Theme B: B3 Organisms - B3.1 Gas Exchange Flashcards
Why do bigger organisms face greater challenges?
the challenges become greater as organisms increase in size because surface area-to-volume ratio decreases with increasing size, and the distance from the centre of an organism to its exterior increases.
in terms of organisms
aerobic
most organisms are aerobic meaing they require oxygen to metabolise energy from organic substances (e.g. glucose).
In addition, organisms need to remove metabolic waste (e.g. carbon dioxide)
how do some organisms like single-celled life forms exchange gases?
they cna exchange oxygen and carbond dioxide directly with the atmosphere through their plasma membrane.
why is it more complicated for large multicellular organisms to exchange gases? generally, how do they overcome this?
the metabolically active tissue of large multicellular organisms may lie deep within them and far away from their environment.
these organisms have evolved comlex adaptations to exhange respiratory gase betweeen the atmosphere or water habitat and their tissue.
what contributes to the problems/challenges of gas exchange for large multicellular organisms?
In short, the problem of getting gases directly to and from an organism’s interior cells is compounded by the surface area-to-volume ratio.
Surface area is a squared function of its dimensions and volume is a cubed function.
Another way of expressing this idea is that the surface area-to-volume ratio decreases with increasing size.
What does the volume and surface area of an organism reflect?
The volume of an organism is a reflection of its metabolic need to exchange respiratory gases.
surface area determines how effectively an organism can interact with its environment for exchange processes. An organism’s ability to take in and release substances is limited by its outer layer surface area.
Where are an organism’s adaptations for gas exchange located?
Organisms that have evolved adpatations for gas exchange must have specialised tissues designed for the molecular exchanges. The specialised tissues are found in:
* the skin of some small organisms
* gills of many aquatic organisms
* the lungs of some larger terrestrial organisms
The exchange of gases sometimes occurs between the air and the living tissue (lungs) or between water and the living tissue gills). In many organisms the gases are immediately exchanged to blood vessels to be circulated to body tissues.
Only the smallest organisms can rely on direct exchange of respiratory gases with their environment, all others must have anatomical and physiological adaptations to get oxygen to internal tissues and take carbon dioxide away.
Gas echange surfaces are characterised by:
- being thin (often only one cell layer), to keep diffusion distances short
- being moist, to encourage gas diffusion
- having a large surface area, for maximum diffusion
- being permeable to respiratory gases (oxygen and carbon dioxide).
These properties allow the maximum volume of gases to be exchanged across the surface in the smallest amount of time.
How are oxygen and carbon dioxide exchanged?
By diffusion. This means that concentration gradients must be maintained for oxygen to diffuse into the blood and carbon dioxide out of the blood.
in terms of fish gills
What are two fluids to take into account for respiratory gas concentrations?
- One fluid is the environmental water passing over the gill tissue.
- The other is the blood within the capillaries of the gills.
in terms of fish
How do conentrations of respiratory gases change or stay the same?
The concentration of respiratory gases in the environmental water does not change as long as the body of water maintains good ecological health and the water is not stagnant around the gills.
The concentrations of oxygen and carbon dioxide do change within the blood of the organism, however.
Use diffusion gradients to explain the gas diffusion that takes place in fish with gills.
When the blood is first circulated to the gills, it has recently been within capillaries of the muscles and other body tissues. The body cells are continuously respiring, which utilizes oxygen and produces carbon dioxide.
The blood that leaves body tissues contains a higher concentration of carbon dioxide and a lower concentration of oxygen compared to levels before the blood reached the active body tissues.
The blood will then be transported to the gill tissue. When this blood reaches the gills, gas exchange occurs: oxygen diffuses into the blood, and carbon dioxide diffuses out, replenishing oxygen levels for circulation.
more detailed on the alveoli flashcard - talk generally abt capillaries
Use diffusion gradients to explain the gas diffusion that takes place in animals with lungs.
Within the lungs are numerous dense capillaries that contain blood that has recently come from respiring body tissues.
