7.4.2 - Ventilation and gas exchange in other organisms (fish)

Question 1

Why do animals that get oxygen from water not need to prevent water loss from their gaseous exchange surfaces like land animals do?

Answer 1

• Water does not evaporate in the same way as air.
• Gaseous exchange surfaces in water animals are not exposed to the air, so there’s no risk of water loss.

Question 2

What challenges do aquatic animals face when obtaining oxygen compared to land animals?

Answer 2

1. Water is 1000 times denser and 100 times more viscous than air, making it harder to move.
2. Water has a much lower oxygen content than air, which reduces the diffusion rate of oxygen.
3. These factors make obtaining oxygen through diffusion much slower in water than in air.

Question 3

Why is moving water in and out of lung-like organs inefficient for aquatic animals?

Answer 3

1. Water is dense and viscous, which requires significant energy to move in and out of lung-like organs.
2. Instead, aquatic animals evolved a more efficient system of moving water in one direction over their gills.

Question 4

How do bony fish like trout and cod obtain oxygen from water?

Answer 4

1. Bony fish have specialized gills that allow them to extract oxygen from water.
2. They maintain a continuous flow of water over the gills in one direction, ensuring efficient gas exchange.

Question 5

What are the features of fish gills that make them suitable for extracting oxygen from water?

Answer 5

1. Gills have a large surface area.
2. They have a rich blood supply.
3. They are composed of thin layers to facilitate gas exchange.

Question 6

Why do fish have a high oxygen demand and what is their challenge in obtaining enough oxygen?

Answer 6

1. Fish are active animals with a high metabolic rate, leading to increased oxygen demand.
2. Their surface area to volume ratio is not large enough to rely on diffusion alone to meet their oxygen needs.
3. The fish’s scaly outer covering prevents gaseous exchange, so they have evolved gills to extract oxygen.

Question 7

What is the role of the gill lamellae in fish respiration?

Answer 7

1. The gill lamellae are the main site of gaseous exchange.
2. They are rich in blood vessels and provide a large surface area for gas exchange.
3. They facilitate the diffusion of oxygen from water into the fish’s blood and carbon dioxide from blood into water.

Question 8

How do gill filaments contribute to gas exchange in fish?

Answer 8

1. Gill filaments are stacked in large plates called gill arches.
2. The flow of water keeps the filaments apart, ensuring that the large surface area is exposed for gas exchange.
3. This structure helps maximize the efficiency of oxygen uptake and carbon dioxide removal.

Question 9

What are the main challenges of gaseous exchange in aquatic environments?

Answer 9

1. Slow diffusion rate: Oxygen diffuses more slowly in water than in air.
2. Low oxygen concentration in water: This limits the amount of oxygen available for diffusion.
3. Maintaining a continuous flow of water: Necessary to keep oxygen concentration gradients in place for efficient gas exchange.

Question 10

How do fish maintain a continuous flow of water over their gills?

Answer 10

1. Fish open their mouths to draw water in and close their operculum to push water over the gills.
2. This coordinated action creates a constant flow of water, even when the fish is stationary.

Question 11

What is ram ventilation in cartilaginous fish, such as sharks and rays? Why do they use it?

Answer 11

1. Ram ventilation is the method used by cartilaginous fish (e.g., sharks and rays) to ventilate their gills.
2. These fish rely on constant movement through the water to force water over their gills.
3. This method is energy-efficient for these species, as they do not need to actively pump water.

Question 12

How do most bony fish ventilate their gills when they are not swimming?

Answer 12

1. Bony fish use their operculum (a bony flap) to actively pump water over their gills.
2. This system allows fish to ventilate their gills even when they are not swimming, ensuring a continuous flow of water for gas exchange.

Question 13

What is the operculum and how does it assist in fish respiration?

Answer 13

1. The operculum is a bony flap that covers and protects the gills.
2. It helps maintain water flow over the gills by opening and closing, creating a pressure difference that moves water across the gills.

Question 14

Why is diffusion of oxygen slower in water than in air?

Answer 14

1. Water has a much lower oxygen content than air.
2. Water is denser and more viscous than air, which increases the difficulty of oxygen diffusion.
3. These properties make it harder for oxygen to reach the fish’s blood through diffusion.

Question 15

How do fish overcome the issue of low oxygen content in water?

