BIOL 446 Final (Non-Cumulative Portion)

Ionoregulation - ionoregulator vs. ionoconformer

Ionoregulation: maintaining a fairly constant concentration of individual inorganic ion species independently of changes in the external environment. - The total extracellular inorganic ionic [ ] of ionoregulators can be in eq'm with seawater, but certain individual ions will not be in eq'm with seawater. Conformer- change to match environment Regulator- regulate ion [ ] interior

What component of respiratory pigments bind oxygen?

Iron or copper containing heme groups

How does the crosscurrent mechanism in bird lungs increase efficiency of respiration?

cross-current mechanism - air comes in and circles around parabronchi (keeps MB up, and O2 levels)

What adaptations enable marine mammals and birds to maintain activity while diving (e.g., bradycardia, peripheral vasoconstriction, etc.)?

diving animals: higher blood volume, myglobin, hematocrit, body size, smaller lungs - can physiologically control the release of red blood cells stored in their unusually large spleen during diving - exhale forcefully before diving - lung cavity is compressible by pressure, which causes alveoli to collapse, thereby keeping blood and air separate (no mixing) --> helps prevent N2 from dissolving into the blood under high pressure, which would lead to "the bends" and nitrogen narcosis - Undergo bradycardia - heart rate falls dramatically (when moving deeper, helps conserve energy, don't need high HR due to peripheral vasoconstriction- reduce blood flow to parts of body that don't need it) - Undertake peripheral vasoconstriction - blood flow is reduced by about 80% in tissues other than the most necessary organs - Regional hypothermia and hypometabolism -- Peripheral tissues (skin, blubber, and some organs) are allowed to cool -- Metabolic rate of cooled and vasoconstricted tissues is considerably reduced, thereby conserving O2

Cutaneous gas exchange and its role in respiration

gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs may be the sole method of gas exchange, or may accompany other forms, such as ventilation amphibians

Fish lungs? Lungs in amphibians and reptiles? Mammalian lungs?

i) Lungs when they exist are simple sacs with only minor subdivision and invaginations at best - Have low SA that does not support high levels of aerobic activity ii) The fish swim bladder appears to be homologous to the lung Amphibians: NO lungs or lungs with only a small degree if subdivision and invaginations usually more than the lung in lungfish. - use a buccal force pump (like fish) to ventilate the lungs Reptiles: modest degree of lung subdivision and invaginations, but they are still not highly aerobic organisms - use a suction pump system to draw air into their lungs (similar to mammals, but less efficient since no diaphragm is present) - Breathing essentially involves swallowing air into their lungs Mammal lungs: highly branched and invaginated - respiratory surface is ventilated using a negative pressure system with a diaphragm - Lung vol and body mass 1:1 ratio - Air flow is bidirectional over the respiratory surface, as it is in any animal that has a lung - capable of supporting higher levels of aerobic metabolism and scales directly with mass

Why then does winter air have such a drying effect on us?

i) we heat up air as we inhale - As cold air is heated, its capacity to hold water greatly increases - Our short snout and poorly invaginated nasal turbinates are incapable of reclaiming that water vapor ii) vapor pressure at the skin surface (36oC and about 100% RH) is greater that in the surrounding air (20oC and about 10-20% RH) - Thus, the resistance to evaporation is low --> more moisture evaporates from your body

Adaptive differences in regulating water balance among plants that are mesophytes, xerophytes, hydrophytes, and halophytes?

mesophytes: terrestrial plants that survive in neither too dry nor too wet conditions (i.e., a plant needing only a moderate amount of water) a. Live where there is an adequate, fairly consistent supply of water. b. They can easily compensate for water lost by transpiration through absorbing water from the soil. --i) Transport of water absorbed by roots from the soil and upward through the xylem occurs in part via transpiration through stomata in the leaves. c. Transpiration also functions to cool the plant when it gets to hot. d. Although stomata are open during the day, they can respond to a short period of water stress (i.e., dry conditions) by closing the stomata during the day. e. Their response to long period of water stress (e.g. drought or freezing temperatures) is to shed leaves to prevent water loss via transpiration and produce seeds that remain dormant until condition for germination are favorable. f. A waxy cuticle coating of leaves also helps to prevent water loss. g. Includes most tropical and temperate zone terrestrial plants including most agricultural crops, fruits and vegetables, grasses, and all the native trees, shrubs, flowers and other plants we see in Pennsylvania. xerophytes: Plants that can survive in dry habitats (e.g., deserts, tundra, alpine etc.) because they are able to withstand prolonged periods of water shortage. b. Includes some pines and most succulent plants (e.g., cacti). Succulants can store water in the vacuoles of large parenchyma tissues. c. Produce seeds with hard, resistant testas (seed coat). d. They utilize a wide range of adaptations to reduce water loss, which are described as follows. ---i) Root system is deep and extensive. Some have an underground organ/tuber that can survive long periods of drought or cold. ---ii) Usually have a short reproductive cycle due to the brief occurrence of rainfall or warm period. ---iii) Leaves are small and fleshy with reduced number of stomata, the plant has fleshy stems instead or in addition to leaves, and/or leaves are reduced to needles, spines or scales. ---iv) All above ground parts of the plant are covered in thick waxy cuticle to decrease water loss from epidermis via evaporation. Many have shiny cuticle to reflect sunlight and prevent overheating. ---v) Sunken stomata allow water vapor to accumulate in grooves around them, thereby decreasing outward diffusion of water. ---vi) Stomata close in the daytime and open at night to reduce evapotranspiration. ---vii) They often have trichome-like hairs on the epidermis. hydrophytes: Plants that grow in very wet, damp terrestrial habitats (e.g., swamps, bogs), grow on fresh water habitats (e.g., rice, water lilies, lotus, water cress, duck weed), or grow submerged mosly or completely in fresh water (Eel grass, horn wort, jungle val, waterweed, cattails). b. Water, nutrients and dissolved gases are absorbed by the whole surface of the plant directly from the surrounding water, especially if submerged. c. Many have leaves with hydathodes, a type of secretory tissue in leaves that secretes water through pores in the epidermis or margin of leaves c. The xylem are poorly developed (don't need as much), the root system is reduced, they have little or no stomata, and they have little cuticle on leaves, especially if submerged d. Most have little lignified tissue (don't need) ; i.e. little sclerenchyma tissue (hard, woody cells that serve the function of support in plants). e. Often have air spaces formed by spongy aerenchyma tissue between cells of leaves and stems to help with floatation and providing an internal atmosphere for gas exchange. ---i) aerenchyma ("air tissue") enables the plants to live in standing water by allowing transport of oxygen into the submerged roots. - Roots with little or no aerenchyma, or open space, require more energy and nutrients to maintain, which limits how long they can grow. - Roots with more aerenchyma have lower metabolic costs and can therefore grow longer to reach water and nutrients. halophytes: Plants that grow submerged in waters of high salinity (sea grass, kelp and other algae) or come in contact with saline water through the roots (mangroves, salt marsh grasses) or by salt spray. a. Halophytes have several adaptive features that help them cope with saline soil. (submerged or partially submerged, will drink water, like marine, stomata act more like xerophytes) ---i) Absorb/drink seawater and transpire via sunken and reduced stomata ---ii) Special root cells accumulate salts via active transport thereby becoming hyperosmotic to their surroundings (i.e., soil or seawater) which allows them to absorb water via osmosis. ---iii) Leaves have salt glands (all in one place) and glandular trichomes that actively secrete the excess salt taken in by the roots. ---iv) The excreted salt often forms a white powdery substance on the surface of the leaf. This material is used by some species (e.g., glasswort, cord-grass, mangrove, etc.) to trap water vapour from the air, which is absorbed by leaf cells. Therefore, this is another way of obtaining additional water. ---v) Leaves are often succulent with a thick layer of cuticle and sunken stomata. ---vi) Some halophytes show viviparity where seeds germinate while attached to the parent. ---vii) Halophytes (and hydrophytes such as cypress) that live in oxygen poor soil (e.g., mud) have pneumatophores (only ones that have lenticels in their roots) that grow above the soil surface so they can absorb oxygen for the roots via lenticels (acquire O2, involved in gas exchange in xylem and phloem, almost all plants have some lenticels- mesophytes, halophytes, hydrophytes). Only hydrophytes (use hydathodes) and halophytes (use root cells, trichomes, etc.) have specific osmoregulatory organs

