ap bio organelle structures

Nucleus

Stores DNA and controls gene expression; surrounded by a double-membrane nuclear envelope.

Nuclear envelope

Double membrane with pores that regulate transport between nucleus and cytoplasm.

Nucleolus

Produces rRNA and assembles ribosomal subunits.

Ribosomes

Build proteins through translation; free ribosomes usually make cytosolic proteins, while bound ribosomes make proteins for membranes, organelles, or secretion.

Chromatin

DNA wrapped around histone proteins; condenses into chromosomes during cell division.

Rough ER

Has ribosomes attached; synthesizes and folds proteins destined for secretion, membranes, or certain organelles.

Smooth ER

Synthesizes lipids and steroids, detoxifies chemicals, and stores calcium ions.

Golgi apparatus

Modifies, sorts, and packages proteins and lipids; cis face receives materials and trans face ships them.

Transport vesicles

Membrane-bound sacs that transport materials between organelles and the plasma membrane.

Lysosomes

Contain digestive enzymes that break down macromolecules, pathogens, and worn-out cell parts; recycle materials.

Vacuoles

Store water, nutrients, pigments, and wastes; the central plant vacuole maintains turgor pressure.

Peroxisomes

Break down fatty acids and detoxify substances; catalase breaks down hydrogen peroxide.

Mitochondria

Site of most aerobic cellular respiration and ATP production; have a double membrane, their own DNA, and ribosomes.

Cristae

Folds of the inner mitochondrial membrane that increase surface area for ATP production.

Mitochondrial matrix

Fluid-filled interior of the mitochondrion where the citric acid cycle occurs.

Chloroplasts

Carry out photosynthesis in plants and algae; contain chlorophyll, their own DNA, and ribosomes.

Thylakoids

Flattened membrane sacs in chloroplasts where the light-dependent reactions of photosynthesis occur.

Grana

Stacks of thylakoids that increase membrane surface area.

Stroma

Fluid surrounding thylakoids; site of the Calvin cycle.

ATP synthase

Enzyme that uses a proton gradient to produce ATP; found in the inner mitochondrial membrane and thylakoid membrane.

Plasma membrane

Selectively permeable phospholipid bilayer that controls transport and enables cell signaling.

Phospholipid bilayer

Hydrophilic heads face water and hydrophobic tails face inward; forms the basic structure of cell membranes.

Cholesterol

Helps regulate membrane fluidity and stability in animal cells.

Cell wall

Provides support, protection, and shape; plants have cellulose walls, fungi have chitin walls, and bacteria have peptidoglycan walls.

Cytoplasm

Includes cytosol and structures suspended within it; many metabolic reactions occur here.

Cytosol

Fluid portion of the cell where many chemical reactions occur.

Cytoskeleton

Network of protein fibers that maintains cell shape, organizes organelles, transports materials, and enables movement.

Microtubules

Made of tubulin; form the mitotic spindle and help build cilia and flagella.

Microfilaments

Made of actin; function in cell movement, muscle contraction, and cytokinesis.

Intermediate filaments

Provide mechanical strength and help cells resist stretching.

Centrosome

Organizes microtubules and helps form the mitotic spindle in animal cells.

Centrioles

Cylindrical structures in many animal cells that help organize microtubules.

Cilia

Short, hairlike structures that move cells or move fluid across cell surfaces; typical eukaryotic cilia have a 9+2 microtubule arrangement.

Flagella

Long structures used for movement; eukaryotic flagella typically have a 9+2 microtubule arrangement.

Gap junctions

Animal cell connections that allow ions and small molecules to pass directly between neighboring cells.

Tight junctions

Animal cell connections that seal spaces between cells and prevent leakage.

Desmosomes

Animal cell connections that anchor cells together and provide mechanical strength.

Plasmodesmata

Channels through plant cell walls that connect neighboring cells and allow communication and transport.

Extracellular matrix (ECM)

Material outside animal cells that provides support, adhesion, and signaling.

Prokaryotic cells

Cells without a nucleus or membrane-bound organelles; include bacteria and archaea.

Eukaryotic cells

Cells with a nucleus and membrane-bound organelles; include animals, plants, fungi, and protists.

Nucleoid

Region of a prokaryotic cell where its DNA is located; not surrounded by a membrane.

Plasmids

Small, usually circular DNA molecules in bacteria that may carry genes such as antibiotic resistance.

