microscope
the instrument that magnifies an object
With few exceptions, individual cells are too small to be seen with the naked eye, so scientists use microscopes to study them.
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
The unified cell theory 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.
eukaryotic cell
a cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs
In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells.
organelle
a membrane-bound compartment or sac within a cell
A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle.
prokaryotic cell
a unicellular organism that lacks a nucleus or any other membrane-bound organelle
When oil immersion lenses are used, magnification is usually increased to 1,000 times for the study of smaller cells, like most prokaryotic cells.
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
Unlike Archaea and eukaryotes, bacteria have a cell wall made of peptidoglycan, comprised of sugars and amino acids, and many have a polysaccharide capsule (Figure 3.6).
central vacuole
a large plant cell organelle that acts as a storage compartment, water reservoir, and site of macromolecule degradation
Plant cells have plasmodesmata, a cell wall, a large central vacuole, chloroplasts, and plastids.
chloroplast
a plant cell organelle that carries out photosynthesis
Plant cells have plasmodesmata, a cell wall, a large central vacuole, chloroplasts, and plastids.
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
When cilia (singular = cilium) are present, however, they are many in number and extend along the entire surface of the plasma membrane.
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
All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles.
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
It is made up of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals.
cytosol
the gel-like material of the cytoplasm in which cell structures are suspended
It is made up of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals.
desmosome
a linkage between adjacent epithelial cells that forms when cadherins in the plasma membrane attach to intermediate filaments
Plasmodesmata (singular = plasmodesma) are junctions between plant cells, whereas animal cell contacts include tight and gap junctions, and desmosomes.
endomembrane system
the group of organelles and membranes in eukaryotic cells that work together to modify, package, and transport lipids and proteins
The endomembrane system (endo = within) is a group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.
endoplasmic reticulum (ER)
a series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids
It includes the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum and the Golgi apparatus, which we will cover shortly.
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
Collectively, these materials are called the extracellular matrix (Figure 3.19).
flagellum
(plural: flagella) the long, hair-like structure that extends from the plasma membrane and is used to move the cell
Flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and are used to move an entire cell, (for example, sperm, Euglena).
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
Plasmodesmata (singular = plasmodesma) are junctions between plant cells, whereas animal cell contacts include tight and gap junctions, and desmosomes.
Golgi apparatus
a eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution
It includes the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum and the Golgi apparatus, which we will cover shortly.
lysosome
an organelle in an animal cell that functions as the cell’s digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles
It includes the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum and the Golgi apparatus, which we will cover shortly.
mitochondria
(singular: mitochondrion) the cellular organelles responsible for carrying out cellular respiration, resulting in the production of ATP, the cell’s main energy-carrying molecule
Mitochondria are oval-shaped, double-membrane organelles (Figure 3.17) that have their own ribosomes and DNA.
nuclear envelope
the double-membrane structure that constitutes the outermost portion of the nucleus
The cytoplasm comprises the contents of a cell between the plasma membrane and the nuclear envelope (a structure to be discussed shortly).
nucleolus
the darkly staining body within the nucleus that is responsible for assembling ribosomal subunits
The nucleolus within the nucleus is the site for ribosome assembly.
nucleus
the cell organelle that houses the cell’s DNA and directs the synthesis of ribosomes and proteins
A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle.
peroxisome
a small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons
Peroxisomes are small, round organelles enclosed by single membranes.
plasma membrane
a phospholipid bilayer with embedded (integral) or attached (peripheral) proteins that separates the internal contents of the cell from its surrounding environment
All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles.
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
Plasmodesmata (singular = plasmodesma) are junctions between plant cells, whereas animal cell contacts include tight and gap junctions, and desmosomes.
ribosome
a cellular structure that carries out protein synthesis
All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles.
rough endoplasmic reticulum (RER)
the region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification
However, these two functions are performed in separate areas of the endoplasmic reticulum: the rough endoplasmic reticulum and the smooth endoplasmic reticulum, respectively.
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
However, these two functions are performed in separate areas of the endoplasmic reticulum: the rough endoplasmic reticulum and the smooth endoplasmic reticulum, respectively.
tight junction
a firm seal between two adjacent animal cells created by protein adherence
A tight junction is a watertight seal between two adjacent animal cells (Figure 3.20 b).
vacuole
a membrane-bound sac, somewhat larger than a vesicle, that functions in cellular storage and transport
Plant cells have plasmodesmata, a cell wall, a large central vacuole, chloroplasts, and plastids.
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
It includes the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum and the Golgi apparatus, which we will cover shortly.
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
The modern understanding of the plasma membrane is referred to as the fluid mosaic model.
concentration gradient
an area of high concentration across from an area of low concentration
A physical space in which there is a different concentration of a single substance is said to have a concentration gradient.
diffusion
a passive process of transport of low-molecular weight material down its concentration gradient
In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion.
facilitated transport
a process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins
However, the substances that undergo facilitated transport would otherwise not diffuse easily or quickly across the plasma membrane.
hypertonic
describes a solution in which extracellular fluid has higher osmolarity than the fluid inside the cell
Three terms—hypotonic, isotonic, and hypertonic—are used to relate the osmolarity of a cell to the osmolarity of the extracellular fluid that contains the cells.
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
Osmosis is the diffusion of water through a semipermeable membrane according to the concentration gradient of water across the membrane.
passive transport
a method of transporting material that does not require energy
Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement.
selectively permeable
the characteristic of a membrane that allows some substances through but not others
In other words, plasma membranes are selectively permeable—they allow some substances through but not others.
solute
a substance dissolved in another to form a solution
Whereas diffusion transports material across membranes and within cells, osmosis transports only water across a membrane and the membrane limits the diffusion of solutes in the water.
tonicity
the amount of solute in a solution.
Tonicity describes the amount of solute in a solution.
active transport
the method of transporting material that requires energy
Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP).
electrochemical gradient
a gradient produced by the combined forces of the electrical gradient and the chemical gradient
The combined gradient that affects an ion is called its electrochemical gradient, and it is especially important to muscle and nerve cells.
endocytosis
a type of active transport that moves substances, including fluids and particles, into a cell
Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell.
exocytosis
a process of passing material out of a cell
In contrast to these methods of moving material into a cell is the process of exocytosis.
phagocytosis
a process that takes macromolecules that the cell needs from the extracellular fluid; a variation of endocytosis
In a process known as phagocytosis, a section of the plasma membrane of the macrophage invaginates (folds in) and engulfs a pathogen.
pinocytosis
a process that takes solutes that the cell needs from the extracellular fluid; a variation of endocytosis
Pinocytosis is a similar process on a smaller scale.
receptor-mediated endocytosis
a variant of endocytosis that involves the use of specific binding proteins in the plasma membrane for specific molecules or particles
If passage across the membrane of the target of receptor-mediated endocytosis is ineffective, it will not be removed from the tissue fluids or blood.
These terms were extracted from Concepts of Biology – 1st Canadian Edition by Charles Molnar and Jane Gair, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter content adapted from Concepts of Biology by OpenStax (© Rice University), licensed under CC BY 4.0.