Animal Evolution, Physiology, Cell Signaling, and Neurobiology Review

Comprehensive practice flashcards covering animal physiological principles, evolutionary biology, endocrine regulation, and neurophysiology based on lecture outlines.

What is the key distinction between genotype and phenotype, and why is phenotype more important concerning natural selection and evolution?

Genotype refers to the genetic makeup of an organism, whereas phenotype refers to its observable physical and physiological traits. Phenotype is more important for selection and evolution because natural selection acts directly on the physical characteristics and functional performance of the organism in its environment, not directly on its genome.

What is the Krogh principle in physiological research?

The Krogh principle states that for such a large number of physiological problems there will be some animal, or a few such animals, on which it can be most conveniently studied.

How do isometric scaling and allometric scaling differ, and what does the exponent $b$ represent in the linear scaling equation?

Isometric scaling occurs when a physiological or anatomical trait scales proportionally with body size ($b = 1$), preserving geometric shape. Allometric scaling occurs when a trait changes non-proportionally with body size ($b \neq 1$). In the log-transformed linear scaling equation $\text{log}(y) = \text{log}(a) + b \times \text{log}(x)$, $b$ represents the scaling exponent or slope of the relationship.

What is the difference between a proximate cause and an ultimate cause in evolutionary physiology?

A proximate cause explains the immediate mechanical, chemical, or physiological mechanism underlying a biological process, whereas an ultimate cause explains the evolutionary origin, adaptive significance, or historical selective pressure that favored the trait.

How do acclimation, acclimatization, and phenotypic plasticity differ from one another?

Phenotypic plasticity is the general capacity of a single genotype to produce multiple phenotypes under different environmental conditions. Acclimation refers to reversible physiological adjustments made under controlled laboratory conditions, whereas acclimatization refers to physiological adjustments made in response to natural environmental changes.

How does a conformer differ from a regulator, and can a conformer ever maintain homeostasis?

A regulator actively maintains internal stability despite external environmental fluctuations, whereas a conformer allows its internal physiological state to match the external environment. A conformer can maintain homeostasis if it lives in an environment that is naturally stable and constant.

What is the progenote, and what basic characteristics did it possess?

The progenote is the hypothetical ancestral organism common to all living domains (Eubacteria, Archaea, and Eukaryota) that existed before the full evolution of modern cellular structures and genomic decoding mechanisms.

What physiological and ecological advantages does multicellularity provide over being a single-celled organism?

Multicellularity allows organisms to attain larger size, escape predation limits, develop cellular specialization and division of labor, form protected internal extracellular environments, and build complex organ systems.

What defines a true tissue, and why are sponges said to lack true tissues?

A tissue is defined as an aggregation of similar specialized cells and their extracellular matrix working together to perform a specific function. Sponges lack true tissues because their cells retain developmental totipotency/flexibility, lack specialized cell junctions, and do not form distinct embryonic germ layers bounded by a basal lamina.

How do diploblastic and triploblastic animals differ in germ layers and representative animal groups?

Diploblastic animals possess two embryonic germ layers (ectoderm and endoderm) and include groups such as Cnidaria and Ctenophora. Triploblastic animals possess three germ layers (ectoderm, mesoderm, and endoderm) and comprise all bilaterians.

What distinguishes protostomes from deuterostomes during embryonic development?

In protostomes, embryonic cleavage is generally spiral and determinant, and the blastopore develops into the mouth. In deuterostomes, embryonic cleavage is radial and indeterminant, and the blastopore develops into the anus.

Why is gene duplication vital to vertebrate physiological evolution, and when did major duplication events occur?

Gene duplication provides redundant copies of genes that can undergo mutation and neofunctionalization without losing original physiological functions. Major whole-genome duplication events occurred early in vertebrate evolution prior to and during the radiation of jawed vertebrates and teleosts.

What critical physiological roles do collagen and $\text{Na}^+/\text{K}^+\text{ ATPase}$ perform in animals?

