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Biology 224 Final Exam Questions And
Answers |Latest 2025 | Guaranteed Pass.
Why is there a constant urgent need of O2 in animals? - Answer✔Most animal cells need a
constant supply of ATP. They have a constant need of breathing (absorb oxygen and excrete
carbon dioxide) in order to survive. O2 is required as the terminal electron aceptor of
respiratory electron transport.
External respiration - Answer✔Between the environment and lungs. the transport of O2 into
and CO2 out of the body. Gas exchanges occur through diffusion.
This involves a gas exchange membrane:
A gas-exchange membrane is a thin layer of one or two simple epithelia.
It separates internal tissues from the environmental medium (air or water).
External respiration is the process by which:
environmental O2 --> membrane --> tissues
dissolved CO2 --> membrane --> environment ( in the opposite direction).
Internal respiration - Answer✔Between the blood and the cell. Transports O2 into and CO2 out
of cells
Cellular respiration - Answer✔Intracellular catabolic reactions that convert stored energy to
ATP
Diffusion Rate: (Fick's Law) - Answer✔J= D.A C1 - C2 divided by x.
C1 & C2 = Regions of high and low concentrations of solutes
A = Diffusion Area
X = Distance separating the concentration regions
D = Diffusion co-efficient, influenced by Physico-chemical properties of the solute, &
temperature
Application of Fick's Law to the diffusion of respiratory gases - Answer✔J= D.A P1 - P2 divided
by x.
1
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
1 & P2 = Regions of high and low partial pressure,
respectively
A = Diffusion Area
X = Distance separating the concentration regions
D = Diffusion co-efficient, influenced by Physico-chemical properties of the gas, & temperature
How small does an animal needs to be to rely on diffusion of O2 alone? - Answer✔Using Fick's
law• Vertebrate muscle requires O2 partial pressure ~ 40 mmHg • Atmospheric O2 partial
pressure = 160 mmHg
The distance inside the tissue where O2 partial pressure
reaches a minimum of 40 mmHg is ~ 1mm
What happens when organisms get larger? - Answer✔Oxygen requirement increases with mass.
However, diffusion distance also increases and the surface area to volume ratio decreases.
Bacteria's surface area to volume ratio is 6,000,000: 1 and a whale's surface area to volume
ratio is 0.06 to 1. Therefore, larger organisms need organs like lungs and gills to help with gas
exchange.
Respiration in larger animals requires multiple steps: - Answer✔Most vertebrate's gas-transfer
system involves: 1) ventilation: to move gas into and out of the lungs. 2) diffusion of oxygen
into the blood. 3) perfusion or transport of blood by the heart to the tissues. 4) diffusion of
oxygen from the blood in the capillaries in the tissues into the mitochondria in the cells. The
steps for the transport of CO2 from the cells to the environment are the reverse of this.
The structure of the gas-exchange system in animals is influenced by: - Answer✔Properties of
the medium- Air vs. water
Requirements of the animal
Anything that increases the diffusion coefficient, increases the surface area of the exchange
surface, enhances the partial pressure gradient, or reduces the thickness of the diffusion path
will speed the rate of diffusion.
Properties of Gases- Dalton's Law: - Answer✔total pressure exerted by a gas mixture (e.g.,
atmosphere) is the sum of individual pressures exerted by each gas in the mixture.
What is partial pressure? - Answer✔The individual pressure exerted by each gas within a
mixture of gases is the partial pressure (Pg).
Partial pressure is calculated by multiplying the fractional composition of that gas by the
atmospheric pressure.
The rate of diffusion of a gas is proportional to its partial pressure
2
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
within the total gas mixture.O2 and CO2 will flow based on their pressure gradient (high to
low).
Partial pressure at sea level vs. atmospheric air: - Answer✔The fractional composition of air at
sea level and at the top of mount Everest is the same, but the partial pressure of each of the
major gasses in air are reduced to 1/3 at sea level.
