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Exchange and transport mechanisms - Coggle Diagram
Exchange and transport mechanisms
Diffusion: the movement of a substance from a high concentration to a low concentration.
Large multicellular organisms cannot rely on simple diffusion because the distances are too great and the would take too long.
B1.10 How the surface area to volume ratio affects the process of exchange and gives rise to specialised systems
Efficient exchange requires three things :
a short diffusion rate
a high concentration gradient
a large surface area
For efficient exchange the surface area must be large in comparison to the volume
Where the surface area is small compared to the volume - organisms cannot rely on simple diffusion across the whole body
Specialised exchange and transport mechanisms are required to maximise the rate of diffusion
Gills and lungs
They are adapted to make the diffusion distance as short as possible
The alveoli is lungs are only a cell thick
Breathing maintains a high concentration gradient by bringing in air that has a higher concentration of oxygen than the blood. (this ensures oxygen diffuses into the blood)
B1.11 The principles of cellular exchange and the transport mechanisms which exist to facilitate this exchange
The phospholipid bilayer
The phospholipid bilayer acts as a barrier to diffusions of many substances and only allows small, non-polar molecules through
Polar substances such as water, glucose , amino a aids or inorganic ions cannot diffuse through the hydrophobic core of the bilayer
The epithilial cells that line the small intestine are specialised cells
The plasma membrane (facing the lumen) is folded into many micro villi (tiny finger-like projections)
This greatly increases the surface area for absorption of the products of digestion
Key Terms:
Fluid mosaic model: describes the Structure of the plasma membrane and now it's components are arranged.
Due to the relatively weak forces between phospholipids, the membrane can be considered to be fluid as these components can move throughout the membrane.
Mechanisms: passive, active and co-transport
Simple diffusion, facilitated diffusion and osmosis are all passive processes ( they don't require energy)
Simple diffusion
The phospholipid bilayer can be a barrier to diffusion to polar substances due to it's hydrophobic core (partially permeable)
Small non-polar molecules can move into the phospholipid bilayer and diffuse across the membrane
Facilitated diffusion
Since polar molecules cannot diffuse across the membrane they rely on facilitated diffusion
This is where diffusion is assisted by proteins in the membrane
Ions and small polar molecules are transported by channel proteins - > these act like pores in the membrane
Larger polar molecules use carrier proteins
Carrier proteins are specific to the substance being transported
The substance binds to the carrier protein like how a substrate binds to an enzyme
The carrier protein then changes shape, which transfers the substance to the other side of the membrane
Some of these can open and close, these are called gated channels
Osmosis
This is a particular type of facilitated diffusion where water moves across a partially permeable membrane from a high concentration of water molecules to a low concentration of water
A dilute solution will have a high concentration of water molecules, whereas a concentrated solution will have a low concentration of water molecules
Water moves by osmosis from pure water or a dilute solution to a more concentrated concentrated solution
Active transport
Substances do not move by themselves from low to high concentration
Active transport is a process that uses energy to move substances against a concentration gradient
Carrier Proteins use ATP as a source of energy
Co-transport mechanisms
B1.12 The advantages of having specialised cells in relation to the rate of transport across internal and external membranes
epithelial cells
single layer of cells on the inside of the body
endothelial cells
single layer of cells on the outside of the body