OCR A Level Biology - Cell Biology Flashcards

Vocabulary flashcards covering cell structure, microscopy, transport mechanisms, organelles, cell division, and interphase based on OCR A Level Biology lecture notes.

Magnification

How many times bigger the image is compared to the actual size of the object.

Resolution

The minimum distance between two points that can still be distinguished as separate entities (the level of detail).

Optical (Light) Microscope

A microscope that uses light rays, with a maximum resolution of ~$200\,\text{nm}$ and maximum magnification of ~$\times 1500$, producing 2D colored images of whole cells or large organelles.

Transmission Electron Microscope (TEM)

A microscope that uses electron beams passed through thin specimens, offering the highest resolution (~$0.2\,\text{nm}$) and magnification ($>\times 500{,}000$), producing 2D black-and-white internal ultrastructure images.

Scanning Electron Microscope (SEM)

A microscope that bounces electrons off the specimen surface, offering high resolution (~$3\text{--}10\,\text{nm}$) and producing 3D surface images.

Magnification Formula

$\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}$ ($M = \frac{I}{A}$), where both measurements must be in the same units ($1\,\text{mm} = 1{,}000\,\mu\text{m}$ and $1\,\mu\text{m} = 1{,}000\,\text{nm}$).

Eyepiece Graticule Calibration

The process of placing a stage micrometer on the microscope stage, aligning its scale with the eyepiece graticule scale, counting the number of eyepiece graticule units ($\text{EGU}$) that align with a known distance on the stage micrometer, and dividing the known stage micrometer distance by the number of $\text{EGU}$ to find the length of $1\,\text{EGU}$ at that specific magnification.

Nucleus

An organelle enclosed by a double membrane (nuclear envelope) with nuclear pores, containing chromatin (DNA wrapped around histone proteins), which functions to store genetic information and control cell activities.

Nucleolus

A dense area inside the nucleus that functions to synthesize ribosomal RNA (rRNA) and assemble ribosome subunits.

Rough Endoplasmic Reticulum (RER)

A membrane system whose surface is studded with ribosomes, which functions to fold and package synthesized proteins into transport vesicles.

Smooth Endoplasmic Reticulum (SER)

A tubular membrane network without ribosomes, which functions to synthesize, store, and transport lipids and carbohydrates.

Golgi Apparatus

An organelle composed of flattened membrane-bound sacs (cisternae) with surrounding vesicles, which functions to modify proteins and lipids (e.g., glycosylation to form glycoproteins) and package them into secretory vesicles or lysosomes.

Mitochondrion

A double-membrane bound organelle whose inner membrane is folded into cristae (site of oxidative phosphorylation) and whose interior fluid matrix (site of the Krebs cycle) contains $70\text{S}$ ribosomes and circular DNA.

Protein Secretion Pathway

The sequence of protein transport: 1. Transcription in nucleus, mRNA exits via nuclear pore; 2. Ribosome on RER translates mRNA into a polypeptide chain; 3. RER packages protein into a transport vesicle; 4. Transport vesicle moves along cytoskeleton tracks to the cis face of the Golgi apparatus; 5. Golgi modifies and packages protein into a secretory vesicle at the trans face; 6. Secretory vesicle moves to and fuses with the plasma membrane to release protein by exocytosis.

Microfilaments

Cytoskeletal components composed of actin that provide mechanical strength, cell movement, and drive cytokinesis.

Microtubules

Cytoskeletal components composed of tubulin that provide structural shape, form spindle fibers, and serve as tracks for vesicle transport.

Intermediate Filaments

Cytoskeletal components that anchor organelles and give mechanical stability.

Prokaryotic vs. Eukaryotic Cells

Comparison across 5 key features: Nucleus (absent/naked circular DNA vs. present/linear DNA in nuclear envelope); Ribosomes ($70\text{S}$ vs. $80\text{S}$); Cell Wall (peptidoglycan/murein vs. cellulose in plants or chitin in fungi); Membrane-bound organelles (absent vs. present); DNA organization (circular without histones plus plasmids vs. linear wrapped around histones).

Phospholipid Bilayer

A structure in the fluid mosaic model where hydrophilic phosphate heads face outward toward the aqueous environment and hydrophobic fatty acid tails point inward, forming a non-polar hydrophobic core that acts as a barrier to water-soluble/polar substances.

Cholesterol (Membrane Role)

A molecule that fits between phospholipid fatty acid tails in biological membranes to regulate membrane fluidity, increase mechanical stability, and reduce permeability to small water-soluble molecules at high temperatures.

Simple Diffusion

The passive net movement of small, non-polar molecules (e.g., $\text{O}_2$, $\text{CO}_2$) directly through the phospholipid bilayer down a concentration gradient.

Facilitated Diffusion

The passive net movement of polar or charged molecules down a concentration gradient via channel proteins or carrier proteins.

Osmosis

The net movement of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential.

Water Potential ($\Psi$)

A measure of water concentration; pure water has a water potential of $0\,\text{kPa}$ (highest), and solutes lower water potential, making it negative.

Cytolysis

The bursting of an animal cell when placed in a hypotonic solution (higher $\Psi$) due to water entering the cell.

Crenation

The shriveling of an animal cell when placed in a hypertonic solution (lower $\Psi$) due to water leaving the cell.

Turgidity

The condition of a plant cell in a hypotonic solution where water enters and causes the cell to swell, with the cell wall preventing bursting.

Plasmolysis

The process in a plant cell placed in a hypertonic solution where water leaves, causing the cytoplasm to pull away from the cell wall.

Active Transport

The movement of substances against a concentration gradient using carrier proteins and energy derived from ATP hydrolysis.

Passive Transport

The movement of substances down a concentration gradient without requiring metabolic energy (ATP).

Endocytosis

A form of bulk active transport of large molecules into the cell by invagination of the plasma membrane to form a vesicle (e.g., phagocytosis).

Exocytosis

A form of bulk active transport where vesicles containing substances fuse with the plasma membrane to release contents outside the cell.

$G_1$ Phase (Gap 1)

The stage of interphase involving cell growth, organelle duplication, and active protein synthesis.

$S$ Phase (Synthesis)

The stage of interphase where DNA replication occurs, doubling the cell's DNA content.

$G_2$ Phase (Gap 2)

The stage of interphase involving error checking of replicated DNA, continued cell growth, and preparation for mitosis.

Prophase

The stage of mitosis where chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and centrioles move to poles to form spindle fibers.

Metaphase

The stage of mitosis where chromosomes align singly along the cell equator and spindle fibers attach to centromeres.

Anaphase

The stage of mitosis where centromeres divide and spindle fibers contract, pulling sister chromatids apart to opposite poles.

Telophase

The stage of mitosis where chromosomes uncoil and new nuclear envelopes reform around each group of chromosomes.

Cytokinesis

The division of the cytoplasm following mitosis; forming a cleavage furrow that pinches animal cells in two, or fusing cell plate vesicles along the equator to form a new cell wall in plant cells.