Chapter 1: Cell Structure - Microscopy and Organelles

Vocabulary practice flashcards covering cell structure, light and electron microscopy, magnification, resolution, and eukaryotic cell organelles based on Chapter 1 of the Cambridge International AS & A Level Biology coursebook.

Resolution

The ability to distinguish between two objects that are very close together; the higher the resolution of an image, the greater the detail that can be seen. For a light microscope, the maximum resolution is $200\,\text{nm}$.

Limit of Resolution Rule

A biological microscopy principle stating that the limit of resolution is approximately one half the wavelength of the radiation used to view the specimen; objects closer or smaller than half the wavelength cannot be distinguished as separate.

Transmission Electron Microscope (TEM)

An electron microscope in which a beam of electrons is transmitted through a thin specimen section to produce an image of internal cell structures, achieving a resolution of up to $0.5\,\text{nm}$.

Scanning Electron Microscope (SEM)

An electron microscope in which an electron beam scans across the surface of a specimen and the reflected electrons are detected, forming a three-dimensional image with a resolution between $3\,\text{nm}$ and $20\,\text{nm}$.

Heavy Metal Stains

Stains containing heavy metal atoms used in electron microscopy to absorb or deflect electrons, enhancing specimen contrast so that densely stained structures appear blacker in the resulting image.

Ultrastructure

The detailed internal architecture of a cell and its organelles as revealed by electron microscopy.

Cell Surface Membrane

An extremely thin (about $7\,\text{nm}$) partially permeable barrier that controls the exchange of substances between the cell and its environment; under high magnification, it appears as two dark, heavily stained layers bordering a narrow pale interior.

Microvilli

Small, finger-like extensions of the cell surface membrane that increase surface area for more efficient absorption or secretion, such as in kidney proximal convoluted tubules and gut epithelial cells.

Nuclear Envelope

A double-membrane system surrounding the nucleus whose outer membrane is continuous with the endoplasmic reticulum and which is perforated by nuclear pores.

Nuclear Pores

Openings in the nuclear envelope that control bidirectional molecular exchange, permitting the exit of $\text{mRNA}$, $\text{tRNA}$, and ribosomal subunits, while allowing entry of proteins, nucleotides, $\text{ATP}$, and hormones.

Chromatin

The structural complex consisting of lengthy $\text{DNA}$ molecules combined with histone proteins and some $\text{RNA}$, coiled and folded into chromosomes inside the nucleus.

Nucleolus

A darkly stained, non-membrane-bound nuclear region containing chromosomal genes that transcribe ribosomal $\text{RNA}$ ($\text{rRNA}$) and $\text{tRNA}$, and assemble ribosomal subunits by combining $\text{rRNA}$ with imported proteins.

Endoplasmic Reticulum (ER)

An extensive network of flattened, membrane-bound sacs (cisternae) in eukaryotic cells that is continuous with the outer membrane of the nuclear envelope and isolates synthetic or transport processes from the cytoplasm.

Rough Endoplasmic Reticulum (RER)

The compartment of the endoplasmic reticulum studded with ribosomes on its outer surface; functions in the synthesis and transport of proteins within its cisternae.

Smooth Endoplasmic Reticulum (SER)

The compartment of the endoplasmic reticulum devoid of ribosomes; synthesises lipids and steroids (such as cholesterol, oestrogen, and testosterone), acts as a calcium ion reservoir in muscle cells, and metabolises drugs in the liver.

Ribosome

A tiny non-membrane-bound organelle comprising a large and small subunit made of roughly equal parts $\text{rRNA}$ and protein; serves as the site of protein translation ($80\text{S}$ in eukaryotic cytoplasm; $70\text{S}$ in prokaryotes, mitochondria, and chloroplasts).

Svedberg Unit (S unit)

A unit quantifying the sedimentation rate of particles in an ultracentrifuge, where higher values correspond to faster sedimentation rates.

Golgi Apparatus

An organelle consisting of a stack of flattened, membrane-bound cisternae formed at one end by vesicles from the endoplasmic reticulum and breaking down at the opposite end into Golgi vesicles; collects, modifies, and packages molecules.

Golgi Vesicles

Small membrane-bound sacs budding from the Golgi apparatus that transport modified molecules to other intracellular organelles or to the cell surface membrane for secretion.

Lysosome

A spherical, single-membrane-bound organelle ($0.1-0.5\,\mu\text{m}$ in animal cells) maintaining an internal acidic environment of $\text{pH } 4-5$ and containing hydrolytic enzymes for the breakdown of unwanted materials, organelles, or cells.

Hydrolases

The class of digestive enzymes found inside lysosomes (including proteases, lipases, and nucleases) that catalyse hydrolysis reactions at optimal acidic $\text{pH}$.

Mucin

A glycoprotein-rich substance released via the Golgi apparatus of goblet cells in the gut and respiratory tract that serves as a primary component of mucus.