What cardiac mechanical events produce the S1 and S2 heart sounds ('lub-dub')?

• S1 ('lub'): Closure of the atrioventricular (AV) valves (Mitral and Tricuspid) at the onset of ventricular systole (isovolumetric contraction). • S2 ('dub'): Closure of the semilunar valves (Aortic and Pulmonic) at the onset of ventricular diastole (isovolumetric relaxation).

What enzymatic and physiological cascade constitutes the Renin-Angiotensin-Aldosterone System (RAAS)?

1. Juxtaglomerular cells detect low renal perfusion/BP -> secrete Renin. 2. Renin cleaves liver Angiotensinogen to Angiotensin I. 3. ACE (endothelial pulmonary enzyme) converts Ang I to Angiotensin II. 4. Ang II triggers systemic vasoconstriction and stimulates adrenal cortex to release Aldosterone.

What are the three classes of hormones based on chemical structure and their signaling mechanisms?

1. Peptide hormones (e.g., Insulin, Glucagon): Hydrophilic, travel free in blood, bind extracellular GPCR/RTK receptors, rapid second-messenger cascades (cAMP, IP3), transient. 2. Steroid hormones (e.g., Cortisol, Estrogen): Lipophilic, require carrier proteins, bind intracellular/nuclear receptors, alter gene transcription, slow onset, long-lasting. 3. Amino acid derivatives: Thyroid hormones (T3/T4 act like steroids); Catecholamines (Epi/Norepi act like peptides).

What hormones are synthesized by the Hypothalamus and released by the Posterior Pituitary (Neurohypophysis)?

Oxytocin (uterine contractions, milk letdown) and Antidiuretic Hormone (ADH / Vasopressin, water reabsorption). They are synthesized in hypothalamic magnocellular neurons (supraoptic and paraventricular nuclei) and transported via axonal projections for storage and release in posterior pituitary.

What pedigree characteristics identify an Autosomal Recessive versus Autosomal Dominant inheritance pattern?

• Autosomal Recessive: Frequently skips generations; unaffected carrier parents (Aa x Aa) have a 25% chance of affected children; equal male/female ratio. • Autosomal Dominant: Appears in every generation (no skipping); affected individual has at least one affected parent; 50% transmission risk if one parent is Aa.

What are the three germ layers established during gastrulation and their adult tissue derivatives?

• Ectoderm: Epidermis, hair, nails, lens of eye, nervous system (neural tube, neural crest: adrenal medulla, melanocytes, Schwann cells). • Mesoderm: Dermis, bone, skeletal/cardiac/smooth muscle, circulatory system, kidneys, gonads, adrenal cortex. • Endoderm: Epithelial lining of digestive tract, respiratory tract, liver, pancreas, thyroid, bladder.

What is the structural basis and physiological purpose of the blood-brain barrier (BBB)?

Composed of brain capillary endothelial cells connected by continuous Tight Junctions (zonula occludens) surrounded by pericytes and astrocyte end-feet. Restricts polar, hydrophilic solutes and large molecules; permits passive diffusion of small nonpolar/lipophilic molecules (O2, CO2, ethanol, steroid hormones) and active transport of glucose (GLUT1).

What are the roles of Osteoblasts and Osteoclasts in bone remodeling and their hormonal regulators?

• Osteoblasts: Build bone matrix, secrete collagen, lower blood Ca2+; stimulated by Calcitonin. • Osteoclasts: Resorb/dissolve bone matrix via acid and enzymes, releasing Ca2+ and PO43- into blood; stimulated by Parathyroid Hormone (PTH) and Calcitriol (Vitamin D).

What is the difference between Primary Active Transport, Secondary Active Transport, and Facilitated Diffusion?

• Facilitated Diffusion: Passive transport down concentration gradient via channels/carriers; no energy. • Primary Active: Directly hydrolyzes ATP to move solutes against gradient (e.g., Na+/K+ ATPase). • Secondary Active: Couples uphill transport of one solute to downhill electrochemical gradient of another (e.g., Na+/glucose symporter SGLT).

