BIOL 1108: Principles of Biology II - Unit 3: Challenges of Life

Comprehensive vocabulary flashcards covering the universal challenges of life, thermodynamics and metabolism, surface-area-to-volume scaling, homeostatic feedback loops, endocrine and nervous signaling, thermoregulation, nutrient acquisition and digestive specialization, gas exchange, osmoregulation, mechanical and chemical defenses, immunology, and reproductive life cycles.

Homeostasis

The active regulation and maintenance of stable internal physiological conditions necessary for continued life function in the face of a changing external environment.

Negative Feedback Loop

A primary homeostatic regulatory mechanism in which a change from a set point triggers a series of responses ($\text{stimulus} \rightarrow \text{sensor} \rightarrow \text{effector} \rightarrow \text{response}$) that counteract and reverse the initial disturbance.

Spontaneous Generation

The historical, disproven hypothesis that living organisms, such as maggots or mold, arise spontaneously from non-living matter; disproved by Louis Pasteur, who demonstrated that microbes travel through the air.

Nucleoid

The non-membrane-bound region in prokaryotic cells where the single circular chromosomal DNA is organized and located.

Nutritional Modes

The distinct strategies organisms use to obtain energy and carbon, classified into photoautotrophy, photoheterotrophy, chemoautotrophy, and chemoheterotrophy.

Phototroph

An organism that captures energy from sunlight to drive cellular processes.

Chemotroph

An organism that derives its cellular energy from chemical compounds.

Autotroph

An organism that synthesizes organic molecules using inorganic carbon sources, primarily carbon dioxide ($\text{CO}_2$).

Heterotroph

An organism that obtains its carbon by consuming preformed organic compounds.

Catabolism

Metabolic reactions that break down complex macromolecules into smaller subunits, releasing energy ($\text{ATP}$) with a negative change in free energy ($-\Delta G$).

Anabolism

Metabolic reactions that consume energy ($\text{ATP}$) with a positive change in free energy ($+\Delta G$) to build complex macromolecules from simple precursor subunits.

Surface Area-to-Volume Ratio ($SA:V$)

The relationship between a cell or organism's surface area and its total volume; as cell size increases, this ratio decreases, constraining diffusion distance and transport rate across membranes.

Mass-Specific Metabolic Rate

The metabolic rate measured per unit of body mass (e.g., $\text{W}\cdot\text{kg}^{-1}$), which is inversely related to overall body size in active mammals.

Endotherm

An animal (such as a mammal or bird) that produces heat internally via high rates of metabolism to maintain a relatively stable core body temperature.

Ectotherm

An animal (such as an invertebrate, fish, amphibian, or non-avian reptile) that obtains heat primarily from the external environment, regulating body temperature largely through behavior.

Thermoneutral Zone (TNZ)

The range of environmental ambient temperatures over which an endotherm can maintain its basal metabolic rate without expending additional energy on active heating or active cooling.

Insulin

A peptide hormone produced by pancreatic $\beta$ cells in response to elevated blood glucose; it stimulates body cells and liver/muscle cells to absorb glucose and store it as glycogen.

Glucagon

A peptide hormone produced by pancreatic $\alpha$ cells in response to low blood glucose; it stimulates liver and muscle cells to break down glycogen and release glucose into the bloodstream.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

A major neuroendocrine pathway coordinating the stress response, in which the hypothalamus secretes corticotropin-releasing hormone ($\text{CRH}$), prompting the anterior pituitary to release adrenocorticotropic hormone ($\text{ACTH}$), stimulating cortisol release from the adrenal cortex.

Peptide and Amine Hormones

Hydrophilic signaling molecules that cannot cross the lipid bilayer, instead binding to cell-surface receptors to initiate rapid intracellular second messenger cascades.

Steroid Hormones

Hydrophobic lipid-soluble signaling molecules that freely cross the plasma membrane and bind to intracellular receptors to alter gene expression over longer timeframes.

Epinephrine

An amine hormone and neurotransmitter involved in the fight-or-flight response that elicits distinct responses in different tissues depending on receptor type (e.g., binds $\beta$ receptors to relax skeletal muscle arteries, and $\alpha$ receptors to constrict digestive tract arteries).

Auxin

A plant hormone synthesized in apical meristems and young leaves that promotes cell wall elongation and regulates phototropism and gravitropism by migrating away from light and toward gravity.

Ethylene

A gaseous plant hormone that acts chemically to promote fruit ripening.

Juvenile Hormone (JH)

An insect hormone that maintains larvae in an immature developmental state; synthetic analogs such as pyriproxyfen prevent larvae from maturing into reproductive adults.

Pheromones

Chemical signals released into the external environment to mediate communication and behavioral responses between different individuals of the same or different species.

