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Terms in this set (54)
Allometry refers to
the changes in physiology or anatomy with body size that are not always proportional
As an object or animal increases in length
volume increases faster than surface area
The relative surface area (surface to volume ratio) is:
greater in smaller animals
Total, or whole-body, metabolic rate tends to:
Increase non-proportionally with body mass
The mass-specific metabolic rate tends to:
Decrease with increasing body mass
The scaling exponent (b) for whole-body metabolic rate across many groups of organisms is:
Usually between 0.6 to 0.8
The allometric equations for metabolic rate as a function of mass:
Can be made linear by taking the logarithm of both sides.
The percentage of oxygen gas in dry, atmospheric air is close to:
If the total atmospheric pressure is 600 mm Hg, then the partial pressure due to oxygen (in dry air) would be:
=600 * 0.2095
Compared with the solubility of oxygen, the solubility of carbon dioxide in water is:
much higher than for oxygen
Which of the following would cause a decrease in oxygen solubility in water?
an increase in temperature
an increase in salinity
What is the driving force for diffusion of gas between two regions?
The difference in gas partial pressures
According to the Fick diffusion equation, the rate of gas transfer across a surface can be incvreased by:
increasing surface area
increasing the partial pressure difference
Larger animals usually require specialized structures/organs for gas exchange because:
the outer relative surface area to volume is too small in larger animals
Which of the conditions may allow an animal to only use its skin, or cutaneous surface, for gas exchange?
Skin is in water or kept moist
the surface area to volume ratio is high
the metabolic rate is low
Compared with air, the properties of water:
make aquatic respiration more dificult than respiring in air
What features of gill function in fishes aid in maximizing gas exchange?
water flow over the gills is uni-directional
the gill epithelium is thin with a large surface area
the flow of water and blood over the exchange surface move in counter-current (opposite) directions
What is 'scaling' or 'allometry'
changes in physiology and anatomy with body size
How does the relative surface are to volume ratio compare in small cersus large animals?
As the animal gets bigger, surface area to volume ratio decreases.
Relative surface area (per volume) available for exchange with environment is greater for small animals than large animals
How does total metabolic rate compare in small versus large animals?
is rises with increasing body mass
How does mass-specific metabolic rate compare in small versus large animals?
It decreases with increasing body mass
What is the equation that describes the relationshup between total metabolic rate and mass? What is the typical scaling exponent?
exponent b= less than 1 often close to 0.75 (&usually between 0.6 & 0.8)
What is the equation that describes the relationship between mass-specific metabolic rate and mass? What is the mass exponent for this equation?
explain: Graph of the relationship between total metabolic rate and mass on a log-log plot
explain: Graph of the relationship between mass-specific metabolic rate and mass on a log-log plot
What is the mass exponent that describes the scaling of surface area?
Does the scaling of surface area with mass (or volume) explain the scaling of metabolic rate with mass? Why or why not?
What is the percentage oxygen content of dry, atmospheric air?
Define the 'partial pressure' of a gas. How is it calculated? How is it affected by water vapor pressure?
Partial pressure= (760 ((partial pressure)) - 18 ((water vapor pressure))= 155 mm HgPO2
*Determines the direction of diffusion
*Partial pressures determine driving gradient for gas diffusion (i.e. from high pressure to low)
*Calculated by multiplying atm of oxygen by % oxygen
*Water vapor is subtracted from total pressure
How does atmospheric pressure change with increases in altitude?
Pressure decreases with an increase in altitude
How does the precentage content of oxygen in the atmosphere change with increases in altitude?
Percentage content of oxygen is the same with increases in altitude
What determines the driving gradient for gas diffusion: Differences in gas content or differences in gas partial pressure?
How is the total content of a gas dissolved in water calculated from the partial pressure?
Total amount of gas dissolved in liquid (or gas constant) determined by solubility (a) & partial pressure of gas phase (Henry's Law) so content= a
How does the solubility of CO2 in water compare with the solubility of O2 in water?