How do elasmobranchs, Chimaeras, coelocanths and marine frogs regulate osmolarity of their body fluids?

osmoconformer and ionoregulator i) Elasmobranches (cartilaginous fish; e.g., sharks, rays and skates) and coelocanths (see Fig. 11.35 above). ii) Sharks and rays have ionic levels more similar to those of other vertebrates, such that the concentration of Na+ and Cl- are less than half of that in seawater. iii) However, the total blood osmotic concentration is nearly equal to that of seawater. iv) The "osmotic gap" (osmotic deficit) is filled (restored) by incorporating high levels of organic material into the blood. v) Urea and a special osmotic effector molecule called trimethylamine N-oxide (TMAO) are used to establish osmoconformation. vi) Thus, elasmobranches are largely osmoconformers, but must be strong ionic regulators (ionoregulators). vii) Only three other marine vertebrates use urea and trimethylamine N-oxide (TMAO) to be osmoconformers in seawater: Chimaera - a cartilagenious fish Coelacanth - a living fossil close to the root of tetrapods and lungfish, and only distantly related to other fish. Crab-eating frog (Fejervarya cancrivora) of Southeast Asian mangrove swamps

Role of stomata in water balance in plants

stomata are important in regulating water loss through evapotranspiration (allows movement of water from the roots to the rest of the plant) (openings in leaves through which plants acquire O2, lose H20) Most plants (except most xerophytes) require the stomata to be open during daytime. The problem is that the air spaces in the leaf are saturated with water vapor, which exits the leaf through the stomata. Therefore, plants cannot readily gain carbon dioxide without simultaneously losing water vapor.

Osmolarity

total concentration of all dissolved solutes (i.e., inorganic ions and small organic molecules or ions) per unit of volume. The osmole (Osm or osmol) is a unit of measurement that defines the number of moles of solute that contribute to the osmotic pressure (tonicity) of a solution.

How is ionoregulation performed in certain plants

vacuole is crucial in regulating the concentration of solutes in the cytoplasm

Summary of the major vertebrate respiratory systems Fish Gills? Mammalian lungs?

Fish Gills: i) Unidirectional flow of the external environmental media (i.e., water) over the gills. ii) Counter current exchange of gasses between the external environmental media and the blood in the gill lamellae. Mammalian lungs i) Bidirectional flow of the external environmental media (i.e., air) over the lungs. ii) Unidirectional exchange of gasses between the external environmental media and the blood. - Alveoli provide a large respiratory SA but do not permit counter or cross current exchange Bird lungs i) Unidirectional flow of the external environmental media (i.e., air) over the lungs. ii) Cross current exchange of gasses between the external environmental media and the blood in the air capillaries of the parabronchi

Maternal vs, fetal hemoglobin

Human fetal Hb has a higher affinity for O2 than maternal Hb. Therefore, fetal Hb can always take up O2 from maternal blood across the placenta.

Function of hydathodes in water balance of certain plants

Hydathodes are structures containing water pores located at leaf margins that connect to the intracellular spaces and to the xylem vascular system Under conditions of water uptake and limited transpiration, such as warm soils and high humidity in the dark, liquid is expelled through the hydathodes in a process termed guttation.

Adapations of invertebrates in hypersaline water

Hypersaline invertebrates a. Artemia (brine shrimp) live in water with salinity up to 8x sea water (e.g., Great Salt Lake). i) Drink lots of water to replace efflux. ii) Use active transport excretion of salts via gland (nymph) or swimming appendages (adult). iii) Spend a large fraction of their total metabolism (> 33%) on osmoregulation, but energy availability is high and costs are easy to meet

Difference among the terms hypoxia, hyperoxia, anoxia, and hypercapnia Oxygen conformers vs. regulators

Hypoxia - temporary or permanent low level of O2 Anoxia - complete absence of O2 Hypercapnia - elevated levels of CO2 (e.g., burrows, soil, other enclosed spaces) Hyperoxia - temporary or permanent high level of O2 Oxygen conformers: Metabolic rate varies in direct proportion to the concentration of O2 in the environment - tend to be sedentary, low MB - marine invertebrates Oxygen regulators: use one or more of the following means to regulate oxygen level in the body relative to its level in the environment. a. Maintain VO2 inside independently of the concentration of environmental O2 down to some critical pO2 b. Maintain VO2 by increasing ventilation rate (breathing frequency, gill flapping, abdomen pumping, etc.) c. Increase the circulation rate of O2 carrying blood

Function of producing copious urine

In freshwater teleosts to create eq'm b/w water and interior --> water wants to move inside, so it is excreted

What pore structures found in plants are used in gas exchange?

