AP Bio Unit 2

Plasma Membrane

The membrane that separates the internal cytoplasm from the external environment of the cell; controls movement of substances in and out of the cell and allows for cell communication.

Phospholipid

The primary lipid component of the plasma membrane; consists of a hydrophilic phosphate head and hydrophobic fatty acid tails.

Phosphate Head

The hydrophilic (water-loving) part of a phospholipid that lines the internal and external surfaces of the membrane.

Fatty Acid Tails

The hydrophobic (water-fearing) part of a phospholipid that is sandwiched in the interior of the membrane.

Phospholipid Bilayer

The double layer of phospholipids that forms the foundation of the plasma membrane; hydrophilic heads face the watery environments, hydrophobic tails face inward.

Fluid-Mosaic Model

A model that describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins, in which components are free to move.

Peripheral Protein

A protein that is found on the inner membrane surface of the phospholipid bilayer.

Integral Protein

A protein that is partially or wholly embedded (transmembrane) within the phospholipid bilayer.

Amphipathic

Having both hydrophobic and hydrophilic regions; describes phospholipids and integral proteins.

Cholesterol

A lipid molecule embedded in the phospholipid bilayer that controls membrane fluidity (makes it more or less fluid depending on temperature).

Carbohydrate Chain

Chains attached to proteins or lipids on the extracellular side of the membrane that contribute to the cell's "fingerprint" for recognition.

Glycoprotein

A protein with an attached carbohydrate chain; functions in cell recognition.

Glycolipid

A phospholipid with an attached carbohydrate chain; functions in cell recognition.

Channel Protein

A membrane protein that allows the passage of specific molecules or ions through a channel in the protein; a type of facilitated transport.

Carrier Protein

A membrane protein that combines with a molecule and changes shape to assist its passage across the membrane; used in both facilitated and active transport.

Cell Recognition Protein

A glycoprotein that helps the body's immune system recognize its own cells.

Receptor Protein

A membrane protein shaped to bind a specific signal molecule, allowing the cell to respond to signals from other cells.

Enzymatic Protein

A membrane protein that catalyzes (speeds up) a specific chemical reaction.

Junction Protein

A membrane protein that attaches adjacent cells so that a tissue can fulfill a function.

Concentration Gradient

The difference in the concentration of a substance from one area to another.

Passive Transport

The movement of substances across the cell membrane without the input of energy; movement is down the concentration gradient.

Diffusion

The net movement of molecules from an area of high concentration to an area of low concentration down their concentration gradient.

Dynamic Equilibrium

The condition in which the net movement of molecules is zero because they move in both directions at equal rates; solute concentration is uniform.

Osmosis

The diffusion of water across a selectively permeable membrane from an area of high water potential to low water potential.

Aquaporin

A specialized channel protein that facilitates the rapid diffusion of water through the membrane.

Isotonic Solution

A solution in which the solute concentration is equal inside and outside the cell; results in no net water movement.

Hypotonic Solution

A solution in which the solute concentration is lower outside the cell than inside; causes net water movement into the cell.

Hypertonic Solution

A solution in which the solute concentration is higher outside the cell than inside; causes net water movement out of the cell.

Turgor Pressure

The pressure exerted by water inside the central vacuole of a plant cell against the cell wall; occurs in a hypotonic environment and is ideal for plant cells.

Lysis

The rupturing of an animal cell due to excess water entering in a hypotonic environment.

Plasmolysis

The process in which a plant cell shrinks away from its cell wall in a hypertonic environment, causing the plant to wilt.

Facilitated Transport

The passive transport of substances that cannot cross the lipid bilayer on their own, using channel or carrier proteins to move down their concentration gradient.

Surface Area-to-Volume Ratio

A key factor in cell size limits; a high ratio is advantageous for efficient material exchange, which is why cells are small.

Microvilli

Small protrusions of the cell membrane that increase surface area for more efficient absorption, e.g., in intestinal cells.