Collagen is a major structural protein of the extracellular matrix that provides tensile strength required for multicellular animal bodies. The $\text{Na}^+/\text{K}^+\text{ ATPase}$ pump maintains cellular ion gradients and resting membrane potentials essential for active transport, neuromuscular excitability, and osmoregulation.

How do direct, autocrine, paracrine, endocrine, and neural cell signaling methods differ?

Direct signaling transfers molecules through gap junctions between adjacent cells; autocrine signaling acts on the secretor cell itself; paracrine signaling diffuses through extracellular fluid to local adjacent cells; endocrine signaling distributes hormones via blood over long distances; and neural signaling travels as electrical action potentials down axons to release neurotransmitters across synapses.

How do the solubility properties of hydrophilic vs hydrophobic signaling molecules dictate their mechanisms of transport and action?

Hydrophilic messengers dissolve easily in aqueous plasma, travel freely, but cannot pass through lipid bilayers, so they bind cell-surface receptors to trigger rapid, reversible second-messenger cascades. Hydrophobic messengers require carrier proteins in plasma, readily cross cell membranes, and bind intracellular receptors to alter gene transcription, yielding slower, sustained effects.

How do peptide hormones differ from steroid hormones in synthesis, storage, and secretion?

Peptide hormones are synthesized on ribosomes, stored in secretory vesicles, and released on demand via exocytosis. Steroid hormones are synthesized from cholesterol on demand in the smooth ER/mitochondria and diffuse immediately out of the cell without vesicle storage.

What is the difference between an agonist and an antagonist in ligand-receptor interactions?

An agonist is a chemical ligand that binds to a receptor and activates it to trigger a biological response. An antagonist binds to a receptor without activating it, physically blocking natural ligands from binding and inhibiting the physiological response.

How does signal amplification occur within G-protein coupled receptor (GPCR) and $\text{cAMP}$ signaling cascades?

Binding of a single hydrophilic ligand to a GPCR activates multiple G-proteins. Each active G-protein stimulates adenylyl cyclase to synthesize many $\text{cAMP}$ molecules from $\text{ATP}$, and each $\text{cAMP}$ activates protein kinase A ($\text{PKA}$), exponentially magnifying the signal at each sequential step.

What defines first-, second-, and third-order endocrine control pathways?

A first-order pathway involves a single tissue sensing a stimulus and releasing a hormone directly. A second-order pathway involves a neurosecretory cell releasing a hormone that stimulates a secondary endocrine gland to secrete a second hormone. A third-order pathway involves three sequential hormones in a cascade (such as the hypothalamus $\rightarrow$ pituitary $\rightarrow$ target gland $\rightarrow$ effect).

How is resting membrane potential generated and maintained in a typical neuron?

Resting potential (typically around $-70\text{ mV}$) is generated by high membrane permeability to $\text{K}^+$ through open leak channels relative to $\text{Na}^+$, driving $\text{K}^+$ outward down its concentration gradient, combined with electrogenic active transport by $\text{Na}^+/\text{K}^+\text{ ATPase}$ pumps ($3\text{ Na}^+$ pumped out for every $2\text{ K}^+$ brought in).

How do temporal summation and spatial summation of graded potentials differ?

Temporal summation occurs when multiple graded potentials generated in rapid succession at a single synapse combine over time. Spatial summation occurs when graded potentials generated simultaneously at multiple distinct synapses across the neuronal membrane sum together.

Which ion flux events dictate depolarization, repolarization, and hyperpolarization during an action potential?

Depolarization is driven by rapid influx of $\text{Na}^+$ through voltage-gated $\text{Na}^+$ channels. Repolarization is driven by inactivation of $\text{Na}^+$ channels and efflux of $\text{K}^+$ through opened voltage-gated $\text{K}^+$ channels. Hyperpolarization occurs because voltage-gated $\text{K}^+$ channels close slowly, permitting prolonged $\text{K}^+$ efflux past resting potential.

What sequence of events occurs at the neuromuscular junction to initiate contraction?

