Cells, Body Systems & Homeostasis

Comprehensive vocabulary flashcards covering cell structure and organelles, cell transport and permeability, human body systems, and homeostatic feedback mechanisms based on lecture slides.

Unicellular Organism

An organism composed of only a single cell that carries out all life functions, such as bacteria, Amoeba, Paramecium, or Chlamydomonas.

Multicellular Organism

An organism composed of many cells that organize into tissues, organs, and organ systems, such as animals, humans, and plants.

Prokaryote

A cellular organism (from 'pro-' meaning before and 'karyo-' meaning nucleus) that lacks a nucleus and membrane-bound organelles, divides by binary fission, possesses a cell wall, and is always unicellular (such as bacteria and archaea).

Eukaryote

An organism (from 'eu-' meaning true and 'karyo-' meaning nucleus) whose cells contain a distinct membrane-bound nucleus and membrane-bound organelles, divides via mitosis, and can be unicellular or multicellular (including animals, plants, fungi, and protists).

Organelle

A specialized membrane-bound structure within a eukaryotic cell that functions like a 'mini organ' to perform specific cellular jobs, primarily working toward protein synthesis.

Cell (Plasma) Membrane

A selectively permeable phospholipid bilayer surrounding the outside of all cells that acts like the 'city limits,' controlling what materials enter and exit.

Cytoskeleton

A network of threadlike protein fibers that provides internal structural support for animal cells, maintains cellular shape, and moves organelles around.

Cytoplasm

A thick, jelly-like fluid largely composed of water that encompasses the interior of the cell, functioning like its atmosphere to hold organelles in place.

Nucleus

The central organelle enclosed by a nuclear membrane that contains and protects genetic material ($\text{DNA}$), functioning as the cell's 'city hall' to control cellular activities.

Nucleolus

A dense region located inside the nucleus responsible for producing $\text{rRNA}$, which forms ribosomes.

Ribosome

A cellular structure composed of proteins and $\text{rRNA}$—found floating in the cytoplasm or bound to the Rough ER—that functions as a factory to synthesize proteins.

Rough Endoplasmic Reticulum (Rough ER)

A membranous network studded with ribosomes along its surface that acts as the protein assembly line and superhighway of the cell.

Golgi Apparatus

A system of folded membrane sacs that receives vesicles containing proteins from the ER to process, sort, and ship them to their destinations ('the post office of the cell').

Lysosome

An enzyme-packed organelle found only in animal cells that acts as a recycling center by breaking down dead cell parts, foreign substances, and executing programmed cell death (apoptosis).

Centrioles

Structures composed of microtubules found exclusively in animal cells that appear during cell division to pull duplicated chromosomes apart.

Cilia

Short, numerous, hair-like projections on the surface of some cells that function to move fluid across the cell surface.

Flagella

Long, whip-like projections (typically present in numbers of $1\text{--}3$) on certain cells that propel and move the entire cell.

Mitochondria

The double-membraned 'powerhouse' of the cell where cellular respiration occurs, breaking down food to release chemical energy stored as $\text{ATP}$.

Chloroplast

A plant-specific organelle containing grana (stacks) and stroma (fluid) where photosynthesis takes place, converting solar energy into glucose.

Cell Wall

A rigid outer protective layer made of cellulose, chitin, or peptidoglycan that maintains the structural shape of plant, fungal, and bacterial cells.

Central Vacuole

A massive, single storage structure found in plant cells that acts like a water tower to maintain cellular turgor and store materials.

Phospholipid Bilayer

The structural foundation of the cell membrane consisting of two layers of phospholipids, featuring polar hydrophilic (water-loving) phosphate heads and nonpolar hydrophobic (water-fearing) fatty acid tails.

Selective Permeability

A property of cellular membranes that allows only specific substances (such as small, nonpolar molecules like oxygen and water) to pass freely while larger or polar molecules require specialized transport proteins.

Passive Transport

The movement of substances across a biological membrane down their concentration gradient (from high to low concentration) without the expenditure of cellular energy ($\text{ATP}$).

Active Transport

The movement of molecules across a cellular membrane against their concentration gradient (from low to high concentration), requiring additional energy in the form of $\text{ATP}$.

Concentration Gradient

The difference in the concentration of a chemical substance across a distance or between two regions, such as across a membrane.