Answer 15

1. Fish have evolved gills with a large surface area and a rich blood supply to maximize oxygen uptake.
2. They maintain a continuous flow of water over their gills, ensuring that oxygen is always available for diffusion.

Question 16

What is the importance of a continuous water flow over the gills of a fish?

Answer 16

1. A continuous flow maintains the oxygen concentration gradient between the blood and the water.
2. This ensures that oxygen is constantly diffused into the blood and carbon dioxide is removed efficiently.

Question 17

How do fish cope with the challenges posed by the viscosity of water?

Answer 17

1. Fish use a highly specialized gill ventilation system to reduce the energy required for water movement.
2. Moving water in one direction over the gills is more energy-efficient than moving it in and out.

Question 18

What is the role of the blood supply in fish gills?

Answer 18

1. The gills are richly vascularized with blood vessels.
2. This high blood supply ensures rapid transport of oxygen into the bloodstream and carbon dioxide out.
3. The blood supply helps maintain the concentration gradients for both oxygen and carbon dioxide.

Question 19

How do fish ensure that the surface area of their gills remains maximized for efficient gas exchange?

Answer 19

1. Water flow keeps the gill filaments separated, preventing collapse and maximizing the surface area for gas exchange.
2. Additionally, gill lamellae increase the surface area where gas exchange occurs.

Question 20

What is the significance of the thin layers in fish gills?

Answer 20

1. Thin layers in the gills allow for faster and more efficient diffusion of oxygen and carbon dioxide.
2. The reduced distance between the water and the blood enhances gas exchange efficiency, which is crucial for meeting the fish’s oxygen demands.

Question 21

How do cartilaginous fish (e.g., sharks and rays) differ from bony fish in terms of gill ventilation?

Answer 21

1. Cartilaginous fish rely on ram ventilation, which requires constant movement through the water to force water over their gills.
2. Bony fish use the operculum to actively pump water over their gills, allowing them to breathe even when stationary.

Question 22

Why is maintaining a high blood flow important for fish during respiration?

Answer 22

1. High blood flow ensures that oxygenated blood is rapidly circulated throughout the body.
2. It also helps quickly remove carbon dioxide from tissues, promoting efficient gas exchange by maintaining the concentration gradients for both gases.

Question 23

How do the gills of fish allow for efficient gas exchange in water?

Answer 23

1. Large surface area: Provided by gill filaments and lamellae, increases space for gas exchange.
2. Rich blood supply: Ensures oxygen is absorbed efficiently.
3. Thin layers: Facilitate quick diffusion.
4. Unidirectional water flow: Ensures constant exposure to oxygenated water.

Question 24

What is the relationship between the fish’s surface area to volume ratio and its need for specialized respiration?

Answer 24

1. Fish have a low surface area to volume ratio, which means diffusion alone is not enough to meet their oxygen needs.
2. This is why fish have evolved gills with a large surface area to efficiently extract oxygen from water.

Question 25

What is the evolutionary advantage of fish using gills instead of lungs?

Answer 25

1. Gills are highly efficient for oxygen extraction from water due to their large surface area and thin membranes.
2. Gills allow fish to extract oxygen efficiently even in low-oxygen environments, unlike lungs, which are adapted for air.

Question 26

What is the mechanism behind the movement of water over fish gills when they are not swimming?

Answer 26

1. Fish open their mouths to draw in water and close their operculum to push it over the gills.
2. This process maintains water flow and ensures continuous gas exchange even when the fish is not swimming.

Question 27

What structural adaptations do gills have to overcome the challenges of water’s lower oxygen content?

Answer 27

1. Large surface area: Increases the area for gas exchange.
2. Rich blood supply: Ensures oxygen is absorbed efficiently.
3. Thin layers: Facilitate quick diffusion of oxygen and carbon dioxide.
4. Unidirectional water flow: Ensures constant exposure to oxygenated water.

Question 28

Describe the steps of inspiration in fish.

Answer 28

1. Mouth Opens & Buccal Cavity Floor Lowers
2. Water Enter
3. Opercular Valve Closes
4. Opercular Cavity Expands
5. Water Moves Over Gills
6. Oxygen Exchange

Question 29

How does the mouth opening & Buccal Cavity Floor Lowering help inspiration in fish?

