Sample Material of Our Online Coaching Programme
Subject: General Science
Topic: The Respiratory System
Cellular respiration involves the breakdown of organic molecules to produce
ATP. A sufficient supply of oxygen is required for the aerobic respiratory
machinery of Kreb’s Cycle and the Electron Transport System to efficiently
convert stored organic energy into energy trapped in ATP. Carbon dioxide is also
generated by cellular metabolismand must be removed from the cell. There must be
an exchange of gases: carbon dioxide leaving the cell, oxygen entering. Animals
have organ systems involved in facilitating this exchange as well as the
transport of gases to and from exchange areas.
RESPIRATION IN SINGLE CELL ANIMALS
Single-celled organisms exchange gases directly across their cell membrane.
However, the slow diffusion rate of oxygen relative to carbon dioxide limits the
size of singlecelled organisms. Simple animals that lack specialized exchange
surfaces have flattened, tubular, or thin shaped body plans, which are the most
efficient for gas exchange. However, these simple animals are rather small in
RESPIRATION IN MULTICULTURAL ANIMALS
Large animals cannot maintain gas exchange by diffusion across their outer
surface. They developed a variety of respiratory surfaces that all increase the
surface area for exchange, thus allowing for larger bodies. A respiratory
surface is covered with thin, moist epithelial cells that allow oxygen and
carbon dioxide to exchange. Those gases can only cross cellmembranes when they
are dissolved in water or an aqueous solution, thus respiratory surfaces must be
ETHODS OF RESPIRATION OF VARIOUS ORGANISMS
(a) Sponges and jellyfish lack specialized organs for gas exchange, so they
take gases directly from the surrounding water.
(b) Flatworms and annelids use their outer surfaces as gas exchange surfaces.
Earthworms have a series of thin-walled blood vessels known as capillaries. Gas
exchange occurs at capillaries located throughout the body as well as those in
the respiratory surface
(c) Amphibians use their skin as a respiratory surface. Frogs eliminate
carbon dioxide 2.5 times as fast through their skin as they do through their
lungs. Eels (a fish) obtain 60% of their oxygen through their skin. Humans
exchange only 1% of their carbon dioxide through their skin. Constraints of
water loss dictate that terrestrial animals must develop more efficient lungs.
(d) Arthropods, annelids, and fish use gills: Gills greatly increase the
surface area for gas exchange. They occur in a variety of animal groups
including arthropods (including some terrestrial crustaceans), annelids, fish,
and amphibians.Gills typically are convoluted outgrowths containing blood
vessels covered by a thin epithelial layer. Typically gills are organized into a
series of plates and may be internal (as in crabs and fish) or external to the
body (as in some amphibians).Gills are very efficient at removing oxygen
fromwater: there is only 1/20 the amount of oxygen present in water as in the
same volume of air.Water flows over gills in one direction while blood flows in
the opposite direction through gill capillaries. This countercurrent flow
maximizes oxygen transfer. Terrestrial vertebrates utilize internal lungs:
(e) Tracheal Systems: Many terrestrial animals have their respiratory
surfaces inside the body and connected to the outside by a series of
tubes.Tracheae are these tubes that carry air directly to cells for gas
exchange. Spiracles are openings at the body surface that lead to tracheae that
branch into smaller tubes known as tracheoles. Body movements or contractions
speed up the rate of diffusion of gases from tracheae into body cells. However,
tracheae will not function well in animals whose body is longer than 5 cm.
(f) Lungs: Lungs are ingrowths of the body wall and connect to the outside by
as series of tubes and small openings. Lung breathing probably evolved about 400
million years ago. Lungs are not entirely the sole property of vertebrates, some
terrestrial snails have a gas exchange structures similar to those in frogs.