Gas Exchange
Breathing is the way that oxygen is taken into bodies and carbon dioxide is removed. Sometimes
this is called ventilation.
Do NOT confuse breathing with respiration.
Respiration is a chemical process that happens in every cell in the body.
1. What gases do organisms need to get into and out of the body?
Animals: In 02, out C02
Plants (photosynthesis) : day = C02 → 02
night = nothing
2. Why does it need to happen fast?
For cells to respire and to release C02 to get rid of toxins, these lead to death
Surface area to volume ratio
● As the organism gets bigger, the SA increases which controls the rate of diffusion
● As the organism gets bigger, the volume increases which controls their requirement
● As the organism gets bigger, the SA to volume ratio decreases
Conclusion
Multicellular organisms with small SA: Volume ratio need a specialised exchange system to
increase rate of diffusion
What is the exchange surface in each case?
1. Humans getting nutrients - villi
2. Plants absorbing water/minerals - root hair cell
3. Mammals exchanging gases - lungs, fish = need large SA in gills
4. Plants exchanging gases - stomata
Human Respiratory System
When we breathe, air is moved into and out of our lungs. This involves different parts of the
respiratory system inside the thorax.
When we breathe in, air enters through the nose and mouth.
The air travels down the trachea to the lungs. Tiny hairs called cilia help to remove dirt and
microorganisms, pathogens
The air enters the lungs through the bronchi which branch and divide to form a network of
bronchioles.
, At the end of the bronchioles are air sacs called alveoli. The alveoli are covered in tiny blood
capillaries. This is where oxygen and carbon dioxide are exchanged between the blood and the air
in the lungs.
This is called Gas Exchange.
Surrounding the lungs are the pleural membranes. Between the membranes is a little fluid that
helps them slide smoothly over each other.
Outside the pleural membranes are ribs, between which are found the intercostal muscles, and
below the lungs is the diaphragm.
Function of the Thorax: Definitions
Thorax The upper half of the torso bounded by the diaphragm and the ribs
Trachea The breathing tube from the throat to the bronchus which is strengthened
by C shaped rings of cartilage to prevent collapse under negative pressures
when inhaling
Bronchus Branch of the trachea that carries air into one lung
Bronchioles The small tubes that carry air into the alveoli
Alveolus Thousands of these tiny air-sacs in the lungs where gas exchange occurs
Surface area Alveoli greatly increase this in the lungs
Diaphragm Big sheet of muscle separating the thorax from the abdomen
Ribs Bones that help to support the thorax
Intercostal Muscles The muscles that contract the move the ribs
Pleural membranes Thin moist membranes forming an airtight seal between the lungs and the
ribs/diaphragm
Pulmonary artery The vessel that carries blood from the heart of the lungs
Capillaries Arteries eventually divide into these tiny tubes which is where exchange of
gases occur
Ventilation Breathing in and out is called this
Diffusion The way that gases cross the membranes of the alveoli
Oxygen A gas that we need to respire
Carbon Dioxide Respiration produces this waste gas
Breathing is the way that oxygen is taken into bodies and carbon dioxide is removed. Sometimes
this is called ventilation.
Do NOT confuse breathing with respiration.
Respiration is a chemical process that happens in every cell in the body.
1. What gases do organisms need to get into and out of the body?
Animals: In 02, out C02
Plants (photosynthesis) : day = C02 → 02
night = nothing
2. Why does it need to happen fast?
For cells to respire and to release C02 to get rid of toxins, these lead to death
Surface area to volume ratio
● As the organism gets bigger, the SA increases which controls the rate of diffusion
● As the organism gets bigger, the volume increases which controls their requirement
● As the organism gets bigger, the SA to volume ratio decreases
Conclusion
Multicellular organisms with small SA: Volume ratio need a specialised exchange system to
increase rate of diffusion
What is the exchange surface in each case?
1. Humans getting nutrients - villi
2. Plants absorbing water/minerals - root hair cell
3. Mammals exchanging gases - lungs, fish = need large SA in gills
4. Plants exchanging gases - stomata
Human Respiratory System
When we breathe, air is moved into and out of our lungs. This involves different parts of the
respiratory system inside the thorax.
When we breathe in, air enters through the nose and mouth.
The air travels down the trachea to the lungs. Tiny hairs called cilia help to remove dirt and
microorganisms, pathogens
The air enters the lungs through the bronchi which branch and divide to form a network of
bronchioles.
, At the end of the bronchioles are air sacs called alveoli. The alveoli are covered in tiny blood
capillaries. This is where oxygen and carbon dioxide are exchanged between the blood and the air
in the lungs.
This is called Gas Exchange.
Surrounding the lungs are the pleural membranes. Between the membranes is a little fluid that
helps them slide smoothly over each other.
Outside the pleural membranes are ribs, between which are found the intercostal muscles, and
below the lungs is the diaphragm.
Function of the Thorax: Definitions
Thorax The upper half of the torso bounded by the diaphragm and the ribs
Trachea The breathing tube from the throat to the bronchus which is strengthened
by C shaped rings of cartilage to prevent collapse under negative pressures
when inhaling
Bronchus Branch of the trachea that carries air into one lung
Bronchioles The small tubes that carry air into the alveoli
Alveolus Thousands of these tiny air-sacs in the lungs where gas exchange occurs
Surface area Alveoli greatly increase this in the lungs
Diaphragm Big sheet of muscle separating the thorax from the abdomen
Ribs Bones that help to support the thorax
Intercostal Muscles The muscles that contract the move the ribs
Pleural membranes Thin moist membranes forming an airtight seal between the lungs and the
ribs/diaphragm
Pulmonary artery The vessel that carries blood from the heart of the lungs
Capillaries Arteries eventually divide into these tiny tubes which is where exchange of
gases occur
Ventilation Breathing in and out is called this
Diffusion The way that gases cross the membranes of the alveoli
Oxygen A gas that we need to respire
Carbon Dioxide Respiration produces this waste gas
