B3.1 Gas exchange Flashcards
What does it mean when an organism is aerobic?
It means that they require oxygen to metabolize energy from organic substances such as glucose. Additionally, organisms need to remove metabolic waste products such as carbon dioxide
The volume of an organism is the reflection of …
its metabolic need to exchange respiratory gases. An organism’s ability to take in and release substances is limited by its outer layer surface area. 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.
Where are the specialized tissues found that organisms have evolved to for gas exchange?
The specialized tissues are found in the skin of some small organisms, gills of many aquatic organisms, and 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
How are gas exchange surfaces characterized?
- Being thing -> to keep diffusion distances short
- being moist -> to encourage gas diffusion
- have a large surface are. -> for maximum diffusion
- being permeable to respiratory gases (oxygen + 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?
They are exchanged through diffusion. This means that concentration gradients must be maintained for oxygen to diffuse into the blood and carbon dioxide out of the blood
which blood vessels permit the exchange of substances?
The only blood vessels that permit the exchange of substances are capillaries. Capillaries are one cell thick
Why are all animals that use gills exothermic (cold-blooded)?
Animals with gills are exothermic because maintaining a constant body temperature requires a high metabolic rate, which depends on high oxygen levels. Since water has lower oxygen availability, it cannot support the high metabolic demands needed to be endothermic
What are the two events that must occur 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
How do diffusion gradients help gas exchange in the lungs?
In the lung capillaries, oxygen diffuses into the blood because its concentration is higher in the air than in the capillaries. On the contrary, carbon dioxide diffuses out of the blood into the lungs because its concentration is higher in the capillaries than in the air. This allows for efficient gas exchange
How do human lungs have the large capacity to expose air to an 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 the 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
What is the function of surfactant in the alveoli?
Surfactant is a phospholipid bilayer and protein film that reduces surface tension in the alveoli, preventing them from collapsing after air is expired
How does the structure of the alveoli maximize gas exchange?
The spherical shape of alveoli provides a large surface area, and their thin walls (one cell thick) minimize the diffusion distance for oxygen and carbon dioxide
How do concentration gradients drive gas exchange in the alveoli?
Oxygen diffuses from the alveoli into the capillaries (higher O2 in alveoli, lower in blood), while carbon dioxide diffuses from capillaries into alveoli (higher CO2 in blood, lower in alveoli) due to concentration differences
What is the role of bronchioles in the respiratory system?
Bronchioles are small tubes that connect alveoli to the trachea, allowing movement of inhaled and exhaled air throughout the lungs
`Which muscles work collectively to either increase/decrease the volume of the thoracic cavity, which leads to pressure changes in lungs?
The tissue that makes up our lungs is passive, not muscular, therefore the lungs themselves are incapable of purposeful movement. However, there are muscles surrounding the lungs, including the diaphragm, muscles of the abdomen, and the external and internal intercostal muscles
What is the mechanism of breathing based on?
It is based on the inverse relationship between pressure and volume.
What is Boyle’s Law?
It states that an increase in volume will lead to a decrease in pressure, and vice versa.
What is the thoracic cavity + what does it contain?
The thoracic cavity (thorax) is a closed space inside the body that houses the lungs. It is connected to the outside air only through the trachea
What is the function of the diaphragm in breathing?
The diaphragm is a dome-shaped muscle that forms the floor of the thoracic cavity. When it contracts, it flattens, increasing the volume of the thoracic cavity allowing inhalation.
What are the steps of inspiration (breathing in)?
- the diaphragm contracts, increasing the volume of thoracic cavity
- At the same time, the external intercostal muscles and one set of the abdominal muscles both contract to help raise the rib cages. These actions also help increase the volume of thoracic activity.
- Because the thoracic cavity has increased in volume, the pressure inside the thoracic cavity decreases. This leads to less pressure “pushin 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 partial vacuum. Air comes in through the open mouth or nose to counter the partial vacuum within the lungs and fills the alveoli
What are the steps of expiring?
- The diaphragm relaxes, returning to its dome shape, which decreases the volume of the thoracic cavity
- the external intercostal muscles relax, and the internal ones contract, pulling the rib cage down and inward, further reducing thoracic cavity volume
- The decrease in thoracic cavity volume leads to an increase in pressure, pushin on the passive lung tissue
- The lung tissue decreases in volume, increasing the pressure inside the lungs
- the air is forced out through the trachea and exits the body via the mouth or nose, as the pressure inside the lungs is now higher than the atmospheric pressure.
