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Physical methods that organisms have to obtain oxygen from their surroundings and remove excess carbon dioxide.

Key Words



Gas exchange



Tracheal tubes

Key Concepts

Gas exchange

Simple organisms




List organs used by humans

Construct model of respiratory system

Study the mechanics of breathing

Respiratory Surface

Surface through which gas exchange takes place

Thin walled


In contact with a source of oxygen

In contact with a transport system

Gas Exchange- takes place by diffusion

Protists- takes place through the body surface (cell membrane). O2 passes into the cytoplasm from the surrounding water and CO2 diffuses out of the cytoplasm into the surrounding water.

Gas exchange

Hydra- cells of the two layers that make up the body are in direct contact with water. The exchange of gases is direct diffusion between body cells and the environment.

Gas exchange

Large, multicellular animals must exchange large amounts of gases across a respiratory surface so gas exchange is different for:

Animals that must breath in water

Animals that breath air

Respiratory Pigments

Respiratory pigments carry oxygen and carbon dioxide between the respiratory surface and the body cells.

They allow blood to carry more O2 and CO2 than plane water.

Example hemoglobin vs. water

Gas Exchange in the Earthworm

The skin is the respiratory surface and must be moist. Damp soil keeps it moist in order for it to work. If the skin gets dry they suffocate. Too much water can drown them. That’s why we see them on the sidewalks after heavy rain.

Capillaries just below the skin carry oxygen to the body cells.

Blood passes oxygen to the cells and picks up carbon dioxide back to the skin where it is diffused into the air.

Gas Exchange in the Grasshopper

Blood does not carry oxygen or carbon dioxide to the cells.

System of air tubes called "tracheal tubes" carry air directly to the cells.

Air enters and leaves through 10 pair (20) openings called "spiracles". From these, the tracheal tubes branch into smaller and smaller tubes

Oxygen diffuses from the tracheal tubes to the body cells and carbon dioxide diffuses from the cells to the tracheal tubes.

"Air sacs" are collapsible chambers that are connected to the tubes and they pump air in and out of the tracheal system.

Gas Exchange Through Gills

Gills are thin layers of tissue that have lots of blood vessels that can provide a large surface area for gas exchange.

Water passes over them and dissolved oxygen diffuse into the blood which carries it to all parts of the body. Carbon dioxide passed from the blood, out the gills and into the water.

Gills require constant water flow. If the water stops, the gills dry out and the animal dies from lack of oxygen.

Section Review

1. Which two gases do organisms exchange in their surroundings?

2. What is a respiratory surface?

3. How does gas exchange occur in portists? In earth worms?

4. Name the gas-exchange organs of such water-dwellers as fish, clams and lobster.

The Human Respiratory System

Structures and function of the human respiratory system

Four phases of gas exchange in humans

How body cells get oxygen and get rid of carbon dioxide

Five diseases of the human respiratory system

Structure of the Human Respiratory System

Lungs-gas exchange organ in air-breathing vertebrates and some other animals

Diaphragm-muscle that forms the floor of the chest cavity and separates the lungs from the abdominal cavity

Pleura- two layered membrane that encloses the lungs. One layer touches the lung, the other is in contact with the diaphragm and other organs in the chest cavity. A lubricating fluid between the two allows for the lungs to move freely during breathing.

The Nose- air enters through the nostrils into the nasal passages into capillaries. Hair in the nose prevents foreign matter from entering the air passages.

Pharynx and Larynx- air passes into the pharynx (throat) into the larynx (voice box). Vocal cords are two membranes that are stretched over the larynx and when air is breathed out they vibrate. The epiglottis prevents food and fluid from entering the larynx.

Trachea- "windpipe"- tube about 12cm long. Held open by rings of cartilage.

Structure of the Human Respiratory System, cont.

Bronchi – two cartilage-ringed tubes that divide from the trachea. These enter the lungs and branch into bronchial tubes.

Bronchioles- a group of tiny tubes that have branched from the bronchial tubes whose ends look like a bunch of grapes.

Alveoli- tiny air chambers at the end of the bronchioles that are the respiratory surface. This is where the exchange of air and carbon dioxide takes place.

The lungs contain approximately 300milliion alveoli.

The Consequences of Smoking

The respiratory system cannot handle smoke. Smoke stops the motion of the cilia that line parts of the respiratory structures and increases the amount of mucus build up in air passages.

Normally, phagocytic macrophages ingest foreign particles, but when increased amounts of particles accumulate from smoking the macrophages can no longer handle the work and damage to lung tissue occurs.

Four Stages of Gas Exchange in Humans

1. Breathing is the movement of air into and out of the lungs.

2.External respiration is the exchange of oxygen and carbon dioxide between the air and the blood in the lungs.

3. Internal respiration is the exchange of oxygen and carbon dioxide between the blood in the capillaries and the body cells.

4. Oxygen and carbon dioxide transport is the movement between the lungs and other body parts.

Breathing (physical process)

Inhalation- draws air into the lungs and is the active phase of breathing. The ribs are pulled up and out and the diaphragm is pulled down, reducing the pressure in the chest cavity. Air rushes down the air passages into the lungs.

Exhalation- passive phase of breathing. The diaphragm relaxes and moves up and the air in the lungs is moved out.

Breathing, cont.

Normal rates 12-25 times per minute.

Breathing is controlled by the respiratory center in the brain.

Chemoreceptors – the aorta and other large arteries can sense the amount of O2 and CO2 in the blood. When the levels of CO2 become elevated, the brain is stimulated to raise the rate of respiration to decrease the amount of carbon dioxide in the blood. This works the same for increased lactic acid in the muscles.

External and Internal Respiration

External- exchange of oxygen and carbon dioxide between the air and the blood.

Internal- exchange of oxygen and carbon dioxide between the blood in the capillaries and the body cells.

Oxygen Transport

Most oxygen is carried from the lungs to the body tissue by the hemoglobin in the red blood cells.

Oxyhemoglobin (HbO2)- Oxygen and hemoglobin combined. Oxygen-rich blood is bright red in color. Blood with lower concentrations of oxygen is dark red or deep purple.

Carbon Monoxide-gas that prevents oxygen from binding with hemoglobin (often seen in smokers)

Carbon Dioxide Transport

Carbon Dioxide is the gas produced by cellular respiration. Carried by the blood in 3 ways:

70% converted with water into carbonic acid which breaks down into hydrogen ions and bicarbonate ions and carried away in the plasma

20% carried away in the hemoglobin (carboxyhemoglobin)

10% diffuses in the blood and is dissolved in the plasma and carried to the lungs

Diseases of the Respiratory System

Asthma- allergic reaction

Bronchitis- inflammation of the bronchial tubes

Emphysema- loss of elasticity of the lungs

Pneumonia- fluid in the alveoli that prevents exchange of gases

Lung Cancer- abnormal cell growth within the lung tissue

Section Review

What role do the nasal passages and the diaphragm play in gas exchange?

What is the name of the respiratory surface in humans?

What are the four phases of gas exchange in humans?

Name three respiratory diseases that are more common in cigarette smokers than non-smokers.

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