has two bodies, the centrioles, with an unknown role in cell division. Lysosomes are the digestive organelles of animal cells. | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Plant cells have a cell wall, chloroplasts, and a central vacuole. The plant cell wall, whose primary component is cellulose, protects the cell, provides structural support, and gives shape to the cell. Photosynthesis takes place in chloroplasts. The central vacuole expands, enlarging the cell without the need to produ... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
The endomembrane system includes the nuclear envelope, the endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, as well as the plasma membrane. These cellular components work together to modify, package, tag, and transport membrane lipids and proteins. | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
The cytoskeleton has three different types of protein elements. Microfilaments provide rigidity and shape to the cell, and facilitate cellular movements. Intermediate filaments bear tension and anchor the nucleus and other organelles in place. Microtubules help the cell resist compression, serve as tracks for motor pro... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Animal cells communicate through their extracellular matrices and are connected to each other by tight junctions, desmosomes, and gap junctions. Plant cells are connected and communicate with each other by plasmodesmata. | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
The modern understanding of the plasma membrane is referred to as the fluid mosaic model. The plasma membrane is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of t... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
The passive forms of transport, diffusion and osmosis, move material of small molecular weight. Substances diffuse from areas of high concentration to areas of low concentration, and this process continues until the substance is evenly distributed in a system. In solutions of more than one substance, each type of molec... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
In living systems, diffusion of substances into and out of cells is mediated by the plasma membrane. Some materials diffuse readily through the membrane, but others are hindered, and their passage is only made possible by protein channels and carriers. The chemistry of living things occurs in aqueous solutions, and bal... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
The combined gradient that affects an ion includes its concentration gradient and its electrical gradient. Living cells need certain substances in concentrations greater than they exist in the extracellular space. Moving substances up their electrochemical gradients requires energy from the cell. Active transport uses ... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
Endocytosis methods require the direct use of ATP to fuel the transport of large particles such as macromolecules; parts of cells or whole cells can be engulfed by other cells in a process called phagocytosis. In phagocytosis, a portion of the membrane invaginates and flows around the particle, eventually pinching off ... | https://openstax.org/books/concepts-biology/pages/3-chapter-summary |
active transport : the method of transporting material that requires energy | https://openstax.org/books/concepts-biology/pages/3-key-terms |
cell wall : a rigid cell covering made of cellulose in plants, peptidoglycan in bacteria, non-peptidoglycan compounds in Archaea, and chitin in fungi that protects the cell, provides structural support, and gives shape to the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
central vacuole : a large plant cell organelle that acts as a storage compartment, water reservoir, and site of macromolecule degradation | https://openstax.org/books/concepts-biology/pages/3-key-terms |
chloroplast : a plant cell organelle that carries out photosynthesis | https://openstax.org/books/concepts-biology/pages/3-key-terms |
chromatin : protein-DNA complex that serves as the chromosomes' building material | https://openstax.org/books/concepts-biology/pages/3-key-terms |
chromosome : structure within the nucleus that comprises chromatin that contains DNA, the hereditary material | https://openstax.org/books/concepts-biology/pages/3-key-terms |
cilium : (plural: cilia) a short, hair-like structure that extends from the plasma membrane in large numbers and is used to move an entire cell or move substances along the outer surface of the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
concentration gradient : an area of high concentration across from an area of low concentration | https://openstax.org/books/concepts-biology/pages/3-key-terms |
cytoplasm : the entire region between the plasma membrane and the nuclear envelope, consisting of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals | https://openstax.org/books/concepts-biology/pages/3-key-terms |
cytoskeleton : the network of protein fibers that collectively maintains the shape of the cell, secures some organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move | https://openstax.org/books/concepts-biology/pages/3-key-terms |
cytosol : the gel-like material of the cytoplasm in which cell structures are suspended | https://openstax.org/books/concepts-biology/pages/3-key-terms |
