B3.1 Gas exchange

Question 1

What does it mean when an organism is aerobic?

Answer 1

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

Question 2

The volume of an organism is the reflection of …

Answer 2

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.

Question 3

Where are the specialized tissues found that organisms have evolved to for gas exchange?

Answer 3

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

Question 4

How are gas exchange surfaces characterized?

Answer 4

• 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

Question 5

How are oxygen and carbon dioxide exchanged?

Answer 5

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

Question 6

which blood vessels permit the exchange of substances?

Answer 6

The only blood vessels that permit the exchange of substances are capillaries. Capillaries are one cell thick

Question 7

Why are all animals that use gills exothermic (cold-blooded)?

Answer 7

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

Question 8

What are the two events that must occur to keep concentration gradients in place?

Answer 8

1. water must be continuously passed over the gills/air must be continuously refreshed (ventilated) in the lungs
2. 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

Question 9

How do diffusion gradients help gas exchange in the lungs?

Answer 9

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

Question 10

How do human lungs have the large capacity to expose air to an large surface area of gas exchange tissue?

Answer 10

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

Question 11

What is the function of surfactant in the alveoli?

Answer 11

Surfactant is a phospholipid bilayer and protein film that reduces surface tension in the alveoli, preventing them from collapsing after air is expired

Question 12

How does the structure of the alveoli maximize gas exchange?

Answer 12

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

Question 13

How do concentration gradients drive gas exchange in the alveoli?

Answer 13

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

Question 14

What is the role of bronchioles in the respiratory system?

Answer 14

Bronchioles are small tubes that connect alveoli to the trachea, allowing movement of inhaled and exhaled air throughout the lungs

Question 15

`Which muscles work collectively to either increase/decrease the volume of the thoracic cavity, which leads to pressure changes in lungs?

Answer 15

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

Question 16

What is the mechanism of breathing based on?

Answer 16

It is based on the inverse relationship between pressure and volume.

Question 17

What is Boyle’s Law?

Answer 17

It states that an increase in volume will lead to a decrease in pressure, and vice versa.

Question 18

What is the thoracic cavity + what does it contain?

Answer 18

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

Question 19

What is the function of the diaphragm in breathing?

Answer 19

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.

Question 20

What are the steps of inspiration (breathing in)?

Answer 20

1. the diaphragm contracts, increasing the volume of thoracic cavity
2. 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.
3. 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
4. The lung tissue responds to the lower pressure by increasing its volume
5. 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

Question 21

What are the steps of expiring?

Answer 21

1. The diaphragm relaxes, returning to its dome shape, which decreases the volume of the thoracic cavity
2. the external intercostal muscles relax, and the internal ones contract, pulling the rib cage down and inward, further reducing thoracic cavity volume
3. The decrease in thoracic cavity volume leads to an increase in pressure, pushin on the passive lung tissue
4. The lung tissue decreases in volume, increasing the pressure inside the lungs
5. 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.

Question 22

What device is used to measure lung volume?

Answer 22

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)

Question 23

the reactions/equations for cell respiration and photosynthesis

Answer 23

These 2 are opposite of eachother.
Cell respiration = glucose + oxygen -> carbon dioxide + water
Photosynthesis = carbon dioxide + water -> glucose + oxygen

Question 24

How are leaves adapted for gas exchange?

Answer 24

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

Question 25

What are the two primary energy-related processes in plants?

Answer 25

Cell respiration (produces ATP using oxygen) and photosynthesis (produces sugar using light)

Question 26

Are the rates of the two energy-related processes the same?

Answer 26

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

Question 27

Leaf's structural adaptation for gas exchange; Waxy cuticle

Answer 27

a wax lipid layer that covers the surface of leaves and prevents uncontrolled and excessive leaf water loss by evaporation

Question 28

Leaf's structural adaptation for gas exchange; palisade mesophyll

Answer 28

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

Question 29

Leaf's structural adaptation for gas exchange; spongy mesophyll

Answer 29

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

Question 30

Leaf's structural adaptation for gas exchange; veins

Answer 30

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

Question 31

Leaf's structural adaptation for gas exchange; a lower epidermis

Answer 31

small cells on the lower surface of leaves that secrete a waxy cuticle. guard cells forming stomata are embedded in this layer

Question 32

Leaf's structural adaptation for gas exchange; stomata

Answer 32

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

Question 33

What is transpiration?