Diffusion of gasses- water vs. air- - Answer✔There is 30 times the amount of O2 in air than in
water for the same partial pressure. This requires aquatic animals to breathe much more in
order to obtain the same volume of O2 as other animals. Density of water is 1000 time more
than air and viscosity is about 50 times more than air. It takes more energy to move water than
air over a respiratory surface.
Advantages of breathing in water than in air - Answer✔CO2 is 20 times more soluble in water
than air, so excretion is much easier during ventilation. Land animals must lose water by
evaporation during ventilation, which can cause their respiratory surface to dry. Therefore, they
must consume water.
Solubility of gas - Answer✔Gases are not equally soluble in different fluids or the same fluid at
different temperatures. Oxygen is far more soluble in lipids than in water, and is more soluble
in cold temperatures than warm. Gas will move down a partial pressure gradient from a region
of high partial pressure to an area of low partial pressure. When oxygen is in equilibrium
between two gases, the concentrations may be different, but the partial pressures will be the
same.
Water Breathers: - Answer✔Gills are invaginations of the body - Respiratory surfaces- Branched
and folded- Increase diffusion area
Water moves over the gills
- Beating of cilia; and contractions of body muscles pump water over gills.
External gills - Answer✔Extend out from the body and do not have protective coverings
Internal Gills - Answer✔Located within the body;
- Protected by chambers of the body
-provides protection for delicate structures
- Currents of water to be directed over the gills.
Double pumping mechanism in bony and cartilaginous fish: - Answer✔+ and - indicate pressure
gradient across the gills and pressure relative to surrounding water
Ram ventilation - Answer✔Pelagic fish like some sharks and mackerel.
Mackerel can't fully oxygenate their blood if prevented from active swimming
3
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
Tracheal system of insects for gas exchange - Answer✔Trachea = windpipe- Invaginations of the
outer
epidermis that branch repeatedly
Air enters and leaves at openings in the insects chitinous exoskeleton through spiracles
each spiricle incorporates a muscle that allows the spiracles to open and close. O2 is consumed
by tissues and CO2 is taken up by the bicarbonate buffering system, resulting in a small
negative pressure in the tracheal system. The small inward current of air moving in through the
spiracle prevents water vapour from escaping. As the bicarbonate buffering system becomes
saturated, Free Co2 builds up inside the insect causing the spiracles to open, allowing CO2 to
move out.
Trachea branches into tracheoles
O2 - ECF - Cells
CO2 - ECF - Tracheoles
Adult amphibians breathing cycle: - Answer✔begins with the expansion of the buccal (mouth)
cavity with the nostrils open and the entrance into the lungs is constricted by the glottis. This
draws fresh air into the mouth. Next, the glottis opens and gas from the lungs enters the buccal
cavity where it mixes with fresh air as it exits via mouth and nostrils. When mouth and nostrils
close, buccal compression forces buccal gas into the lungs. The glottis then closes. Much carbon
dioxide is lost through the skin, as well.
bird lungs - Answer✔birds have up to nine pairs of air sacs that branch off the respiratory tract.
Bird lungs are rigid and do not expand or contract. However, the air sacs do. The air flows in
one direction. There are two cycles of inhalation and ventilation. Air flows from back to front
through parabronchi.
Cross-current gas exchange in birds: - Answer✔During first inhale, oxygen mostly moves
directly to the posterior air sacs. Anterior air sacs also expand but do not receive any oxygen.
Then during exhalation, both of the anterior and posterior air sacs contract. Oxygen from the
posterior sacs flow into the bronchi. During the next inhalation, air from lung moves to the
anterior sacs. During second exhalation air from the anterior sacs moves out of the bird through
the trachea.
Gas transport in Insects - Answer✔Length of tissue diffusion path limit the size of the tissue
Simple diffusion in tracheoles may work for small insectsà
larger ones use ventilation
Ventilation involves opening/closing of spiracles and abdominal muscles
Cross-current Gas Exchange - Answer✔Blood flow branches into multiple streams, each of
which meets the air along only part of the air's path.