What anterior pituitary hormones are regulated by hypothalamic releasing factors?

FLAT ChAMP (FLAT = tropic; PEG = direct): • FSH and LH (stimulated by GnRH) • ACTH (stimulated by CRH) • TSH (stimulated by TRH) • Prolactin (tonically inhibited by Dopamine) • Endorphins • Growth Hormone (GH, stimulated by GHRH, inhibited by Somatostatin).

What is the functional difference between MHC Class I and MHC Class II molecules?

• MHC-I: Present on ALL nucleated cells; presents endogenous intracellular antigens (viral/tumor proteins) to CD8+ Cytotoxic T cells ('1 * 8 = 8'). • MHC-II: Present ONLY on professional Antigen-Presenting Cells (APCs: dendritic cells, macrophages, B cells); presents exogenous antigens to CD4+ Helper T cells ('2 * 4 = 8').

What factors shift the Hemoglobin-Oxygen dissociation curve to the RIGHT (Bohr Effect)?

Right shift decreases oxygen affinity, facilitating O2 unloading to metabolically active tissues ('CADET, face Right'): • Increased CO2 • Increased Acidity (low pH / high [H+]) • Increased 2,3-BPG • Increased Exercise • Increased Temperature.

How do Sympathetic and Parasympathetic nervous systems differ in pre- and postganglionic neurotransmitters?

• Sympathetic: Short preganglionic neuron releases Acetylcholine (ACh) onto nicotinic receptors; long postganglionic neuron releases Norepinephrine (NE) onto adrenergic receptors (exception: sweat glands use ACh). • Parasympathetic: Long preganglionic neuron releases ACh; short postganglionic neuron releases ACh onto muscarinic receptors.

What is the countercurrent multiplier function of the Loop of Henle?

• Descending Limb: Highly permeable to water, impermeable to solutes; water leaves into hypertonic medulla, concentrating tubular fluid. • Thick Ascending Limb: Impermeable to water; actively transports Na+/K+/2Cl- out into medulla via NKCC2 cotransporter, creating a hyperosmotic renal medullary gradient.

What is the electrical conduction pathway of the human heart?

SA Node (intrinsic pacemaker in right atrium, ~70 bpm) -> Internodal pathways -> AV Node (intrinsic 0.1s delay to allow ventricular filling) -> Bundle of His -> Left and Right Bundle Branches -> Purkinje Fibers (rapid conduction across ventricular myocardium).

What are the structural distinctions between eukaryotic and prokaryotic ribosomes?

• Eukaryotes: 80S ribosomes composed of 60S (large) and 40S (small) subunits. • Prokaryotes: 70S ribosomes composed of 50S (large) and 30S (small) subunits. This difference enables antibiotics (e.g., aminoglycosides, tetracyclines) to target bacterial translation selectively.

What pedigree features identify an X-Linked Recessive condition?

Males are affected significantly more frequently than females (males are hemizygous, requiring only 1 mutant allele). An affected father NEVER transmits the disorder to his sons, but ALL of his daughters become obligate carriers.

What are the primary cell cycle checkpoints and what is the role of p53?

• G1/S Checkpoint (restriction point): Checks for DNA damage and cell size before replication; p53 arrests cycle and induces p21 (CDK inhibitor) or apoptosis if damage is unrepairable. • G2/M Checkpoint: Ensures complete DNA replication before mitosis. • M Checkpoint (spindle assembly): Verifies all chromosomes are attached to kinetochore microtubules before anaphase.

What are the characteristics of the Universal Genetic Code?

• Degenerate / Redundant: Multiple 3-nucleotide codons can encode the same amino acid (wobble hypothesis at third base). • Unambiguous: Each codon codes for one and only one amino acid. • Non-overlapping and Commaless: Read contiguously in sets of 3 from Start codon (AUG = Met) to Stop codons (UAA, UAG, UGA).