Essential Nutrients

Compounds that an animal cannot synthesize on its own in sufficient quantities (such as the $8$ essential amino acids in humans, minerals, and vitamins) and must therefore acquire directly from its diet.

Suspension Filter Feeding

An aquatic feeding mode where food particles (plankton, krill) are strained directly out of the surrounding water solvent by specialized filtering structures, as seen in baleen whales, scallops, and barnacles.

Foregut Fermenters

Herbivorous mammals (e.g., ruminants like cows and sheep) that house cellulose-digesting symbiotic microbes in an enlarged anterior stomach compartment (the rumen) prior to the small intestine.

Hindgut Fermenters

Herbivorous mammals (e.g., horses, rabbits, koalas) that house cellulose-digesting symbiotic microbes in an enlarged cecum or colon located after the small intestine.

Nematophagous Fungi

Carnivorous fungi, such as oyster mushrooms, that trap, paralyze, and digest nematode worms using specialized structures to balance their nitrogen and protein requirements while growing on carbohydrate-rich wood or straw.

Bulk Flow

The pressure-driven movement of fluids and dissolved substances over long distances through specialized transport tubes, such as animal blood vessels or plant vascular tissues ($\text{xylem}$ and $\text{phloem}$).

Countercurrent Exchange

An anatomical arrangement in fish gills where capillary blood flows opposite to the direction of water movement, maintaining a continuous concentration gradient for maximal oxygen diffusion across the entire exchange surface.

Tracheal System

A terrestrial respiratory network in insects consisting of spiracles, branching tracheae, and microscopic tracheoles that delivers oxygen gas directly to body tissues independently of the circulatory fluid.

Open Circulatory System

A low-pressure circulatory arrangement in which a muscular vessel pumps hemolymph into an open body cavity where it bathes tissues directly, found in arthropods and not used for gas transport in insects.

Closed Circulatory System

A high-pressure circulatory arrangement in which blood remains completely enclosed within interconnected blood vessels, allowing rapid transport of gases and nutrients over large body sizes.

Osmoregulation

The active homeostatic process by which organisms regulate their internal water and solute concentrations to prevent excessive cellular swelling or dehydration.

Osmolarity

The measure of total solute concentration per unit volume of solution.

Nitrogenous Waste Forms

The three major metabolic waste products derived from the breakdown of proteins and nucleic acids: ammonia, urea, and uric acid, each varying in toxicity, energy required to synthesize, and water needed for excretion.

Ammonia

A highly toxic, water-soluble nitrogenous waste excreted primarily by aquatic organisms (including many fishes) that requires little energy to produce but massive amounts of water to eliminate.

Urea

A nitrogenous waste of intermediate toxicity and energy cost produced by mammals, adult amphibians, sharks, and some bony fishes, requiring moderate water for excretion.

Uric Acid

A non-toxic, insoluble nitrogenous waste excreted as a paste by birds, insects, reptiles, and land snails; it requires the highest energy expenditure to synthesize but conserves the most water.

Secondary Metabolites

Chemical compounds produced by plants (such as alkaloids, cardenolides, and terpenes) that do not function in primary growth or metabolism, but evolved as defensive mechanisms against herbivores and pathogens.

Innate Immunity

The evolutionarily conserved, non-specific internal immune defense (second line of defense) present in all animals, consisting of phagocytic white blood cells, antimicrobial proteins, and the inflammatory response.

Adaptive Immunity

A specialized, highly specific third line of defense primarily found in vertebrates that learns to recognize distinct pathogen antigens and forms long-lasting immunological memory cells.

Antibody

A Y-shaped defense protein produced by plasma B cells that contains specific antigen-binding fragments designed to bind and neutralize distinct foreign antigens.

Autoimmune Disorder

A pathological condition occurring when the adaptive immune system loses self-tolerance and attacks the body's own healthy tissue antigens (e.g., rheumatoid arthritis, type 1 diabetes, multiple sclerosis).

Alternation of Generations

A plant life cycle characterized by having two distinct multicellular generations: a haploid ($1n$) gametophyte phase and a diploid ($2n$) sporophyte phase.

Gametophyte

The multicellular haploid ($1n$) plant generation that produces haploid gametes (eggs and sperm) via mitotic cell division.

Sporophyte

The multicellular diploid ($2n$) plant generation that undergoes meiosis to produce genetically diverse haploid spores.

Parthenogenesis

A form of asexual reproduction in which unfertilized eggs develop directly into viable offspring, observed in water fleas (Daphnia) during favorable conditions and in some squamate reptiles like Komodo dragons.

Plasmodium falciparum Life Cycle

The complex life cycle of the malaria-causing obligate protist requiring humans as intermediate hosts for asexual reproduction and female Anopheles mosquitoes as definitive hosts for sexual reproduction.