Biology Topic 1

The heart and circulation's primary purpose is to move substances around the body, in small organisms, diffusion can be used for this as the diffusion distance is short, so diffusion is fast enough to meet the organism's requirements. However more complex organisms are too large for diffusion to move substances fast enough. So a mass transport system is used to move substances efficiently by mass flow. Animals usually have blood to carry the vital substances around the body and a heart to pump it.

Open circulatory systems are when blood circulates in large open spaces, a simple heart pumps blood into cavities surrounding the organs. Substances can diffuse between blood and cells. When the heart relaxes, blood is drawn from the cavity back into the heart throgh small valved openings.

Closed circulatory systems are when the blood is enclosed in tubes called blood vessels. This generates higher blood pressures as the blood is forced along fairly narrow channels instead of flowing into large cavities, this allows blood to travel faster and so the blood system is more efficient at delivering substances around the body. The blood leaves the heart under pressure along arteries, then arterioles, then capillaries. The capillaries come into close contact with most of the cells in the body where substances are exchanged between blood and cells. After the capillaries, the blood goes through venules then veins. Animals with closed systems usually are larger and more active than those that have open systems.

Single circulatory systems are when the blood flows through the heart once for each complete circuit of the body. An example of this type of system is a fish, the heart pumps deoxygenated blood to the gills. Gaseous exchange takes place in the gills, carbon dioxide from the blood diffuses into the water and oxygen from the water diffuses into the blood in the gills. Then blood leaving the gills flows round the rest of the body, before eventually returning to the heart.

Double circulatory systems are when the blood flows through the heart twice for each complete circuit of the body. The heart gives the blood returning from the lungs an extra boost that reduces the time it takes for the blood to circulate around the body. This allows animals such as birds and mammals to have a high metabolic rate, so oxygen and other substances required for metabolic processes can be delivered more rapidly to cells and meet the needs of the animal.

Water is a polar molecule, as it has an unevenly distributed charge. The hydrogen ends are slightly positive, and the oxygen end is slightly negative, this is because electrons are more concentrated here. This makes water dipolar.

Solvent Due to their dipole nature, many chemicals can dissolve in water, allowing them to be free to move around and react, water can also be involved in these reactions (hydrolysis and condensation). Hydrophilic (water-loving) susbtances will dissolve in water, however hydrophobic, non-polar substances will not dissolve in water, to enable the lipids to be transported in the blood, they must combine with proteins.

Aorta->Artery->Arterioles->Capillaries->Venules->Vein->Vena cava

Arteries have an outer coat of connective tissue with collagen in, this is a tough and fibrous protein that strengthens the wall. Arteries also have a thick of smooth muscle, allowing them to constrict and dilate, as well as elastic tissue, allowing for stretch and recoil. The flow of blood in the arteries is assisted by the contraction of the artery behind the blood due to the elastic recoil. The blood in the arteries is under high pressure, which is why the arteries have thick walls. Key things to remember about the arteries: narrow lumen, thicker walls, more collagen, smooth muscle, and elastic fibres, and no valves.

Veins have the same outer coat with collagen in as the arteries, as well as the same layer of smooth muscle and elastic tissue, however, in the veins, these layers are thinner, this is because the blood is at a low pressure. The flow of blood in the veins is assisted by the contraction of skeletal muscle, compressing the vein, when moving limbs and breathing. Key things to remember about veins: wide lumen, thinner walls, less collagen, smooth muscle, and elastic fibres, valves.

Capillaries have a thin wall, which is one cell thick, this allows for the exchange of materials between the blood and tissues as there is only a small diffusion distance.

Atrial systole is when blood returns to the heart from around the body. The blood, under low pressure, flows into the atria from the pulmonary veins and vena cava. As the atria fill, the increasing pressure of the blood pushes the atrioventricular valves open, blood leaks into the ventricles, and the atria walls contract, forcing more blood into the ventricles. 

Ventricular systole is when the ventricles contract from the base of the heart upwards, increases the pressure in the ventricles. The pressure forces the semilunar valves open, pushing blood up and out through the pulmonary arteries and aorta. The pressure of blood against the atrioventicular valves closes them, preventing blood from flowing backwards into the atria. 

Cardiac diastole is when the atria and ventricles relax. The elastic recoil of the relaxing heart walls lowers pressure in the atria and ventricles. Blood under higher pressure in the pulmonary arteries and aorta is drawn back towards the ventricles, closing the semilunar valves, preventing backflow of blood into the ventricles. During cardiac diastole, the coronary arteries fill with blood. Low pressure in the atria draws blood into the heart from the veins. 

