lifestyle, health and risk

This is the revision notes on topic 1 for the biology AS exam. Hope it helps :)

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  • Created on: 05-01-12 22:54
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Closed circulatory system:
Blood leaves the heart under high pressure and flows along arteries and then
arterioles to capillaries.
Capillaries come in large numbers and they exchange substances between blood and
After passing through capillaries, blood goes back to the heart via venules and then
Valves in veins ensure blood flows in one direction.
Open circulatory system:
In large and other animal groups, blood circulates in large open spaces.
Blood is pumped from the heart through blood vessels but then it leaves the blood
vessels and enters body cavities, where the organs are bathed in blood.
Single circulatory system:
Heart pumps deoxygenated blood to gills.
There is gaseous exchange which transports substances by diffusion.
Blood leaves the gills, flows around the body returning back to the heart.
Double circulatory system:
Right ventricles pumps deoxygenated blood to the lungs where it receives oxygen.
The oxygenated blood returns back to the heart to be pumped a second time by the
left ventricle out to the rest of the body.
Water as a transport medium:
Water is liquid at room temperature.
Water has a high boiling point as the hydrogen bonds require a lot of energy to break
the strong bonds.
Polar molecules can easily dissolve in water.
Non-polar molecules do not easily dissolve in water e.g. lipids
Many water molecules can form hydrogen bonds as the negatively charged oxygen
joins with the positively charged hydrogen.
Arteries and veins:
Arteries have a narrow lumen, more collagen elastic fibre and smooth muscle.
Arteries have thicker walls, with no valves.
Veins have wider lumen, less collagen, elastic fibre and smooth muscle.
Veins have thinner walls with valves.
Capillaries are one cell thick and join small arteries (arterioles) and veins (venules)
Collagen is a tough fibrous protein which makes is strong and durable.
Elastic fibres help to stretch and recoil.
Smooth muscles allow walls to constrict and dilate.
Cardiac cycle:

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Atrial systole:
Blood under lower pressure flows along pulmonary veins and vena cava.
As atria fills with blood, pressure against the atrioventricular valves cause them to
open, leaking blood into the ventricles.
As atria walls contract more blood is forced into the ventricles.
Ventricular systole:
Ventricles contracts base upwards increasing the pressure.
Blood moves up and out through the arteries.
The pressure of blood against atrioventricular valve closes them preventing the
backflow of blood into the atria.
During diastole, the atria and ventricles relax.…read more

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The enzymes thrombin catalyses the conversion of fibrinogen in to fibrin.
The long fibrin strands forms a mesh and traps blood cells to form a clot.
Large-scale studies:
Cohort study:
A group of people are followed over time to see who develops the disease.
Case control study:
A group of people who have the disease are compared with another group of people
who have the disease.…read more

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The most common lipids we eat are triglycerides
Used as energy stores in plants and animals
They are made up of three fatty acid and one glycerol molecule
These are linked together by condensation reactions
The bond that forms between them is an ester bond
Three ester bonds are formed in a triglyceride
Saturated fats:
If the fatty acid chains in the lipid contain the maximum number of hydrogen atoms
they are saturated.
They have no double bonds.…read more

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A high salt intake cans cause kidneys to retain water. This also increase blood
In stressful situations the release of adrenaline causes arteries and arterioles to
constrict resulting in raised blood pressure.
Heavy drinking raises blood pressure, irregular heartbeat and obesity.
Reducing the risk of CVD:
Taking more exercise will ensure that the person is less likely to develop the disease
Reducing the amount of salt intake will lower blood pressure.…read more


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