Lenticels Stomata

What adaptations of mangroves help them perform osmo and iono regulation?

Salt sequestration Salt secretion

Acid rain and its causes

"Acid rain" is a popular term referring to the deposition onto the land or water of wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components Caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air --> can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain

Osmotic gap and the role of osmotic effector molecule in marine animals

"Osmotic gap" is the total solute concentration of the remaining solutes (i.e., other than the major ones) Ca2+ = effector --> enhances O2 affinity

Why is the P50 for myoglobin so much lower than that for hemoglobin?

(Differences in Hb-oxygen affinity among species is due to differences in amino acid sequence of the globin molecules) A convenient measure of oxygen affinity is P50, which is the partial pressure of oxygen at which one-half of the heme groups have bound oxygen. ****Lower P50 higher O2 Affinity****

Differential roles of ventilation and circulation when oxygen levels decline or under hypoxic conditions How aquatic or terrestrial animals handle variable or low oxygen levels

**Ventilation allows o2 acquisition directly (most beneficial), circulation uses too much energy when moving blood and O2 around* Increase ventilation and blood circulation rates

What is a boundary layer?

Layer of reduced velocity in air or water immediately adjacent to the surface of a solid past which the air or water is flowing

What are the two of the means by which osmosis of water can occur in biological organisms?

--

Scaling effects on respiration via diffusion and convection

1. Convective mechanisms are necessary because diffusion is very slow when distances are large. 2. Fick's laws of diffusion: rate of diffusion of a solute or a gas from regions of high concentration to regions of low concentration is proportional to the concentration gradient. - Rate of diffusion α surface area (A) for exchange. - Rate of diffusion is inversely proportional to the distance away from the source of high molecule concentration. -- One consequence of this relationship is that diffusion does not work rapidly over large biologically relevant distances -- Small (less than a few mm in diameter) inactive organisms depend primarily on diffusion and tend to be oxygen conformers -- Large and active organisms depend primarily on convection (e.g., ventilation) and tend to be oxygen regulators 3. The extent of SA used for gas exchange with the surrounding environment is associated with the animal's way of life (i.e. active fish maintain a higher gill SA than sluggish fish) - For adequate gas exchange in water (recall O2 availability in water is much lower than in air), a high rate of water flow and close contact between water and gill surface are necessary **Scaling of respiratory (gill or lung) surface area (SA) is α M^0.75 (M¾)**

What does the leftward shift of the hemoglobin oxygen binding curve tell us about the affinity of hemoglobin for oxygen?

Leftward shift means Hb has a higher affinity for O2

In aquatic or amphibian ectotherms, why would CGE play a more important roll in respiration at low temperatures than that of lungs or gills?

A. Oxygen demand is less at low temperaturesbecause metabolic rate decreases with temperature C. Ability to perform convection (e.g., ventilation) decreases with temperature just like that of general mobility

What are the primary differences between marine invertebrates and nearly all marine teleosts?

A.Nearly all marine teleosts are osmo and iono regulators, while marine invertebrates are largely osmo and iono conformers B.Nearly all marine teleosts have body fluid that is hypoosmotic to their external environment, while marine invertebrates have body fluid that is largely isosmotic to their external environment.

Function of abscisic acid

Abscisic acid (ABA) is an important hormone in helping plants to conserve water. It causes stomata to close and stimulates root growth so that more water can be absorbed. (Necessary when nutrients are low, hypoxia, drought → need more roots or longer roots to find water)

Functions of pneumatophores, prop roots and buttresses

All of these structures enhance above ground surface area near root tissues to ensure an adequate O2 supply below ground - Prop roots also provide support that helps reduce the effect of wave action that can scour away soil during a storm. pneumatophores are like snorkels for roots Buttressed roots provide expanded surface area to deliver oxygen to its roots in hypoxic conditions.

Role of teleost kidneys and gills in osmoregulation

All other marine vertebrates must osmo and iono regulate e.g., teleosts (bony fish), cetaceans, and marine tetrapods (land living vertebrates). 1. Ionic and total osmotic concentrations inside their bodies are much lower than seawater (hyposmotic relative to seawater). 2. They face constant water loss and salt gain. 3. Marine teleosts cope with the inward passage of salts and outward passage of water as follows. a. They must drink copiously in order to keep up with water loss, but that means that they are also taking in copious amounts of ions. b. Uptake (70-80%) of this water and univalent ions (Na+, K+, Cl−) from the imbibed seawater occurs through the gut wall, particularly the esophagus. However, there is minimal gut uptake of divalent ions (Ca2+, Mg2+, SO42−), which are passed with the feces and urine. c. Most of the excess univalent ions absorbed in the gut are eliminated via special chloride cells in the gill surface by a process that creates ionic charge (electrochemical) gradients by using the Na+/K+/2Cl− cotransporter to move a sodium ion (Na+), a potassium ion (K+) and two chloride ions (2Cl−) into the cell. The Cl− move down its concentration gradient to exit the cell via a chloride channel to the seawater. The K+ move down their concentration gradient to exit the cell via a channel to the blood. A Na+/K+ active pump uses ATP to move the Na+ up its concentration gradient to the blood. (Passage of Na/Cl inside → out) d. Varying levels of cutaneous transport in the gill and body skin aided by an electrochemical gradient also help eliminate excess univalent ions. e. Excess divalent salts are excreted through the kidney, via an isotonic urine in which the concentrations of Mg2+ and SO42− are unusually high. f. Urine volume is rather low, and the glomeruli are reduced in number, sometimes even lacking (where urine is produced by secretion rather than filtration). 4. The fluid retained by the kidneys restores the balance of the blood and is hypotonic to both the ingested seawater and the urine. Marine teleosts are essentially distilling seawater in their bodies. 5. Marine teleosts also use the gill epithelia as a major route for excretion of nitrogenous wastes, with NH3 (ammonia) and NH4+ (ammonium) leaking passively outwards. 6. A somewhat similar process occurs in elasmobranches where salt influx is countered by active transport of ions by rectal glands and gills.

