OCR A Level Biology: 2.11 Cell Structure Flashcards

A set of vocabulary flashcards defining key microscopy concepts, slide preparations, eukaryotic organelles, protein synthesis pathways, and prokaryotic structures from OCR A Level Biology.

Resolution

The minimum distance between two objects in which you can still view them as separate.

Magnification

How many times larger the image is compared to the actual object being viewed, calculated as $\text{Magnification} = \frac{\text{Size of Image}}{\text{Size of Real Object}}$.

Dry Mount

A light microscope slide preparation method where thin slices or a whole specimen are placed directly on a glass slide with a coverslip placed on top.

Wet Mount

A light microscope slide preparation method where specimens are added to water or a stain before a coverslip is lowered at an angle using a mounted needle to prevent air bubbles.

Squash Slide

A light microscope slide preparation method where a wet mount is pressed down on the coverslip to create a very thin layer of cells so light can pass through.

Smear Slide

A light microscope slide preparation method created by placing a drop of sample at one end of a slide and using the edge of another slide held at an angle to smear it across.

Eyepiece Graticule

A glass disc with a scale inserted inside the eyepiece of a microscope, used to measure the size of an object under a microscope.

Stage Micrometer

A glass slide containing a scale where each division is worth $10\,\mu\text{m}$, placed on the stage to calibrate the eyepiece graticule at different magnifications.

Differential Staining

A staining technique involving multiple chemical stains to stain different parts of cells distinct colors, making organelles visually obvious.

Crystal Violet

A positively charged chemical stain that is attracted to and stains negatively charged components of a cell.

Nigrosin

A negatively charged chemical stain repelled by the cytosol that stains the background instead of entering cells, allowing unstained cells to stand out.

Transmission Electron Microscope (TEM)

An electron microscope that transmits a beam of electrons through an extremely thin slice of a specimen in a vacuum to produce a $2\text{D}$ image of internal cell structures.

Scanning Electron Microscope (SEM)

An electron microscope that beams electrons onto the surface of a specimen in a vacuum, scattering them off surface contours to form a $3\text{D}$ image.

Laser Scanning Confocal Microscope

A fluorescent microscope that uses a focused laser beam and high light intensity to scan a fluorescently stained specimen point-by-point to produce high-resolution $2\text{D}$ or $3\text{D}$ images with depth selectivity.

Nucleus

A double-membrane bound organelle containing a nuclear envelope, nuclear pores, nucleoplasm, linear chromosomes bound to histone proteins, and a nucleolus; site of DNA replication and transcription.

Nucleolus

A small dense sphere within the nucleus responsible for producing RNA and synthesizing ribosomes.

Flagella

A whip-like tail projection found on certain cells used primarily for mobility or as a sensory organelle for chemical stimuli.

Cilia

Hair-like projections on cells that can be mobile (moving in a wave-like motion to sweep substances along) or stationary (functioning in sensory organs).

Centrioles

Structures composed of microtubules that occur in pairs to form a centrosome, involved in forming spindle fibers during mitosis and meiosis.

Cytoskeleton

A cytoplasmic network of microfilaments, microtubules, and intermediate fibers that provides mechanical strength, maintains cell shape, holds organelles in place, and enables cell movement.

Rough Endoplasmic Reticulum (RER)

A network of folded membranes (cisternae) studded with ribosomes, responsible for synthesizing and transporting proteins destined to leave the cell.

Smooth Endoplasmic Reticulum (SER)

A network of folded membranes (cisternae) lacking ribosomes, responsible for synthesizing and storing lipids and carbohydrates.

Golgi Apparatus

A structure of folded membranes (cisternae) and secretory vesicles that modifies, packages, and labels proteins and lipids, forms glycoproteins, produces secretory enzymes, and creates lysosomes.

Lysosomes

Vesicles formed by the Golgi apparatus containing digestive enzymes used to hydrolyze pathogens inside phagosomes or break down dead cells.

Mitochondria

Double-membrane bound organelles containing cristae, a fluid matrix, $70\text{S}$ ribosomes, and circular DNA; serving as the site of aerobic respiration and ATP production.

Ribosomes

Non-membrane-bound organelles composed of protein and RNA responsible for protein synthesis ($80\text{S}$ in eukaryotic cytoplasm; $70\text{S}$ in prokaryotes, mitochondria, and chloroplasts).

Chloroplasts

Double-membrane bound plant organelles containing thylakoid membrane stacks (grana) and fluid stroma; serving as the site of photosynthesis.

Cell Wall

An outer structural layer providing mechanical strength, composed of cellulose microfibrils in plants, chitin in fungi, and peptidoglycan in prokaryotes.

Plasma Membrane

A phospholipid bilayer containing embedded channel proteins, carrier proteins, receptors, and cholesterol that regulates what enters and leaves cells or organelles.

Plasmids

Small additional loops of non-protein-bound circular DNA found in varying numbers in some prokaryotic cells, carrying genes such as antibiotic resistance.

Capsule

A slimy outer layer made of protein found on certain prokaryotic cells that prevents desiccation and covers antigens from host immune detection.