Atherosclerosis is the disease process that leads to coronary heart disease and strokes. It leads to fatty deposits forming, narrowing the lumen of an artery, this then means that the artery can either be blocked, or increases the chance of being blocked by a blood clot (called a thrombosis). If the artery is blocked, cells can be permanently damaged, in coronary arteries, this leads to a myocardial infarction, in the brain, this leads to a stroke. 

• The endothelium (the inside layer) of an artery becomes damaged and dysfunctional.
• There is then an inflammatory response, meaning that white blood cells move to the artery wall.
• These cells accumulate chemicals such as cholesterol. A fatty deposit builds up, this is called an atheroma.
• Calcium salts and fibrous tissue build up at the site, resulting in a hard plaque forming. As a result of this, the artery wall loses some of its elasticity.
• The plaque causes the lumen to narrow. This makes it more difficult for the heart to pump blood around the body, leading to a rise in blood pressure. 
• A high blood pressure increases the likelihood of more endothelial damage.

Clotting Cascade

1. Platelets stick to the damaged wall and to each other, forming a platelet plug, the platelets and damaged tissue release thromboplastin.

2. The thromboplastin, Ca2+ and vitamin K are used for the conversion of prothrombin into thrombin. 

3. The thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin.

4. A mesh of fibrin forms that traps more platelets and red blood cells to form a clot.

Role in CVD 

Usually blood does not clot inside the blood vessels as the platelets don't stick to the endothelium as it is smooth and has substances that repel platelets, however if there is atherosclerosis and the endothelium is damaged, a clot can form. Atherosclerosis increases the chance of an artery being blocked by a blood clot, called a thrombosis, this can cause the blood supply to be blocked completely. 

Genetics, some people will have higher cholesterol levels, some people will have a higher blood pressure. 

Diet, a diet high in salt means that the kidneys retain water, the higher fluid levels in the blood result in a higher blood pressure. A diet high in saturated fats means that the fats combine with cholesterol to form LDLs, which build up in the bloodstream, causing atheromas, leading to the narrowing of arteries. Some vitamins acts as antioxidants, these protect against radical damage as radicals are highly reactive and can damage many cell components (such as enzymes and genetic material). An example of a radical is superoxide O₂‧, some vitamins provide hydrogen atoms that stabilise the radical by pairing up with its unpaired electron.

High blood pressure, known as hypertension, increases the chance that the endothelium of the artery will be damaged, which then causes an inflammatory response, meaning an atheroma forms.

Smoking, carbon monoxide in the smoke binds to the haemoglobin (which transports oxygen) instead of the oxygen that is supposed to be transported, this reduces oxygen supply to the cells, resulting in an increased heart rate as the body reacts to provide enough oxygen for the cells. The nicotine in the smoke stimulates the production of adrenaline, which causes an increase in heart rate, and causes the arteries and arterioles to constrict, increases the blood pressure. The chemicals in the smoke can cause damage to the endothelium of the arteries, causing atherosclerosis. Smoking is also linked to a decrease in HDL levels. 

Inactivity, activity can help to prevent high blood pressure, maintain a healthy weight, and increases HDL levels without affecting LDL levels. 

Age, with age, the walls of the arteries become less elastic, and are more easily damaged.

Gender, males have a higher risk of cardiovascular disease than females. 

Basal metabolic rate (BMR) is the energy needed for metabolic processes, such as pumping the heart, breathing, and maintaining a constant body temperature. It is measured when at complete rest, and is linked to total and lean body mass. People with a higher proportion of muscle will have a higher BMR as muscle requires more energy for maintenance than fat. This is why men usually have a higher BMR, and older people have a lower BMR. 

The balance of energy intake and energy requirements will determine whether you gain or lose weight. If you eat fewer kilojoules per day than you use, you have a negative energy balance and energy stored in the body will be used up to meet the demand. A regular shortfall of energy intake will result in weight loss. If you routinely eat more energy than you use, you have a positive energy balance, the additional energy will be stored and will result in weight gain. Energy intake can be changed with diet and energy requirements can be changed with diet/

Energy is stored in the chemical bonds in food, as they are broken, the energy is release. The amount of energy contained in food can be measured with a calorimeter. 

Body mass index (BMI) is used for classifying body weight relative to height. An issue with BMI is that it does not account for the fact the muscle weighs more than fat. Waist to hip ratio is also used. 