Water Potential (ψ)

A measurement of the potential energy in water, representing its tendency to move; water flows from high ψ to low ψ; measured in bars.

Solute Potential (ψs)

The component of water potential that is dependent on solute concentration; always zero or negative; calculated as ψs = -iCRT.

Pressure Potential (ψp)

The component of water potential that is due to physical pressure, such as that from a plant cell wall against the turgid cell; can be positive.

Active Transport

The movement of substances against their concentration gradient (from low to high concentration), requiring energy (e.g., ATP) and carrier proteins.

Sodium-Potassium Pump

A vital active transport mechanism that uses ATP to pump 3 Na+ out of and 2 K+ into the cell, establishing an electrochemical gradient.

Electrochemical Gradient

A gradient produced by the combined forces of the concentration gradient of an ion and the electrical charge gradient across the membrane.

Membrane Potential

The voltage (charge difference) across a cell membrane, measured in millivolts (mV); in neurons, it is usually negative inside when at rest.

Cotransport

The transport of a solute against its gradient, powered by the simultaneous transport of a second solute down its gradient; uses energy indirectly from ATP.

Bulk Transport

The process of moving large molecules (proteins, polysaccharides) into or out of the cell using vesicles, which requires energy.

Vesicle

A small, membrane-bound sac that transports substances within a cell or during bulk transport.

Exocytosis

The process by which an intracellular vesicle fuses with the plasma membrane to secrete large substances out of the cell.

Endocytosis

The process by which a cell takes in substances by forming vesicles from the plasma membrane.

Phagocytosis

"Cell eating"; a type of endocytosis where large, solid material (e.g., debris, viruses) is engulfed.

Pinocytosis

"Cell drinking"; a type of endocytosis where vesicles form around liquid or very small particles.

Receptor-Mediated Endocytosis

A highly specific type of endocytosis where receptor proteins in a coated pit bind to specific molecules (e.g., hormones) to initiate their uptake.

Ionization Constant (i)

A factor in the solute potential equation representing the number of particles a solute dissociates into in water (e.g., NaCl i=2, Glucose i=1).

Pressure Constant (R)

The constant 0.0831 L·bar/mol·K used in the solute potential (ψs) calculation.

Cell

The simplest collection of matter that can be alive; the basic unit of life. All living things are made of cells, which only come from preexisting cells.

Cytoplasm

All the material contained inside the plasma membrane. It consists of the cytosol and all the particulates suspended in it.

Cytosol

The semifluid, intracellular fluid substance found inside the cell.

Genetic Material

Instructions needed for growth, development, functioning, and reproduction, contained in chromosomes. In almost all cells, this material is DNA.

Ribosomes

Small structures made of ribosomal RNA (rRNA) and protein, consisting of a small and a large subunit. They build proteins using instructions from genes found in the DNA.

Selective Semi-Permeable Membrane

Another term for the plasma membrane, indicating that it allows some substances to cross while blocking others.

Prokaryotic Cell

A simple cell characterized by the absence of a nucleus and membrane-bound organelles. All prokaryotes are single-celled organisms.

Eukaryotic Cell

A complex cell characterized by having a true nucleus and other membrane-bound organelles. Eukaryotes can be single-celled or multicellular.

Nucleus

The organelle that houses the cell's DNA, which is organized into chromosomes. It is enclosed by a double membrane called the nuclear envelope.

Organelles

Specialized, membrane-bound compartments in eukaryotic cells that perform specific functions.

Nucleoid

A region in a prokaryotic cell where the DNA is located. It is not surrounded by a membrane.

Cell Wall

A rigid structure found outside the cell membrane in plants, fungi, bacteria, and some protists. It provides structural support and protection.

Peptidoglycan

The carbohydrate polymer that makes up the cell wall of bacteria.

Capsule

A jelly-like outer coating found in many prokaryotes.

Flagella

Long, whip-like locomotion organelles of some bacteria and some eukaryotic cells (e.g., sperm cells).

Chromosomes

Discrete units into which DNA is organized. Humans have 46. Each chromosome contains one long DNA strand coiled around proteins.

