BSCI207 Exam 3 Key Ideas

How does Ficks Law guide our understanding of gas exchange systems?

Organisms maximize gas flow rate by increasing exchange surface area, maintaining steep partial pressure gradients, and decreasing barrier thickness. Also shows structural compromises: because natural selection does not change diffusion coefficient, gas exchange organs must be large and thin, making them fragile and vulnerable to high circulatory fluid pressures.

What is the gas exchange approach of unicellular organisms?

Unicellular organisms rely exclusively on passive diffusion across their cell membrane without specialized respiratory organs. Their small sizes provides a large surface area to volume ratio relative to metabolic volume, and internal diffusion distances are so shirt that diffusion time is negligible.

What challenges do plants have and how do they solve them?

Plants face a direct conflict between opening their tissues to acquire CO2 for photosynthesis and losing essential water vapor to the dry atmosphere. Plants seal their leaf surfaces with a waxy, impermeable cuticle and restrict gas exchange to microscopic pores called stomata, which open into loose internal mesophyll tissue with high surface area.

Stomatal Opening Mechanism

1. Proton Pumping: Photoreceptors detect blue light, activating H+ ATPases to pump protons (H+) out of guard cells.

2. Ion Influx: The resulting electrochemical gradient drives K+ into guard cells through ion channels and Cl- through H+/CL- cotransporters.

3. Osmotic Water Entry: Solute accumulation causes water to enter the guard cells by osmos

4. Turgor Swelling: Guard cells become turgid, bowing outward due to radially oriented cellulose microfibrils and opening the stomatal pore.

What are some of the animal solutions to evolving a gas exchange system? How do they vary in different habitats or activity levels?

1. Simple Aquatic Animals (Sponges, Flatworms): rely on short difussion distances across simple body surfaces)

2. Crustaceans and Mollusks evolve specialized gills with high surface area and thin lamellae to overcome low oxygen availability in dense, viscous water.

3. Insects avoid gill collapse in air by evolving an internal tracheal system. Air enters regulatable spiracles on the body wall and travels through branching trachea directly to tissues. Small or low activity insects rely on passive diffusion through tubes, while larger or highly active insects contract their body cavities to drive bulk flow ventilation.

Benefits of a two-pump circulatory/gas exchange system

Coupling a ventilatory pump with a circulatory pump minimizes the diffusion distance by bringin external air/water and internal blood into extremely close proximity across thin membrances. It also maximizes the partial pressure gradient across the exchange surface

How do water ad air differ as media in which to “breathe”?

Water contains low oxygen concentrations (1/30th of air) and is dense and viscous, making bulk flow energetically expensive and diffusion slow. Aquatic organisms must move ~24,000 times more mass of water to extract equal oxygen. Air is oxygen-dense, lightweight, non-viscous, and permits rapid gas diffusion. This allows terrestrial orgnism to use bidirectional breathing without massive energy costs.

Key traits that have evolved as part of vertebrate ventilatory systems through evolutionary time?

1. Pharyngeal Slits & Muscular Pump: early chordates using slits and pumps for feeding

2. Gills & Countercurrent Flow: Boy fish developed two-phase pumps and gill lamellae with countercurrent blood/water flow.

3. Lungs: Evolved in ancestral aquatic bony fish to gulp surface air in stagnant waters

4. Negative Pressure breathing: evolved in reptiles, mammals, and birds, utilizing rib muscles and diaphragms to pull air inward rather than pushing it down.

5. Alveoli vs Unidirectional Air Sacs: Mammals evolved alveolar lungs with bidirectional flow, while birds evolved rigid parabronchial lungs connected to air sacs which rive continuous, unidirectional, countercurrent gas exchange.

What are some benefits of countercurrent exchange? Name a squatic and a terrestrial gas exchange example

Countercurrent exchange maintains a partial pressure gradient across the entire contact distance between medium and blood, preventing earl equilibration and achieving much higher final blood oxygen saturation.

Water flows across gill lamellae in the opposite direction of blood flowing therough lamellar capillaries, allowing oxygen to diffuse into blood along the entire pathway.

Air flows unidirectionally through parabronchi while blood floows in the opposite direction through adjacent capillaries, enabling high oxygen extract at low atmoshpheric partial pressures.

How do we determine whether two varaibles are scaling isometrically or allometrically?

1. Calculate the actual scaling exponent (b_actual) from empirical data using a log-log slope.

2. Determine the theoretical isometric expectation (b_isometric) by comparing the dimensional length exponents of both variables

3. Compare the values

   1. b_actual = b_isometric, growth is isometric

   2. b_actual > b_isometric, growth is positive allometric

   3. b_actual < b_isometric, growth is negative allomteric

How do we calculate the actual value for the scaling coefficient b?

