IGCSE, Respiration Structures for Gas Exchange

Gas Exchange Basics Organisms need to exchange O 2 and CO 2 with the environment. Gas exchange occurs by DIFFUSION.

Basics (continued) Single cells, and small organisms living in an aquatic environment can exchange gasses through body surfaces, because of large SURFACE TO VOLUME RATIO. Marine flatworm

5 1 Total surface area (height  width  number of sides  number of boxes) Total volume (height  width  length  number of boxes) Surface-to-volume ratio (surface area  volume)

Basics (continued) As size increases, surface to volume DECREASES, making specialized gas exchange structures necessary. Sea slug. Fleshy “gills” on its back increase surface area.

Basics (continued) Marine worm (polychaete), unjointed limbs serve for locomotion and for gas exchange. Parapodia

Specialized Gas Exchange Surfaces Larger animals have specialized surfaces just for gas exchange. Gills Trachial Systems Lungs

Gills Some marine worms and arthropods, mollusks, and fish have gills. Gills are tissues with a rich blood supply, divided into plates or filaments to increase surface area.

Gills of a Christmas Tree Worm

Gills of a Salmon

Crayfish, shell removed to show gills

“Book Gills” of a Horseshoe Crab

Trachial Systems Land arthropods (insects, spiders, scorpions, etc.) breath through trachial systems. Spiracle Tracheae Air sacs Air sac Body cell Air Trachea Tracheole Tracheoles Body wall

Trachial Systems (continued) In a trachial system, air is circulated to a system of air sacs throughout the animal’s body. Thus every cell is near a source of air.

Lungs Some fish, amphibians, all reptiles, birds and mammals use lungs. Lungs are large bags, divided into millions of tiny air sacs called alveoli. Alveoli increase surface area.

Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole Branch from the pulmonary artery (oxygen-poor blood) Alveoli Colorized SEM SEM 50 µm Heart Left lung Nasal cavity Pharynx Larynx Diaphragm Bronchiole Bronchus Right lung Trachea Esophagus The mammalian respiratory system

Negative pressure breathing Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air inhaled Air exhaled INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up) Diaphragm Lung

Circulatory Systems Distributing Oxygen, Eliminating Carbon Dioxide in Multicellular Organisms

Circulatory Systems consist of Heart – pumps blood Arteries – carry blood away from the heart Veins – carry blood back to the heart Capillaries – connect arteries to veins, allow for gas exchange with tissues

Heart Hemolymph in sinuses surrounding organs Interstitial fluid Heart Small branch vessels in each organ Anterior vessel Lateral vessels Ostia Tubular heart Dorsal vessel (main heart) Ventral vessels Auxiliary hearts (a) An open circulatory system(b) A closed circulatory system Open and closed circulatory systems

Hearts Fish – 2 chambered heart (atrium and ventricle), one circuit Amphibians – 3 chambered heart (2 atria, one ventricle, 2 circuits (pulmonary and systemic) Reptiles – 3 chambered with some division of ventricle, 2 circuits Mammals & Birds – 4 chambered heart, 2 circuits

Figure 42.4 Vertebrate Circulatory Systems FISHES AMPHIBIANS REPTILES MAMMALS AND BIRDS Systemic capillaries Lung capillaries Lung and skin capillariesGill capillaries Right Left RightLeft Right Left Systemic circuit Pulmocutaneous circuit Pulmonary circuit Systemic circulation Vein Atrium (A) Heart: ventricle (V) Artery Gill circulation A V V VVV A A A AA Left Systemic aorta Right systemic aorta