3.1 - Exchange Surfaces Flashcards
Why do single-celled organisms not need exchange surfaces?
- Metabolic activity is low - low demand for oxygen for respiration
- Large surface area to volume ratio
Why are exchange surfaces necessary for larger organisms?
- High metabolic activity
- Smaller surface area to volume ratio
- Larger distances between cells where oxygen is needed and the supply of oxygen
How is the surface area to volume ratio calculated?
Ratio = surface area / volume
How does the size of an organism correlate it its SA:V?
The bigger the organism, the smaller its SA:V
Describe and explain the features of efficient exchange surfaces
Large surface area
- Provides more surface for diffusion to take place through
- e.g. root hair cells
Thin
- Short diffusion pathway
- e.g. epithelial cells of alveoli
Good blood supply
- Maintains steep concentration gradient
- e.g. dense capillary network around alveoli
Good ventilation
- Maintains steep concentration gradient
- e.g. fish gills maintain steady flow of water over exchange surfaces
Define gas exchange in mammals
Process whereby oxygen enters the blood capillaries in the alveoli and carbon dioxide leaves
Outline the structure and function of the nasal cavity
- Good blood supply - warms air to body temperature
- Hairy lining - traps dust and bacteria
- Moist surfaces - increases humidity of oncoming air
Outline the structure and function of the trachea
- Carries clean, warm air from nose to chest
- Supported by C-shaped rings of cartilage - stop trachea from collapsing (but allow food to move down neighbouring oesophagus)
- Smooth muscle contracts to narrow lumen
- Elastic fibres allow lumen to dilate
- Lined with goblet cells and ciliated epithelium - produce mucus to trap
pathogens and move it to throat
Outline the structure and function of the bronchus
- Lead to left and right lungs
- Supported by smaller C-shaped rings of cartilage
- Smooth muscle contracts to narrow lumen
- Elastic fibres allow lumen to dilate
Outline the structure and function of the bronchioles
- Narrow tubes leading from bronchi to alveoli - Made from smooth muscle and elastic fibres - can contract and relax to
control air flow
Outline the structure and function of the alveoli
- Site of gas exchange
- Elastic fibres allow alveoli to stretch and recoil to return to original shape
Describe what happens in alveoli
- Gas exchange
- Oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air
- Oxygen binds to haemoglobin in red blood cells
- Volume of alveoli increases during inspiration
- Concentration gradients of gases maintained
How are the alveoli adapted for gas exchange?
- Very large surface area
- Large surface area to volume ratio
- Thin walls (single cell thick) - short diffusion distance
- Moist - lined with lung surfactant - allows gases to dissolve and keeps alveoli inflated
- Good blood supply from capillaries - maintains steep concentration gradient
- Good ventilation - breathing maintains steep diffusion gradient
Define ventilation
Inhalation and exhalation of air between the lungs and the outside
What is the role of ventilation?
- Maintains concentration gradients of oxygen and carbon dioxide
- Concentration of oxygen remains higher in alveoli than in blood
- Concentration of carbon dioxide remains higher in blood than alveoli
Outline the mechanism of ventilation in the lungs during inhalation
During inhalation:
- External intercostal muscles contract moving rib cage up and out
- Diaphragm contracts and becomes flatter
- Increase in volume in thorax
- Decrease in pressure in thorax
- Air flows into lungs as atmospheric pressure is higher than pressure in thorax
Outline the mechanism of ventilation in the lungs during exhalation
During exhalation:
- Internal intercostal muscles contract so ribs move in and down
- Diaphragm relaxes and becomes domed in shape
- Decrease in volume in thorax
- Increase in pressure in thorax
- Air moves out until pressure in lungs falls
- Abdominal muscles can be used to make a stronger exhalation
Define antagonistic muscles
- Muscles that oppose the action of each other
- e.g. internal and external intercostal muscles
Define breathing rate
Number of inhalations or exhalations per minute
Define ventilation rate
Total volume of air inhaled per minute
Define tidal volume
The volume of air moved into or out of the lungs during a normal breath
Define vital capacity
Maximum volume of air that can be breathed in