desmosome : a linkage between adjacent epithelial cells that forms when cadherins in the plasma membrane attach to intermediate filaments | https://openstax.org/books/concepts-biology/pages/3-key-terms |
diffusion : a passive process of transport of low-molecular weight material down its concentration gradient | https://openstax.org/books/concepts-biology/pages/3-key-terms |
electrochemical gradient : a gradient produced by the combined forces of the electrical gradient and the chemical gradient | https://openstax.org/books/concepts-biology/pages/3-key-terms |
endocytosis : a type of active transport that moves substances, including fluids and particles, into a cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
endomembrane system : the group of organelles and membranes in eukaryotic cells that work together to modify, package, and transport lipids and proteins | https://openstax.org/books/concepts-biology/pages/3-key-terms |
endoplasmic reticulum (ER) : a series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids | https://openstax.org/books/concepts-biology/pages/3-key-terms |
eukaryotic cell : a cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs | https://openstax.org/books/concepts-biology/pages/3-key-terms |
exocytosis : a process of passing material out of a cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
extracellular matrix : the material, primarily collagen, glycoproteins, and proteoglycans, secreted from animal cells that holds cells together as a tissue, allows cells to communicate with each other, and provides mechanical protection and anchoring for cells in the tissue | https://openstax.org/books/concepts-biology/pages/3-key-terms |
facilitated transport : a process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins | https://openstax.org/books/concepts-biology/pages/3-key-terms |
flagellum : (plural: flagella) the long, hair-like structure that extends from the plasma membrane and is used to move the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
fluid mosaic model : a model of the structure of the plasma membrane as a mosaic of components, including phospholipids, cholesterol, proteins, and glycolipids, resulting in a fluid rather than static character | https://openstax.org/books/concepts-biology/pages/3-key-terms |
gap junction : a channel between two adjacent animal cells that allows ions, nutrients, and other low-molecular weight substances to pass between the cells, enabling the cells to communicate | https://openstax.org/books/concepts-biology/pages/3-key-terms |
Golgi apparatus : a eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution | https://openstax.org/books/concepts-biology/pages/3-key-terms |
hypertonic : describes a solution in which extracellular fluid has higher osmolarity than the fluid inside the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
hypotonic : describes a solution in which extracellular fluid has lower osmolarity than the fluid inside the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
isotonic : describes a solution in which the extracellular fluid has the same osmolarity as the fluid inside the cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
lysosome : an organelle in an animal cell that functions as the cellâs digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles | https://openstax.org/books/concepts-biology/pages/3-key-terms |
microscope : the instrument that magnifies an object | https://openstax.org/books/concepts-biology/pages/3-key-terms |
mitochondria : (singular: mitochondrion) the cellular organelles responsible for carrying out cellular respiration, resulting in the production of ATP, the cellâs main energy-carrying molecule | https://openstax.org/books/concepts-biology/pages/3-key-terms |
nuclear envelope : the double-membrane structure that constitutes the outermost portion of the nucleus | https://openstax.org/books/concepts-biology/pages/3-key-terms |
nucleolus : the darkly staining body within the nucleus that is responsible for assembling ribosomal subunits | https://openstax.org/books/concepts-biology/pages/3-key-terms |
nucleus : the cell organelle that houses the cellâs DNA and directs the synthesis of ribosomes and proteins | https://openstax.org/books/concepts-biology/pages/3-key-terms |
organelle : a membrane-bound compartment or sac within a cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
osmolarity : the total amount of substances dissolved in a specific amount of solution | https://openstax.org/books/concepts-biology/pages/3-key-terms |
osmosis : the transport of water through a semipermeable membrane from an area of high water concentration to an area of low water concentration across a membrane | https://openstax.org/books/concepts-biology/pages/3-key-terms |
passive transport : a method of transporting material that does not require energy | https://openstax.org/books/concepts-biology/pages/3-key-terms |
peroxisome : a small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons | https://openstax.org/books/concepts-biology/pages/3-key-terms |
phagocytosis : a process that takes particulate matter like macromolecules, cells, or cell fragments that the cell needs from the extracellular fluid; a variation of endocytosis | https://openstax.org/books/concepts-biology/pages/3-key-terms |
