CELL STRUCTURE & FUNCTION

Tight junctions form a continuous fluid-tight seal between adjacent cell membranes, preventing materials from leaking between cells.

Without functional cellulose synthase complexes, the cell cannot build a primary cell wall, causing expanding cells to burst under turgor pressure.

The nucleolus functions as a ribosome manufacturing center, transcribing rRNA and combining it with proteins to form ribosomal subunits.

Inhibiting actin prevents the assembly of the contractile ring, blocking cleavage furrow formation and leaving the cell with two nuclei.

The smooth ER in hepatocytes contains cytochrome P450 enzyme families that chemically modify and detoxify hydrophobic drugs and toxins.

Proposed by Singer and Nicolson, the fluid mosaic model describes the membrane as a fluid phospholipid bilayer embedded with proteins.

Amyloplasts are a specific type of leukoplast that converts glucose into starch grains, storing them in roots, tubers, and seeds.

Polar molecules cannot pass through the hydrophobic lipid core directly; they require channel or carrier proteins to cross without using energy.

The stroma contains the soluble enzymes (such as RuBisCO) required to fix carbon dioxide into sugars during the Calvin cycle.

The cytoskeleton is a dynamic network of microfilaments, intermediate filaments, and microtubules that governs cell shape and movement.

Pits are thin depressions in the secondary wall where only the primary wall and middle lamella remain, allowing water to pass between cells.

The rough ER is studded with active ribosomes, serving as the primary site for translating and folding proteins destined for membranes or export.

Both plant and animal cells rely on the conserved F1​F0​-ATP synthase complex to generate ATP through oxidative phosphorylation.

A desmotubule is a continuous tube of specialized endoplasmic reticulum that runs through the center of a plasmodesmatal channel.

Exocytosis involves routing transport vesicles from the Golgi to the plasma membrane, where they fuse to release their contents outside.

Bacterial cell walls are made of peptidoglycan (glycan chains cross-linked by short peptides), whereas plant walls rely on cellulose.

A hypertonic environment draws water out of the animal cell, collapsing its volume and causing the cell membrane to wrinkle and shrivel.

Invaginating the inner mitochondrial membrane into cristae creates a large surface area for housing electron transport chain complexes.

The smooth ER houses the key enzyme pathways required for lipid metabolism, cholesterol processing, and steroid hormone biosynthesis.