Transport Medium: Fluid that transports substances around the body.
I.e. Blood
Pump: Forces the transport medium through the system of tubes.
I.e. Heart.
System of Tubes: Network to transport substances around the body.
I.e. Blood Vessels – arteries, capillaries, veins
Exchange Surface: A medium for substances to be exchanged between.
I.e. Alveoli, Capillary endothelium
Open Circulatory System: Contains no blood vessels.
Closed Circulatory System: Contains blood vessels.
Importance of a mass transport system
Mass transport movement is faster than diffusion through individual cells.
A mass transport system is used to move substances to exchange surfaces, so that they can be exchanged between all
of the cells.
Advantages of Closed Circulatory System over Open Circulatory System:
1. Having a system of (narrow) blood vessels generates a higher blood pressure, so blood travels faster.
2. Blood can be transported to a specific area.
Single Circulation System Vs. Double Circulation System:
• In a single circulation system, the blood passes through the heart once before it completes one full circuit
through the body.
• In a double circulation system, the blood passes through the heart twice before it completes one full circuit
through the body.
• An advantage of double circulation systems is that the heart gives the blood returning from the lungs an extra
boost, reducing the time it takes to move around the body.
, Junaid Ali Topic 1 Revision Notes 2
Water as a Solvent
• Water has an unevenly distributed charge, making it a polar molecule.
• The hydrogen end is slightly positive and the oxygen ends are slightly negative, since the electrons are more
concentrated at that end.
• Ionic molecules dissolve easily in water.
o The positive ion gets attracted to the negative (oxygen) ends.
o The negative ion gets attracted to the positive (hydrogen) ends.
• The ions as a result become hydrated in aqueous solution (i.e. surrounded by water molecules).
• E.g. the amine group (-NH2) in amino acids dissolves in water so that it can be transported through the blood.
Specific Heat Capacity
• The hydrogen bonds between water molecules are very strong, so large amounts of energy are required to
break them.
• This means water has a high specific heat capacity, meaning it takes a large amount of energy to heat 1g of
water by 1°C.
• Therefore, a large input of energy is equivalent to only a small increase in temperature.
• E.g. this helps organisms to avoid rapid changes in their internal structure, so they can maintain a steady
temperature, even when the surrounding temperature changes dramatically.
Specific Latent Heat of Vapourisation and Specific Latent Heat of Fusion
• (Same reasoning as above)
• Water absorbs a lot of energy before it changes state.
• E.g. sweating / panting is used to cool the body as heat is absorbed by the water.
High Surface Tension
• Water molecules form hydrogen bonds with other water molecules. This gives water a cohesive nature.
• The cohesive forces between water molecules are shared with all neighbouring molecules.
• However, those on the surface have no neighbouring molecules above them, so they form even stronger bonds
with molecules besides them.
• This allows water to better resist an external force, which means it has a high surface tension.
• E.g. transpiration streams are held together by cohesion, such as in xylem vessels.
Hydrolysis Reactions
• Hydrolysis reactions use water to breakdown polymers into monomers.
• They polymer is broken into 2 components
• E.g. the body breaks down complex carbohydrates into monosaccharides via hydrolysis so it is small enough
to get absorbed by cells.
Change in Density with Temperature
• As temperature decreases, water molecules slow down (less kinetic energy) and are able to form more stable
hydrogen bonds, locking them into position.
• Since they aren’t moving, they aren’t able to form as many hydrogen bonds with other molecules.
• This leads to ice water molecules not being as close together as in the case of liquid water, so ice has a lower
density.
• E.g. this allows many organisms to survive below the surface of ice.
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