The concentration of oxygen in the lung capillaries is lower than that of air inspired into the lungs. In addition, the concentration of carbon dioxide in the lung capillaries is higher than that in the air inspired.
What two events must occur in order to keep concentration gradients in place?
- water must be continuously passed over the gills/air must be continuously refreshed (ventilated) in the lungs
- there must be a continuous blood flow to the dense network of blood vessels in both the body tissues and the tissues of the gills or lungs.
function + location
Alveolus (plur. alveoli)
Simple defintion: An alveolus is a small, air-filled sac in the lungs where gas exchange occurs. It is surrounded by capillaries, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood into the alveolar air for exhalation.
More info:
* Our lungs have an amazing capacity to expose life-giving air to an incredibly large surface area of gas exchange tissue.
* The lungs do this by subdividing their volume into microscopic spheres called alveoli. Each alveolus is at a terminal end of one of the branches of tubes that started as the trachea.
* Every time you breathe in (inspire) and breathe out (expire) you replace most of the air in millions of alveoli.
* The spherical shape of the alveoli provides a vast surface area for the diffusion of oxygen and carbon dioxide.
* The diffusion of respiratory air is also helped by the dense network of capillaries surroudning the alveoli. Each alveolus has close access to a capillary.
surfactant
A thin phospholipid and protein film that lines the inner surface of each alveolus. Specific alveolar cells secrete the surfactant. The surfactant acts to reduce surface tension of the moist inner surface and helps prevent each alveolus from collapsing each time air is expired.
bronchioles
The inside of each lung is subdivided into several lobes, which are in turn subdivided into the millions of spherical alveoli all connected by small tubes called bronchioles. All of the bronchioles are ultimately connected into the trachea for access to inspired and expired air.
Use diffusion and concentartion gradients to describe gas exchange between capillaries and alveoli.
- Air in the alveoli has a higher concentration of oxygen and a lower concentration of carbon dioxide compared to the blood in capillaries.
- Oxygen diffuses from the alveoli (high concentration) into the capillaries (low concentration), and carbon dioxide diffuses from the capillaries (high concentration) into the alveoli (low concentration).
- Because capillaries are just one cell thick and each alveolus is just one cell thick, the respiratory gases only need to diffuse through two cells to enter or exit the blood stream.
- The oxygen-rich blood is now ready to return to the heart to be pumped out into actively respiring tissues. The entire process is ongoing as long as the heart continues to send blood to the capillaries within the lungs, and air continues to be refreshed within the alveoli.
what type of tissue is out lungs made of?
the tissue that makes up our lungs is passive and not muscular, therefore the lungs themselves are incapable of purposeful movement, hencing breathing usually happens without our conscious thought.
What muscles surround the lungs?
diaphragm, muscles of the abdomen, and the extrernal and interanl inercostal muslces (surrounding your ribs. All of these muscles work colletcively to either increase or decrease the volume of the thoracic cavity, leading to pressure changes in the lungs.
What is the mechanism of breathing based on?
Boyle’s Law
the mechanism of brathing is based on the inverse relationship between pressure and volume.
Boyle’s law states that an increase in volume will lead to a decrease in pressure. and vice versa.
thoracic cavity (throax)
the lungs are locates within the thoracic cavity (or thorax). The thoracic cavity is closed to the outside air, where the lungs only have one opening through your trachea (via your mouth and nasal passage).
The diaphragm is a large, dome-shaped muscle that forms the “floor” of the thoracic cavity. when it contracts it flattens the dome shape and increases the colume of the thoracic cavity.
Inspiration (breathing in)
- the diaphragm contracts, increasing the volume of the thoracic cavity by flattening the curvature of the muscle.
- at the same time, the external intercostal muscles and one set of abdominal muscles both contract to help raise the rib cage. these actions also helo increase the volume of the thoracic cavity.
