AP Biology: Cell Structure, Organelles, and Membrane Transport

Ribosomes

Made of rRNA + proteins, no membrane; builds protein from mRNA instructions; found in all cells (prokaryotes and eukaryotes).

Endoplasmic Reticulum

Rough ER: Has ribosomes on it → makes and folds proteins, ships them to Golgi; Smooth ER: No ribosomes → makes lipids.

Golgi Apparatus

Structure: flattened stacks of membranes; Function: modifies, packages, and ships proteins/lipids.

Mitochondria

Structure: double membrane, inner membrane = folded; inside: matrix; Function: performs cellular respiration → makes ATP cell energy; Has its own DNA.

Lysosomes

Structure: membrane sac with enzymes; Function: Breaks down waste.

Vacuole

Structure: membrane bound sac; Function: stores water, food, waste.

Chloroplasts

Structure: Double membrane; thylakoids (stacks = grana) + stroma; Function: Does photosynthesis — turns sunlight → glucose.

Mitochondrion Structure

Includes cristae/inner membrane and space between inner and outer membrane, supporting key function during respiration.

Chloroplast Structure

Includes thylakoid/granum and stroma, in between inner and outer membrane, where photosynthetic processes occur.

SA:V Ratio

The surface area to volume ratio of a cell or organism can affect its ability to obtain resources, eliminate wastes, and acquire or dissipate heat.

Selective Permeability of Biological Membranes

The structure of biological membranes enables its selective permeability, aiding in the acquisition of nutrients and elimination of wastes.

Phospholipid

A molecule that is a major component of cell membranes, consisting of a hydrophilic head and two hydrophobic tails.

Bilayer

A double layer of phospholipids that makes up the cell membrane.

Cell membrane

The semipermeable membrane surrounding the cytoplasm of a cell, composed of a phospholipid bilayer with embedded proteins.

Ribosome

A cellular structure that synthesizes proteins by translating messenger RNA.

Chloroplast

An organelle found in plant cells that conducts photosynthesis, converting solar energy into chemical energy.

Cytoskeleton

A network of fibers that provides structural support and shape to the cell, and facilitates movement.

Prokaryote

A unicellular organism that lacks a nucleus and membrane-bound organelles.

Eukaryote

An organism whose cells contain a nucleus and other membrane-bound organelles.

Cellulose

A polysaccharide that is a major component of plant cell walls.

Cellular respiration

The process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water.

Photosynthesis

The process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.

Thylakoid

A membrane-bound compartment inside chloroplasts where the light-dependent reactions of photosynthesis occur.

Granum

A stack of thylakoids in a chloroplast.

Stroma

The fluid-filled space surrounding the thylakoids in chloroplasts where the light-independent reactions of photosynthesis occur.

Inner membrane (Mito)

The membrane that encloses the mitochondrial matrix and is involved in ATP production.

Outer membrane (mito)

The membrane that surrounds the mitochondrion and contains porins that allow the passage of small molecules.

Matrix (mito)

The space within the inner membrane of a mitochondrion, containing enzymes for the Krebs cycle.

Intermembrane space

The space between the inner and outer membranes of a mitochondrion.

Active transport

The movement of molecules across a cell membrane against their concentration gradient, requiring energy.

Passive transport

The movement of molecules across a cell membrane without the use of energy, following their concentration gradient.

Facilitated diffusion

The process of passive transport of molecules across a cell membrane via specific transmembrane integral proteins.

Cholesterol

A lipid molecule that is an essential component of cell membranes, helping to maintain fluidity.

Endocytosis

The process by which cells internalize substances by engulfing them in a vesicle.

Exocytosis

The process by which cells expel materials in vesicles that fuse with the plasma membrane.

Volume

The amount of space occupied by a substance, typically measured in liters or cubic centimeters.

Solute

A substance that is dissolved in a solvent to form a solution.

Solvent

A substance that dissolves a solute, forming a solution.

Solution

A homogeneous mixture composed of two or more substances.

Diffusion

The process by which molecules spread from areas of high concentration to areas of low concentration.

Osmosis

The diffusion of water across a selectively permeable membrane.

Ribosomes in life

Ribosomes are found in all forms of life, reflecting the common ancestry of all known life.

Endoplasmic Reticulum (ER)

ER occurs in 2 forms- smooth and rough.

Rough ER

Rough ER is associated with membrane-bound ribosomes and compartmentalizes the cell.