pinocytosis : a process that takes solutes that the cell needs from the extracellular fluid; a variation of endocytosis | https://openstax.org/books/concepts-biology/pages/3-key-terms |
plasma membrane : a phospholipid bilayer with embedded (integral) or attached (peripheral) proteins that separates the internal contents of the cell from its surrounding environment | https://openstax.org/books/concepts-biology/pages/3-key-terms |
plasmodesma : (plural: plasmodesmata) a channel that passes between the cell walls of adjacent plant cells, connects their cytoplasm, and allows materials to be transported from cell to cell | https://openstax.org/books/concepts-biology/pages/3-key-terms |
prokaryotic cell : a unicellular organism that lacks a nucleus or any other membrane-bound organelle | https://openstax.org/books/concepts-biology/pages/3-key-terms |
receptor-mediated endocytosis : a variant of endocytosis that involves the use of specific binding proteins in the plasma membrane for specific molecules or particles | https://openstax.org/books/concepts-biology/pages/3-key-terms |
ribosome : a cellular structure that carries out protein synthesis | https://openstax.org/books/concepts-biology/pages/3-key-terms |
rough endoplasmic reticulum (RER) : the region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification | https://openstax.org/books/concepts-biology/pages/3-key-terms |
selectively permeable : the characteristic of a membrane that allows some substances through but not others (also known as semipermeable) | https://openstax.org/books/concepts-biology/pages/3-key-terms |
smooth endoplasmic reticulum (SER) : the region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies chemicals like pesticides, preservatives, medications, and environmental pollutants, and stores calcium ions | https://openstax.org/books/concepts-biology/pages/3-key-terms |
solute : a substance dissolved in another to form a solution | https://openstax.org/books/concepts-biology/pages/3-key-terms |
tight junction : a firm seal between two adjacent animal cells created by protein adherence | https://openstax.org/books/concepts-biology/pages/3-key-terms |
tonicity : the amount of solute in a solution. | https://openstax.org/books/concepts-biology/pages/3-key-terms |
unified cell theory : the biological concept that states that all organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells | https://openstax.org/books/concepts-biology/pages/3-key-terms |
vacuole : a membrane-bound sac, somewhat larger than a vesicle, that functions in cellular storage and transport | https://openstax.org/books/concepts-biology/pages/3-key-terms |
vesicle : a small, membrane-bound sac that functions in cellular storage and transport; its membrane is capable of fusing with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus | https://openstax.org/books/concepts-biology/pages/3-key-terms |
Cells perform the functions of life through various chemical reactions. A cellâs metabolism refers to the combination of chemical reactions that take place within it. Catabolic reactions break down complex chemicals into simpler ones and are associated with energy release. Anabolic processes build complex molecules o... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
In studying energy, the term system refers to the matter and environment involved in energy transfers. Entropy is a measure of the disorder of a system. The physical laws that describe the transfer of energy are the laws of thermodynamics. The first law states that the total amount of energy in the universe is constant... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
Enzymes are chemical catalysts that speed up chemical reactions by lowering their activation energy. Enzymes have an active site with a unique chemical environment that fits particular chemical reactants for that enzyme, called substrates. Enzymes and substrates are thought to bind according to an induced-fit model. En... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
ATP functions as the energy currency for cells. It allows cells to store energy briefly and transport it within itself to support endergonic chemical reactions. The structure of ATP is that of an RNA nucleotide with three phosphate groups attached. As ATP is used for energy, a phosphate group is detached, and ADP is pr... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
Glycolysis is the first pathway used in the breakdown of glucose to extract energy. Because it is used by nearly all organisms on earth, it must have evolved early in the history of life. Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for separation into two three-carbon sugars... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
The citric acid cycle is a series of chemical reactions that removes high-energy electrons and uses them in the electron transport chain to generate ATP. One molecule of ATP (or an equivalent) is produced per each turn of the cycle. | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
The electron transport chain is the portion of aerobic respiration that uses free oxygen as the final electron acceptor for electrons removed from the intermediate compounds in glucose catabolism. The electrons are passed through a series of chemical reactions, with a small amount of free energy used at three points to... | https://openstax.org/books/concepts-biology/pages/4-chapter-summary |
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