Root effect vs Bohr effect

Bohr effect: The oxygen binding affinity of Hb is inversely related both to acidity and to the concentration of carbon dioxide - Magnitude of the Bohr effect increases with increasing Hb concentration, increasing temperature, increasing pH, and/or increasing ionic strength of plasma. Root effect: an extreme rightward shift resulting from increased CO2 or decreased pH that results in incomplete saturation at high pO2. - appears to be an exaggerated Bohr effect - occurs in teleosts where it plays an important role in secretion of oxygen into the swim bladder (i.e., delivery of O2 for a buoyancy function rather than a metabolic function)

What is a major source of sulfur dioxide (SO2) and nitrogen oxides (NOx) currently entering the Earth's atmosphere?

Anthropogenic fossil fuel burning

What do the oxygen dissociation/affinity curves for respiratory pigment molecules tell us about their function in oxygen transport?

As a monomer, Mb shows a hyperbolic dissociation curves (i.e., oxygen equilibrium curves), suggesting that Mb has a high affinity for O2 --> transports O2 to muscles - Mb picks up O2 from Hb at low PO2 (resting tissues) and it does not release O2 until PO2 is very low (working tissues), thereby forming an oxygen storage pool within muscle. The binding of oxygen at one site of the tetrameric Hb facilitates the binding of oxygen at other sites --> results in a sigmoid dissociation curve --> determined by the affinity of Hb for oxygen *High alt or low O2 env. = Greater binding affinity for O2 (pO2 is lower)* i.e. lama high alt env

Effect of acid rain on osmoregulation

As it flows through the soil, acidic rain water can leach aluminum from soil clay particles and then flow into streams and lakes decreasing fish's ability to take in oxygen, salt and nutrients The pH of water decreases and aluminum levels increase creating toxic water to fish Acid molecules in the water cause mucus to form in their gills and this prevents the fish to absorb oxygen *Especially important for freshwater fish

Ecological importance of mangroves

Beneficial effects of mangroves on the marine/estuarine ecology i) Form the base of a complex marine food chain ii) Create breeding habitat that offers protection for maturing offspring iii) Filter and assimilate pollutants (e.g., nitrate and phosphates) from upland run-off, thereby improving water quality iv) Stabilize bottom sediments in coastal areas v) Protect of shorelines from erosion (e.g., 2004 Indian Ocean tsunami) Mangrove adaptations of interest i) Salt exclusion via active transport in roots. Some species can exclude more than 90% of the salt in seawater. ii) Salt tolerance: total osmolarity of mangrove extracellular fluids is about 250 mOsm. Non halophytic plants cannot withstand this level of salinity. iii) Salt secretion: like most other halophytes mangroves have salt glands on the underside of their leaves that excrete salt in nearly solid form. iv) Salt sequestration: most mangroves store salt in specialized cells in older leaves and bark. Shedding these leaves is a way of eliminating salt. v) Viviparous (bringing forth live young): mangroves produce seed that germinate (called propagules) while still attached to the parent, where the seedling is not exposed to growth inhibition by high salt concentration. vi) Seedling dispersal: mangrove seedlings float horizontally in full strength seawater, but the root end sinks in brackish water. vii) Prop roots and pneumataphores Estuarine sediments are frequently anoxic, thus threatening oxygen supply to mangrove roots. Solution = prop roots buttresses pneumataphores

What molecule in the freshwater teleost figure results in the excretion of water from chloride cells to the external environment?

Bicarbonate

Bulk water and its role in osmotic pressure and cellular ion concentrations

Bulk water: water not bound to charged molecules and free to function as a solvent. - There is little bulk water inside cells (most is bound or structured by charged molecules to form a hydration shell). There are 16 molecules of water associate with a sodium ion (Na+), whereas 10 molecules of water associate with a potassium ion (K+). The smaller hydration shell of K+ allows it to more readily leak into cells thereby establishing a higher concentration inside than out compared to Na+. Note that the osmotic pressure (OP) stays the same (intra vs. extracellularly) despite differences among compartments in levels of individual inorganic ions. It is better to have K+ inside cells than Na+ because K+ has a lower charge density and therefore structures less water (i.e., has a smaller hydration shell) and leaves more water free to be an effective solvent.

Cutaneous gas exchange in relation to size and role of lungs in amphibians and fish

Cutaneous gas exchange (CGE): gas exchange across the exterior body surfaces (also called cutaneous respiration) - mostly through skin in verts - works in both air and water, but requires the skin to be thin, moist and highly vascularized to be effective CGE by small inactive invertebrates (e.g., planarians, nematodes, young sponges, insect endoparasitoids, chironomids, flatworms, etc.). - Simple diffusion of O2 through the body surface directly to tissues in sufficient, so no circulatory system is needed - The diffusion barrier consists of both of the following factors: 1. Thickness of the respiratory surface 2. Thickness of the unstirred boundary layer of the respiratory medium (usually O2 depleted) immediately adjacent to the respiratory surface Boundary layers may account for 80-90% of the total resistance to diffusion in aquatic situations, so they may limit gas exchange in water **Not important in air due to the much faster rates of diffusion compared to that in water** *Bigger boundary layer, longer the diffusion is* CGE by large invertebrates (e.g., older/larger sponges, coelenterates, coral, jellyfish, etc.). - may also depend on simple diffusion across the integument, in association with internal channels though which water may pass so that diffusion distances to the cells are greatly reduced. CGE by complex Invertebrates (e.g., aquatic insect larvae, echinoderms, earthworms and other annelids) i) Some lack specialized respiratory structures. ii) Cutaneous respiration is accompanied by the appearance of a circulatory system that functions to transport gas from the skin to the tissues. iii) Blood vessels close to the skin surface pick up the O2 and carry it to the tissues. iv) Body size no longer limits O2 diffusion to the tissues. v) Cutaneous gas exchange (CGE) remains important, even in those groups of invertebrates with specialized respiratory structures. It may account for 20-50% of total gas exchange in these organisms. CGE by vertebrates i) Many fish, amphibians and a few reptiles rely to a variable extent on CGE, although a small degree of CGE is present in essentially all vertebrates. ii) CGE is trivial in most birds and mammals, accounting for less than 1-2% of total gas exchange, except in bats, which may lose up to 12% of their CO2 through their wing membranes under certain conditions. iii) CGE may account for 50% of O2 uptake in some fish. iv) Virtually all amphibians rely on CGE to some extent. Some salamanders (Plethodontidae) lack lungs entirely and depend to a great degree on CGE (supplemented with vascularized mouth regions). v) Relative importance of skin and lungs or gills for respiration changes with temperature in aquatic or amphibian vertebrates, which are ectotherms. **CGE is more important at low temperatures. **Lungs or gills are more important at high temperatures. Result is seasonal differences in the relative importance of respiratory structures.