Dynamic Equilibrium

The continuous, balanced movement of molecules across a membrane where no concentration gradient exists and equal concentrations are maintained on both sides.

Osmosis

The passive transport and diffusion of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Aquaporin

A specialized membrane channel protein that facilitates the rapid passage of water molecules during osmosis.

Hypertonic Solution

A solution that has a higher solute concentration (and lower water concentration) compared to the cell's cytoplasm, causing net water to move out and the cell to shrivel.

Hypotonic Solution

A solution that has a lower solute concentration (and higher water concentration) compared to the cell's cytoplasm, causing net water to rush in and the cell to swell.

Isotonic Solution

A solution whose solute and water concentrations are identical to those inside the cell's cytoplasm, resulting in no net movement of water and maintaining cell size.

Facilitated Diffusion

A form of passive transport that uses specific carrier or channel proteins to move larger molecules (such as glucose) down their concentration gradient.

Endocytosis

An active bulk transport mechanism where the cell membrane engulfs external fluids, nutrients, and particles into vesicles to bring them inside the cell.

Exocytosis

An active bulk transport process in which intracellular vesicles fuse with the plasma membrane to excrete waste products and large molecules out of the cell.

Sodium-Potassium Pump

An active transport membrane mechanism that consumes $\text{ATP}$ to pump sodium ($Na^+$) and potassium ($K^+$) ions across nerve and muscle cells against their gradients.

Tissue

A coordinated group of similar cells working together to perform a specialized function, such as connective, nervous, epithelial, or muscle tissue.

Integumentary System

The organ system consisting of the skin that serves to protect internal tissues and sense the environment.

Skeletal System

The body system composed of bones, cartilage, and ligaments that protects and supports internal organs and provides structure for movement.

Muscular System

The organ system containing skeletal muscles and tendons that functions primarily to generate force and body movement.

Nervous System

The rapid body communication network composed of the brain, spinal cord, and nerves that relays sensory signals and coordinates bodily functions.

Endocrine System

The organ system comprising the pituitary, thyroid, adrenal glands, pancreas, and gonads that secretes regulatory hormones into the bloodstream.

Cardiovascular System

The circulatory network made of the heart and blood vessels that transports blood, oxygen, and vital nutrients throughout the organism.

Lymphatic System

The organ system containing lymph nodes and lymphatic vessels that filters and cleanses bodily fluids and provides immune defenses.

Respiratory System

The organ system consisting of the nasal cavity, trachea, and lungs that exchanges oxygen ($O_2$) and carbon dioxide ($CO_2$) between the body and atmosphere.

Digestive System

The organ system containing the mouth, esophagus, stomach, and intestines that breaks down food and absorbs nutrients.

Urinary System

The organ system including the kidneys, ureters, bladder, and urethra that eliminates waste and maintains fluid balance.

Reproductive System

The organ system including the gonads (testes and ovaries) and uterus that creates sex cells (sperm and eggs) and facilitates fetal development.

Homeostasis

The ability of an organism to regulate and maintain a relatively stable and constant internal physiological state despite changes in the external environment.

Receptor

A sensory nerve ending or organ in a feedback loop that senses an environmental change (stimulus) and transmits an afferent signal to the control center.

Control Center

The component of a homeostatic loop (typically the brain or spinal cord) that processes sensory information, evaluates set points, and determines the appropriate physiological output.

Effector

An organ, muscle, or gland in a feedback loop that enacts the direct response signaled by the control center until homeostasis is restored.

Negative Feedback

An inhibitory homeostatic response mechanism that detects deviation from a set point and triggers an opposite reaction to reverse the change (e.g., thermoregulation and blood sugar control).

Positive Feedback

A stimulatory biological mechanism that amplifies a response in the same direction as the stimulus to accelerate a process to completion (e.g., blood clotting and labor contractions).

Insulin

A hormone secreted by beta cells of the pancreas when blood glucose levels rise, signaling the liver and somatic cells to take up glucose and convert it into stored glycogen.

Glucagon

A hormone secreted by alpha cells of the pancreas when blood glucose levels drop, directing the liver to break down glycogen and release glucose into the blood.

Somatic Reflex Arc

An involuntary neural pathway where sensory receptors relay input via afferent neurons to an integration center in the spinal cord, sending output via efferent neurons to stimulate muscle movement.