What is reabsorbed in the Proximal Convoluted Tubule (PCT) of the renal nephron?

Bulk reabsorption (~65-70% of total filtrate): 100% of glucose and amino acids (via secondary active Na+ symport), ~65% of Na+, Cl-, and H2O (isotonically), and ~85% of HCO3-. Secretes H+, urea, NH3, and medications (Dump the HUNK).

What is the stoichiometry, electrogenic effect, and function of the Na+/K+ ATPase pump?

Pumps 3 Na+ OUT of the cell and 2 K+ INTO the cell per 1 ATP hydrolyzed. It is electrogenic (net -1 charge per cycle), maintaining low intracellular [Na+], high intracellular [K+], cell osmotic balance, and resting membrane potential.

What cells in the stomach secrete Pepsinogen, Hydrochloric Acid, and Intrinsic Factor?

• Chief cells: Secrete Pepsinogen (zymogen activated by acid to pepsin for protein cleavage). • Parietal cells: Secrete HCl (cleaves pepsinogen, denatures dietary proteins, kills microbes) and Intrinsic Factor (essential for vitamin B12 absorption in the terminal ileum). • G-cells: Secrete Gastrin (stimulates parietal cells).

How do Innate and Adaptive immune responses differ?

• Innate Immunity: Non-specific, immediate response, no immunological memory; physical barriers (skin, mucus), neutrophils, macrophages, dendritic cells, NK cells, complement. • Adaptive Immunity: Highly antigen-specific, delayed primary response (days), forms long-lasting immunological memory; B cells (humoral antibodies) and T cells (cell-mediated cytotoxicity).

What is the difference between the Absolute and Relative Refractory Periods in neurons?

• Absolute: Voltage-gated Na+ channels are inactivated (inactivation gate closed); NO action potential can be triggered regardless of stimulus strength. • Relative: Voltage-gated Na+ channels have de-inactivated (closed state), but K+ efflux causes hyperpolarization; a stronger-than-normal suprathreshold stimulus is required.

How does an action potential trigger chemical synaptic neurotransmitter release at the axon terminal?

Depolarization of the presynaptic terminal opens voltage-gated Ca2+ channels -> Ca2+ influx -> Ca2+ binds synaptotagmin, triggering SNARE-complex-mediated exocytosis of neurotransmitter vesicles into the synaptic cleft.

What are the Hardy-Weinberg equilibrium equations and what 5 conditions are required?

Equations: p + q = 1 (allele frequencies) and p^2 + 2pq + q^2 = 1 (genotype frequencies). Conditions: (1) Infinitely large population; (2) Random mating; (3) No mutation; (4) No migration / gene flow; (5) No natural selection.

How do Aldosterone and Antidiuretic Hormone (ADH / Vasopressin) differ in their renal mechanism and effect on serum osmolarity?

• Aldosterone (steroid from adrenal cortex): Upregulates Na+/K+ pumps in DCT and collecting duct -> reabsorbs Na+ and excretes K+/H+; water follows Na+ isotonically -> increases blood volume and pressure WITHOUT changing serum osmolarity. • ADH (peptide from posterior pituitary): Inserts Aquaporin-2 into collecting duct -> reabsorbs free water -> increases blood volume and DECREASES serum osmolarity.

What molecular steps describe the Sliding Filament Theory of skeletal muscle contraction?

1. Action potential propagates down T-tubules -> DHP/RyR receptors release Ca2+ from sarcoplasmic reticulum. 2. Ca2+ binds Troponin C -> Tropomyosin shifts, exposing actin myosin-binding sites. 3. Myosin head (bound to ADP + Pi) binds actin, forming cross-bridge. 4. Power stroke: ADP + Pi released, pulling actin filament toward M-line. 5. ATP binds myosin head, causing detachment from actin. 6. ATP hydrolysis recocks myosin head to high-energy state.