- because the thoracic cavity has increased in volume, the pressure inside decreases. this leads to less pressure “pushing on” the passive lung tissue
- the lung tissue responds to the lower pressure by increasing its volume
- this leads to a decrease in pressure inside the lungs, also known as a partial vacuum. air comes in through the open mouth or nasal passgaes to counter the partial vacuum within the lungs, and fills the alveoli.
summary:
* external intercostal muslces contract
* ribcage moves up and out
* diaphragm contracts and flattens
* volume of thorax decreases
* air is drawn in
external intercostal muscles
External intercostal muscles are muscles located between the ribs. They contract to elevate the ribs during inhalation, expanding the thoracic cavity and decreasing pressure, allowing air to flow into the lungs.
internal intercostal muscles
Internal intercostal muscles are muscles located between the ribs, but they lie deeper than the external intercostals. They contract to depress the ribs during exhalation, reducing the volume of the thoracic cavity and increasing pressure, helping expel air from the lungs.
Exhalation (breathing out)
- The diaphragm relaxes, returning to its dome-shaped position, which decreases the volume of the thoracic cavity.
- At the same time, the internal intercostal muscles contract to depress the rib cage, further reducing the volume of the thoracic cavity.
- As the thoracic cavity’s volume decreases, the pressure inside increases, “pushing” against the passive lung tissue.
- The lung tissue responds to the increased pressure by decreasing its volume.
- This causes the pressure inside the lungs to rise above atmospheric pressure, and air is forced out of the lungs through the open mouth or nasal passages.
summary:
* internal intercostal muscles contract
* ribcage moves down and in
* diaphragm relaxes and becomes dome shaped
* volume of throax decreases
* pressure inside thorax increases
* air is forced out
what can it be used for
spirometer
A device used to measure lung volume. A range of air volumes can be measured, including the following.
* Tidal volume - the volume of air that is breathed in or out during a typical cycle when a person is at rest. The term “tidal” volume comes from the idea of an ocean tide coming in and out.
* Inspiratory reserve volume - the maximum volume of air that a person can breathe in (measured from the maximum point of the tidal volume).
* Expiratory reserve volume - the maximum volume of air that a person can breathe out (measured from the minimum point of the tidal volume).
* Vital capacity - the sum of the inspiratory reserve volume, the tidal volume and the expiratory reserve volume.
general properties
How are leaves adapted to allow plants to exchange respiratory gases with the atmosphere?
- A typical leaf is thin, comprising only a few cell layers, so that the diffusion of gases can be quick and efficient.
- This also permits a relatively large surface area-to-volume ratio for efficient diffusion.
What are the primary energy-related processes within plants?
- cell respiration: The cells of a plant are always using aerobic cell respiration to synthesize adenosine triphosphate (ATP) molecules for energy-requiring reactions.
- photosynthesis; In addition, when light is available, plants are using photosynthesis to make sugars as fuel for cell respiration.
The summary reactions for cell respiration and photosynthesis are the opposite of each other.
* Cell respiration: glucose + oxygen → carbon dioxide + water
* Photosynthesis: carbon dioxide + water - glucose + oxygen
the rates of these two sets of ractions are not equal. The rate of cell respiration is failry constant, while photosynthesis is heavily dependent on light availability. though when conditions are optimal for photosynthesis, its rate is far greater compared to cell respiration.
List the structural adaptations of a leaf that help facilitate the exchange of gases.
- waxy cuticle
- palisade mesophyll
- spongy mesophyll
- veins
- lower epidermis
- stomata
in order of their location in the leaf (top layer - bottom layer)
waxy cuticle
a waxy lipid layer that covers the surface of leaves and prevents uncontrolled and excessive leaf water loss by evaporation (transpiration)
palisade mesophyll
a densely packed region of cylindrical cells in the upper portion of the leaf. these cells contain numerous chlorplasts and are located to recieve maximum sunlight for photosynthesis.
spongy mesophyll
loosely packed cells located below the palisade mesophyll and just above the stomata. they ahev few chloroplasts and many air spaces, providing a large surface area for gas exchange.
in plants
veins
these strcuture enclose the fluid transport tubes called the xylem and phloem. veins are located centrally within a leaf, to provide acess to all the cell layers.
xylem
Xylem is a type of vascular tissue in plants responsible for the transport of water and dissolved minerals from the roots to the rest of the plant.
phloem
Phloem is a type of vascular tissue in plants responsible for the transport of sugars, nutrients, and other organic compounds from the leaves (where they are produced through photosynthesis) to other parts of the plant.
lower epidermis
small cells on the lower surface of leaves that secrete a waxy cuticle. Guard cells forming stomata are embedded in this layer.
stomata (singular stoma)
numerous microscopic openings on the lower surface of leaves.