Answer 29

The fish opens its mouth, and the floor of the buccal cavity lowers, increasing the cavity’s volume and reducing pressure inside.

Question 30

How does water enter the fish during inspiration?

Answer 30

1. As the floor of the buccal cavity lowers, the pressure inside drops.
2. This creates a pressure difference, causing water to flow into the buccal cavity.

Question 31

What happens after the water enters the buccal cavity in fish respiration?

Answer 31

1. The opercular valve closes, trapping the water inside the buccal and opercular cavities.
2. This prevents water from escaping.

Question 32

What occurs after the opercular valve closes during inspiration in fish?

Answer 32

1. The opercular cavity expands, further lowering the pressure inside the cavity.
2. This allows for more water to be drawn in.

Question 33

How is water moved over the gills in fish during inspiration?

Answer 33

1. The floor of the buccal cavity rises, increasing pressure inside the buccal cavity.
2. This increased pressure forces the water over the gills.

Question 34

What happens during oxygen exchange in the fish’s gills?

Answer 34

1. Oxygen diffuses from the water into the fish’s blood.
2. Carbon dioxide diffuses from the blood into the water.

Question 35

What is the process that occurs during expiration in fish?

Answer 35

1. The mouth closes to prevent water from re-entering the buccal cavity.
2. The operculum opens to allow water to exit.
3. The opercular cavity contracts, increasing pressure inside.
4. The increased pressure forces water over the gills, expelling carbon dioxide and retaining oxygen.
5. The water exits through the operculum, and the floor of the buccal cavity rises to maintain pressure and push the water out.

Question 36

How does the process of expiration ensure water flows across the gills?

Answer 36

1. The closure of the mouth, the opening of the operculum, and the movement of the opercular cavity all work together.
2. This maintains pressure, forcing water out while the buccal cavity floor rises to maintain the flow of water over the gills.

Question 37

What structural features of fish gills aid in effective gaseous exchange in water?

Answer 37

1. Gills have a large surface area for diffusion.
2. Gills have a rich blood supply, maintaining steep concentration gradients.
3. The thin layers of the gills provide short distances for diffusion.

Question 38

What is the function of the overlapping tips of adjacent gill filaments?

Answer 38

1. The overlapping tips increase the resistance to the flow of water over the gills.
2. This slows down the movement of water, providing more time for gaseous exchange to occur.

Question 39

How does the flow of water and blood in fish gills contribute to efficient gas exchange?

Answer 39

1. The water moving over the gills and the blood in the gill filaments flow in different directions.
2. This creates a steep concentration gradient, enhancing diffusion efficiency.

Question 40

What is a countercurrent exchange system in fish respiration?

Answer 40

1. In a countercurrent system, blood and water flow in opposite directions over the gills.
2. This maintains a concentration gradient between the water and the blood, allowing continuous diffusion of oxygen into the blood and carbon dioxide into the water.

Question 41

How does a countercurrent exchange system improve gas exchange efficiency in fish?

Answer 41

1. The countercurrent flow ensures that oxygen continues to diffuse into the blood along the entire length of the gills.
2. This results in a much higher level of oxygen saturation in the blood compared to a parallel system.

Question 42

What is a parallel system in fish respiration?

Answer 42

1. In a parallel system, blood and water flow in the same direction over the gills.
2. Oxygen diffusion occurs until the oxygen concentration of the blood and water reach equilibrium, reducing the efficiency of oxygen uptake.

Question 43

How much oxygen can bony fish and cartilaginous fish extract from water using their respective systems?

Answer 43

1. Bony fish with a countercurrent exchange system can extract about 80% of the oxygen from the water flowing over their gills.
2. Cartilaginous fish with a parallel exchange system can only extract about 50% of the oxygen from the water.

Question 44

Why is a countercurrent exchange system more efficient than a parallel system for oxygen extraction?

Answer 44

1. In a countercurrent system, the oxygen concentration gradient is maintained all along the gill filaments.
2. This ensures that oxygen continues to diffuse into the blood throughout the gill surface, making the process more efficient.

Question 45

What is the effect of the countercurrent exchange system on oxygen saturation in fish blood?

Answer 45

1. The countercurrent exchange system ensures a higher level of oxygen saturation in the blood compared to a parallel system.
2. Oxygen continues to diffuse into the blood as long as there is a concentration gradient, leading to more efficient oxygen uptake.