How does the Bohr effect versus the Haldane effect describe blood gas transport?

• Bohr Effect: Increased pCO2 and [H+] lowers hemoglobin affinity for O2, promoting O2 unloading in peripheral tissues. • Haldane Effect: Oxygenation of hemoglobin promotes dissociation of CO2 and H+, facilitating CO2 unloading in pulmonary capillaries.

What key events during Meiosis I generate genetic diversity?

1. Crossing Over (homologous recombination): Occurs between non-sister chromatids of homologous chromosomes during Prophase I at chiasmata. 2. Independent Assortment: Random orientation and segregation of maternal and paternal homologous chromosome pairs during Metaphase I / Anaphase I (2^n combinations).

What sequence of ion channel gating drives a neuronal Action Potential?

1. Depolarization to threshold (~ -55 mV): Voltage-gated Na+ channels open rapidly -> massive Na+ influx. 2. Peak (+35 mV): Voltage-gated Na+ channels inactivate; delayed voltage-gated K+ channels open. 3. Repolarization: K+ efflux drives potential negative. 4. Hyperpolarization: K+ channels close slowly; Na+/K+ pump restores resting potential (~ -70 mV).

How does cholesterol modulate cell membrane fluidity at high versus low temperatures?

Cholesterol is a bidirectional fluidity buffer: • At HIGH temperatures: Restricts phospholipid movement, increasing membrane rigidity and reducing permeability. • At LOW temperatures: Prevents fatty acid chains from packing tightly, preventing crystallization and increasing fluidity.

Biochimie — Débutant (A1/A2) 4: Biology Cell Physiology, Genetics & Organ Systems

[Français] Biochimie: Organelles, membrane transport, action potential propagation, Mendelian genetics, pedigree analysis, renal nephron physiology, endocrine hormones, and cardiac cycle.