Answer 33

Transpiration is the evaporation of water through open stomata in a leaf as a consequence of gas exchange for photosynthesis

Question 34

Why must stomata remain open for photosynthesis?

Answer 34

Stomata open to allow carbon dioxide to enter for photosynthesis, but this also leads to water loss through transpiration

Question 35

What happens to water lost through transpiration?

Answer 35

The evaporated water can be traced back to the water absorbed by the roots, which moves upward through the plant.

Question 36

What are the factors that influence rate of transpiration?

Answer 36

- 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

Question 37

Influential environmental factor on transpiration rate; increased light

Answer 37

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

Question 38

Influential environmental factor on transpiration rate; increased temperature;

Answer 38

This increases rate of transpiration. This increases molecular movement, including increased evaporation of water

Question 39

Influential environmental factor on transpiration rate; Increased wind speed

Answer 39

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

Question 40

Influential environmental factor on transpiration rate; increased humidity

Answer 40

This decreases rate of transpiration. Increased humidity lessens the water concentration gradient between the inside and outside of the leaf

Question 41

What is haemoglobin?

Answer 41

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

Question 42

What is the structure of the haemoglobin molecule?

Answer 42

Haemoglobin has a quaternary structure, composed of four polypeptide chains, each with a haem group containing an iron atom

Question 43

How does haemoglobin bind to oxygen?

Answer 43

Oxygen binds reversibly to the iron atom within each haem group, allowing haemoglobin to transport oxygen in the blood

Question 44

How many oxygen molecules can one haemoglobin molecule trasnport?

Answer 44

Since haemoglobin has 4 haem groups, it can bind up to four oxygen molecules

Question 45

What does it mean when haemoglobin is saturated?

Answer 45

Haemoglobin is saturated when all four haem groups are bound to oxygen, carrying the maximum possible amount of oxygen

Question 46

What is cooperative binding in haemoglobin?

Answer 46

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

Question 47

Why does haemoglobin with 3 oxygen molecules have a higher affinity for oxygen than haemoglobin with no oxygen molecules?

Answer 47

Each oxygen binding changes haemoglobin's shape, increasing it's affinity for the next oxygen molecule, making it easier to fully saturate

Question 48

What is allosteric binding in haemoglobin?

Answer 48

Allosteric binding occurs when carbon dioxide binds to the polypeptide chains (not the iron in the haem group), reducing haemoglobin's oxygen affinity

Question 49

What is the Bohr shift, and how does it affect haemoglobin?

Answer 49

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)

Question 50

What does the structural difference in fetus + mother haemoglobin enable?

Answer 50

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

Question 51

How does gas exchange occur between mother and foetus in the placenta?

Answer 51

The mother's and the fetus's capillaries are very close together, allowing oxygen and carbon dioxide to diffuse across the placenta

Question 52

Why does oxygen diffuse from the mother's blood to the foetus?

Answer 52

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

Question 53

How does foetal haemoglobin help in oxygen transfer?

Answer 53

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, allowing it to attract oxygen more effectively from maternal blood.

Question 54

What is the bohr shift?

Answer 54

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

Question 55

Why does the bohr shift occur in respiring tissues?

Answer 55

Respiring tissues produce CO2 which binds to haemoglobin and reduces its oxygen affinity, ensuring oxygen is delivered where it is needed most

Question 56

How does haemoglobin behave differently in the lungs compared to the body tissues?

Answer 56

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

Question 57

Why is the oxygen dissociation curve s-shaped?

Answer 57

The curve is s-shaped due to cooperative binding, meaning each oxygen molecule that binds increases haemoglobin's affinity for thee next oxygen molecule

Question 58

What does the oxygen dissociation curve show?

Answer 58

shows the relationship between partial pressure of oxygen and haemoglobin saturation, demonstrating how readily haemoglobin binds to and releases oxygen

Question 59

How does haemoglobin saturation change between lungs and body tissues?

Answer 59

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

Question 60

What would happen to the oxygen dissociation curve if haemoglobin did not have cooperative binding?

Answer 60

Without cooperative binding, the graph would be linear instead of s-shaped, as oxygen affinity would remain constant rather than increasing with each binding

Question 61

Why is the oxygen dissociation curve for foetal haemoglobin shifted to the left compared to maternal haemoglobin?

Answer 61

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

Question 62

Why does the oxygen dissociation curve shift to the right in environments with high CO2 (bohr shift)?

Answer 62

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