Chapter 4 Biology Honors: Cell Structure and Function

Comprehensive vocabulary flashcards covering Chapter 4 Biology Honors, focusing on light and electron microscopy, cell theory, prokaryotic and eukaryotic structures, organelle functions, cytoskeleton components, energy thermodynamics, and membrane transport mechanisms.

Magnification

The increase in an object's image size compared with its actual size.

Resolution

A measure of the clarity of an image, defined as the ability to distinguish two nearby objects as separate.

Light Microscope (LM)

An optical instrument with lenses that refract (bend) visible light to magnify images and project them into a viewer's eye or photographic film; it can resolve down to $0.2\,\mu\text{m}$ and effectively magnify about $1{,}000\times$.

Robert Hooke

The scientist who in 1665 used a crude microscope to examine cork bark and coined the term 'cells' because the structures resembled rooms in monasteries.

Antoni van Leeuwenhoek

A scientist who worked with more refined lenses than Hooke, examined numerous subjects, and produced detailed drawings and descriptions of his microscopic discoveries.

Cell Theory

The foundational biological generalization stating that all organisms consist of one or more cells, the cell is the smallest unit of life, all cells arise from pre-existing cells, and cells pass hereditary material to offspring.

Electron Microscope (EM)

A microscope introduced in the 1950s that uses electromagnets to focus an electron beam through or onto a specimen, achieving a resolution of about $2\,\text{nm}$ (a hundredfold greater than a light microscope).

Cell Ultrastructure

The complex internal anatomy of a cell revealed through the high resolution of an electron microscope.

Scanning Electron Microscope (SEM)

An electron microscope that uses a beam to scan the gold-coated surface of a specimen, exciting surface electrons to project a 3D-appearing image onto a monitor.

Transmission Electron Microscope (TEM)

An electron microscope that directs an electron beam through thinly sectioned specimens stained with heavy metals to study details of internal cell architecture.

Differential Interference Contrast Microscopy

An optical light-microscopy technique that amplifies differences in density so that structures in living cells appear three-dimensional.

Surface-to-Volume Ratio

A geometric relationship dictating that as a cell increases in size, its volume grows proportionally faster than its surface area, limiting maximum cell size to ensure sufficient transport of nutrients and wastes.

Plasma Membrane

The selective phospholipid bilayer boundary with embedded proteins found in every cell that regulates the movement of ions and molecules into and out of the cell.

Phospholipid

A molecule consisting of a negatively charged hydrophilic phosphate head and two non-polar, hydrophobic fatty acid tails that spontaneously self-assembles into a bilayer.

Fluid Mosaic Model

A description of membrane structure depicting a fluid bilayer of continuously moving phospholipids embedded with a mosaic of diverse proteins.

Prokaryotic Cell

A type of cell found only in Bacteria and Archaea that lacks a membrane-enclosed nucleus and membrane-bound organelles, typically one-tenth the size of a eukaryotic cell.

Eukaryotic Cell

A cell type featuring a membrane-enclosed nucleus housing most of its DNA along with distinct membrane-enclosed organelles; evolved approximately $1.8\,\text{billion}$ years ago.

Cytosol

The thick, jellylike semifluid portion of the cytoplasm in which cellular components and organelles are suspended.

Cytoplasm

The contents of a eukaryotic cell between the plasma membrane and the nucleus, or the entire interior space of a prokaryotic cell.

Nucleoid

A non-membrane-bounded region in a prokaryotic cell where the concentrated DNA resides.

Capsule

A sticky protective outer coat surrounding the cell wall of certain prokaryotes that helps glue cells to surfaces or to other cells in a colony.

Flagella

Long cellular appendages specialized for locomotion that propel cells through liquid environments; in eukaryotes, they possess a '9+2' microtubule arrangement.

Organelle

A membrane-enclosed intracellular structure with a specialized lipid and protein composition adapted to carry out a specific cellular function.

Cellular Metabolism

The collective term for all chemical activities occurring within a cell, typically partitioned into specific membrane-bound compartments.

Nucleus

The genetic control center of a eukaryotic cell that contains chromosomes made of chromatin and controls activities by directing protein synthesis.

Chromatin

The complex of packaged DNA and associated proteins that forms chromosomes within the eukaryotic nucleus.

Nuclear Envelope

A double membrane perforated with protein pores that encloses the nucleus, regulates nucleocytoplasmic traffic, and connects to the endoplasmic reticulum.

Nucleolus

A dense structure inside the nucleus where ribosomal RNA (rRNA) is synthesized and assembled with imported cytoplasmic proteins into ribosomal subunits.

Messenger RNA (mRNA)

A transcription of the protein-building instructions encoded in DNA that travels to the cytoplasm to be translated by ribosomes into amino acid sequences.

Ribosomes

Non-membranous complexes of ribosomal RNA and protein consisting of two subunits that function as the cellular sites of protein synthesis.

Endomembrane System

An interrelated network of internal membranes within a eukaryotic cell connected either directly or through transport vesicles, including the nuclear envelope, ER, Golgi, lysosomes, vesicles, vacuoles, and plasma membrane.

Transport Vesicle

A small membranous sphere in the cytoplasm that buds off from an organelle, carries synthesized molecules, and fuses with another destination membrane.

Endoplasmic Reticulum (ER)

The largest component of the endomembrane system; a continuous network of flattened membranous sacs and tubules extending from the outer nuclear membrane.

Smooth Endoplasmic Reticulum

The portion of the ER that lacks bound ribosomes; synthesizes lipids (oils, phospholipids, steroids), detoxifies drugs and harmful substances, and stores calcium ions.

Rough Endoplasmic Reticulum

The ribosome-studded region of the ER responsible for synthesizing secretory proteins, modifying glycoproteins, and manufacturing new membrane for the cell.