Level: basic
Languages: fr → fr
Cards: 32
Markdown: Biochimie — Débutant (A1/A2) 4: Biology Cell Physiology, Genetics & Organ Systems (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What cardiac mechanical events produce the S1 and S2 heart sounds ('lub-dub')?	• S1 ('lub'): Closure of the atrioventricular (AV) valves (Mitral and Tricuspid) at the onset of ventricular systole (isovolumetric contraction). • S2 ('dub'): Closure of the semilunar valves (Aortic and Pulmonic) at the onset of ventricular diastole (isovolumetric relaxation).
2	What enzymatic and physiological cascade constitutes the Renin-Angiotensin-Aldosterone System (RAAS)?	1. Juxtaglomerular cells detect low renal perfusion/BP -> secrete Renin. 2. Renin cleaves liver Angiotensinogen to Angiotensin I. 3. ACE (endothelial pulmonary enzyme) converts Ang I to Angiotensin II. 4. Ang II triggers systemic vasoconstriction and stimulates adrenal cortex to release Aldosterone.
3	What are the three classes of hormones based on chemical structure and their signaling mechanisms?	1. Peptide hormones (e.g., Insulin, Glucagon): Hydrophilic, travel free in blood, bind extracellular GPCR/RTK receptors, rapid second-messenger cascades (cAMP, IP3), transient. 2. Steroid hormones (e.g., Cortisol, Estrogen): Lipophilic, require carrier proteins, bind intracellular/nuclear receptors, alter gene transcription, slow onset, long-lasting. 3. Amino acid derivatives: Thyroid hormones (T3/T4 act like steroids); Catecholamines (Epi/Norepi act like peptides).
4	What hormones are synthesized by the Hypothalamus and released by the Posterior Pituitary (Neurohypophysis)?	Oxytocin (uterine contractions, milk letdown) and Antidiuretic Hormone (ADH / Vasopressin, water reabsorption). They are synthesized in hypothalamic magnocellular neurons (supraoptic and paraventricular nuclei) and transported via axonal projections for storage and release in posterior pituitary.
5	What pedigree characteristics identify an Autosomal Recessive versus Autosomal Dominant inheritance pattern?	• Autosomal Recessive: Frequently skips generations; unaffected carrier parents (Aa x Aa) have a 25% chance of affected children; equal male/female ratio. • Autosomal Dominant: Appears in every generation (no skipping); affected individual has at least one affected parent; 50% transmission risk if one parent is Aa.
6	What are the three germ layers established during gastrulation and their adult tissue derivatives?	• Ectoderm: Epidermis, hair, nails, lens of eye, nervous system (neural tube, neural crest: adrenal medulla, melanocytes, Schwann cells). • Mesoderm: Dermis, bone, skeletal/cardiac/smooth muscle, circulatory system, kidneys, gonads, adrenal cortex. • Endoderm: Epithelial lining of digestive tract, respiratory tract, liver, pancreas, thyroid, bladder.
7	What is the structural basis and physiological purpose of the blood-brain barrier (BBB)?	Composed of brain capillary endothelial cells connected by continuous Tight Junctions (zonula occludens) surrounded by pericytes and astrocyte end-feet. Restricts polar, hydrophilic solutes and large molecules; permits passive diffusion of small nonpolar/lipophilic molecules (O2, CO2, ethanol, steroid hormones) and active transport of glucose (GLUT1).
8	What are the roles of Osteoblasts and Osteoclasts in bone remodeling and their hormonal regulators?	• Osteoblasts: Build bone matrix, secrete collagen, lower blood Ca2+; stimulated by Calcitonin. • Osteoclasts: Resorb/dissolve bone matrix via acid and enzymes, releasing Ca2+ and PO43- into blood; stimulated by Parathyroid Hormone (PTH) and Calcitriol (Vitamin D).
9	What is the difference between Primary Active Transport, Secondary Active Transport, and Facilitated Diffusion?	• Facilitated Diffusion: Passive transport down concentration gradient via channels/carriers; no energy. • Primary Active: Directly hydrolyzes ATP to move solutes against gradient (e.g., Na+/K+ ATPase). • Secondary Active: Couples uphill transport of one solute to downhill electrochemical gradient of another (e.g., Na+/glucose symporter SGLT).
10	What anterior pituitary hormones are regulated by hypothalamic releasing factors?	FLAT ChAMP (FLAT = tropic; PEG = direct): • FSH and LH (stimulated by GnRH) • ACTH (stimulated by CRH) • TSH (stimulated by TRH) • Prolactin (tonically inhibited by Dopamine) • Endorphins • Growth Hormone (GH, stimulated by GHRH, inhibited by Somatostatin).
