Introduction to Cells and Microscopy

A set of vocabulary flashcards covering the properties of cells, historical discovery milestones, cell theory, units of biological measurement, and various microscopy and fractionation techniques used to study them.

Cell

The basic unit of structure and function in an organism and the smallest unit of organization that can perform all activities required for life.

Cell Theory

A theory stating that all organisms are composed of one or more cells, cells are the smallest living things or basic units of organization, and cells arise only by division of a previously existing cell.

Robert Hooke (1665)

A curator for the Royal Society of London who first saw cell walls in cork tissue and coined the term "cells" because they reminded him of monastery cells.

Antonie van Leeuwenhoek

The first person to observe living cells, which he referred to as "animalcules" in the late 1600s.

Schleiden and Schwann (1839)

Scientists who established that cells are the basic unit of structure and function in living things.

Virchow

The scientist who, 20 years after Schleiden and Schwann, added the principle to cell theory that "all cells originate from cells."

Micrometer ($\mu m$)

A unit of measurement equal to $10^{-6}\,m$ ($1/1,000,000$ of a meter) or $1/1,000$ of a millimeter.

Nanometer ($nm$)

A unit of measurement equal to $10^{-9}\,m$ ($1/1,000,000,000$ of a meter).

Angstrom ($\text{\AA}$)

A unit of length equal to $10^{-10}\,m$ or $0.1\,nm$, named after the Swedish physicist Anders Jonas \u00c5ngstr\u00f6m.

Surface area to volume ratio

A critical logistics factor for cellular metabolism where, as surface area increases by a factor of $n^2$, volume increases by $n^3$; small cells have a greater ratio than large cells.

Magnification

The ratio of an object's image size to its real size.

Resolution

The measure of the clarity of an image, or the minimum distance two points can be separated and still be distinguishable.

Contrast

Visible differences in parts of a sample.

Light Microscope (LM)

A microscope that uses visible light to illuminate a specimen, magnifying effectively up to about $1,000$ times the actual size.

Brightfield Microscopy

A technique that passes light directly through a specimen; staining is often used to enhance contrast but kills the cells.

Phase-contrast Microscopy

A technique that enhances contrast in unstained cells by amplifying variations in density; especially useful for examining living, unpigmented cells.

Differential-interference-contrast (Nomarski)

A microscopy technique that uses optical modifications to exaggerate differences in density, making the image appear almost 3-D.

Fluorescence Microscopy

A technique where fluorescent stains bind to specific molecules, absorbing UV light and emitting visible light to detect locations of specific molecules.

Confocal Microscopy

A fluorescent "optical sectioning" technique that uses a pinhole aperture to eliminate out-of-focus light, creating sharp 3-D reconstructions from many planes.

Scanning Electron Microscope (SEM)

A microscope that focuses a beam of electrons onto the surface of a specimen coated in gold to provide 3-D appearing images.

Transmission Electron Microscope (TEM)

A microscope that focuses a beam of electrons through a thinly cut specimen to study internal cell ultrastructure.

Cell Fractionation

A process using centrifugation of broken-up cells to separate and purify subcellular structures based on their size and density.

Differential Centrifugation

A technique where the homogenate is spun at increasing speeds to settle out different subsets of cellular components into a pellet.

Microsomes

Pieces of plasma membranes and the cell's internal membranes that are collected as a pellet after centrifugation at $80,000\,g$ for 60 minutes.