We linearize y=ax^b into log(y) = log(a) + blog(x). Give data points for two conditions (x₁, y₁) and (x₂, y₂), we can caulte the slope of the log-log line.

How do we estimate the isometric expectation of the scaling coefficient, b?

We express both varaibles x and y in terms of linear length.

What does this tell us about scaling for body size proportions and heat loss in large vs small animals?

• Body Size Proportions: Because mass scales with L³ while leg cross-sectional area scales with L², larger animals face severe structural challenges. To kepp from collapsing under gravity, larger animals must either alter their stance or evolve thicker, disproportionately heavy bones (positive allometry).

• Heat Loss & energy Demands: Cooling rate scales inversely with length (SA/V proportional to L^-1). Small animals have a very high surface area-to-volume ratio, causing them to lose heat rapidly and work significantly harder metabolically to maintain body temperature. Conversely, large animals have small SA/V ratio, cooling much slower and easily maintaining a high temperature gradient relative to sold environments.

How and when do organisms us diffusion (Fick’s law( and bulk flow (H-P eqn)?

• Diffusion is used over short distances (delta(x) <= 0.5 mm), such as movement across alveolar/capillary membrances in lungs, across leaf stomata, or from capillary blood into individual tissue cells.

• Bulk flow (H-P Equation( is used for long distance transport, moving bulk fluids (air, blood, sap) rapidly across macroscopic body dimensions in response to physical pressure gradients.

What makes water flow in plants? In animals?

• In Plants: Water flow is pulled upward from soil through the xylem by negative pressure (tension) generated by solar-powered evaporation (transpiration) at the leaves.

• In Animals: Blood flow is pushed forward through continuous blood vessels by positive pressure generated by the contraction of a muscular pump (the heart).

How do plant and animal circulatory systems differ? How have they evolved to perform the same tasks by different strategies?

• Structural Differences: Plants use open and flow through pathways with high internal resistance due to narrow, cell-derived conduits. Animals use closed circulatory systems featuring wide, low resistance main vessels couple with dense, short capillary beds.

• Evolutionary Strategies: Plants compensate for high resistance by generating massive negative pressure gradients vis transpiration. Animals minimize overall vessel resistance so they can deliver high volumetric flow rates using low to moderate positive pressure pumps.

What impacts bulk flow rates through tubes (think H-P equation)?

1. Pressure difference: directly proportional

2. Vessel Radius: extremely sensitive; flow scales to r⁴

3. Vessel Length: inversely proportional

4. Fluid Viscosity: inversely proportional

What are the scaling implications?

Because blood vessel flow rate scales with r⁴ while metabolic needs scale with body mass (r³), blood flow per body size increases with overall organism size. Small animals cannot significantly increase blood pressure to force fluid through their narrow vessels without risking tissue damage. Consequently, small animals meet their high mass-specific metabolic demands by elevating heart rate rather than blood pressure.

In a closed circulatory system, how does flow rate, pressure, and resistanec vary?

• Flow rate: total volumetric flow rate remains constant throughout all sequential parts of the system to conserve mass

• Pressure: Is highest in major arteries exiting the heart, drops drastically across arterioles and capillary beds, and reaches its lowest levels in veins returning blood to the heart

• Resistance: Is lowest in large conducting arteries and veins, but extremely high across capillary beds because resistance is inversely proportional to vessel radius to the fourth power.

How has the vertebrate circulatory system evolved? What are some key innovations?

• Fish (Single Circulation): A two-chambered heart pumps blood through a single circuit (Heart → Gills → Body → Heart).

• Lungfish & Amphibians (Partial Double Circulation): Evolved lungs, a three-chambered heart (two atria, one ventricle) and a secondary pulmonary circuit to give blood a pressure boost after passing respiratory organs

• Reptiles (Incomplete Septum): Evolved an incomplete ventricular septum allowing flexible anatomical shunting of blood past the lungs during apneas

• Mammals & Birds (Divided Double Circulation): Evolved a completely divided 4 chambered heart (2 atria, 2 ventricles) that completely separates systemic and pulmonary circuits.

What are the benefits of a divided circulatory system?

• Independent Pressure Control: It allows high systemic blood pressure to deliver blood efficiently across large body distances while maintaining low pulmonary blood pressure to protect delicate lung capillaries from edema and mechanical rupture

• Complete Separation of Blood: completely prevents deoxygenated blood returning from systemic tissues from mixing with oxygenated blood returning fro the lungs, maximizing the tissue oxygen delivery.

