Comprehensive Biology: Cell Structure, Membrane Transport, Energy, and Photosynthesis

Comprehensive practice flashcards matching lecture notes on cell theory, organelles, eukaryotic vs. prokaryotic structures, membrane transport, bioenergetics, enzymes, cellular respiration, and photosynthetic light and dark reactions.

Cell Theory

A foundational biological principle stating that all living organisms are composed of one or more cells, and that all cells arise exclusively from other, preexisting cells through cell division.

Robert Hooke

The English scientist who, in 1665, observed thin slices of cork from a cork oak plant under an early microscope and coined the word "cells" after their resemblance to monks' monastery rooms or dormitories.

Prokaryotic Cell

A relatively small ($1\text{--}4\,\mu\text{m}$) and structurally simple single-celled organism that lacks a nucleus and membrane-bound organelles, possessing a cell wall, ribosomes, cytoplasm, and circular genetic material.

Eukaryotic Cell

A larger ($10\text{--}100\,\mu\text{m}$), structurally complex cell containing a true membrane-bound nucleus and specialized membrane-enclosed organelles that perform distinct biochemical functions.

Cytoplasm

The semi-fluid, jelly-like internal environment of a cell, composed predominantly of water, that supports organelles, genetic material, dissolved proteins, and ions.

Fluid Mosaic Model

A conceptual model describing the plasma membrane as a dynamic, fluid phospholipid bilayer interspersed with diverse proteins and lipids that move freely within the plane of the membrane.

Selective Permeability

The property of the cellular phospholipid bilayer that freely allows small, hydrophobic molecules (such as $\text{O}_2$ and $\text{CO}_2$) to cross while remaining impermeable to large polar molecules and ions without specific transport proteins.

Concentration Gradient

The difference in the concentration of a chemical substance across a biological membrane or between two distinct regions.

Passive Transport

The spontaneous movement of molecules across a membrane from an area of higher concentration to an area of lower concentration down a concentration gradient without an expenditure of cellular energy.

Simple Diffusion

A mode of passive transport where small, non-polar molecules and gases diffuse directly through the hydrophobic interior of the phospholipid bilayer without the assistance of membrane proteins.

Facilitated Diffusion

The passive transport of large, polar, or charged substances across a biological membrane down their concentration gradient with the assistance of specific channel or carrier proteins.

Osmosis

The passive diffusion of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Hypotonic Solution

An external solution with a lower concentration of solutes compared to the cell interior, causing net water influx that swells plant cells and may cause animal cells to burst.

Hypertonic Solution

An external solution with a higher concentration of solutes relative to the cell's cytoplasm, resulting in the net movement of water out of the cell and cellular shrinkage.

Isotonic Solution

An extracellular environment with a solute concentration equal to that of the intracellular fluid, resulting in equal, balanced rates of water movement into and out of the cell.

Hemolysis

The severe, life-threatening rupturing of red blood cells caused by rapid water influx when the blood plasma becomes dangerously hypotonic due to severe overhydration.

Active Transport

The transport of substances across a cell membrane against their concentration gradient (from low to high concentration), requiring an input of cellular energy, typically supplied by ATP.

Primary Active Transport

Active transport that directly hydrolyzes ATP to power membrane pump proteins, moving solutes like $\text{H}^+$ or $\text{Na}^+$ against their concentration gradient.

Secondary Active Transport

A transport process in which a membrane protein moves one molecule against its concentration gradient using the electrochemical gradient established by a primary active transport pump.

Vesicle

A small, spherical membrane-bound sac formed of a phospholipid bilayer used to store, compartmentalize, and transport large molecules or bulk materials within and outside a cell.

Endocytosis

An active transport mechanism by which a cell engulfs extracellular materials by invaginating its plasma membrane to form an internal vesicle.

Exocytosis

The active process by which intracellular transport vesicles fuse with the plasma membrane to secrete their molecular contents into the extracellular space.

Phagocytosis

A specialized form of endocytosis by which large particles or whole microorganisms (such as pathogenic bacteria) are engulfed and internalized by cells like macrophages.

Nucleus

The prominent genetic control center of a eukaryotic cell that houses and protects hereditary DNA and directs cellular activities.