4
Biology 224 Final Exam Questions And
Answers |Latest 2025 | Guaranteed Pass.
Why is there a constant urgent need of O2 in animals? - Answer✔Most animal cells need a
constant supply of ATP. They have a constant need of breathing (absorb oxygen and excrete
carbon dioxide) in order to survive. O2 is required as the terminal electron aceptor of
respiratory electron transport.
External respiration - Answer✔Between the environment and lungs. the transport of O2 into
and CO2 out of the body. Gas exchanges occur through diffusion.
This involves a gas exchange membrane:
A gas-exchange membrane is a thin layer of one or two simple epithelia.
It separates internal tissues from the environmental medium (air or water).
External respiration is the process by which:
environmental O2 --> membrane --> tissues
dissolved CO2 --> membrane --> environment ( in the opposite direction).
Internal respiration - Answer✔Between the blood and the cell. Transports O2 into and CO2 out
of cells
Cellular respiration - Answer✔Intracellular catabolic reactions that convert stored energy to
ATP
Diffusion Rate: (Fick's Law) - Answer✔J= D.A C1 - C2 divided by x.
C1 & C2 = Regions of high and low concentrations of solutes
A = Diffusion Area
X = Distance separating the concentration regions
D = Diffusion co-efficient, influenced by Physico-chemical properties of the solute, &
temperature
Application of Fick's Law to the diffusion of respiratory gases - Answer✔J= D.A P1 - P2 divided
by x.
1
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
1 & P2 = Regions of high and low partial pressure,
respectively
A = Diffusion Area
X = Distance separating the concentration regions
D = Diffusion co-efficient, influenced by Physico-chemical properties of the gas, & temperature
How small does an animal needs to be to rely on diffusion of O2 alone? - Answer✔Using Fick's
law• Vertebrate muscle requires O2 partial pressure ~ 40 mmHg • Atmospheric O2 partial
pressure = 160 mmHg
The distance inside the tissue where O2 partial pressure
reaches a minimum of 40 mmHg is ~ 1mm
What happens when organisms get larger? - Answer✔Oxygen requirement increases with mass.
However, diffusion distance also increases and the surface area to volume ratio decreases.
Bacteria's surface area to volume ratio is 6,000,000: 1 and a whale's surface area to volume
ratio is 0.06 to 1. Therefore, larger organisms need organs like lungs and gills to help with gas
exchange.
Respiration in larger animals requires multiple steps: - Answer✔Most vertebrate's gas-transfer
system involves: 1) ventilation: to move gas into and out of the lungs. 2) diffusion of oxygen
into the blood. 3) perfusion or transport of blood by the heart to the tissues. 4) diffusion of
oxygen from the blood in the capillaries in the tissues into the mitochondria in the cells. The
steps for the transport of CO2 from the cells to the environment are the reverse of this.
The structure of the gas-exchange system in animals is influenced by: - Answer✔Properties of
the medium- Air vs. water
Requirements of the animal
Anything that increases the diffusion coefficient, increases the surface area of the exchange
surface, enhances the partial pressure gradient, or reduces the thickness of the diffusion path
will speed the rate of diffusion.
Properties of Gases- Dalton's Law: - Answer✔total pressure exerted by a gas mixture (e.g.,
atmosphere) is the sum of individual pressures exerted by each gas in the mixture.
What is partial pressure? - Answer✔The individual pressure exerted by each gas within a
mixture of gases is the partial pressure (Pg).
Partial pressure is calculated by multiplying the fractional composition of that gas by the
atmospheric pressure.
The rate of diffusion of a gas is proportional to its partial pressure
2
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
within the total gas mixture.O2 and CO2 will flow based on their pressure gradient (high to
low).
Partial pressure at sea level vs. atmospheric air: - Answer✔The fractional composition of air at
sea level and at the top of mount Everest is the same, but the partial pressure of each of the
major gasses in air are reduced to 1/3 at sea level.