CO2 is roughtly 30x more soluble than oxygen in water
How is gas solubility in water affected by increases in temperature? Increases in salinity?
Oxygen solubility decreases with increasing temperature & salinity
What is the process of gas exchange?
The process of getting gasses across respiratory epithelia
What is the equation that describes the rate of gas diffusion across a membrane? Define all of the terms in the equation.
A= surface area (eg cm2)
P1-P2= Partial pressure difference across membrane
X= diffusion distance
M= rate of transfer of gas (quantity of gas diffusing per unit time)
K= diffusion coefficient (measure of velocity @ which gas diffuses through medium
Based on the equation (M=K
((P1-P2))/X) in what waus can the rate of gas diffusion be increased?
Optimize M by maximizing:
*A- surface area relative to body size (eg. Complex lungs & gills)
*P1- oxygen in air or water @ respiratory surface (e.g ventilate, minimize boundary layer)
Optimize M by minimizing:
*P2- oxygen in blood delivered to repspiratory surface (eg. counter-current exchange)
*X- diffusion distance across respiratory surface (eg. thin respiratory epithelia- often single layer of cells)
Why do larger animals need specialized tissues or organs for gas exchange?
*As size increases, volume increases @ a faster rate than surface area
*So larger animals require specialized tissue to create sufficient surface area for gas exchange.
What are the four primary types of structures found in animals for gas exchange, and in what types of animals are each found?
1. Skin- small animals whose metabolic rate is low, or whose skin is highly folded or vascularized
2. Gills- animals living in water, fish, crustaceans, bivalves
3. Lungs- animals living in air, tetrapod vertebrates, gastropods, spiders
4. Tracheal systems- air-dwelling animals without body capacity for lungs- insects
Under what conditions is cutaneous (skin) respiration sufficient to support an animal's metabolism? Provide some examples.
*Very small animals where metabolic rate is low & surface area to volume ratio is high.
*some fish larvae lack gills & rely soley on this
*Protozoans, flatworms, jellyfish
*some bats lose CO2 across wings
Why is it often more difficult for aquatic respiring animals, compared with air breathers, to get access to sufficient oxygen?
Air contains much more oxygen than same volume of water.
How does oxygen content in air and water compare? Oxygen diffusion rates?
*Oxygen diffuses much faster in air than water
How does the density of water affect aquatic respiration?
It is very dense so moving it across the boundary layer requires energy.
Why must aquatic-respiring animals, compared with air breathers, move more of the medium (water or air) over their respiratoru surface?
To extract an equivalent amount of oxygen
What is the general structure of a 'gill'?
*blood flows through them on the inside and water flows over them on the outside.
*The epithelium is thin & so the gills are often protected.
Describe how fish ventilate (move water over their gills)
in through the mouht- through the gill arches0 through filaments with lamenae
What are the benefits of moving water unidirectionally (in one direction) over the gills?
lower cost of moving large amounts of water (as opposed to tidal flow in mammalian lung)
Also, ensures delivery of fresh oxygenated water to gills.
In which direction does water flow past the gill lamellae: from the front (anterior) to back (posterior), or from the back (posterior) to the front (anterior)
water flows front to back
In which direction does blood flow past the gill lamellae: from the front (anterior) to back (posterior), or from the back (posterior) to the front (anterior)
blood flows back to front
How do oxygen levels change in the water as it flows past the lamellae?
How do oxygen levels change in the blood as it flows through the lamellae
Picks up oxygen
What is the benefit of countercurrent flow in the gill (compared with concurrent flow)?
maintains larger difference in oxygen partial pressures from water to blood along entire length of the enchange sufa
aids diffusion of gas- more efficient than co-current flow
How does the efficiency of oxygen extraction in the fish gill compare with the mammalian lung?
*Fish are able to extract 75% of oxygen in water.
*Mammals remove only about 1/4 of oxygen present in lung air before exhaled.
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