Capsule

Protective outer covering found in some bacteria; can help with protection and attachment.

Prokaryotic ribosomes

Smaller than eukaryotic cytosolic ribosomes; synthesize proteins.

Endosymbiotic theory

Mitochondria and chloroplasts evolved from free-living bacteria engulfed by ancestral cells.

Evidence for endosymbiotic theory

Mitochondria and chloroplasts have circular DNA, bacterial-like ribosomes, double membranes, and divide by binary fission.

Surface area-to-volume ratio

Smaller cells have a higher ratio; as a cell grows, volume increases faster than surface area, reducing exchange efficiency.

Compartmentalization

Membrane-bound organelles separate reactions and create specialized environments, improving efficiency.

Protein pathway

DNA → mRNA → ribosome on rough ER → transport vesicle → Golgi → vesicle → plasma membrane or secretion; not all proteins follow this pathway.

Membrane fluidity

Phospholipids move laterally; unsaturated fatty acid tails generally increase fluidity, while cholesterol helps regulate it in animal cells.

Selective permeability

Small nonpolar molecules cross membranes more easily; ions and most large or polar molecules require transport proteins.

Osmosis

Net movement of water across a selectively permeable membrane toward the side with higher effective solute concentration.

Hypotonic solution

Lower solute concentration outside the cell; water enters the cell.

Hypertonic solution

Higher solute concentration outside the cell; water leaves the cell.

Isotonic solution

Equal effective solute concentrations; no net movement of water.

Plant cell in a hypotonic solution

Water enters and the cell becomes turgid; the cell wall prevents excessive expansion.

Plant cell in a hypertonic solution

Water leaves and the membrane pulls away from the cell wall; this is called plasmolysis.

Animal cell in a hypotonic solution

Water enters; the cell may swell and lyse.

Animal cell in a hypertonic solution

Water leaves and the cell shrinks.

Cotransport

Movement of one substance down its gradient provides energy to move another substance against its gradient.

Plant cell structures

Plant cells have cellulose cell walls, chloroplasts in photosynthetic cells, and typically a large central vacuole.

Animal cell structures

Animal cells lack cell walls and chloroplasts; they commonly have lysosomes and centrosomes.

Bacterial cell structures

Bacteria lack a nucleus and membrane-bound organelles; most have a cell wall containing peptidoglycan.

Mitochondria vs. chloroplasts

Mitochondria perform cellular respiration; chloroplasts perform photosynthesis.

Rough ER vs. Golgi apparatus

Rough ER synthesizes and folds many proteins; Golgi modifies, sorts, and packages them.

Lysosomes vs. peroxisomes

Lysosomes digest and recycle materials; peroxisomes break down fatty acids and detoxify substances.

Cell wall vs. plasma membrane

The cell wall provides support and protection; the plasma membrane regulates selective transport.

Free vs. bound ribosomes

Both make proteins; free ribosomes usually make cytosolic proteins, while bound ribosomes make proteins for secretion, membranes, and certain organelles.

Endomembrane system

Includes the nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, and plasma membrane; coordinates synthesis, modification, and transport.

Fluid mosaic model

Describes the cell membrane as a flexible phospholipid bilayer containing proteins and other molecules.

Active transport

Moves substances against their concentration or electrochemical gradients using energy, directly or indirectly.

Facilitated diffusion

Passive movement down a concentration or electrochemical gradient through membrane proteins; does not directly require ATP.

Simple diffusion

Passive movement down a concentration gradient without transport proteins.

Exocytosis

Vesicles fuse with the plasma membrane and release substances outside the cell.

Endocytosis

The plasma membrane folds inward to bring substances into the cell in vesicles.

Receptor proteins

Bind specific signaling molecules and help cells detect and respond to signals.

Cell signaling and membranes

Membrane receptors detect signals that cannot easily cross the phospholipid bilayer.

ATP production in mitochondria

Electrons moving through the electron transport chain help establish a proton gradient that powers ATP synthase.

Photosynthesis in chloroplasts

Light reactions occur in thylakoid membranes; the Calvin cycle occurs in the stroma.

Cellular respiration and photosynthesis

Cellular respiration transfers energy from organic molecules to ATP; photosynthesis stores light energy in organic molecules.

Cytokinesis

The division of the cytoplasm; actin microfilaments form a cleavage furrow in animal cells, while plants form a cell plate.