What device is used to measure lung volume?
The device called spirometer. A range of air volumes can be measured; tidal volume (air breathed in/out during a typical cycle when at rest), Inspiratory reserve volume (maximum volume of air that a person can breathe in), expiratory reserve volume (maximum volume of air a person can breathe out), and vital capacity (the sum of the volumes)
the reactions/equations for cell respiration and photosynthesis
These 2 are opposite of eachother.
Cell respiration = glucose + oxygen -> carbon dioxide + water
Photosynthesis = carbon dioxide + water -> glucose + oxygen
How are leaves adapted for gas exchange?
Leaves are thin and have a large surface-area-to-volume ratio, allowing for quick and efficient gas diffusion
- A waxy cuticle
- palisade mesophyll
- spongy mesophyll
- veins (xylem + phloem)
- stomata
- lower epidermis
What are the two primary energy-related processes in plants?
Cell respiration (produces ATP using oxygen) and photosynthesis (produces sugar using light)
Are the rates of the two energy-related processes the same?
No, in a plant the rate of cell respiration is constant, whilst photosynthesis is dependent on light availability. When conditions are optimal for photosynthesis -> its rate is far greater than the rate of cell respiration
Leaf’s structural adaptation for gas exchange; Waxy cuticle
a wax lipid layer that covers the surface of leaves and prevents uncontrolled and excessive leaf water loss by evaporation
Leaf’s structural adaptation for gas exchange; palisade mesophyll
a densely packed region of cylindrical cells in the upper portion of the leaf. These cells contain numerous chloroplasts and are located to receive maximum sunlight for photosynthesis
Leaf’s structural adaptation for gas exchange; spongy mesophyll
these loosely packed cells are located below the palisade layer and just above the stomata. They have few chloroplasts and many air spaces, providing a large surface area for gas exchange
Leaf’s structural adaptation for gas exchange; veins
these structures enclose the fluid transport tubes (xylem + phloem). Water moves up from the root system to the leaves in the xylem. Water and dissolved sugars are distributed to other parts of the plant in the phloem. Veins are located centrally within a leaf, to provide access to all the cell layers
Leaf’s structural adaptation for gas exchange; a lower epidermis
small cells on the lower surface of leaves that secrete a waxy cuticle. guard cells forming stomata are embedded in this layer
Leaf’s structural adaptation for gas exchange; stomata
numerous microscopic openings on the lower surface of leaves. Each stoma is composed of 2 guard cells. A pair of guard cells can create and opening or close it, as needed. When open, stomata permit carbon dioxide to enter the leaf and at the same time water vapor and oxygen 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
What is transpiration?
Transpiration is the evaporation of water through open stomata in a leaf as a consequence of gas exchange for photosynthesis
Why must stomata remain open for photosynthesis?
Stomata open to allow carbon dioxide to enter for photosynthesis, but this also leads to water loss through transpiration
What happens to water lost through transpiration?
The evaporated water can be traced back to the water absorbed by the roots, which moves upward through the plant.
What are the factors that influence rate of transpiration?
- Increased light
- Increased temperature
- Increased wind speed
- Increased humidity
if lack of light results in stomata being closed, the rate of transpiration will be 0. In that situation, changing the other three factors will have no effect
Influential environmental factor on transpiration rate; increased light
This increases the rate of transpiration. 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 + oxygen out
Influential environmental factor on transpiration rate; increased temperature;
This increases rate of transpiration. This increases molecular movement, including increased evaporation of water
Influential environmental factor on transpiration rate; Increased wind speed
This increases the rate of transpiration. Wind removes water vapor at the entrance of stomata, thereby increasing the water concentration gradient between the inside and outside of the leaf
Influential environmental factor on transpiration rate; increased humidity
This decreases rate of transpiration. Increased humidity lessens the water concentration gradient between the inside and outside of the leaf
What is haemoglobin?
Haemoglobin is the protein molecule found in erythrocytes (red blood cells) that is responsible for carrying most of the oxygen within the bloodstream. Each erythrocyte is basically a plasma membrane surrounding cytoplasm filled with haemoglobin molecules. Erythrocytes have no nuclei + few organelles. Each haemoglobin molecule is capable of reversibly binding to both oxygen and carbon dioxide molecules
What is the structure of the haemoglobin molecule?