An action potential invades the presynaptic terminal, opening voltage-gated $\text{Ca}^{2+}$ channels. Influx of $\text{Ca}^{2+}$ triggers exocytosis of acetylcholine ($\text{ACh}$) into the synaptic cleft. $\text{ACh}$ binds nicotinic receptors on the postsynaptic muscle membrane, opening ion channels to depolarize the motor endplate, after which acetylcholinesterase ($\text{AChE}$) degrades $\text{ACh}$ to stop transmission.

How do axon diameter and myelination increase action potential conduction velocity?

Increasing axon diameter decreases internal axoplasmic resistance ($r_i$), allowing longitudinal electrical current to flow faster down the axon. Myelination increases membrane resistance ($r_m$) and decreases membrane capacitance ($C_m$), insulating the axon and enabling rapid saltatory conduction from node to node.

How do ionotropic and metabotropic receptors differ in mechanism and operational speed?

Ionotropic receptors are neurotransmitter-gated ion channels that open directly upon ligand binding to produce rapid, short-lived electrical responses. Metabotropic receptors are G-protein coupled receptors that act through intracellular second-messenger pathways, producing slower, longer-lasting physiological responses.

What is the primary distinction between adaptation and genetic drift in evolution?

Adaptation is an allele frequency change driven by natural selection that enhances relative biological fitness, whereas genetic drift is a random change in allele frequencies due to chance events, independent of fitness.

How do homologous, analogous, and homoplastic structures differ?

Homologous structures are derived from a shared evolutionary ancestor despite potential functional differences. Analogous structures share similar functions due to convergent evolution from distinct lineages. Homoplastic structures resemble one another through convergence or evolutionary reversal without shared ancestral origin.

What is the functional difference between negative and positive feedback mechanisms in physiological regulation?

Negative feedback counteracts a physiological stimulus to return a variable toward its set point to maintain homeostasis. Positive feedback amplifies a physiological change, driving a system away from its set point until a specific endpoint is reached.

How do electrical and chemical synapses differ in structure and function?

Electrical synapses directly couple adjacent cells via gap junctions for rapid, bidirectional current flow. Chemical synapses use neurotransmitters released across a synaptic cleft, enabling unidirectional, highly regulated, and modifiable signaling.

What distinct roles do oligodendrocytes and Schwann cells perform in myelinating axons?

Oligodendrocytes synthesize and maintain myelin sheaths around central nervous system (CNSCNS) axons, whereas Schwann cells provide myelin sheaths for peripheral nervous system (PNSPNS) axons.

How do the absolute and relative refractory periods of an action potential differ mechanism-wise?

The absolute refractory period occurs when voltage-gated Na+Na+ channels are inactivated, preventing new action potentials regardless of stimulus strength. The relative refractory period occurs when voltage-gated K+K+ channels remain open, requiring a suprathreshold stimulus to initiate an action potential.

How do gaseous signaling molecules like nitric oxide (NONO) differ from peptide and amine neurotransmitters?

Gaseous messengers are synthesized on demand, freely diffuse across cellular lipid membranes without vesicle storage or membrane receptors, and act locally on intracellular targets before rapidly breaking down.

How do internal axoplasmic resistance (riri​) and membrane resistance (rmrm​) affect passive current spread along an axon?

Higher membrane resistance (rmrm​) reduces current leakage across the axonal membrane to increase spatial spread, while lower internal axoplasmic resistance (riri​) decreases resistance to longitudinal current flow down the axon.

How does coelom development differ between protostomes and deuterostomes?

In protostomes, the coelom forms through schizocoely, where solid mesodermal tissue splits. In deuterostomes, the coelom forms through enterocoely, where mesodermal pouches fold and pinch off from the archenteron.

What is synaptic plasticity and what primary cellular mechanisms drive it?

Synaptic plasticity is the activity-dependent modification of synaptic strength over time, driven by mechanisms such as changes in neurotransmitter release probability, postsynaptic receptor density, or dendritic spine morphology.