IB BIOLOGY HL B2.2 Organelles and Compartmentalisation

A set of vocabulary flashcards covering the core concepts of organelles, cell fractionation, nuclear and cytoplasmic compartmentalisation, and protein secretion pathways as defined in the IB Biology HL B2.2 syllabus.

Organelle

A discrete subunit of a cell that is adapted to carry out a particular function; includes both membrane-bound structures and non-membrane-bound subunits like ribosomes.

Nucleus

A discrete double-membrane compartment containing DNA and supporting the process of transcription.

Mitochondrion

A membrane-bound organelle specialised for energy conversion, specifically aerobic $ATP$ production.

Chloroplast

A double-membrane bound organelle found in plants specialized for photosynthesis and energy conversion.

Ribosome

A non-membrane-bound subunit, consisting of small and large subunits made of rRNA and proteins, that is specialised for polypeptide synthesis.

Vesicle

A small membrane-bound sac used for transport, storage, or digestion that allows material to move between compartments without mixing with the cytosol.

Lysosome

A membrane-bound organelle containing hydrolytic enzymes and an acidic lumen for efficient digestion of cellular debris or engulfed material.

Plasma membrane

A specialised boundary that controls exchange and cell signalling, treated as an organelle in this syllabus.

Cell wall

An extracellular supporting layer that is not considered an organelle because it is outside the cell.

Cytoskeleton

A network of protein filaments treated as a structural system rather than a discrete organelle.

Cell fractionation

A scientific technique used to investigate organelle functions by homogenising cells and using differential centrifugation to separate components.

Differential centrifugation

A method that separates cell components by size and density, where progressively higher speeds pellet smaller structures.

Transcription

The process occurring in the nucleus where DNA is converted into $\text{pre-mRNA}$.

Translation

The process occurring in the cytoplasm where mature mRNA is used by ribosomes to synthesise polypeptides.

Post-transcriptional modification

Changes to $\text{pre-mRNA}$ including splicing of introns and the addition of a $5'$ cap and poly-A tail to produce stable mature mRNA.

Nuclear envelope

A structure consisting of inner and outer membranes that separates chromatin and nucleoplasm from the cytoplasm.

Nuclear pores

Protein complexes spanning the nuclear envelope that selectively regulate the transport of mature mRNA, proteins, and ribosomal subunits.

Phagocytic vacuole

A compartment formed when a cell engulfs a large particle, which can fuse with lysosomes for isolated digestion.

Cristae

Folds of the inner mitochondrial membrane that greatly increase surface area for electron-transport chains and $\text{ATP}$ synthase.

Mitochondrial matrix

The internal space of the mitochondrion containing enzymes and substrates for the link reaction and Krebs cycle.

Intermembrane space

The small space in mitochondria where pumped $H^+$ ions accumulate to quickly produce a steep electrochemical gradient.

Thylakoid membranes

Internal chloroplast membranes providing a large surface area for chlorophyll, photosystems, and the light-dependent reactions.

Stroma

The fluid-filled internal space of a chloroplast containing enzymes for the Calvin cycle, including $\text{RuBP}$ and $\text{Rubisco}$.

Thylakoid lumen

The small volume inside thylakoids where $H^+$ concentration rises rapidly to drive $\text{ATP}$ synthesis.

Free ribosomes

Ribosomes suspended in the cytosol, typically in polysomes, that synthesise proteins for use within the cell.

Rough Endoplasmic Reticulum (Rough ER)

An interconnected system of flattened membrane sacs called cisternae with ribosomes attached for synthesising proteins destined for secretion or membranes.

Golgi apparatus

A stack of flattened cisternae that modifies, sorts, and packages proteins received from the ER into vesicles.

Cis face

The side of the Golgi apparatus that receives transport vesicles from the Endoplasmic Reticulum.

Trans face

The side of the Golgi apparatus that packages processed proteins into secretory vesicles.

Exocytosis

A process where a secretory vesicle fuses with the plasma membrane to release soluble contents outside the cell.

Endocytosis

A process where the plasma membrane folds inward to form a vesicle containing material from the extracellular environment.

Clathrin

A protein that assembles into a curved lattice to help the membrane form a coated pit and bud during receptor-mediated endocytosis.