Cell Structure and Microscopy Practice Flashcards

Comprehensive vocabulary flashcards covering microscopy, micrometry, eukaryotic/prokaryotic cell structures, and viral components as per the AS Level biology transcript.

Magnification

The number of times an image is enlarged compared with the actual size of the object, often denoted with a symbol like "x" in front of the number.

Resolution

The ability to distinguish between two points clearly as separate, measured in units like $nm$. It is determined by the wavelength of radiation used, where the maximum resolution is equal to $\frac{1}{2}$ of the wavelength.

Transmission Electron Microscope (TEM)

A type of microscope that uses a beam of electrons passing through a specimen to provide 2D images showing details of internal cell structures and membranes.

Scanning Electron Microscope (SEM)

A type of microscope with lower resolution than a TEM that scans the surfaces of specimens to create a 3D appearance.

Light Microscope

A microscope using visible light ($400-700\,nm$) focused by glass lenses, with a maximum magnification of $x1,500$ and a maximum resolution of $200\,nm$. It is suitable for viewing live specimens.

Electron Microscope

A microscope using free electrons ($1\,nm$ wavelength) in a vacuum, with a maximum magnification of $x250,000$ and a maximum resolution of $0.5\,nm$. It can only examine dead material.

Eyepiece Graticule (EPG)

A scale placed on the eyepiece lens consisting of $100$ arbitrary units that appear constant regardless of the magnification used.

Stage Micrometer

A slide with a known true length (usually $10\,mm$ with $100$ small divisions) used to calibrate the eyepiece graticule. It appears larger as magnification increases.

Magnification Formula

$M = \frac{I}{A}$, where $M$ is magnification, $I$ is the measured length of the image, and $A$ is the actual size of the object.

Organelle

A functionally and structurally distinct part of a cell, often surrounded by membranes to allow for compartmentalization of chemical reactions.

Cell Surface Membrane

A partially permeable phospholipid bilayer approximately $7\,nm$ thick that appears trilaminar at $x100,000$ magnification. It controls the movement of substances into and out of the cell.

Nucleolus

The densest region of the nucleus, which serves as the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.

Chromatin

A structure within the nucleus composed of DNA and its associated proteins.

80S Ribosomes

Ribosomes approximately $25\,nm$ in diameter found in the cytoplasm and on the Rough ER of all eukaryotes, serving as the site of protein synthesis.

70S Ribosomes

Smaller ribosomes ($18\,nm$) found in all prokaryotes, as well as within the mitochondria and chloroplasts of eukaryotes.

Rough Endoplasmic Reticulum (RER)

An extensive system of cisternae (flattened membrane sacs) with $80S$ ribosomes attached, involved in protein synthesis, folding, glycosylation, and transport.

Glycosylation

The chemical process of adding carbohydrate chains to proteins, typically occurring in the RER or Golgi body.

Smooth Endoplasmic Reticulum (SER)

Endoplasmic reticulum without ribosomes that serves as the site for lipid and steroid synthesis, such as cholesterol and steroid hormones.

Golgi Body

A stack of cisternae not connected to each other or the nuclear envelope, responsible for modifying proteins/lipids, packaging molecules into vesicles, and forming lysosomes.

Lysosomes

Small, spherical sacs containing hydrolytic enzymes (lysozymes) that breakdown unwanted structures, worn-out organelles, or bacteria via hydrolysis in an acidic environment.

Mitochondria

Relatively large organelles with double membranes (inner membrane forms cristae) that serve as the site of aerobic respiration and synthesize ATP. They contain $70S$ ribosomes and circular DNA.

Chloroplasts

Oval-shaped organelles in plants with two membranes, containing chlorophyll, thylakoids stacked into grana, and stroma. They are the site of photosynthesis.

Cell Wall

A thick, rigid, and permeable layer made of cellulose fibers that provides structural support, prevents bursting, and limits cell size.

Plasmodesmata

Strands of cytoplasm that pass through channels in cell walls to allow the rapid transport of substances like water, sucrose, and ions between adjacent cells.

Tonoplast

The partially permeable membrane that surrounds the large, permanent central vacuole in plant cells.

Centrioles

Cylindrical structures made of $9$ groups of $3$ microtubules, involved in cell division and acting as a Microtubule Organising Centre (MTOC) for cilia and flagella.

Microtubules

Long, rigid, hollow tubes ($25\,nm$ diameter) made of tubulin dimers that form the cytoskeleton and spindle fibers for cell division.

Microvilli

Finger-like extensions of the cell surface membrane found in animal cells (e.g., intestines, kidneys) that increase surface area for absorption and secretion.

Prokaryotic Cell

Unicellular organisms ($1-5\,\mu m$) that lack membrane-bound organelles and a nucleus, possessing a peptidoglycan cell wall and naked circular DNA.

Peptidoglycan

The material that makes up the cell wall of bacteria, consisting of chains cross-linked by amino acids.

Capsid

The protective protein coat that surrounds the nucleic acid core (DNA or RNA) of a virus.

Exocytosis

The process by which the contents of a secretory vesicle are released outside the cell through fusion with the cell surface membrane.