Chromatin

The extended, unwound complex of linear DNA packaged with histone proteins found in the nucleus during non-dividing stages, which condenses into distinct chromosomes during cell division.

Nucleolus

The dense, dark-staining region within the eukaryotic nucleus containing genes dedicated to ribosomal RNA transcription and the assembly of ribosomal subunits.

Nuclear Membrane

The double-membrane barrier, composed of two distinct phospholipid bilayers and embedded with nuclear pores, that envelops and compartmentalizes the nucleus.

Nuclear Pores

Protein-lined channel complexes penetrating the nuclear membrane that regulate the bidirectional exchange of macromolecules, including mRNA, proteins, and ribosomal subunits.

Cytoskeleton

A dynamic intracellular network of protein filaments in the cytoplasm that maintains cell architecture, anchors organelles, assists in vesicular transport, and enables cell motility.

Microtubules

Thick, hollow cytoskeletal cylinders that act as internal tracks for motor proteins carrying transport vesicles, form the mitotic spindle, and provide structure to cilia and flagella.

Intermediate Filaments

Durable, rope-like cytoskeletal fibers made of overlapping proteins that provide high mechanical tensile strength and structural integrity to animal cells.

Microfilaments

Solid, slender, rod-like protein fibers that assist in full-cell crawling, muscle contractions, and cytokinesis during eukaryotic cell division.

Cilia

Short, hair-like cellular extensions containing microtubules that beat coordinately to move extracellular fluids and particles along cell surfaces, such as moving eggs within the human oviduct.

Flagella

Long, whip-like microtubule-based cellular appendages whose undulating motion propels whole cells forward through liquid media (such as human sperm cells).

Mitochondrion

A double-membraned eukaryotic organelle that acts as an all-purpose cellular energy converter, using oxygen to convert energy in food molecules into cellular ATP.

Mitochondrial DNA (mtDNA)

Circular DNA molecules located inside mitochondria that replicate independently of nuclear chromosomes and are inherited strictly maternally via the egg cell.

Endosymbiosis

The evolutionary theory stating that mitochondria and chloroplasts originated as independent prokaryotic cells (aerobic bacteria and cyanobacteria) that were engulfed by an ancestral host eukaryote.

Lysosome

A membrane-bound digestive organelle maintaining an acidic interior ($\text{pH} \approx 5.0$) via $\text{H}^+$ pumps, packed with acid hydrolases to break down cellular wastes, worn-out organelles, and engulfed pathogens.

Endomembrane System

A coordinated intracellular network of membrane-bound organelles (including the rough ER, smooth ER, transport vesicles, and Golgi apparatus) that synthesizes, modifies, packages, and exports biomolecules.

Rough Endoplasmic Reticulum

A convoluted membranous organelle continuous with the nuclear envelope and studded with ribosomes, responsible for the initial synthesis, folding, and vesicular packaging of proteins.

Smooth Endoplasmic Reticulum

A tubular endomembrane network lacking ribosomes that synthesizes lipids (phospholipids, fatty acids, and steroid hormones) and detoxifies drugs and metabolic waste products (highly abundant in liver cells).

Golgi Apparatus

A series of flattened, stacked membranous cisternae that receives transport vesicles from the endoplasmic reticulum, chemically modifies their contents, and sorts them for cellular delivery or exocytosis.

Cell Wall

A rigid extracellular matrix made primarily of cellulose fibers in plants that provides physical structural strength, prevents excessive water uptake, and defends against pathogens.

Plasmodesmata

Microscopic, membrane-lined cytoplasmic channels perforating plant cell walls that allow the intercellular transport of water, nutrients, and chemical signals between adjacent plant cells.

Central Vacuole

A large plant organelle that stores nutrients and water, degrades wastes, accumulates defensive poisonous compounds, harbors pollinator-attracting pigments, and provides turgor pressure for physical support.

Kinetic Energy

The energy possessed by an object due to its motion, including thermal energy, sound, mechanical motion, and the radiant energy of photons.

Potential Energy

Stored energy dependent on the physical position, structure, or state of matter, prominently stored within the covalent chemical bonds of organic molecules.

