What are the functions of water ● It is a solvent - some substances dissolve for biological reactions to take place in a
solution
● It transports substances - easier if substance dissolved in a solvent
What is the structure of a water molecule ● One oxygen, two hydrogen - shared hydrogen pulled towards oxygen so the other
side of hydrogen has a slight positive charge. Unshared electrons on the oxygen
give it slight negative charge - dipolar molecule
What is hydrogen bonding ● Slight negative oxygen atoms attract slightly positive hydrogen atoms of other
water molecules
How does water's dipole nature make it good ● Water is very cohesive - attraction between water molecules allows water to flow
for transporting substances ● Water is a good solvent - can surround ionic substances
Why do single celled organisms not need mass ● Materials can diffuse directly across cell membrane due to shorter distance and
transport systems larger SA;V ratio
Why do multicellular organisms have mass ● Carry raw materials from specialised exchange organs to body cells and remove
transport systems metabolic waste
The heart and blood vessels
Why is the left ventricle thicker ● More muscular walls to contract more powerfully and pump blood round body
What do the atrioventricular valves do ● Stop blood flowing back into the atria when the ventricles contract
Role of the semilunar valves ● Link ventricles to arteries and stop backflow when the ventricles contract
What do valves do ● Only open one way depending on pressure behind to help blood flow in one
direction
Features and function of an artery ● Carry blood to the rest of the body
● Thick walled, muscular and elastic tissue to cope with high pressure
● Folded endothelium to allow expansion
● Contains collagen to avoid rupture
● Smooth endothelium to reduce resistance
● Elastic fibres stretch to accommodate high pressure and recoil to maintain
Features and function of a vein ● Take blood back to the heart
● Wider with less elastic and muscle tissue
● Contain valves to prevent backflow
Features and function of a capillary ● Where metabolic exchange occurs
● Networks increase surface area for exchange
● Walls only one cell thick to allow fast diffusion
Cardiac cycle
Explain atrial systole ● Atria contract to decrease chamber volume and increase pressure
● Blood pushed into ventricle to cause slight increase in ventricle pressure and
volume due to passive filling
Explain ventricular systole ● Atria relax and ventricles contract to increase pressure and decrease volume
● Pressure higher in ventricles to force AV valves shut and also higher than the
arteries so SL valves are forced open so blood forced into arteries
Explain cardiac diastole ● Ventricles and atria relax. Higher pressure in arteries closes SL valves
● Blood returns to heart and atria fill again due to higher pressure in vena cava and
PV. pressure in atria increases and ventricular pressure falls below so AV valves open
and blood flows passively into ventricles before atria contract
What do the adjustment knobs do ● Coarse - Changes the height of the objective lens
● Fine - adjust focus to see clearer image
Ethical issues of using invertebrae ● Can't give consent and may be subjected to painful procedures
● However, simpler organisms due to simple nervous system
● Causes distress and suffering by exposure to extreme conditions
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