Cell structure, membranes and division: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Biology Topic 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
Magnification is how much larger the image is; resolution is the smallest distance at which two points stay distinguishable. Light microscopes are limited by wavelength.
Transmission electron microscope
Fires electrons through a thin section, giving very high resolution internal detail — but only of dead, chemically fixed specimens.
Cell fractionation
Homogenise in cold, isotonic, buffered solution, then centrifuge at rising speeds. Organelles pellet in order of density: nuclei, then mitochondria, then ribosomes.
Rough endoplasmic reticulum
Ribosome-studded membrane network that folds and transports proteins destined for secretion or the cell surface.
Golgi apparatus
Modifies proteins arriving from the ER, adding carbohydrate or lipid groups, then packages them into vesicles for export.
Prokaryote vs eukaryote
Prokaryotes have no nucleus or membrane-bound organelles, a murein cell wall, and smaller 70S ribosomes rather than 80S.
Fluid mosaic model
Membranes are a fluid phospholipid bilayer with proteins scattered through it like tiles in a mosaic, free to move laterally.
Cholesterol in membranes
Sits between phospholipid tails, restricting their movement. Reduces fluidity at high temperature and prevents rigidity at low temperature.
Facilitated diffusion
Passive movement down a concentration gradient through channel or carrier proteins. Needs no ATP but is limited by the number of proteins.
Osmosis
Net movement of water from a less negative to a more negative water potential, across a partially permeable membrane.
Water potential
The tendency of water to move out of a solution, measured in kilopascals. Pure water is zero; adding solute always makes it negative.
Active transport
Movement against a concentration gradient using carrier proteins and ATP hydrolysis. Inhibited by anything that stops respiration.
Co-transport
Two substances move through one carrier together. In the ileum, a sodium gradient set up by active transport drags glucose in with it.
Mitosis
One division producing two genetically identical diploid daughter cells. Used for growth, repair and asexual reproduction.
Meiosis
Two divisions producing four genetically distinct haploid cells. Independent segregation and crossing over generate the variation.
Mitotic index
The proportion of cells in a sample visibly undergoing mitosis. A raised value in a tissue sample can indicate uncontrolled division.