* Each stoma is composed of two guard cells. A pair of guard cells can create an opening or close it, as needed.
* When open, stomata permit carbon dioxide to enter the leaf and at the same time water vapour and oxygen to exit the leaf.
* These three gases move by diffusion as a result of their concentration gradients.
* At night many plants close their stomata.
* Their location on the lower surface of leaves limits water loss as a result of transpiration, because the lower surface of leaves experiences lower temperatures compared to the upper surface.
transpiration
The evaporation of water through open stomata in leaves. Transpiration is a natural consequence of a leaf’s function to accomplish photosynthesis:
* Stomata open to allow carbon dioxide to enter as a reactant of photosynthesis, where excess oxygen is then diffused out while the stomata are opened.
* The mesophyll area of the leaf is very humid and water will also evaporate through any open stomata.
* The water evaporated can be traced back to the water that entered the roots and has now reached the upper sections of the plant. This water loss helps to draw water and minerals up from the roots through the xylem
* The leaf can open or close its stomata but it cannot filter which gases pass through the openings.
* Transpiration can amount to a significant volume of water when conditions are optimal.
what factors influence the rate of transpiration
- increased light (increases rate): Light stimulates guard cells to open stomata. Increased light also stimulates the rate of photosynthesis to increase. Open stomata permit diffusion of carbon dioxide in and oxygen out
- increased temperature (increases rate): Increased molecular movement, including increased evaporation of water
- increased wind speed (increases rate): Wind removes water vapour at the entrance of stomata, thereby increasing the water concentration gradient between the inside and outside of the leaf
- increased humidity (decreases rate): Increased humidity lessens the water concentration gradient between the inside and outside of the leaf
note that if a lack of light results in stomata being closed, the rate of transpiration will be zero. in that situation, changing the other 3 factors will have no effect.
& how to measure stomata
what do studies show about the desnity of stomata in plant species?
they show that the density of stomata varies between species of plants and even varies within a single species based on long-term environmental factors.
to study any factor that may be correlated with stomata density, you need to be able to view the stomata and measure the area you are viewing. stomata desnity can be expressed as number of stomata mm^-2 or number of stomata micrometer^-2.
when is haemoglobin said to be saturated?
When haemoglobin reversibly binds to an oxygen molecule, it is the iron atom within the haem group that is bonding with the oxygen. Because haemoglobin has a total of four iron atoms within four haem groups, it has the capacity to transport four oxygen molecules (402). When in that form, haemoglobin is said to be saturated.
cooperative binding
the phenomenon where the molecular shape of haemoglobin is influences by its bonding with oxygen moleucles. Any oxygen molecule bonded to haemoglobin increases its affinity (attraction for) more oxygen. this is called cooperative bonding because the oxygen molecule are acting in concert with each other to increase the haemoglobin’s affinity for oxygen.
haemoglobin molecules carrying 3 oxygen molecules gace the greatest affinity for oxygen. haemoglobin carrying no oxygen molecules have the least affinity for oxygen. haemoglobin carring four oxygens has no affinity for oxygen.
allostery (allosteric binding)
the binding of carbon dioxide to the polypeptide chains of haemoglobin and teh resulting change in haemoglobin’s affinity for oxygen (where haemoglbin can bind to CO2 as well as O2).
CO2 binds to the polypeptides region of the molecule, unlike O2 which binds to the iron of the haem group. the allosteric site of the polypeptide is the area where CO2 binds to. the binding of CO2 to haemoglobin results in an increase in the release of oxygen molecules and is known as the Bohr shift.
how does the molecular structure of haemoglobin in a foetus differ compared to haemoglobin in a an adult?
the structural difference enables foetal haemoglobin to have a higher affinity for oxygen compared to the haemoglobin of the mother:
* In the placenta of a pregnant female, her capillaries come very close to the capillaries of the foetus. This allows molecular exchanges between the mother and foetus, including oxygen and carbon dioxide.
