Respiratory Systems: Fish and Animals
Fish Respiratory system
Countercurrent exchange is an adaptive tool that the fish use to maximise the exchange of oxygen from the water into the blood with the smallest use of energy. Countercurrent exchange uses Diffusion to passively (no energy required) transfer the oxygen across to the blood.
There are lots of gill filaments which each have a capillary network inside them. This increases the surface area available for this fish to use for gas exchange.
Because water is more water soluble at lower temperatures, it dissolves more easily into the blood and therefore fish do not require hemoglobin to assist with dissolving the oxygen in blood for transportation. Fish have lower metabolic rates than humans, and so their oxygen requirements are much lower than mammals and can live without hemoglobin. Q1) Why does the fish need oxygen? Q2) If we take a fish out of water why does it suffocate? |
Human Respiratory Systems
Breathing (respiration) for humans depends on pressure change created within the chest and expansion of the lungs in order for the air to move into the chest.
We use the intercostal muscles and the diaphragm in order to expand the chest cavity to change the pressure inside. Air moves along a pressure gradient, from areas of higher pressure to areas of lower pressure. Head to Dynamic Science to access the human respiratory system to learn more about how the respiratory system works |
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Surfactant
The oxygen molecule can only move into the tissues if it is dissolved into liquid. Therefore there is a layer of fluid that covers the epithelial cells of the alveoli.
Water and fluid has what we call surface tension. Surface tension basically means that the water molecules like each other but don't like to be separated and so they cling together. If we allowed the water molecules to simply sit inside the alveolus, the surface tension of the water molecules would pull so tightly that the alveolus would collapse.
Water and fluid has what we call surface tension. Surface tension basically means that the water molecules like each other but don't like to be separated and so they cling together. If we allowed the water molecules to simply sit inside the alveolus, the surface tension of the water molecules would pull so tightly that the alveolus would collapse.
The body balances this surface tension of water by producing surfactant. Surfactant (little yellow molecules) has a hydrophillic head (Water loving) which clings to the water molecules. It has a hydrophobic tail (Water hating) which sits away from the water molecule. This creates a sort of barrier around the water molecules and decreases the surface tension, allowing the alveoli to remain inflated so that air can move into them and dissolve in the water to be exchanged across the basement membrane.
Answers:
Q1) To perform cellular respiration for energy production: Glucose + Oxygen --> Carbon dioxide + Water + Energy
Q2) Animals with lungs can actively inhale and exhale to keep air flowing through them. This allow them to obtain more oxygen and expel more CO2. Fish mainly rely on their movement in the water to keep water flowing over their gills (there are exceptions to this). Out of water a fish has no way of moving air through its gills.
Also out of water gills don't keep their shape. They evolved in a relatively weightless environment and rely on that to spread out. Out of water they lose that support. Think of a persons hair underwater versus being wet on land and thats the effect you get. The gills intricate network that provides the large surface area needed is weighed down and inefficient on land.
Q1) To perform cellular respiration for energy production: Glucose + Oxygen --> Carbon dioxide + Water + Energy
Q2) Animals with lungs can actively inhale and exhale to keep air flowing through them. This allow them to obtain more oxygen and expel more CO2. Fish mainly rely on their movement in the water to keep water flowing over their gills (there are exceptions to this). Out of water a fish has no way of moving air through its gills.
Also out of water gills don't keep their shape. They evolved in a relatively weightless environment and rely on that to spread out. Out of water they lose that support. Think of a persons hair underwater versus being wet on land and thats the effect you get. The gills intricate network that provides the large surface area needed is weighed down and inefficient on land.