Smooth ER

Smooth ER functions include detoxification and lipid synthesis.

Golgi Functions

Functions include the correct folding and chemical modification of newly synthesized proteins and packaged for protein trafficking.

Cellular Function

Organelles and subcellular structures, and the interactions among them, support cellular function.

Mitochondrial Double Membrane

Mitochondrial double membrane provides compartments for different metabolic reactions.

Lysosomal Function

Lysosomes contain hydrolytic enzymes, which are important in intracellular digestion, the recycling of a cell's organic materials, and apoptosis.

Vacuole Functions

Vacuoles have many roles, including storage and release of macromolecules and cellular waste products. In plants, it aids in retention of water for turgor pressure.

Inner Membrane Folding

The folding of the inner membrane increases the surface area, which allows for more ATP to be synthesized.

Thylakoids

Within the chloroplast there are thylakoids and the stroma.

Grana

The thylakoids are organized in stacks, called grana.

Photosystems

Membranes contain chlorophyll pigments and electron transport proteins that comprise the photosystems.

Calvin Cycle

The carbon fixation (Calvin cycle) reactions of photosynthesis occur in the stroma.

Krebs Cycle

The Krebs cycle reactions occur within the matrix of the mitochondria.

Electron Transport

Electron transport and ATP synthesis occur in the inner mitochondrial membrane.

Plasma Membrane SA

The SA of the plasma membrane must be large enough to adequately exchange materials.

Cell Size Limitations

These limitations can restrict cell size and shape. Smaller cells typically have a higher surface area-to-volume ratio and more efficient exchange of materials with the environment.

Complex Cellular Structures

More complex cellular structures (e.g., membrane folds) are necessary to adequately exchange materials with the environment.

Organism Size Effect

As organisms increase in size, their surface area-to-volume ratio decreases, affecting properties like rate of heat exchange with the environment.

Efficient Exchange Strategies

Organisms have evolved highly efficient strategies to obtain nutrients and eliminate waste.

Phospholipids

Molecules that have both hydrophilic and hydrophobic regions, with hydrophilic regions oriented toward aqueous environments and hydrophobic regions facing each other within the membrane.

Embedded proteins

Proteins that can be hydrophilic with charged polar side groups or hydrophobic with nonpolar side groups.

Fluid Mosaic Model

A model describing cell membranes as a structural framework of phospholipids embedded with proteins, steroids, glycoproteins, and glycolipids that can flow around the surface.

Selective permeability

The ability of the cell membrane to allow certain substances to pass while blocking others, influenced by the membrane's structure.

Small nonpolar molecules

Molecules like N2, O2, and CO2 that pass freely through the cell membrane.

Hydrophilic substances

Larger, polar molecules and ions that move across the membrane through embedded channels and transport proteins.

Polar uncharged molecules

Molecules such as H2O that pass through the membrane in small amounts.

Cell wall

A structural boundary that provides a permeability barrier for some substances to the internal environments of cells.

Aquaporins

Membrane proteins that allow large quantities of water to pass through the membrane.

Channel proteins

Proteins that allow charged ions, like sodium and potassium, to move through the membrane.

Sodium and potassium pump

A mechanism that contributes to the maintenance of the membrane potential through active transport.

Concentration gradients

Differences in solute concentration across a membrane that affect the movement of molecules.

Hypotonic

An external environment with lower solute concentration compared to the internal environment of cells.

Hypertonic

An external environment with higher solute concentration compared to the internal environment of cells.

Isotonic

An external environment with equal solute concentration compared to the internal environment of cells.

Osmoregulation

The process that maintains water balance and allows organisms to control the internal solute composition and water potential.

Bulk transport

Processes including passive transport, active transport, endocytosis, and exocytosis that allow ions and other molecules to move across membranes.

Eukaryotic cell compartmentalization

The organization of membranes and membrane-bound organelles that compartmentalize intracellular metabolic processes and specific enzymatic reactions.

Internal membranes

Membranes that facilitate cellular processes by minimizing competing interactions and increasing surface areas where reactions occur.

Endosymbiotic Theory

The theory that membrane-bound organelles evolved from once free-living prokaryotes via endosymbiosis.

Prokaryotes

Cells that generally lack internal membrane-bound organelles but have internal regions with specialized structures and functions.

Eukaryotic cells

Cells that maintain internal membranes that partition the cell into specialized compartments.