5.5 bio notes

Gas Exchange and Circulation

Gas exchange is localized, necessitating a circulatory system to transport gases throughout the body.
Gases are transported in fluids: blood in vertebrates and hemolymph in invertebrates.
Circulation refers to the movement of gases dissolved in these fluids.
The circulatory system comprises organs and structures involved in circulating blood/hemolymph.

Gases are transported in a water-based environment.
Oxygen gas (O_2) has poor solubility in water due to its non-polar nature.
Only about 1.5% of oxygen in the blood is dissolved in water.
Multicellular organisms require assistance to carry sufficient oxygen.
Oxygen is transported by oxygen-binding proteins.
Hemoglobin is the oxygen-binding protein in vertebrates; it appears red when bound to oxygen.
Invertebrates use hemoglobin or hemocyanin as oxygen carriers.
Hemocyanin appears blue when bound to oxygen.
Carbon dioxide (CO_2) also dissolves poorly in water due to its non-polar nature.
Only 5-7% of carbon dioxide in the blood is dissolved in water.
Carbonic anhydrase is an enzyme present in blood and hemolymph.
Carbonic anhydrase catalyzes the conversion of carbon dioxide and water into carbonic acid (H2CO3):
CO2 + H2O \rightleftharpoons H2CO3
Carbonic acid presence regulates blood pH.
Lowering breathing rate decreases blood pH.
Increasing breathing rate increases blood pH.
Hyperventilation leads to dizziness and fainting due to high blood pH, reducing blood flow to the brain.

Invertebrates utilize a tracheal system for gas exchange.
Hemolymph surrounds the tracheal system.
Oxygen and carbon dioxide exchange directly between air and hemolymph.
Oxygen binds to hemoglobin or hemocyanin.
Carbonic anhydrase converts carbonic acid back into carbon dioxide, which diffuses out of the hemolymph.
Most invertebrates do not require a complex circulatory system because gas exchange occurs throughout the entire body.
Many invertebrates possess an open circulatory system.
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