What is Henry’s Law and how does it help explain the uptake and release of gases?

• Henry’s Law states that the concentration of a dissolved gas in liquid is directly proportional to the partial pressure of that gas above the liquid (C = H * P)

• Uptake & Release: High partial pressure of oxygen in lung alveoli drives oxygen into solution and onto hemoglobin. In systemic capillary beds, lower tissue partial pressure of oxygen drives the net diffusion of oxygen out of the blood and into surrounding body cells.

How does hemoglobin bind to O2? What determines how much O2 is released around the body?

• Binding Mechanism: Hemoglobin binds oxygen cooperatively across its four subunits, resulting in a sigmoidal saturation curve where binding one oxygen molecule increases the affinity for subsequent molecules?

• Determining Factor for Release: The primary driver is the partial pressure gradient at the tissue level. At resting tissue partial pressures, hemoglobin releases 25% - 30% of its oxygen. During exercise, tissue PO2 drops further into the steep section of the sigmoidal curve causing hemoglobin to rapidly unload up to 80% - 90% of its bound oxygen to active muscle cells.

How do organisms use short term behavioral changes and long term genetic changes to adapt to low O2 levels?

• Short term / Behavioral: Organisms can reduce overall metabolic demand and activity levels, take faster or deeper breaths, or increase heart rate to elevate oxygen delivery

• Long-Term / Genetic: Over evolutionary time, populations acquire inherited genetic mutations that alter hemoglobin gene expression (such as adult llamas retaining fetal Hb), expand muscle capillary networks to shorten diffusion distances, or alter vascular dilation via elevated nitric oxide production

How does having multiple Hb genes help animals adapt to different life stages or environmental conditions?

Hemoglobin genes are organized in tandem arrays that are expressed selectively across embryonic, fetal, and adult stages. Expressing different globin subunits allows animals to adjust blood oxygen affinity for specific physiological demands - such as pulling oxygen from maternal blood across the placenta in utero or scavenging oxygen from thin air at high altitudes.

What properties of Hb can be altered to capture more O2 from the air?

• Oxygen Affinity: Decreasing P_{O2, 50} shifts the binding curve to the left, allowing blood to bind oxygen more tightly at low partial pressures

• Hemoglobin Concentration: Increasing total hemoglobin concentration (and hematocrit) increases the total oxygen-carrying capacity of the blood.

• Cooperativity & Modifiers: Adjusting subunit cooperativity or sensitivity to internal modifiers alters how easily oxygen binds at the respiratory surface versus unbinds in tissues.

How have different human populations adapted to higher elevations?

Tibetans and Andeans present a classic example of convergent evolution through distinct physiological mechanisms:

• Tibetans adapt by increasing ventilation volume, elevating exhaled nitric oxide (NO) to dilate blood vessels for faster blood flow, and increasing muscle capillary density to shorten oxygen diffusion distance

• Andeans adapt by elevating red blood cell production to achieve higher hemoglobin concentrations, allowing their blood to carry more oxygen per volume despite lower ventilation and flow rates.

What are the different kinds of transporters that increase diffusion in digestive systems? How do they work in plants?

Types of Transporters:

• Channels: Membrane pores allowing rapid passive transport of specific ions down electrochemical gradients

• Carriers/Transporters: Facilitated diffusion proteins moving uncharged molecules down concentration gradients, or Cotransporters coupling downhill ion movement to uphill nutrient transport

• ATP-Dependent Pumps: Primary active transporters using ATP to push ions against gradients

How they work in plants: Plant root hair membranes use ATP-driven H+-ATPase pumps to pump protons out into soil. This creates an extracellular positive/acidic gradient, allowing cations to enter root cells through selective channels, while anions and sugars are pulled in via H+ cotransporters. Roots also release protons into soil to displace mineral cation s bound to negatively charged soil particles.

How do electrochemical gradients contribute to nutrient assimilation?

Electrochemical gradients combine chemical concentration differences and electrical charge differences across lipid bilayers.

• In Plants/Fungi/Prokaryotes: H+-ATPases pump protons out, creating a steep proton gradient. This proton-motive force powers secondary active symporters that bring sucrose, amino acids, and anions into the cell.

• In Animals: Na+/K+-ATPase pumps push 3Na+ out for ever 2K+ brought in, creating a low intracellular Na+ concentration. This steep Na+ electrochemical gradient drives apical Na+/glucose and Na+/amino acid cotransporters to drag nutrients into intestinal epithelial cells against steep concentration gradients.

