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Haemoglobin structure

Quaternary structure protein


Loading on oxygen dissociation curves

Hb has high affinity for oxygen
Percentage saturation of blood with oxygen is high (lungs)
Oxygens diffuses into red blood cells and forms oxyhaemoglobin


Unloading on oxygen dissociation curves

Occurs when there is a low percentage of oxygen saturation in blood, e.g respiring tissue
CO2 in blood lowers affinity
Curve shifts right in respiration
More oxygen released from haemoglobin


Bohr effect

Dissociation curve shifts right
Hb has a lower affinity for oxygen, more oxygen will be unloaded
Caused by increase in acidity and temperature
Beneficial as tissues become more active they require more oxygen for the increased rate of respiration, so shifting the curve right and lowering the affinity will provide more energy for the tissues


Foetal haemoglobin

Has a higher affinity for oxygen so it can take oxygen from its mothers blood


The cardiac cycle

-Atrial systole (Pressure builds in atrium)
- AV valve closes
- Ventricular systole (Pressure builds in ventricle)
- SL valve opens
- SL valve closes
- Diastole (All valves closed)
- AV valve opens (Pressure builds in atrium)p


Caridac output, stroke volume and heart rate

Stroke volume - volume of blood pumped by the left ventricle at rest
Heart rate - number of times the heart beats per minute
Cardiac output - Stroke volume x heart rate
(how much blood is pumped out of the heart in one minute)


Contraction of heart

Myogenic contraction - involuntary
Myocytes in heart are polarised, when their charges are reversed and are depolarised they contract
-SAN 'pace maker' impulse in the wall of the left atrium
-Then short delay to allow atria to empty
-Then AVN impulse
-Travels down septum, to bundle of his and along the purjinke fibres
-Ventricular systole


Structure of arteries?

-Carries oxygenated blood from heart to tissues
-Thick walls of muscle ad elastic tissue to withstand high pressure
-Small lumen to maintain pressure
-smooth muscle contracts to cause vasoconstriction


Structure of capillaries?

-Exchange of materials
-Thin (1 cell thick) permeable walls to allow for exchange
-Very small lumen, only 1 red blood cell at a time - advantageous
-Blood pressure falling


Structure of veins?

-Carries blood from tissue to heart
-Walls are thin as blood is at low pressure (little elastic tissue and smooth muscle)
-Large lumen to reduce resistance to flow
-valves to prevent back flow
- movement maintained by skeletal muscles, 'suction' from heart and valves


Tissue Fluid

At aterial end:
- Hydrostatic pressure bigger than osmotic pressure due to high blood pressure from artery
-Water and small molecules forced out of capillary (protein stays in)

At venous end:
- Hydrostatic pressure is lower than osmotic pressure due to low blood pressure in veins
-Water and small molecules return to capillary

Tissue fluid is fluid that leaks out of capillary


How are xylem vessels adapted for their function?

- Thick cell walls: Withstand tension
- Liginin in cell walls: Walls waterproof and to withstand tension
- Xylem cells have no end walls: a continuous column of water
- Narrow tubes: allows capillarity


Functions of water in plants?

Turgidity - Keeps stems and leaves rigid, increases light absorption and photosynthesis


Cohesion tension theory

Cohesion: H bonding between water molecules forms a continuous column
Tension: Negative pressure created in the xylem, which causes the xylem vessels to be drawn downwards, reduces diameter of tree trunk during the day


Factors affecting the rate of transpiration

Temperature: affects kinetic energy of molecules so diffusion is faster
Humidity: Affects water potential gradient
Light: Causes stomata to open
Wind speed: affects water potential gradient


Setting up potometer

-Cut the stem at an angle underwater
-Do not get leaves wet
-Submerge potometer
-Seal all joints with waterproofing substances
-Control envrionmental conditions



-Sucrose is actively transported from companion cells into sieve tubes
-Lowers water potential of sieve tubes
-Water enters the sieve tubes by osmosis
-Increases pressure in sieve tubes
-Fluid moves to lower pressure by sink cell
-Sucrose moves into sink cell
-Reduces water potential so water moves into sink cell
-Difference in pressure between the source and sink cell causes movement of fluid inside the sieve to flow from source to sink.


The heart?

