Gas exchange and membrane transport Flashcards
Why do large multicellular organisms require specialised exchange surfaces?
-Small SA:V ratio
-Diffusion is insufficient to provide all cells with the required oxygen and nutrients
-Exchange surfaces increase the rate of diffusion and shorten the diffusion distance
How is the surface area to volume ratio calculated?
Ratio = surface area/volume
3 properties of an efficient exchange surface
-Large surface area to volume ratio
-Small diffusion distance
-Large concentration difference
How does diffusion distance affect the rate of diffusion?
The greater the distance, the further the molecules have to travel hence the slower the rate of diffusion.
How does concentration gradient affect the rate of diffusion?
The steeper the concentration gradient, the faster the rate of diffusion.
How does surface area to volume ratio affect the rate of diffusion?
The larger the SA:V ratio, the faster the rate of diffusion.
How can the rate of diffusion be calculated?
Using Fick’s law:
Rate of diffusion= (surface area x concentration gradient) / thickness of membrane
Name the 7 main parts of the mammalian respiratory system
Trachea, Bronchus, Bronchiole, Diaphragm, Alveolus, Ribs, Intercostal muscles
Describe the trachea and its function in the mammalian gaseous exchange system
Wide tube supported by C-shaped cartilage rings to keep air passage open during pressure changes. Lined by ciliated epithelium cells which move mucus towards the throat. Mucus produced by goblet cells. Carries air to the bronchi.
Describe the bronchi and their function in the mammalian gaseous exchange system
Like the trachea but smaller (structure)
There are two of them, one in each lung. They allow the passage of air into bronchioles.
Describe the bronchioles and their function in the mammalian gaseous exchange system
Narrower than the bronchi. They don’t need to be kept open by cartilage. They have mostly smooth muscle and elastic fibres so they can open and close during ventilation. They allow the passage of air into the alveoli.
Describe the alveoli and their function in the mammalian gaseous exchange system
Mini air sacs lined with epithelium cells. They’re the site of gas exchange and their walls are only one cell thick, covered with a network of capillaries.
300 million in each lung. Their characteristics facilitate gas diffusion
Explain the process of inspiration and the changes that occur in the thorax
External intercostal muscles contract while the internals relax, pulling the ribs up and out. The diaphragm contracts and flattens. The volume of thorax increases and air pressure outside the lungs is higher than inside, so air moves in to rebalance.
Explain the process of expiration and the changes that occur in the thorax
External intercostal muscles relax (while internals contract) bringing ribs down and in. The diaphragm relaxes and returns to its dome-like shape. Volume of the thorax decreases and air pressure in the lungs is higher than outside. Air moves out to rebalance.
Describe the structure and components of a typical cell membrane.
It has a phospholipid bilayer which is studded with various proteins. It also contains cholesterol which sits in the hydrophobic portion of the membrane to regulate fluidity. Other molecules (glycoproteins and glycolipids) may portrude from the membrane.
State 5 functions of cell membranes
-Act as selectively permeable barriers
-Contain receptors used for communication
-The site of chemical reactions
-Allow for signal transduction
-Are used for the transport and uptake of substances
What is the fluid-mosaic model?
A model that describes the membrane structure as a sea of mobile phospholipids studded with various proteins.