Glycoprotein

A protein covalently bonded to one or more short carbohydrate chains, commonly assembled and modified inside the rough ER and Golgi apparatus.

Golgi Apparatus

A stack of non-connected flattened membranous sacs discovered in 1898 by Camillo Golgi that receives, modifies, sorts, and ships ER products via transport vesicles.

Lysosome

A membrane-enclosed digestive organelle containing hydrolytic enzymes used to dismantle engulfed food particles, destroy pathogens, or recycle damaged cell organelles within an acidic interior.

Central Vacuole

A large membranous sac occupying most of the volume of mature plant and algal cells that absorbs water for growth and stores pigments, nutrients, and toxic wastes.

Contractile Vacuole

A specialized organelle found in freshwater protists that collects and expels excess water to prevent the cell from swelling and bursting.

Peroxisome

A metabolic organelle not belonging to the endomembrane system that uses enzymes to transfer hydrogen to oxygen, producing hydrogen peroxide ($H_2O_2$), which is subsequently degraded into water.

Mitochondria

Double-membraned energy-processing organelles in eukaryotic cells where cellular respiration occurs, consuming $O_2$ and releasing $CO_2$ to convert chemical energy from food into ATP.

Mitochondrial Matrix

The fluid-filled inner compartment enclosed by the folded inner mitochondrial membrane containing mitochondrial DNA, ribosomes, and enzymes of the citric acid cycle.

Chloroplast

The photosynthetic organelle of plants and algae that absorbs sunlight to drive the synthesis of organic sugars from carbon dioxide ($CO_2$) and water ($H_2O$).

Stroma

The thick fluid compartment enclosed by the inner chloroplast membrane that surrounds the thylakoid system and houses chloroplast DNA, ribosomes, and metabolic enzymes.

Thylakoids

Interconnected membranous sacs suspended within the chloroplast stroma containing embedded chlorophyll molecules that capture solar energy; stacks are called grana.

Cytoskeleton

A dynamic network of protein fibers extending throughout the cytoplasm of a eukaryotic cell that provides mechanical structural support, anchors organelles, and enables cell motility.

Microtubules

The thickest cytoskeleton fibers, consisting of hollow cylinders of tubulin protein dimers that guide chromosome and vesicle movements and compose cilia and flagella.

Centrosome

The microtubule-organizing center in animal cells containing two centrioles that forms the mitotic spindle during cell division.

Intermediate Filaments

Fibrous protein cables of intermediate diameter that act as permanent structural reinforcements to maintain cell shape and anchor specific organelles like the nucleus.

Microfilaments

The thinnest cytoskeleton fibers, consisting of twisted solid helical rods of globular actin proteins that support cell shape, drive amoeboid movement, and form the cleavage furrow.

Motor Proteins

Specialized ATP-powered proteins that interact with cytoskeleton fibers to generate movement of whole cells, organelles, or internal cellular structures.

Cilia

Short, numerous cellular appendages with a '9+2' microtubule doublet core that beat rhythmically to propel cells or sweep fluids across tissue surfaces (such as the respiratory tract).

Primary Cilium

A solitary, typically nonmotile antenna-like cilium lacking a central microtubule pair that functions in sensory reception and signal transduction in vertebrate cells.

Cell Wall

A rigid extracellular layer outside the plasma membrane composed of cellulose fibers embedded in a polysaccharide matrix that protects plant cells and keeps plants upright.

Plasmodesmata

Open cytoplasmic channels passing through adjacent plant cell walls that allow water, nutrients, and signaling molecules to circulate freely between cells.

First Law of Thermodynamics

The physical principle establishing that energy can neither be created nor destroyed, only transformed from one form to another.

Second Law of Thermodynamics

The law stating that every energy conversion increases the entropy (disorder) of the universe because some energy is inevitably lost to the surroundings as thermal energy (heat).

Entropy

A thermodynamic measure of molecular disorder or randomness in a system.

Adenosine Triphosphate (ATP)

The primary cellular energy currency composed of adenosine linked to three high-energy phosphate groups; energy is released when a terminal phosphate bond is broken.

Diffusion

The spontaneous net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.

Osmosis

The diffusion of free water across a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Tonicity

The ability of an extracellular solution to cause a cell to gain or lose water, determined by its relative concentration of non-penetrating solutes.

Hypotonic Solution

A solution containing a lower solute concentration than the cell; causes animal cells to swell and lyse, and plant cells to become firm and turgid.

Hypertonic Solution

A solution containing a higher solute concentration than the cell; causes animal cells to shrivel and plant cells to undergo plasmolysis.

Isotonic Solution

A solution possessing an equal solute concentration relative to the cell's interior, resulting in no net water movement (the ideal state for animal cells, but causing plant cells to become flaccid).

Facilitated Diffusion

A type of passive transport where specific channel or carrier transport proteins allow polar or charged solutes to cross the membrane down their concentration gradient without requiring energy.

Aquaporin

A membrane transport protein pore featuring a hydrophobic exterior and hydrophilic channel that facilitates the rapid, selective diffusion of water across the membrane.

Active Transport

The energy-requiring (ATP-dependent) movement of a substance across a membrane against its concentration gradient via specific protein pumps.

Exocytosis

A form of bulk transport where a cytoplasmic transport vesicle fuses with the plasma membrane to secrete macromolecules out of the cell.

Phagocytosis

A type of endocytosis, termed 'cellular eating,' where a cell engulfs large particles or whole microorganisms into a food vacuole that fuses with a lysosome.

Pinocytosis

A type of endocytosis, termed 'cellular drinking,' where the cell engulfs droplets of extracellular fluid containing dissolved solutes into small vesicles.