Oxygen availability versus altitude

Decreasing O2 with altitude (incr) - not in percentage (20.95% is constant no matter what the altitude up to about 100 km) but in volume of O2 with per volume (i.e., liters) of air, number of molecules of O2 per volume of air, or partial pressure as total air pressure declines with altitude pO2 = FO2 x Pb , where pO2 is oxygen partial pressure, FO2 is the fractional concentration of O2 (0.2095) and Pb is total atmospheric pressure

Role of thermal water pollution on the availability of oxygen to ectotherms What does partial pressure of a gas refer to?

Ectotherm mortality is the main danger of thermal pollution (from power plants, waste water treatment facilities, decreased stream shade, and urban/suburban rainwater run off, etc.) in streams and rivers - Mortality due to "high" temperature occurs because the metabolic rate of ectotherms increases with temperature at the same time that oxygen availability is decreasing the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own

How do terrestrial organism obtain water in dry environments?

Ectotherms: - Avoid dry habitats (stay under cover along soil surface or below surface) - Store water - Build a water-proof mucus cocoon (e.g., lungfish) - Find scarce water (e.g., dig, drink dew drops) - Avoid using evaporative cooling - Excrete highly concentrated urine or excrete nitrogenous waste as uric acid in exceedingly dry feces - Absorb water from unsaturated air (arthropods only; Namib desert beetle, Stenocara gracilipes) Endotherms: i.e. banner tail kangaroo rat - nocturnal: active during the coolest time period. - dig a complex burrow (acts like nasal turbinate) - nasal turbinates - recover about 50% of respiratory water loss from the lungs - no sweat glands and fairly impermeable skin (minimizes water loss from the body surface) - *excrete dry fecal pellets* - *recover metabolic water* - produce highly concentrated urine

What is hypercapnia?

Elevated level of CO2

What is counter current exchange in some respiratory systems?

Exchange of gases between an external solution and an internal solution flowing in opposite directions

What is cross current exchange in avian respiratory systems?

Exchange of gases between convected air and blood flowing at right angles to each other

Gills and gill ventilation

Gills - Animal must provide a flow of water over the gill surface, otherwise water at the gill surface would be rapidly depleted of O2 because diffusion in water is relatively slow - Flow of water over the gill is accomplished in two ways i) Moving the gill through the water - used by small aquatic invertebrates (e.g., aquatic insect larvae) and amphibians with external gills (when in still water) ii) Moving water over the gills (i.e., ventilation) - This can be accomplished by living in moving water (e.g., streams) or by one of the following three methods in still water. Ciliary Flow: cilia create water currents; used in mollusc gills. Pump-like Action: water is pumped over the gills; used by fish, crabs, and some worms in tubes and burrows. Ram Ventilation: swimming thorough water with the mouth open; used by tuna, mackerel, sharks, and paddlefish. Gill Surface Area is associated with the animal's way of life. For example, active fishes maintain a higher gill surface area than sluggish fishes. For adequate gas exchange in water (recall O2 availability in water is much lower than in air), a *high rate of water flow and close contact between water and gill surface are necessary*

How does countercurrent gas exchange in gills increase efficiency of respiration?

Gills lie under a bony plate = operculum (opens to the outside) - provides protection and allows sufficient flow of water over the gills Extraction of O2 at the gill lamellae (vascularized) involves countercurrent exchange between the water and blood in the gills that flow in opposite directions --> increasing efficiency and degree by which O2 is extracted (diffusion) from the water

Differences between hemoglobin and myoglobin in their roles in oxygen transport Hemocyanins?

Hemoglobin (Hb); iron-containing oxygen-transport metalloprotein. - exists in two forms, a taut (i.e., tense) form and a relaxed form --> high pO2 favors the relaxed (high affinity) state - low pO2 (e.g., in respiring tissues) favors the taut (low affinity) state - O2 binds to Fe in Heme group - Nearly all vertebrate hemoglobins have 4 subunits (each with heme + globin). *The heme group binds the oxygen* - Some hemoglobins have special adaptations such as ability to bind and transport sulfate (chemoautotrophs) Myoglobin (Mb), a form of Hb found in muscle cells of many vertebrates (nearly all mammals) - contains only one subunit (it is monomeric) **Each subunit has one O2 binding site (e.g., a heme group) Hemocyanins: copper-containing oxygen-transport metalloprotein. - Unlike hemerythrins and hemoglobins, hemocyanins are not bound to blood cells but are instead suspended directly in the blood

What means are used to obtain oxygen when oxygen regulators experience hypoxic conditions?

Increase ventilation (and blood circulation rates?)

Which direction does a freshwater fish need to pump water?

Inside to outside saltier inside → water rushes in --> must use ATP pump to get water out

Intracellular vs. extracellular fluids

Intra: within cells Extra: surrounds cells in body - composed of plasma and interstitial fluid

What is the Bohr effect?

Inverse relationship between oxygen binding affinity of Hb and the acidity and concentration of carbon dioxide in the blood

Isomotic versus hyperosmotic versus hyposmotic

Isosmotic: extracellular fluids of an organism have the same osmolarity as the surrounding environment. Hypoosmotic: extracellular fluids of an organism have a lower osmolarity than the surrounding environment. Hyperosmotic (hypertonic): extracellular fluids of an organism have a higher osmolarity than surrounding environment.

What happens when water undergoes diffusion via osmosis?

It moves passively across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration

Adaptive consequences of oxygen binding by hemoglobin and low PO2 in certain environmental conditions (e.g., altitude, hypoxia, etc.)