Diffusion of gasses- water vs. air- - Answer✔There is 30 times the amount of O2 in air than in
water for the same partial pressure. This requires aquatic animals to breathe much more in
order to obtain the same volume of O2 as other animals. Density of water is 1000 time more
than air and viscosity is about 50 times more than air. It takes more energy to move water than
air over a respiratory surface.
Advantages of breathing in water than in air - Answer✔CO2 is 20 times more soluble in water
than air, so excretion is much easier during ventilation. Land animals must lose water by
evaporation during ventilation, which can cause their respiratory surface to dry. Therefore, they
must consume water.
Solubility of gas - Answer✔Gases are not equally soluble in different fluids or the same fluid at
different temperatures. Oxygen is far more soluble in lipids than in water, and is more soluble
in cold temperatures than warm. Gas will move down a partial pressure gradient from a region
of high partial pressure to an area of low partial pressure. When oxygen is in equilibrium
between two gases, the concentrations may be different, but the partial pressures will be the
same.
Water Breathers: - Answer✔Gills are invaginations of the body - Respiratory surfaces- Branched
and folded- Increase diffusion area
Water moves over the gills
- Beating of cilia; and contractions of body muscles pump water over gills.
External gills - Answer✔Extend out from the body and do not have protective coverings
Internal Gills - Answer✔Located within the body;
- Protected by chambers of the body
-provides protection for delicate structures
- Currents of water to be directed over the gills.
Double pumping mechanism in bony and cartilaginous fish: - Answer✔+ and - indicate pressure
gradient across the gills and pressure relative to surrounding water
Ram ventilation - Answer✔Pelagic fish like some sharks and mackerel.
Mackerel can't fully oxygenate their blood if prevented from active swimming
3
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED 2:49PM A+
Tracheal system of insects for gas exchange - Answer✔Trachea = windpipe- Invaginations of the
outer
epidermis that branch repeatedly
Air enters and leaves at openings in the insects chitinous exoskeleton through spiracles
each spiricle incorporates a muscle that allows the spiracles to open and close. O2 is consumed
by tissues and CO2 is taken up by the bicarbonate buffering system, resulting in a small
negative pressure in the tracheal system. The small inward current of air moving in through the
spiracle prevents water vapour from escaping. As the bicarbonate buffering system becomes
saturated, Free Co2 builds up inside the insect causing the spiracles to open, allowing CO2 to
move out.
Trachea branches into tracheoles
O2 - ECF - Cells
CO2 - ECF - Tracheoles
Adult amphibians breathing cycle: - Answer✔begins with the expansion of the buccal (mouth)
cavity with the nostrils open and the entrance into the lungs is constricted by the glottis. This
draws fresh air into the mouth. Next, the glottis opens and gas from the lungs enters the buccal
cavity where it mixes with fresh air as it exits via mouth and nostrils. When mouth and nostrils
close, buccal compression forces buccal gas into the lungs. The glottis then closes. Much carbon
dioxide is lost through the skin, as well.
bird lungs - Answer✔birds have up to nine pairs of air sacs that branch off the respiratory tract.
Bird lungs are rigid and do not expand or contract. However, the air sacs do. The air flows in
one direction. There are two cycles of inhalation and ventilation. Air flows from back to front
through parabronchi.
Cross-current gas exchange in birds: - Answer✔During first inhale, oxygen mostly moves
directly to the posterior air sacs. Anterior air sacs also expand but do not receive any oxygen.
Then during exhalation, both of the anterior and posterior air sacs contract. Oxygen from the
posterior sacs flow into the bronchi. During the next inhalation, air from lung moves to the
anterior sacs. During second exhalation air from the anterior sacs moves out of the bird through
the trachea.
Gas transport in Insects - Answer✔Length of tissue diffusion path limit the size of the tissue
Simple diffusion in tracheoles may work for small insectsà
larger ones use ventilation
Ventilation involves opening/closing of spiracles and abdominal muscles
Cross-current Gas Exchange - Answer✔Blood flow branches into multiple streams, each of
which meets the air along only part of the air's path.
4