11	What is the functional difference between MHC Class I and MHC Class II molecules?	• MHC-I: Present on ALL nucleated cells; presents endogenous intracellular antigens (viral/tumor proteins) to CD8+ Cytotoxic T cells ('1 * 8 = 8'). • MHC-II: Present ONLY on professional Antigen-Presenting Cells (APCs: dendritic cells, macrophages, B cells); presents exogenous antigens to CD4+ Helper T cells ('2 * 4 = 8').
12	What factors shift the Hemoglobin-Oxygen dissociation curve to the RIGHT (Bohr Effect)?	Right shift decreases oxygen affinity, facilitating O2 unloading to metabolically active tissues ('CADET, face Right'): • Increased CO2 • Increased Acidity (low pH / high [H+]) • Increased 2,3-BPG • Increased Exercise • Increased Temperature.
13	How do Sympathetic and Parasympathetic nervous systems differ in pre- and postganglionic neurotransmitters?	• Sympathetic: Short preganglionic neuron releases Acetylcholine (ACh) onto nicotinic receptors; long postganglionic neuron releases Norepinephrine (NE) onto adrenergic receptors (exception: sweat glands use ACh). • Parasympathetic: Long preganglionic neuron releases ACh; short postganglionic neuron releases ACh onto muscarinic receptors.
14	What is the countercurrent multiplier function of the Loop of Henle?	• Descending Limb: Highly permeable to water, impermeable to solutes; water leaves into hypertonic medulla, concentrating tubular fluid. • Thick Ascending Limb: Impermeable to water; actively transports Na+/K+/2Cl- out into medulla via NKCC2 cotransporter, creating a hyperosmotic renal medullary gradient.
15	What is the electrical conduction pathway of the human heart?	SA Node (intrinsic pacemaker in right atrium, ~70 bpm) -> Internodal pathways -> AV Node (intrinsic 0.1s delay to allow ventricular filling) -> Bundle of His -> Left and Right Bundle Branches -> Purkinje Fibers (rapid conduction across ventricular myocardium).
16	What are the structural distinctions between eukaryotic and prokaryotic ribosomes?	• Eukaryotes: 80S ribosomes composed of 60S (large) and 40S (small) subunits. • Prokaryotes: 70S ribosomes composed of 50S (large) and 30S (small) subunits. This difference enables antibiotics (e.g., aminoglycosides, tetracyclines) to target bacterial translation selectively.
17	What pedigree features identify an X-Linked Recessive condition?	Males are affected significantly more frequently than females (males are hemizygous, requiring only 1 mutant allele). An affected father NEVER transmits the disorder to his sons, but ALL of his daughters become obligate carriers.
18	What are the primary cell cycle checkpoints and what is the role of p53?	• G1/S Checkpoint (restriction point): Checks for DNA damage and cell size before replication; p53 arrests cycle and induces p21 (CDK inhibitor) or apoptosis if damage is unrepairable. • G2/M Checkpoint: Ensures complete DNA replication before mitosis. • M Checkpoint (spindle assembly): Verifies all chromosomes are attached to kinetochore microtubules before anaphase.
19	What are the characteristics of the Universal Genetic Code?	• Degenerate / Redundant: Multiple 3-nucleotide codons can encode the same amino acid (wobble hypothesis at third base). • Unambiguous: Each codon codes for one and only one amino acid. • Non-overlapping and Commaless: Read contiguously in sets of 3 from Start codon (AUG = Met) to Stop codons (UAA, UAG, UGA).
20	What is reabsorbed in the Proximal Convoluted Tubule (PCT) of the renal nephron?	Bulk reabsorption (~65-70% of total filtrate): 100% of glucose and amino acids (via secondary active Na+ symport), ~65% of Na+, Cl-, and H2O (isotonically), and ~85% of HCO3-. Secretes H+, urea, NH3, and medications (Dump the HUNK).
21	What is the stoichiometry, electrogenic effect, and function of the Na+/K+ ATPase pump?	Pumps 3 Na+ OUT of the cell and 2 K+ INTO the cell per 1 ATP hydrolyzed. It is electrogenic (net -1 charge per cycle), maintaining low intracellular [Na+], high intracellular [K+], cell osmotic balance, and resting membrane potential.