Long-term adaptation to high altitude a. Increased elevation results in decreased pO2. b. Species that live at high altitude often have locally adapted Hb with a higher oxygen affinity (i.e., decreased P50) relative to low altitude species. c. This higher affinity allows increased oxygen loading of Hb in the lungs, but this increased affinity means that Hb is more reluctant to unload O2 at the tissues. d. The net result is delivery of oxygen at levels similar to that in organism living at low altitudes. f. High altitude species often show increased red blood cell (hematocrit) and hemoglobin concentrations; both increase oxygen carrying capacity. i) Humans native to high altitude show 5-15% increase in hematocrit and 10-20% increase in hemoglobin concentration. Acclimation to high altitude causes some of these same effects (i.e., altitude training, the effect mimicked by "blood doping"), but they are temporary. ii) Some lizards also show increased hematocrit and hemoglobin concentration at moderately high altitudes. Burrowing a. Burrowing animals often experience chronic hypoxia and hypercapnia. b. These animals also tend to have Hb with relatively high oxygen affinity as an adaptation to low oxygen levels in burrows.

Role of blood condition in oxygen loading in the respiratory organ (e.g., lung, gill) vs oxygen unloading in the tissues

Low pH and high CO2 at the level of the tissues favor the taut form, which has low oxygen affinity and releases oxygen in the tissues (i.e, rightward shift in the dissociation curve) Conversely, a high pH and low CO2 favors the relaxed form, which has a higher oxygen affinity and can better bind oxygen in the lungs (i.e, leftward shift in the dissociation curve)

Fish that live in hypoxic conditions?

Lungfish are the most adept at supplementary air breathing (some are obligate air-breathers), but they still can't support high levels of activity this way because their lings have a low surface area compared to the lungs of terrestrial vertebrates. i) The lungfish lung is a simple vascularized pouch off of the esophagus. Gulps of air are swallowed to fill this lung. ii) A system of valves can shunt blood circulation either to the gills or to the lung, thereby allowing respiration in either air or water. iii) During extreme drought periods, when the ponds they are living in dry up, African lungfish will aestivate (dormant state) within a mucous case. They may survive in this state for five years or more, until the ponds fill up again. iv) Partial mucous-mud membrane around an aestivating lungfish.

Osmoregulation in invertebrates - salt vs. fresh water

Marine invertebrates a. They are near osmotic equilibrium with seawater. b. Ion gradients tend to be small (about 0.2x less than seawater). c. Thus, relatively little energy is spent on ionoregulation. d. They come close to being osmo and iono conformers. e. Molluscs and crustaceans use amino acids and other methylamine compounds (e.g., betaine and taurine) as osmotic effectors. Brackish water (estuarine) invertebrates a. Show a wide range of strategies including fairly good osmoregulation. b. euryhaline vs. stenohaline

What is the primary difference between marine invertebrates and freshwater invertebrates?

Marine invertebrates are often osmo and iono conformers, while freshwater invertebrates are always osmo and iono regulators.

What animals have the ability to excrete salt in a nearly solid form like mangroves?

Marine tetrapods (e.g., Galapagos iguana)

What is a major difference between mesophytes and xerophytes besides where they can live?

Mesophytes keep stomata open in the daytime to allow transpiration, while xerophytes keep them open at night to reduce evapotranspiration

Structure and functions of nasal turbinates

Nasal turbinates are convoluted structures of thin bone or cartilage located in the nasal cavity an organ used by mammals and birds to *recover heat and water* from expired air in the nasal passages - The bone or cartilage is lined with heavily vascularized tissue and mucous membranes that can warm and moisten inhaled air, and extract heat and moisture from exhaled air to prevent desiccation of the lungs. *more convoluted turbinate = more gradual temperature gradient from inside to outside (vice versa) --> resulting in increased water and heat recovery* also improve the sense of smell by increasing the area available to absorb airborne chemicals

Adaptations in terrestrial animals that reduce water loss via the body surface and excretion

Nasal turbinates reduce water loss - Wider noses are more common in warm-humid climates, while narrower noses are more common in cold-dry climates. altering permeability of body: permeability of the wax layer increases sharply if the wax melts (this applies to plants) Hardened mucus is better in environments that reach high ambient temperatures

In addition to oxygen, what element comprises most of the remaining air at sea level?

Nitrogen

Can organisms in freshwater be osmoconformers?

No

Marine vertebrates can be:

Osmo and ionoconformer (Hagfish) osmoconformer and ionoregulator (Sharks and rays) All other marine vertebrates must osmo and iono regulate (teleosts)

Osmoregulation - osmoregulatory vs. osmoconformer

Osmoregulation: maintaining a fairly constant concentration of total dissolved solutes independently of changes in the external environment. - Osmoregulation affects water flux, or tonicity Organsims living in seawater are *hypoosmotic* relative to their environment. Organsims living in freshwater are *hyperosmotic* relative to their environment. Osmoconformer - osmolarity inside = outside - Example osmoconformers: hagfish, sharks, marine invertebrates, etc. Osmoregulator - osmolarity inside ≠ outside **Organisms can be osmoconformers, osmoregulators, ionoregulators, or both an osmoregulator and ionoregulator, or both an osmoconformer and an ionoregulator

Oxygen availability in air versus water

Oxygen availability in water (5-8 L) is much lower than it is in air (9 L) at sea level Lower viscosity of air = convection much easier saturation constant in rivers and lakes in mountainous areas is usually lower than in lowlands, because it is pressure dependent

Active, passive, and facilitative transport in osmoregulation

Passive diffusion: water Facilitated diffusion and active transport: ion movement Facilitated diffusion requires protein-based channels for moving the solute Active transport requires energy in the form of ATP conversion, carrier proteins, or pumps in order to move ions against the concentration gradient.

What adaptation is used by diving mammals and birds to concentrate blood flow to essential organs during a dive?

Peripheral vasoconstriction

If respiratory SA α M^0.75 and MR α M^0.75, how does respiratory SA scale with MR? Hint: Remember that metabolic rate (MR) scales to the ¾ power of the animal's mass (Kleiber's law); MR α M0.75

Respiratory SAα MR^1.0

Difference between locomotor respiratory coupling in quadrupeds and bipeds

Running quadrupeds (e.g., horses, dogs, cheetah, etc.) use *locomotor respiratory coupling* that involves posterior-to-anterior movements of the viscera that function as a piston to assist the diaphragm in ventilation - frequency of limb movement and respiratory frequency are phase locked - Quadrupedal species (e.g., rabbits, dogs, horses, cats, etc.) typically synchronize the locomotor and respiratory cycles at a constant *ratio of 1:1* (strides per breath) in both the trot and gallop Bipeds: Human runners differ from quadrupeds by employing several phase-locked patterns (4:1, 3:1, 2:1, 1:1, 5:2, and 3:2 strides per breath), although a *2:1 coupling ratio* appears to be favored - Evolution of bipedal gait has reduced the mechanical constraints on respiration in humans, however, it has not eliminated the need for the synchronization of respiration and body motion during sustained running - Locomotor-respiratory coupling may be a vital factor in the sustained aerobic exercise of endothermic vertebrates, especially those in which the stresses of locomotion tend to deform the thoracic complex