What are the primary stages in animal nutrient assimilation

1. Prey Capture/Ingestion: Acquring and ingesting food via the mouth.

2. Prey Reduction & Storage: Mechanical grinding (teeth/gizzard) and temporary storage/sterilization in the crop or stomach using HCl.

3. Digestion (Chemical Breakdown): Enzymatic cleavage of complex polymers into monomeric units within the small intestine lumen.

4. Absorption: Moving digest monomers across intestinal villi/microvilli membranes into blood capillaries or lymph

5. Elimination: Reabsorbing water and salts in the large intestine (colon) and expelling undigested waste (feces) via the anus.

How do different elements of animal digestive system contribute to digestion?

• Mouth & Salivary Glands: Mechanical chewing; salivary amylase begins starch breakdown

• Esophagus: Peristaltic transport tube connecting mouth to stomach.

• Stomach: Stores food, secretes HCl to kill pathogens and denature proteins, and secretes pepsinogen (activated to pepsin) for initial protein cleavage.

• Liver & Gallbladder: Liver produces bile (stored in gallbladder) which emulsifies fat droplets to increase surface area for lipases

• Pancreas: Secretes bicarbonate and a cocktail of digestive enzymes into the small intestine

• Small Intestine: Primary site of chemical digestion and absorption; brush border epithelial enzymes complete breakdown while villi/microvilli absorb nutrients.

• Large Intestine (Colon): Reabsorbs water, salts, and minerals, housing gut microbiota and compacting waste.

How and where are different types of macromolecules digested?

• Carbohydrates: Digestion vegins in the mouth (salivary amylase), continues in the small intestine (pancreatic amylase), and finishes on small intestine microvilli. Monosaccharides are absorbed via Na+/glucose cotransport.

• Proteins: Digestion begins in the stomach, continues in the small intestine lumen, and finishes on microvilli. Amino acids are absorbed via Na+/amino acid cotransport.

• Fats (Triglycerides): Emulsified by liver bile salts in the small intestine lumen, then cleaved by pancreatic lipase into fatty acids and monoglycerides. Because fats are lipophilic, they diffuse passively across epithelial cell membranes into lymph lacteals.

• Nucleic Acids (DNA/RNA): Digested in the small intestine lumen by pancreatic nucleases into nucleotides, then broken down by intestinal nucleosidases and nucleosidases into nitrogenous bases, sugars, and phosphates.

What are some medical challenges during digestion?

• Stomach Acid & Ulcers/Heartburn: Hydrochloric acid can damage stomach or esophageal tissues if mucous linings degrade. Antacids raise gastric pH to relieve pain.

• Secretory Diarrhea & Cholera: Toxins from pathogens like Vibrio cholerae cause massive fluid and ion loss into the intestine, lading to rapid, fatal dehydration.

• Oral Rehydration Therapy (ORT) Solution: Administering a precise mix of salt and sugar in water activates apical Na+/glucose cotransporters in enterocytes. this drives rapid solute uptake, pulling water back into blood by osmosis and effectively curing dehydration without requiring intravenous lines.

What are conformers and regulators?

• Ionoconformers: Organisms whose internal fluid matches both the total osmolarity and specific ionic concentrations of the surrounding environment.

• Osmoconformers: Organisms that match their overall internal osmolarity to the environment - preventing net osmotic water gain or loss - while actively regulating specific internal ion concentrations

• Osmoregulators: Organisms that maintain a strictly constant internal osmolarity and solute concentration independent of external environment conditions

How do different types of organisms deal with water/salt balance? Where in their body are the gains and losses? How do they compensate?

Freshwater Fish:

• Gains/Losses: Gain water passively by osmosis across gills/skin; lose salts by diffusion into hypotonic water

• Compensation: Do not drink water, actively transport salts inward across gill epithelia, and excrete large volumes of dilute urine.

Marine Bony Fish:

• Gains/Losses: Lose water continuously by osmosis across gills; gain excess salts via diffusion and ingestion.

• Compensation: Drink seawater, actively pump out excess NA+ and Cl- across gills, and excrete small amounts of concentrated urine.

Marine Birds:

• Gains/Losses: Ingest high salt loads from marine prey and seawater.

• Compensation: Excrete high concentrated salt solution through specialized countercurrent nasal salt glands.

How do organisms differ in getting rid of nitrogenous waste?

• Ammonia: Excreted directly across body surfaces or gills by aquatic animals with abundant water.