Haemoglobin has a quaternary structure, composed of four polypeptide chains, each with a haem group containing an iron atom
How does haemoglobin bind to oxygen?
Oxygen binds reversibly to the iron atom within each haem group, allowing haemoglobin to transport oxygen in the blood
How many oxygen molecules can one haemoglobin molecule trasnport?
Since haemoglobin has 4 haem groups, it can bind up to four oxygen molecules
What does it mean when haemoglobin is saturated?
Haemoglobin is saturated when all four haem groups are bound to oxygen, carrying the maximum possible amount of oxygen
What is cooperative binding in haemoglobin?
Cooperative binding occurs when the binding of one oxygen molecule to haemoglobin increases its affinity for oxygen, making it easier for additional oxygen molecules to bind
Why does haemoglobin with 3 oxygen molecules have a higher affinity for oxygen than haemoglobin with no oxygen molecules?
Each oxygen binding changes haemoglobin’s shape, increasing it’s affinity for the next oxygen molecule, making it easier to fully saturate
What is allosteric binding in haemoglobin?
Allosteric binding occurs when carbon dioxide binds to the polypeptide chains (not the iron in the haem group), reducing haemoglobin’s oxygen affinity
What is the Bohr shift, and how does it affect haemoglobin?
The bohr shift occurs when carbon dioxide binds to haemoglobin, causing the release of oxygen, which is useful in actively respiring tissues that need more O(2)
What does the structural difference in fetus + mother haemoglobin enable?
The molecular structure of haemoglobin in a foetus is slightly different compared to haemoglobin in an adult. This difference enables Foetal haemoglobin to have a higher affinity for oxygen compared to the haemoglobin of the mother
How does gas exchange occur between mother and foetus in the placenta?
The mother’s and the fetus’s capillaries are very close together, allowing oxygen and carbon dioxide to diffuse across the placenta
Why does oxygen diffuse from the mother’s blood to the foetus?
The foetus is actively respiring, making foetal blood low in oxygen and high in CO(2), creating a concentration gradient that drives oxygen diffusion from the mother
How does foetal haemoglobin help in oxygen transfer?
Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, allowing it to attract oxygen more effectively from maternal blood.
What is the bohr shift?
The bohr shift is the decrease haemoglobin’s affinity for oxygen in the presence of high carbon dioxide level, causing the to be released more easiyl
Why does the bohr shift occur in respiring tissues?
Respiring tissues produce CO2 which binds to haemoglobin and reduces its oxygen affinity, ensuring oxygen is delivered where it is needed most
How does haemoglobin behave differently in the lungs compared to the body tissues?
In the lungs, CO2 levels are low, so haemoglobin has a higher affinity for oxygen and bind to it. In tissues, C02 is higher, triggering the bohr shift and oxygen release
Why is the oxygen dissociation curve s-shaped?
The curve is s-shaped due to cooperative binding, meaning each oxygen molecule that binds increases haemoglobin’s affinity for thee next oxygen molecule
What does the oxygen dissociation curve show?
shows the relationship between partial pressure of oxygen and haemoglobin saturation, demonstrating how readily haemoglobin binds to and releases oxygen
How does haemoglobin saturation change between lungs and body tissues?
In the lungs, haemoglobin is 95% saturated due to high oxygen partial pressure. In body tissues, haemoglobin saturation drops to 65% meaning about 30% is oxygen is released for cellular respiration
What would happen to the oxygen dissociation curve if haemoglobin did not have cooperative binding?
Without cooperative binding, the graph would be linear instead of s-shaped, as oxygen affinity would remain constant rather than increasing with each binding
Why is the oxygen dissociation curve for foetal haemoglobin shifted to the left compared to maternal haemoglobin?
Foetal haemoglobin has a higher affinity for oxygen than maternal haemoglobin, allowing it to extract oxygen from the mother’s blood. This ensures sufficient oxygen transfer across the placenta for the foetal development
Why does the oxygen dissociation curve shift to the right in environments with high CO2 (bohr shift)?
in high CO2 environments (such as actively respiring tissues), haemoglobin’s affinity for oxygen decreases, causing oxygen to be released more easily where it is needed most. This shift to the right ensures that working muscles receive more oxygen during exercies