Osmo and iono reguation of salt water teleosts vs. and fresh water teleosts

Salt water teleosts (previous) Freshwater teleosts 1. The blood freshwater teleosts has an osmotic and ionic concentration less than that of marine fish, but still much higher than surrounding water. 2. They face constant water influx and ion efflux 3. Therefore, they drink very little water and produce copious volumes of dilute urine. 4. Use ATP dependent ion pumps to actively uptake ions via the gills and reuptake ions via the kidney nephrons (e.g., compare divalent ion and water flux in marine fish kidney, Fig. 11.36 above, with that in freshwater fish kidney, Fig. 13.15 below). 5. Freshwater fish also cover as much of the body as possible with an impermeable coat, and leave much of the water exchange to special chloride cells in the gills. 6. Compared to marine fish, freshwater fish have large numbers of chloride cells that work differently than those in marine fish. a. Chloride cells in freshwater fish create ionic charge gradients by using ATP to move hydrogen ions (H+) and sodium ions (Na+) into and out of the cells as shown in the figure (red for active transport). b. In the process, chloride ions are facilitatively moved into the cell in exchanged for bicarbonate. c. The inside of the cell becomes negatively charged making it easier to actively pump H+ and Na+. move against their concentration gradients (larger inside than outside)

Role of sclerenchyma tissue

Sclerenchyma cells are strong, thick cells that provide most of the support in a plant

Role of respiratory water loss in terrestrial animal

Skin surface: amphibians, barely prominent in humans --> must develop more efficient lungs --

Oxygen solubility in fresh and saline water

Solubility of O2 is inversely proportional to salt content in water *Freshwater contains more O2*

Effect of temperature on O2 level in aquatic habitats

Solubility of gases in liquids decreases with increasing temperature (opposite the effect on solubility of solids) Increasing temperature of aquatic habitats decreases O2 availability, particularly for large active species such as fish and certain macroinvertebrates, such as mayflies and stoneflies, that are highly sensitive to low O2

Adaptations of mangroves for living in salt water and oxygen poor soil

Solution = prop roots buttresses pneumataphores

Euryhaline vs. stenohaline

Stenohaline ("steno" meaning narrow, and "haline" meaning salt) describes an organism that cannot tolerate a wide fluctuation in salinity. Euryhaline decribes organisms able to tolerate a broad range of environmental salinity - Ways to be euryhaline i) Osmoregulate (e.g., Culex, Gammarus, Carsinus, Palaeomonetes, Ligia, Artemia, Calinectes) by altering surface permeability, use ion transport mechanisms, and/or cellular osmoregulation (increase or decrease concentration of organic molecules, primarily amino acids that make up a substantial proportion of the normal cellular osmotic concentration). ii) Osmoconform, but tolerate a wide range of salinity in extracellular fluids -(e.g., Mercierella, Sabella, Mytilus). iii) Mixed strategy of imperfect osmoregulation and tolerance (e.g., Cancer, Nereis, Patella).

What factors increase evapotranspiration? Role of plant evapotranspiration

Strong winds, low humidity and high temperatures all increase evapotranspiration from leaves. loss of water via transpiration is crucial to create a driving force to move water and nutrients in the xylem from the soil to tissues Note: The phloem is involved primarily in transport of water dissolved food and nutrients, such as sugar and amino acids, from leaves to other parts of the plant.

What are the effects of pH, temperature, and CO2 on oxygen dissociation/affinity curves and P50 of for respiratory pigment molecules?

Temperature (cooler = higher affinity for O2) ****Affinity decreases with increases temperature**** - An increase in temperature weakens these bonds and favors dissociation of oxygen from Hb. An increase in temperature shifts the dissociation curve to the right pH (low pH = lower affinity for O2) ****Increasing pH increases affinity**** - Decreased pH shifts the dissociation curve to the right. ii) This shift is helpful for releasing O2 in tissues that are starting to produce lactic acid (i.e., oxygen shortage leading to anaerobiosis). CO2 (high CO2 = low affinity for O2) ****Decreasing CO2 increases Affinity**** - Increased CO2 shifts the dissociation curve to the right. - CO2 affects oxygen affinity directly by binding to Hb and altering its conformation. - CO2 indirectly affects the oxygen affinity of Hb by decreasing pH (CO2 + H2O → H+ + HCO3-). - The effect of CO2 on the oxygen affinity of Hb is helpful for releasing O2 in tissues that are working very hard. It is good for taking up O2 in the lungs after CO2 rapidly passes into the air. **Decreased affinity increases p50 value**

What are book lungs?

Term used to describe the "lungs" of arachnids (example = spiders), in which a gill like structure is housed within the body cavity of a terrestrial air breather.

What is hemoglobin cooperativity?

The binding of oxygen at one site of the tetrameric Hb facilitates the binding of oxygen at other sites, called cooperativity, and results in a sigmoid dissociation curve --> determined by the affinity of Hb for oxygen i) Binding of oxygen to the iron-II heme pulls the iron into the plane of the porphyrin ring, causing a slight conformational shift --> encourages oxygen to bind to the three remaining hemes within hemoglobin (thus, oxygen binding is cooperative) ii) The Hb dissociation curve relates oxygen saturation and partial pressure of oxygen in the blood (pO2).

Hagfish adaptations

The hagfish unique amongst marine vertebrates in having blood much like seawater (i.e., it is an osmoconformer and mostly an ionoconformer) Hagfish blood has a concentration of Na+ and Cl- that makes it slightly hyperosmotic relative to seawater

What environmental factor most affects the availability of oxygen to ectotherms in aquatic biomes?

Water temperature

How does convection of air occur in birds?