• Urea: Synthesized by terrestrial mammals and sharks to convert ammonia into a less toxic form, requiring moderate water expenditure.

• Uric Acid: Synthesized by birds, reptiles, and insets as an insoluble paste to eliminate nitrogen with minimal water loss.

How do organisms use electrochemical gradients to control osmolarity?

All 4 systems rely on a unified cellular mechanism: primary active cation pumps establish electrochemical gradients that power secondary ion transport, causing water to follow passively by osmosis.

How does the filtrate concentration vary as it moves through a nephron? What is lost where? Where is the movement active and passive?

• Bowmans Capsule: Blood is filtered under pressure to produce an iso-osmotic filtrate.

• Proximal Tubule: Active Na+/K+ pumping sets up an electrochemical gradient driving secondary active cotransport of Na+, Cl-, glucose, amino acids, and vitamins out of the lumen. Water leaves passively via aquaporins following the osmotic gradient.

• Descending Limb of Loop of Henle: Highly permeable to water, impermeable to solutes. Water moves passively out into the hyperosmotic renal medulla, concentrating the filtrate to a maximum at the apex.

• Ascending Limb of Loop of henle: Impermeable to water NaCl leaves passively out of the thin lower segment and is actively pumped out by the thick upper segment into the medulla. The filtrate becomes hypo-osmotic as it enters the distal tubule.

• Distal Tubule & Collecting Duct: Ions are actively reabsorbed or secreted in the distal tubule. In the collecting duct, water moves passively out through ADH-reglated aquaporins into the hyperosmotic interstitial fluid, and urea diffuses passively near the bottom to concetrate final urine.

What is homeostasis and why is it important? How is it set?

• Definition & Importance: Homeostasis is the active physiological maintenance of a stable internal environment despite external environmental fluctuations. It is a critical because cellular enzymes and transport proteins operate efficiently only within narrow temperature, pH, solute, and gas concentration ranges.

• How It Is Set: Homeostasis relies on negative feedback loops. Internal sensors (such as thermoreceptors or osmoreceptors in the hypothalamus) continuously monitor blood conditions against a physiological set point. When conditions deviate, the control center triggers physiological or behavioral effectors to restor variables to normal levels.

What are different mechanisms of energy transfer?

1. Radiation: Transfer of thermal energy via electromagnetic waves between non-contacting surfaces.

2. Conduction: Direct transfer of thermal energy between contacting molecules, described by dQ/dt = k*A*delta(T)/delta(x)

3. Convection: heat transfer facilitated by the bulk movement of gas or liquid currents across a surface

4. Evaporation: Heat absorption driven by the phase change of liquid water into gas from moist body surfaces.

How do organisms generate needed heat?

• Shivering/Muscle Contraction: Involuntary, rapid contract of skeletal muscles hydrolyzes ATP, producing waste heat to warm core tissues.

• Non-Shivering Thermogenesis (Brown Fat): Specialized brown adipose tissue, packed with mitochondria, uncouples oxidative phosphorylation to convert metabolic energy directly into heat.

• Voluntary Exercise: Whole body physical activity increases metabolic rate and metabolic heat output.

How do organisms adapt to minimize heat loss?

• Insulation: Evolved thick blubber layers or fur/feathers that trap air layers with low thermal conductivity

• Vascular Control: Trigger vascoconstriction to restrict blood flow to peripheral skin capillaries

• Countercurrent Heat Exchange: Arrange arteries and veins in close contact within extremities so outgoing arterial heat warms incoming venous blood

• Behavioral Adjustments: huddle together, seek shelter, and enter daily torpor or season hibernation, or migrate to warmer regions.

How do organisms adapt to maximize heat loss?

• Vascular control: trigger vasodilation to flush skin capillaries with warm blood for thermal radiation

• Evaporative Cooling: Pant or sweat to remove heat via the latent heat of vaporization

• Structural Extensions: Increase surface area for heat radiation

Is it easier big or small animals to stay warm/cold? Why does surface area/volume matter?

• It is much easier for large animals to stay warm in cold environments. Heat generation depends on body volume/mass (L³), whereas heat loss aoccurs across surface area (L²).

• Why Surface Area/volume Matters: The surface area to volume ratio scales as L²/L³= L^-1. Small animals have a very high SA/V ratio, resulting in rapid cooling rates and forcing them to consume significantly more energy per gram of tissue to maintain core temperature. Large animals have a small SA/V ratio, retaining heat effectively and maintaining a steep temperature gradient above ambient surroundings.