Chromatin

The complex of DNA and proteins that makes up chromosomes.

Nuclear Envelope

The double membrane (two lipid bilayers) that encloses the nucleus.

Nuclear Pores

Pores in the nuclear envelope that allow material to enter and leave the nucleus.

Nucleolus

A dense region of DNA inside the nucleus where ribosomes are synthesized.

Endomembrane System

A system of membrane-bound organelles inside eukaryotic cells, including the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, vacuoles, and the plasma membrane.

Endoplasmic Reticulum (ER)

An extensive network of membrane continuous with the nuclear envelope that increases the surface area inside the cell for synthesis.

Rough ER

The region of the endoplasmic reticulum that is embedded with ribosomes. Its major function is to synthesize proteins destined for secretion, incorporation into the membrane, or for lysosomes.

Smooth ER

The region of the endoplasmic reticulum that lacks ribosomes. Its functions include lipid synthesis (fats, steroids, phospholipids) and detoxification.

Lumen

The internal space or cavity of an organelle, such as the inside of the ER.

Transport Vesicle

A membrane-bound vesicle that buds off from the ER or Golgi apparatus, carrying proteins to their next destination.

Bound Ribosomes

Ribosomes attached to the endoplasmic reticulum.

Free Ribosomes

Ribosomes found suspended in the cytoplasm. They make proteins destined for use inside the cytosol.

Golgi Apparatus

An organelle made of flattened membranous sacs (cisternae) that modifies, stores, and sorts products from the ER before sending them to other destinations.

Cis Face

The receiving end of the Golgi apparatus, where vesicles from the ER fuse.

Trans Face

The shipping end of the Golgi apparatus, where modified products pinch off in vesicles for transport.

Lysosomes

A vesicle (not usually found in plants) containing hydrolytic enzymes that digest macromolecules. Functions include breaking down food, recycling cell components, and apoptosis.

Hydrolytic Enzymes

Enzymes that break down macromolecules by adding water (hydrolysis). They are produced by the rough ER and found in lysosomes.

Apoptosis

Programmed cell death. During apoptosis, lysosomes release their enzymes to break down cellular structures.

Vacuoles

Large vesicles created by the ER and Golgi that perform a variety of functions, such as storage.

Food Vacuole

A vacuole formed by phagocytosis to digest food particles.

Contractile Vacuole

A vacuole found in many freshwater protists that pumps excess water out of cells.

Central Vacuole

A large vacuole found in plant cells that stores water, nutrients, pigments, and waste products. It is not found in animal cells.

Cytoskeleton

A network of fibers extending throughout the cytoplasm that supports the cell, maintains its shape, anchors organelles, and assists in movement.

Microtubules

The thickest component of the cytoskeleton.

Microfilaments

The thinnest component of the cytoskeleton; also called actin filaments.

Intermediate Filaments

Fibers with diameters in a middle range between microtubules and microfilaments.

Cilia

Short, numerous hair-like protrusions from the cell surface that move fluid and material over a tissue (e.g., in the trachea) or, in some cases, move the cell.

Flagellum (Eukaryotic)

A long, whip-like protrusion from a cell, usually limited to one per cell, used for locomotion (e.g., sperm cell).

Cell Junctions

Sites of direct contact between neighboring cells in tissues, allowing them to adhere, interact, and communicate.

Plasmodesmata

Channels that perforate the cell walls of plant cells, connecting the cytoplasm of adjacent cells and allowing water and materials to pass through.

Tight Junctions

A type of animal cell junction where the plasma membranes of neighboring cells are tightly pressed and bound together, creating a seal that prevents fluid leakage (e.g., in skin).

Desmosomes

A type of animal cell junction that functions like rivets, fastening cells together into strong sheets (e.g., in muscle tissue).

Gap Junctions

A type of animal cell junction where membrane proteins create channels between cells, allowing ions, sugars, and other small molecules to pass for communication (e.g., in heart tissue).