First Law of Thermodynamics

The fundamental law of physics asserting that energy can neither be created nor destroyed; it can only be transferred or transformed from one form to another.

Second Law of Thermodynamics

The physical principle dictating that every energy transformation increases universal entropy (disorder), resulting in the unavoidable release of some energy as unusable heat.

Endergonic Reaction

A non-spontaneous chemical reaction that requires a net input of free energy ($\Delta G > 0$), yielding products that possess higher potential energy than the starting reactants.

Exergonic Reaction

A spontaneous chemical reaction that releases net free energy ($\Delta G < 0$), producing products that contain less potential energy than the initial reactants.

Activation Energy ($E_a$)

The initial investment of energy required to contort reactant molecules into an unstable transition state so that their covalent bonds can break and proceed through a chemical reaction.

Catabolic Reaction

A biochemical reaction or metabolic pathway that breaks down complex molecules into simpler units, typically releasing energy via an exergonic mechanism (e.g., hydrolysis).

Anabolic Reaction

A biochemical reaction or pathway that constructs complex macromolecules from smaller building blocks, requiring an input of energy via an endergonic process (e.g., condensation or dehydration synthesis).

Enzyme

A biological catalytic protein that dramatically accelerates the rate of specific biochemical reactions by lowering their activation energy barrier without being permanently consumed.

Adenosine Triphosphate (ATP)

A rechargeable cellular nucleotide composed of adenine, ribose, and three negatively charged phosphate groups, whose terminal phosphoanhydride bond stores high potential energy that powers cellular work.

Chloroplast

The green, double-membraned organelle in plant cells that contains thylakoids and stroma, serving as the biological site where light energy is harvested to synthesize glucose.

Thylakoid

A coin-shaped membranous sac inside a chloroplast arranged in stacks, whose membrane hosts chlorophyll pigments, photosystems, and electron transport chains where the light-capturing "photo" reactions take place.

Stroma

The fluid-filled space within a chloroplast surrounding thylakoids where the "synthesis" reactions of photosynthesis (Calvin cycle) assemble glucose molecules from $\text{CO}_2$.

Chlorophyll

The primary light-absorbing photosynthetic pigment embedded in thylakoid membranes featuring a central magnesium ($\text{Mg}$) atom that absorbs blue and red-orange wavelengths while reflecting green light.

Photon

A discrete, wave-like packet of electromagnetic light energy traveling from the sun, where photons with shorter wavelengths carry higher energetic levels.

Photosystem

A multi-protein light-harvesting complex in the thylakoid membrane packed with pigment molecules that funnel absorbed solar energy to a central chlorophyll a special pair and primary electron acceptor at the reaction center.

Water-Splitting Photosystem

The initial photosystem in the photosynthetic light reactions that absorbs light, transfers excited electrons to a primary electron acceptor, and extracts replacement electrons by splitting $\text{H}_2\text{O}$, releasing $\text{O}_2$ and $\text{H}^+$.

NADPH-Producing Photosystem

The second photosystem of the thylakoid membrane that absorbs light to boost electrons donated from the electron transport chain, transferring them to $\text{NADP}^+$ to produce high-energy $\text{NADPH}$.

ATP Synthase

A rotary enzyme complex spanning the thylakoid and inner mitochondrial membranes that harnesses the kinetic energy of protons rushing down their electrochemical gradient to generate ATP from ADP and $\text{P}_i$.

Calvin Cycle

The light-independent "synthesis" pathway occurring in the chloroplast stroma that consumes ATP and NADPH to construct three-carbon G3P sugars from atmospheric carbon dioxide through fixation, sugar creation, and regeneration.

Rubisco

The primary photosynthetic enzyme in the stroma responsible for carbon fixation, catalyzing the attachment of carbon atoms from atmospheric $\text{CO}_2$ to an organic acceptor molecule.

G3P (Glyceraldehyde 3-phosphate)

The direct three-carbon sugar product synthesized by the Calvin cycle, which is combined in pairs to yield six-carbon monosaccharides such as glucose and fructose.

Cellular Respiration

The aerobic metabolic pathway in which cells break down food molecules like glucose in the presence of oxygen ($\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP} + \text{Heat}$) to produce usable energy.