UNIT 3 – Internal Systems
 Gas exchange / Respiratory systems
 Transport / Circulatory systems
 Digestive systems
 Pig Dissection
 multi-celled organisms require coordinated systems in order to
supply the specialized cells with materials they require (and removal
of waste materials)
The Breath of Life
Aerobic organisms require Oxygen (O2)
 O2 is necessary for cellular respiration
 releases energy to drive all cellular functions
 CO2 is the waste product of cellular respiration that must be disposed of
Gas Exchange:
 the process that ensures O2 enters each cell of an organism and CO2 can
leave each cell.
Gas exchange systems/Respiratory systems vary for different organisms
but all must have TWO requirements:
1. Surface Area:
 Must be large enough for enough O2 to enter and CO2 to leave in order to
meet the metabolic needs of the organism.
2. Moist Environment:
 Allows for gas exchange to take place
 since O2 and CO2 must be dissolved in order to be transported
Unicellular organisms – eg. amoeba, algae
 Exchange gas through membrane by diffusion
 Membrane must be moist (live in moist environment)
Larger Multicellular organisms
 Require specialized systems !
 greater need for O2 and
 greater distance O2 must travel to reach all cells
PROBLEMS with being multicellular:
1. Diffusion is only effective over a distance of a few cells.
2. As the body surface becomes more specialized, the surface area available for
gas exchange is reduced.
SOLUTIONS:  Specialized Respiratory Systems
Skin Respiration
eg. earthworms, leeches (see textbook p. 252)
 Skin must remain moist
 Skin lined with tiny capillary vessels
 O2 carried through circulatory vessels to other cells of the organism
eg. fish, crayfish (see textbook p. 253)
 Structural changes increase the surface area of the body parts involved
in gas exchange
 Mechanism has evolved which enables the organism to ventilate this
 oxygen-containing aquatic medium moves over respiratory surface
Example: fish gills
 feathery tissue structures consisting of numerous delicate branches
 ensures a large surface area in a limited space
 connected to vascular system to transport O2 and CO2 to and from cells
What about Terrestrial Organisms?
 they have an internal gas exchange system
 is an important process as it forces O2 across the gas exchange surface.
 It relies on a basic law of physics
 air moves from a region of high pressure to a region of low pressure
until equilibrium is reached. (see textbook p. 254)
Tracheal Respiratory System
eg. insects like grasshoppers
 An internal system allows to maintain a moist environment
 Consists of external pores called “spiracles”  controlled by valves
 Connected to internal network of tubes called “tracheae”
 Air is ventilated via contraction and relaxation of the abdomen
The circulatory system is separate from the respiratory system
 branches of tracheal tubes ensure contact with the cells
Be able to distinguish between the following terms:
 Breathing
 Gas Exchange
 Cellular Respiration
The Gas Exchange System:
What is its overall function?
 To supply cells with O2 and to remove CO2
Note: there is a need for a circulatory system to transport the gases to and
from the cells
Why is our system highly specialized?
 Since we are warm blooded  must maintain constant internal temp.
 To maintain the temp  requires lots of energy
 lots of O2 is needed for cellular respiration
Our Gas Exchange System must have:
1. Large surface area  to maximize O2 exchange
2. Moist surface area  for diffusion
3. Ventilation Mechanism  force O2 across lung surface
Breathing  Gas Exchange  Cellular Respiration
What is inhalation? Inspiration?  breathing in
What is exhalation? Expiration?  breathing out
INHALATION – Journey through Respiratory Tract
Upper Respiratory Tract:
Why does it usually take place through the nose?
 Nose hair  filters dust from air
 Capillaries close to surface  warm the air
 Mucus  moistens the air
Where does air go after the nose?
 Pharynx  opening to digestive system (esophagus)
 opening (glottis) to gas exchange system (trachea)
Note: Why don’t we choke when we eat?
 epiglottis closes over trachea when swallowing
What adaptations does the trachea have? Why?
 Larynx  voice box
 Mucus/Cilia  move dust and foreign particles out of lungs
 Cartilage Rings  to maintain an open airway
Lower Respiratory Tract:
After the trachea, where does the air go?
 Bronchi (two branches of the trachea)  branches further to “Bronchioles”
What is the actual site of Gas Exchange?
 grape-like cluster of tiny sacs at the end of each bronchiole
 kept moist for gas exchange
 sac wall is a thin membrane (1 cell thick)
 capillary bed (containing blood) surrounds air sac
Structure of Lungs:
Where are the lungs located? Why?
 in the pleural or chest cavity  protected by ribs
What stops the lungs from collapsing?
 Pleural membrane surrounds lungs
 two layers with lubricating fluid between them
 Elastic connective tissue fills the spaces in between the structure
 Alveoli lined with a lubricating film
How many lobes does each lung have?
 Right lung  3 lobes
 Left lung  2 lobes
How does enough air get down to the alveoli?
 By “Breathing Movements”
(see text p. 260, coursepack p. 41)
GAS EXCHANGE – Some More Details
O2 and CO2 are exchanged across the cell membrane.
 Alveoli and adjacent capillaries are only one cell thick.
 Inhaled Air contains:
 ~ 20.94 % O2
 ~ 0.04 % CO2
 Oxygen diffuses into blood from the alveoli (by simple and facilitated
 Exhaled Air contains:
 ~ 16.49 % O2
 ~ 4.49 % CO2 (CO2 diffuses out of the blood into the alveoli)