AP Biology Unit 2: Cell Structure and Membrane Transport

Vocabulary flashcards covering cellular organelles, membrane structure, mechanisms of transport, and tonicity from AP Biology Unit 2.

Nucleus

A double-membrane organelle containing nuclear pores that stores genetic material, serves as the site for transcription, and assembles ribosomes.

Nuclear Envelope

The double-membrane boundary of the nucleus containing pores that allow synthesized mRNA to exit into the cytosol for translation.

Rough Endoplasmic Reticulum (Rough ER)

A membrane organelle studded with ribosomes that synthesizes membrane-bound and secreted proteins, provides mechanical support, and assists in intracellular transport.

Smooth Endoplasmic Reticulum (Smooth ER)

A membrane network of cisternae lacking ribosomes that functions in lipid and steroid synthesis, detoxification, and calcium storage.

Sarcoplasmic Reticulum

A specialized smooth ER in muscle cells that stores calcium ions to be released as secondary messengers in cell communication.

Golgi Apparatus

A series of flattened membrane sacs (cisternae) responsible for modifying, packaging, and trafficking proteins and carbohydrates received from the rough ER.

Ribosome

A non-membrane-bound cellular structure made of rRNA and proteins, composed of a large and small subunit, that translates mRNA into a polypeptide chain.

Cristae

The highly folded inner membrane of the mitochondria that houses the electron transport chain and increases surface area for oxidative phosphorylation and ATP synthesis.

Mitochondrial Matrix

The internal fluid-filled space enclosed by the cristae where the Krebs cycle takes place.

Intermembrane Space

The region between the outer membrane and inner membrane (cristae) of the mitochondria into which protons are pumped by the electron transport chain.

Endosymbiotic Theory

The theory that mitochondria and chloroplasts evolved from free-living prokaryotes, supported by their circular DNA, autonomous ribosomes, and double membranes.

Thylakoid

Flattened membrane sacs inside chloroplasts containing chlorophyll pigments that absorb solar energy to drive the light reactions of photosynthesis.

Granum

A stack of thylakoid sacs within the chloroplast that increases surface area for light absorption.

Stroma

The fluid-filled interior space of the chloroplast surrounding the thylakoids where the Calvin cycle (Calvin-Benson cycle) occurs.

Lysosome

A membrane-bound sac containing hydrolytic enzymes that performs intracellular digestion, recycles organic materials, and carries out programmed cell death (apoptosis).

Central Vacuole

A large membrane-bound organelle in plant cells that retains water to generate turgor pressure, providing rigidity and structural support.

Contractile Vacuole

A specialized organelle in freshwater unicellular organisms, such as paramecia, that pumps excess intracellular water out to prevent lysis.

Surface Area-to-Volume Ratio

The mathematical relationship between a cell's exterior surface and its internal volume; higher ratios are favored because they optimize diffusion of nutrients and wastes.

Cholesterol (Membrane Buffer)

A lipid in the plasma membrane that buffers fluidity by preventing gaps at high temperatures and preventing solid packing at low temperatures.

Glycolipids and Glycoproteins

Carbohydrates attached to lipids or proteins on the plasma membrane surface that function in cell communication and recognition.

Simple Diffusion

A passive transport process where small, nonpolar molecules pass directly through the phospholipid bilayer down their concentration gradient without energy.

Facilitated Diffusion

Passive transport moving polar or charged molecules down their concentration gradient across a membrane with the assistance of channel or carrier proteins.

Channel Protein

A transport protein that forms a specific hydrophilic pore through the membrane to allow target molecules or ions to diffuse passively.

Carrier Protein

A transport protein that binds to a specific solute and undergoes a conformational shape change to move the solute across the membrane.

Active Transport

The movement of substances against their concentration gradient requiring transport proteins (pumps) and an input of cellular energy ($ATP$).

Phagocytosis

A form of endocytosis ('cellular eating') in which pseudopodia engulf large molecules or bacteria to form a food vacuole for lysosomal digestion.

Pinocytosis

A form of endocytosis ('cellular drinking') where the membrane invaginates to take in droplets of extracellular fluid and dissolved solutes.

Receptor-Mediated Endocytosis

A targeted bulk transport mechanism triggered when specific extracellular ligands bind to cell-surface receptors, causing membrane invagination.

Exocytosis

An active bulk transport process requiring $ATP$ where internal vesicles fuse with the plasma membrane to secrete substances out of the cell.

Osmosis

The diffusion of water across a selectively permeable membrane from an area of low solute concentration (high free water) to high solute concentration (low free water).

Hypertonic Solution

A solution with a higher solute concentration and lower free water concentration relative to another solution, causing cells to lose water.

Hypotonic Solution

A solution with a lower solute concentration and higher free water concentration relative to another solution, causing water to enter cells.

Isotonic Solution

A solution having an equal solute concentration relative to another solution, resulting in zero net movement of water across the membrane.

Plasmolysis

The shrinking of a plant cell's cytoplasm where the plasma membrane pulls away from the cell wall due to water exiting into a hypertonic environment.

Turgor Pressure

The outward hydrostatic pressure exerted by water inside the central vacuole against the plant cell wall, creating structural rigidity.

Crenation

The shriveling of an animal red blood cell resulting from water loss when placed into a hypertonic solution.

Lysis

The bursting of an animal cell caused by excessive water entry when placed in a hypotonic solution.

CFTR Protein

A gated ion channel in the plasma membrane that requires $ATP$ binding to permit chloride ions to diffuse across the membrane.