BIO2242 Lecture Notes - Lecture 9: Water Balance, Photosynthesis, Homeostasis
Lecture 9 – Respiration
The need for Respiration
• Need to fuel metabolism
• Environment cellular metabolism
• Nutrients
• Respiratory gasses
• Waste products
• Water/salts
Sources of Oxygen
• Air and water
• Air breathers have a massive advantage
• Mass of water very high
• Environmental oxygen is not constant in space or time
o Turbulent vs stagnant
o Cold water has more
o Diurnal fluctuations e.g. algae
o Oxygen availability varies with altitude
▪ Air at higher altitude exposed to lower pressure of O2
o Photosynthesis generates oxygen
o Fresh water environments receive more oxygen than sea water
environments
Respiration in Water
• Animals without respiratory organs are usually small, thin or porous
o Respiratory organs increase diffusive surface area
• Low oxygen requirement –
diffusion
o Large surface area: volume
ratio
o Small animal – large
surface area
o Large animals, large
demands
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• Gills are efficient in water but not in air
o Oxygenated blood and water flow in opposite directions
o Increase in surface area facilitates gas exchange, also:
▪ Arrangement in which water flows over the surface area and
blood flows against the water
• Challenges of exchanging water in oxygen environment:
o Water is dense, heavy, viscous
o Diffusion is slow, animals, continuously sucking oxygen out of water
→ water is still → deplete oxygen around them → hypoxia → need to
ventilate gills
• Fish (vertebrates) use active gill pumping mechanisms
▪ Fish balance their gill area with metabolic requirement
• Fish with high metabolic demands have high gill
surface area: smaller diffusion distances (tuna)
• Gill ventilation
o Expend energy in order to move water out of gills
▪ Cost energy to do this because water is heavy and viscous
o Pumping motion: sucking water into mouth, closing cavity and
pushing water out of gills
o Hydrophobic hairs allow it to carry air
o Gill area is proportional to activity level to supply oxygen requirement
o Blood very close to water, constantly at risk of exchanging ions and
losing ions to environment → difficult to maintain homeostasis
▪ Fish balance their gill area with metabolic requirement
• Fish with high metabolic demands have high gill
surface area: smaller diffusion distances (tuna)
• Toadfish doesn’t move so has low gill surface area
because it doesn’t want to lose ions to environmental
• E.g. tuna vs toadfish
▪ Ram ventilation vs opercular pumping
• Mouth opens during swimming: water flows through
mouth and across the gills
• Metabolic rate drops – rate of oxygen consumption
declines (benefits)
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