Vena Cava
Pulmonary artery
Pulmonary Vein



Wall of artery made of several layers
Endothelium is smooth and unbroken
If damaged (e.g. by high blood pressure) then white blood cells and lipids clump together to form fatty streaks
Over time these cells and connective tissue build up and harden to form a fibrous plaque called an atheroma
Plaque partially blocks the lumen of the artery and restricts blood flow - causes blood pressure to increase
Coronary heart disease (CHD) is a cardiovascular disease
Occurs when the arteries have lots of atheroma in them which restrict blood flow to the heart muscle
Can lead to myocardial infarction - cell death of heart muscle



Balloon like swelling
Atheroma increase the likelihood
Atheroma plaques damage and weaken arteries + narrow arteries - increases blood pressure
Blood travels through a weakened artery at high pressure it may push the inner layers of the artery through the outer elastic layer to form a balloon-like swelling - aneurysm
Aneurysm may burst causing a haemorrhage



Formation of a blood clot
Atheroma increase the likelihood
Atheroma plaque may rupture the endothelium of an artery
Damages the artery wall and leaves a rough surface
Platelets and fibrin (protein) accumulate at the site of damage and form a blood clot (thrombosis)
Blood clot can cause a complete blockage of the artery, or it can become dislodged and block a blood vessel elsewhere in the body
Debris from the rupture can cause another blood clot to form further down the artery


Myocardial Infarction?

Heart muscle supplied blood by coronary arteries
Blood contains oxygen needed by heart muscle cells to carry out respiration
If a coronary artery becomes completely blocked (by a blood clot) an area of the heart muscle will be totally cut off from its blood supply, receiving no oxygen
Causes a myocardial infarction - heart attack
Can cause damage or death to heart muscle
Symptoms include pain in the chest and upper body, shortness of breath and sweating
If large areas of the heart are affected complete heart failure can occur


Factors increasing risk of cardiovascular disease: High cholesterol and poor diet?

If blood cholesterol is high (above 240 mg per 100cm3)
Cholesterol is one of the main components of fatty deposits which form atheromas
A diet high in saturated fat is associated with high blood cholesterol levels
A diet in high salt also increases the risk as it raises blood pressure


Factors increasing risk of cardiovascular disease: Cigarette smoking?

Nicotine and carbon monoxide in cigarrete smoke increase the risk
Nicotine risks high blood pressure
Carbon monoxide combines with haemoglobin and reduces the amount of oxygen transported in the blood and so reduces the amount of oxygen available to tissues - if heart muscle does not receive enough oxygen then a heart attack can occur
Smoking decreases the number of antioxidants in the blood - important from protecting cells from damage - increases likelihood of atheroma formation


Factors increasing risk of cardiovascular disease: High blood pressure?

Increases risk of damage to the artery wallsIncreases risk of atheroma formation - causing further increase in blood pressure
Things that risk high blood pressure: being overweight, not exercising, excessive alcohol consumption


Factors increasing risk of cardiovascular disease: other factors?

Most in our control - just eliminate risk factors
Some genetic however -genetic predisposition for coronary heart disease and/or high blood pressure


Evidence for mass flow?

- If a ring of bark is removed from a woody stem, a bulge forms above the ring - fluid from the bulge has a higher concentration of sugars than the fluid from below the ring - evidence for a downward flow of sugars
- Radioactive tracer can be used to track the movement of organic substances in a plant (14C)
- Pressure in the phloem can be investigated using aphids - sap flows out quicker nearer the leaves than further down the stem - evidence thats theres a pressure gradient
- Metabolic inhibitor is put into the phloem - translocation stops - evidence active transport is involved


Evidence against mass flow?

Sugar travels to many sinks - not just to the one with the highest water potential
The sieve plates would create a barrier to mass flow - a lot of pressure would be needed for the solutes to get through at a reasonable rate


Experiment to demonstrate translocation?

Supply a leaf with an organic substance that has a radioactive label (carbon dioxide containing 14C)
Radioactive carbon with then be incorporated into the organic substances produced by the leaf (sugars produced by photosynthesis) which will be moved around the plant by translocation
The movement tracked by autoradiography. To reveal where the tracer has spread to in the plant, the plant is killed, and the whole plant is placed on photographic film - present where film turns black
Results show the tracer moves from source to sink