Gas Exchange in Fish Gills
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of diffusion and surface area to volume ratio to understand how aquatic organisms obtain oxygen from water.
Name a substance that diffuses out of cells?
Carbon dioxide
Describe how surface area affects the rate of diffusion.
Increased surface area increases the rate of diffusion
Why do organisms have thin exchange surfaces?
Reduces the diffusion distance so increases the rate of diffusion
Topic Explainer Video
Check out this @JoeDoesBiology video that explains gas exchange in fish gills, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Gas Exchange in Fish Gills
What Are Gills?
- Gills are the gas exchange organs in fish.
- Located on either side of the fish’s head, behind the operculum (gill cover).
- Made up of gill filaments, which are covered in lamellae (thin plates) for increased surface area.
Process of Gas Exchange in Gills
1. Water enters through the fish’s mouth and flows over the gills.
2. Oxygen in the water diffuses into the blood in the gill capillaries.
3. Carbon dioxide diffuses out of the blood into the water.
Adaptations of Gills for Efficient Exchange
|
Adaptation |
Explanation |
|
Large surface area |
Provided by many gill filaments and lamellae for more diffusion. |
|
Thin exchange surface |
The filaments and lamellae are thin to provide a short diffusion distance between water and blood. |
|
Rich blood supply |
Capillaries in the lamellae carry away oxygen in the blood quickly to maintain a steep concentration gradient. |
|
Counter-current flow |
Water and blood flow in opposite directions to maintain a steep concentration gradient. For example, water with a higher concentration of oxygen will always be next to blood with a lower concentration of oxygen, so oxygen will continue to diffuse from the water into the blood. Equilibrium will never be reached. |
Key Terms
- Concentration gradient – difference in concentration between two areas
- Equilibrium - where the concentrations are equal (and diffusion will stop)
No answer provided.
Exam Tips
- Link the adaptations of the fish gills to the factors that affect the rate of diffusion.
- These factors are common - large surface area, thin walls to decrease diffusion distance and a good blood supply to maintain a steep concentration gradient.
No answer provided.
Fish gills have many capillaries. Explain why. (2 marks)
- Many capillaries increases the blood supply which maintains the concentration gradient
- Which increases the rate of diffusion
More Practice
Try to answer the practice question from the TikTok video on your own, then watch the video to see how well you did!