They have a complicated air sac respiratory system that uses a bellows (kind of like bagpipes) to constantly generate a unidirectional airflow of high, 21% oxygen containing air over finely subdivided and invaginated lungs. ii) Gas exchange occurs in air capillaries, which open to a parabronchus, through which air passes in only one direction. iii) Blood flow in the avian lung is via a crosscurrent mechanism relative to airflow. This mechanism functions similar to a countercurrent system and is highly efficient for O2 extraction. In crosscurrent exchange, air passing through air capillaries and blood moving through blood capillaries generally travel at right angles to each other in what is called cross-current flow. Bidirectional system of air sacs cross-current mechanism - air comes in and circles around parabronchi (keeps MB up, and O2 levels) iv) The bird respiratory system is capable of supporting the very high levels of aerobic metabolism associated with flight in birds. v) It also allows normal activity at high altitudes Bird respiration: https://www.youtube.com/watch?v=kWMmyVu1ueY

Why do hydrophytes have little sclerenchyma tissue?

They rely on the density of water and buoyancy provided by aerenchyma tissue for support

What change in direction of chloride ion movement must occur in chloride cells when salmon move from saltwater into freshwater?

Water to chloride cells to blood Other way??

How do insect tracheae increase efficiency of respiration?

Tracheae: System of internal tubes connected to the outside via a valve-like spiracle ii) Used by terrestrial arthropods such as insects, scorpions, some arachnids, ticks, millipedes, centipedes, and onchyophorans (velvet worms). iii) *They feature complex tubular arrays that, supplemented by air sacs, deliver gases directly to all cells within the body via primarily diffusion* iv) Insect trachea and air sacs are often autoventilated by movements of the muscles and exoskeleton or purposeful ventilation by abdominal pumping. Autoventilation and purposeful ventilation couples increased muscular demand with increased exchange. v) Openings to the tracheal system are the spiracles, whose aperture can be varied with respect to width and opening rate (e.g., fluttering) to limit water loss.

What is unidirectional airflow?

Unidirectional flow means that air moving through bird lungs is largely 'fresh' air & has a higher oxygen content

Vapor pressure Vapor pressure deficit Saturation vapor pressure

Vapor pressure is a measurement of the amount of moisture in the air. It is technically the pressure of water vapor above a surface. When air reaches the saturation vapor pressure, the water vapor in it will condense. Vapor pressure deficit is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. Once air becomes saturated water will condense. The saturation vapor pressure is the pressure of a vapor when it is in equilibrium with the liquid phase. It is solely dependent on the temperature. As temperature rises the saturation vapor pressure rises as well. An example: If you fill a glass jar half-full of water and put the lid on it, the process of evaporation in the jar will proceed until there are as many molecules returning to the liquid as there are escaping into the jar above the water. At this point the vapor in the jar above the water is said to be saturated, and the pressure of that vapor is called the saturated vapor pressure.

Water vs. air breathers in osmoregulation

Water breathers (e.g., gills) - always need to have contact with fluid - unavoidable water and ion flux across the exchange surface resulting in osmoregulation being a big issue -two choices in managing ion and water flux across the exchange surface: 1) Ionoconform or continually engage in active transport, where the later requires energy (ATP). - Actively transporting ions is harder in salt water than in fresh water (think about why). 2) Osmoconform or continually counteract water flux, where the later also requires energy (ATP). - Actively transporting water is harder in fresh than salt water (think about why) Air breathers (e.g., use a lung to breath atmospheric air at the water surface or on land) - No bulk exchange of water and ions with environment occurs; osmoregulation is not too difficult compared to water breathers - The main challenge is water conservation in dry environments or salt excretion in a marine environment - Marine organisms without access to fresh water need to rid themselves of excess salt (e.g., nasal glands of birds and reptiles) - An interesting exception among air breathers is animals with fluid diets (e.g., nectarivores, phloem feeders) who need to rid themselves of excess water without losing too much salts

What is the role of parabronchi in bird lungs?

Within the parabronchi tubes are the small air capillaries that have cross-current gas exchange and thus provide oxygen. Birds have two sets of air sacs. -unidirectional flow of air

What is the difference between the source of materials transported by xylem and phloem?

Xylem transport materials from the roots, while phloem transport materials from the leaves

Adapations of invertebrates in freshwater

a. All are osmo and ionoregulators, often against large gradients --- internal osmolarity and ion concentration is much higher than that in the external environment. b. Urinate copiously to offset continual influx of water c. Utilize active transport to uptake ions d. Ion uptake is pH sensitive, which is why acid rain kills both invertebrates and vertebrates in freshwater habitats. Sodium ion pumps are specifically inhibited by high H+ concentration, thereby inhibiting active sodium uptake and increasing diffusional sodium loss. Acid in the water also releases toxins like aluminum from the sediments, which affect gill function. e. It can be costly to osmoregulate in fresh water too, for example a mosquito larva spends 22% of resting metabolism on osmoregulation and urine formation.

Osmoregulation in anadromic and catadromic fish

a. Anadromic fishes are born in fresh water, spend most of their life in the sea, and return to fresh water to spawn. Salmon, smelt, shad, striped bass, and sturgeon are common examples. b. Catadromic fishes do the opposite; live in fresh water and enters salt water to spawn. Most of the eels are catadromous. c. They switch from salt-to-fresh and fresh-to-salt at certain points in life cycle. d. Undergo hormonally regulated phenotypic changes in drinking behavior and apical cell types in the gills and kidney that alter the direction of transport pumps within 1-2 days of habitat shift.

How is oxygen carried in the body? Small, inactive invertebrates More active invertebrates Plants and insects

a. In small, inactive invertebrate animals with low metabolic rates, O2 absorbed via CGE is dissolved in the body fluids or blood. b. In more active invertebrates and all vertebrates, O2 dissolved only in body fluids or blood is insufficient, so blood contains respiratory pigments. c. In plants and insects, oxygenated fluid has little role in gas exchange. These organisms use air spaces or tubes to carry gases directly to the tissues (tracheae in insects, spongy layer in plant tissues). i) The xylem and phloem do not participate in gas transport because plants do not have O2 carrier molecules. Each part of the plant takes care of its own gas exchange needs; stomata in leaves and lenticels in mature roots and woody stems.

Role of the ambient temperature and humidity of air in the loss of water from terrestrial organism

a. Warmer air holds more water than cooler air. b. However, the rate of evaporation does NOT depend entirely on relative humidity (RH). c. The rate of evaporation from a body surface also depends on the vapor pressure deficit (i.e., saturation deficit) and the difference in water vapor density (i.e., pressure) between the organism and the surrounding air d. The reason that rate of evaporation does NOT depend entirely on relative humidity (RH) is that the water vapor deficit increases with temperature. For example, air at 35oC and 70% RH has more drying power than 20oC air at 50% RH