22	What cells in the stomach secrete Pepsinogen, Hydrochloric Acid, and Intrinsic Factor?	• Chief cells: Secrete Pepsinogen (zymogen activated by acid to pepsin for protein cleavage). • Parietal cells: Secrete HCl (cleaves pepsinogen, denatures dietary proteins, kills microbes) and Intrinsic Factor (essential for vitamin B12 absorption in the terminal ileum). • G-cells: Secrete Gastrin (stimulates parietal cells).
23	How do Innate and Adaptive immune responses differ?	• Innate Immunity: Non-specific, immediate response, no immunological memory; physical barriers (skin, mucus), neutrophils, macrophages, dendritic cells, NK cells, complement. • Adaptive Immunity: Highly antigen-specific, delayed primary response (days), forms long-lasting immunological memory; B cells (humoral antibodies) and T cells (cell-mediated cytotoxicity).
24	What is the difference between the Absolute and Relative Refractory Periods in neurons?	• Absolute: Voltage-gated Na+ channels are inactivated (inactivation gate closed); NO action potential can be triggered regardless of stimulus strength. • Relative: Voltage-gated Na+ channels have de-inactivated (closed state), but K+ efflux causes hyperpolarization; a stronger-than-normal suprathreshold stimulus is required.
25	How does an action potential trigger chemical synaptic neurotransmitter release at the axon terminal?	Depolarization of the presynaptic terminal opens voltage-gated Ca2+ channels -> Ca2+ influx -> Ca2+ binds synaptotagmin, triggering SNARE-complex-mediated exocytosis of neurotransmitter vesicles into the synaptic cleft.
26	What are the Hardy-Weinberg equilibrium equations and what 5 conditions are required?	Equations: p + q = 1 (allele frequencies) and p^2 + 2pq + q^2 = 1 (genotype frequencies). Conditions: (1) Infinitely large population; (2) Random mating; (3) No mutation; (4) No migration / gene flow; (5) No natural selection.
27	How do Aldosterone and Antidiuretic Hormone (ADH / Vasopressin) differ in their renal mechanism and effect on serum osmolarity?	• Aldosterone (steroid from adrenal cortex): Upregulates Na+/K+ pumps in DCT and collecting duct -> reabsorbs Na+ and excretes K+/H+; water follows Na+ isotonically -> increases blood volume and pressure WITHOUT changing serum osmolarity. • ADH (peptide from posterior pituitary): Inserts Aquaporin-2 into collecting duct -> reabsorbs free water -> increases blood volume and DECREASES serum osmolarity.
28	What molecular steps describe the Sliding Filament Theory of skeletal muscle contraction?	1. Action potential propagates down T-tubules -> DHP/RyR receptors release Ca2+ from sarcoplasmic reticulum. 2. Ca2+ binds Troponin C -> Tropomyosin shifts, exposing actin myosin-binding sites. 3. Myosin head (bound to ADP + Pi) binds actin, forming cross-bridge. 4. Power stroke: ADP + Pi released, pulling actin filament toward M-line. 5. ATP binds myosin head, causing detachment from actin. 6. ATP hydrolysis recocks myosin head to high-energy state.
29	How does the Bohr effect versus the Haldane effect describe blood gas transport?	• Bohr Effect: Increased pCO2 and [H+] lowers hemoglobin affinity for O2, promoting O2 unloading in peripheral tissues. • Haldane Effect: Oxygenation of hemoglobin promotes dissociation of CO2 and H+, facilitating CO2 unloading in pulmonary capillaries.
30	What key events during Meiosis I generate genetic diversity?	1. Crossing Over (homologous recombination): Occurs between non-sister chromatids of homologous chromosomes during Prophase I at chiasmata. 2. Independent Assortment: Random orientation and segregation of maternal and paternal homologous chromosome pairs during Metaphase I / Anaphase I (2^n combinations).
31	What sequence of ion channel gating drives a neuronal Action Potential?	1. Depolarization to threshold (~ -55 mV): Voltage-gated Na+ channels open rapidly -> massive Na+ influx. 2. Peak (+35 mV): Voltage-gated Na+ channels inactivate; delayed voltage-gated K+ channels open. 3. Repolarization: K+ efflux drives potential negative. 4. Hyperpolarization: K+ channels close slowly; Na+/K+ pump restores resting potential (~ -70 mV).
32	How does cholesterol modulate cell membrane fluidity at high versus low temperatures?	Cholesterol is a bidirectional fluidity buffer: • At HIGH temperatures: Restricts phospholipid movement, increasing membrane rigidity and reducing permeability. • At LOW temperatures: Prevents fatty acid chains from packing tightly, preventing crystallization and increasing fluidity.