* Remember that the mother is breathing but the foetus is not.
* The foetus is actively carrying out cell respiration, and the blood sent to the foetal side of the placenta is relatively low in oxygen and high in carbon dioxide.
* The concentration gradient between the blood of mother and foetus, aided by the foetal haemoglobin’s greater affinity for oxygen, encourages diffusion of the mother’s oxygen to the foetus.
Bohr shift
The change in affinity of haemoglobin in the presence of carbon dioxide. When haemoglobin bonds to a carbon dioxide molecule, its affinity for oxygen decreases. Another way of saying this is that haemoglobin has a greater tendency to give up oxygen molecules in the presence of carbon dioxide.
explain the phsyiological reasoning behind the Bohr shift
binding to carbon dioxide is most likely to occur where carbon dioxide is at greater concentrations, in muscles and other body tissues, as a product of cell respiration. This is also where oxygen is most needed.
The opposite is true in lung tissue. The alveoli of the lungs have relatively low concentrations of carbon dioxide and high concentrations of oxygen, permitting haemoglobin to lose carbon dioxide and thereby giving the haemoglobin a renewed affinity for bonding to oxygen.
oxygen dissociation curve
the characeristics of haemoglobin can be explain using this graph.
* y-axis: percantage of haemoglobin saturation. this is the percentage of haemoglobin that is transporting the maxiumum of four oxygen molecules.
* x-axis: shows the partial pressure of oxygen.
especilaly in terms of oxygen (relevant for oxygen dissociation curve)
partial pressure
oxygen partial pressure varies depending on where the blood is within the body. the partial pressure of a gas is the pressure exerted by a single gas within a mixture of gases. the partial pressure of oxygen decreases in the body and blood as it is used for aerobic cellular respiration.
analyse partial pressure on a oxygen dissociation curve for human adult haemoglobin
Typically two vertical dashed red lines from each axis that meet at a point of the curve.
The dashed line to the right is the partial pressure that corresponds to the oxygen partial pressure in the lungs. The dashed line to the left corresponds to the oxygen partial pressure in body tissues where cell respiration is utilizing oxygen.
If you subtract the left y-axis intersect point on the graph (~65%) from the right y-axis intersect point (~95%) you can calculate the percentage of oxygen released to the tissues (~30%).
These values vary from person to person and are only meant to show the pattern demonstrated by haemoglobin’s release of oxygen to respiring tissues.
analyse the oxygen dissociation curve of maternal and foetal haemoglobin
we can see the effect of the enhaced affinity of foetal heamoglobin over maternal haemoglobin by comparing their oxygen dissocation curves.
the foetal haemoglobin’s curve is shifted to the left of the mother’s, indicating a greater affintity for oxygen at almost every partial pressure of oxygen.
Bohr shift
analyse the oxygen dissociation curve showing adult haemoglobin in different CO2 envionments.
When haemoglobin binds to one or more carbon dioxide molecules, its affinity for oxygen is reduced. Increased carbon dioxide leads to a shift to the right (hence the curve showing haemoglobin in an environment where partial pressure of CO2 is relatively low is on the left, and the latter is on the right.)
Bohr shift and the process of inhalation + exhalation during exercise
All the steps become more frequent and exaggerated when you are exercising and thus breathing deeply. For example, the abdominal muscles and intercostal muscles achieve a greater initial thoracic volume. This leads to deeper breathing and more air moving into the lungs.
Consider the physiological advantage of the Bohr shift when actively exercising. During strenuous activity, your muscles need more oxygen for cell respiration. The increased rate of cell respiration leads to increased carbon dioxide production, which will bind to haemoglobin in the nearby capillaries. The Bohr effect will then lead to an increased release of oxygen to the muscles, where it is needed.