Glycerol and three fatty acids join together to form a triglyceride, in a condensation reaction, meaning that water molecules are made. During this reaction, an ester bond forms. 

The image on the left shows the formation of the triglyceride, and the image on the right shows the location of the ester bond formed during this reaction. 

Unsaturated fats contain unsaturated fatty acids, which contain double bonds as well as single bonds. Due to the double bonds, the lipid has a lower melting point, this means that they are usually liquid at room temperature. Saturated fats contain saturated fatty acids, which contain single bonds only. Saturated fats are solid at room temperature.

The picture shows the that the difference between saturated and unsaturated fats is whether there are single bonds only in the fatty acid.

CP1- Investigate the effect of caffeine on heart rate in Daphnia

Variables Independent=Caffiene concentration Dependent=Heart rate of daphnia (bpm) Control=Temperature, volume of solutions, stress of daphnia, size of daphnia, time for daphnia to acclimatise.

Equipment Microscope, cavity slide, pipettes, stopwatch, different concentrations of caffeine (distilled water, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M), daphnia

Method Take 1 daphnia with a pipette and place in a cavity slide, add 3 drops of the caffeine solution and wait 5 minutes for the daphnia to acclimatise. Place under a microscope and count the heart rate for 1 minute. Repeat using the different caffeine concentrations and repeat at least 5 times with different daphnia. Place results into a table and draw a graph.

The graph should show that as the caffeine concentration increases, the heart rate increases, this is because caffeine is a cardiac stimulant.

For using daphnia:

• Daphnia have simple nervous systems, so don't feel pain. 

Against using daphnia:

• Use of any animal for science experiments is wrong, as we can't be sure what the daphnia can feel.
• During this practical, there is a possibility that the daphnia could die.
• The daphnia can't give consent. 

Control measures

During the experiment, take care when handling the daphnia to prevent them from dying.  Time should be given for the daphnia to acclimatise. The daphnia should be returned to their natural habitat after being used. 

CP2- Investigate the vitamin C content of food and drink

Variables Independent=type of juice, dependent=volume of juice required to decolourise DCPIP, control=temperature,concentration and volume of DCPIP, end colour.

Equipment 1% DCPIP, 1% vitamin C, fruit juices, conical flask, pipette, burette.

Method Pipette 1cm3 of DCPIP into flask. Fill burette with fruit juice. Titrate until there is a colour change when the DCPIP decolourises from blue. Record how much volume of fruit juice was required. Repeat with different fruit juices and different concentrations of vitamin C (1%, 0.5%, 0.25%, 0.125%, 0.0625%). With the vitamin C results, draw a calibration curve and compare the volumes of fruit juice needed to this curve to calculate how much vitamin C is in the juice.

Antihypertensives reduce blood pressure, this reduces the risk of cardiovascular disease and damage to other organs, this is because high blood pressure can weaken the heart muscle and cause it to work less efficiently. A disadvantage of antihypertensives is that the blood pressure may go too low, there are other side effects such as dizziness and abnormal heart rhythms.

Statins lower cholesterol levels, balance ratio of LDLs:HDLs, and reduce inflammation in arteries. This is because cholesterol causes a build up of plaque in arteries, leading to atherosclerosis. A disadvantage of statins is that they can cause muscle inflammation, liver damage, tiredness, and muscle weakness.

Anticoagulants interfere with the manufacture of prothrombin, this therefore interferes with the blood clotting cascade. Due the anticoagulants preventing the blood from clotting, it means that there is a risk of bleeding internally.

Platelet inhibitors make platelets less sticky, this therefore reduces clotting ability. Treatments that reduce clotting ability treat CVD because blood clots can block blood vessels, which could cause a build up of plaque. A disadvantage of platelet inhibitors is that they irritate the stomach lining, and can cause internal bleeding, similar to anticoagulants.

Correlation If one variable changes, another variable changes

Causation One variable changing causes another variable to change

A valid experiment will have kept control variables constant, with repeats. To see validity on a graph, error bars can be used. If the error bars overlap, the experiment is not valid, if the error bars do not overlap, the experiment may be valid.

For studies, the sample size needs to be taken in account, whether it is large (more likely to be valid) or if it is small (you won't get many results, so hard to identify outliers, and less likely to be valid.

Age, gender, and other factors not being studied such as smoking or activity levels need to be taken into account, especially when the study concerns areas such as atherosclerosis and CVD, as these factors may impact the factor being studied.