Edexcel A-level Biology Topic 1 PDF

Edexcel (A) Biology A-level Topic 1: Lifestyle, Health and Risk Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

Edexcel (A) Biology A-level Topic 1: Lifestyle, Health and Risk Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Transport of Substances In order to survive, animals require essen al substances (e.g. oxygen, carbon dioxide) to enter and leave the body in sufficient quan es and be transported around the body. The needs of small organisms can be served through diffusion (alone) due to the large surface area to volume ra o of the body. However, as the size of the organism increases: Surface area to volume ra o decreases Diffusion distance increases Metabolic rate (hence input and output requirements) increase Diffusion becomes insufficient. As a result of that, larger organisms have a mass transport system, consis ng of heart and circula on which moves the substances around the body and allows exchange of substances to take place. Features of a mass transport system: 1. A network to move through (eg. vessels) 2. A medium for movement (a fluid eg. blood) 3. Controlled direc on - to move substances to / from where they are needed (eg. blood is moved along a pressure gradient created by the heart, the direc on of flow controlled by valves) 4. Maintenance of speed - (eg. contrac on of the heart + elas c recoil of arteries helps to maintain the pressure gradient, thus speed) Water Water is a polar molecule, due to uneven distribu on of charge within the molecule – the hydrogen atoms have a par al posi ve charge and the oxygen atom has a par al nega ve charge due to the difference in electronega vity, causing one end of the molecule to be more posi ve than the other. Water is a polar solvent and can be used to transport many biological molecules (as many of them are also polar, thus can be dissolved in water). Hydrogen bonding between water molecules creates cohesion and adhesion, which enables effec ve transport of water and dissolved substances through xylem vessels. Hydrogen bonding is a rela vely strong type of bonding, thus causing water to have a high heat specific capacity meaning that a lot of energy is required to change the temperature of water, therefore minimising temperature fluctua ons in living things (an important part of homeostasis). https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Blood Vessels - Arteries - Carry oxygenated blood to the body ssues (other than the pulmonary artery) - Have a small lumen to maintain high blood pressure - Smooth inner endothelial lining (a smooth surface means there’s less resistance to blood flow) - Thick layer of smooth muscle (contract and relax to dilate and constrict blood vessels - controlling their diameter) and elas c fibres (stretch and recoil) - Lots of collagen fibres (for strength and support) - Veins - Carry deoxygenated blood to the lungs (except the pulmonary vein) - Large lumen (minimises resistance to flow) - Thinner layer of muscle and elas c fibres - Reduced collagen fibres - Valves (to prevent backflow) - Capillaries - Very small (to fit between cells) - Narrow Lumen - Thin endothelium - one cell thick (to maintain short diffusion distance and fit between cells) Heart and Cardiac Cycle 1. Four chambers - right and le atria, right and le ventricles 2. Four main blood vessels pulmonary vein (from lungs to le atrium) , aorta (from le ventricle to body), vena cava (from body to right atrium), pulmonary artery (from right ventricle to lungs) 3. Atrioventricular valves - mitral or tricuspid/bicuspid - separate atria from ventricles 4. Semilunar valves - pulmonary/aortic - separate arteries from ventricles 5. Tendinous chords/valve tendons - prevent atrioventricular valves turning inside out due to pressure 6. Septum - muscle and connective tissue - prevents oxygenated/deoxygenated blood mixing https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 7. Coronary arteries - wrapped around the heart to supply blood to cardiac muscle 8. Cardiac muscle - thicker on the LHS because higher pressure is needed to pump blood further There are 3 stages of the cardiac cycle: 1) Atrial systole – during atrial systole the atria contract forcing the atrioventricular valves open and blood flows into the ventricles. 2) Ventricular systole – contrac on of the ventricles causes the atrioventricular valves to close and semilunar valves to open thus allowing blood to leave the le ventricle through the aorta and right ventricle through the pulmonary artery. 3) Cardiac diastole – atria and ventricles relax and pressure inside the heart chambers decreases causing semilunar valves in the aorta and pulmonary arteries close, preven ng backflow of blood. Atherosclerosis Atherosclerosis is the hardening of arteries caused by the build-up of fibrous plaque called an atheroma. Atheroma forma on is the cause of many cardiovascular diseases and occurs as following: The endothelium which lines the arteries is damaged, for instance by high cholesterol levels, smoking or high blood pressure This increases the risk of blood clo ng in the artery and leads to an inflammatory response causing white blood cells to move into the artery Over me, white blood cells, cholesterol, calcium salts and fibres build up and harden leading to plaque (atheroma) forma on. The build-up of fibrous plaque leads to narrowing of the artery and restricts blood flow thus increasing the blood pressure which in turn damages the endothelial lining and the process is repeated - an example of posi ve feedback. Atherosclerosis is mul -factorial and has modifiable and non-modifiable risk factors: Gene cs (gene c predisposi on to high blood pressure etc.) Age (arteries become less elas c with age) Diet (diet can increase cholesterol) Gender (oestrogen makes arteries more elas c) High blood pressure (can damage endothelium) https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  High cholesterol levels (increases the likelihood of forma on of plaque) Smoking (nico ne narrows arteries) Physical inac vity (increases obesity risk) Obesity (increases blood pressure etc.) Thus risk of CVD can be reduced by stopping smoking, regular exercise, reducing consump on of alcohol, dietary changes and maintaining healthy body weight. Atherosclerosis can lead to cardiovascular diseases (CVD) including angina, stroke, myocardial infarc on and aneurisms. Blood Clo ng Thrombosis also known as blood clo ng prevents blood loss when a blood vessel is damaged, it also prevents the entry of disease causing microorganisms and provides a framework for repair. A series of reac ons which lead to clot forma on: When a blood vessels is damaged, platelets a ach to exposed collagen fibres A protein called thromboplas n is released from platelets and this protein triggers the conversion of inac ve prothrombin which is a protein into ac ve thrombin which is an enzyme. In order for the conversion to occur calcium ions and vitamin K must be present. These are known as clo ng factors. Thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin Fibrin forms a network of fibres in which platelets & red blood cells are trapped to form a blood clot. Energy Balance Energy balance is the balance of calories consumed through ea ng and drinking, compared to calories burned through physical ac vity. Therefore, if a greater number of calories is burned through physical ac vity than is consumed it leads to weight loss. If fewer calories are burned than consumed it leads to weight gain. The ways of determining whether an individual is overweight, underweight or healthy weight include: BMI is the body mass index which can be calculated by dividing the body mass in kilograms by height in metres squared. The value obtained is then compared to a chart, for instance a value below 18 indicates that the individual is underweight, while a value above 30 indicates the individual is obese. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Waist-to-hip ra o can be used to determine how likely a person is to get heart disease based on the distribu on of fat in the body. A value above 1 suggests a health risk. Carbohydrates Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen. They are long chains of sugar units called saccharides. There are three types of saccharides - monosaccharides, disaccharides and polysaccharides. Monosaccharide = simple sugar monomer Disaccharide = two monosaccharides Polysaccharide = many monosaccharides Monosaccharides can join together to form disaccharides and polysaccharides by glycosidic bonds which are formed in condensa on reac ons (in which a molecule of water is removed) Monosaccharides Glucose is a monosaccharide containing six carbon atoms in each molecule and is the main substrate for respira on. There are two main isomers found in living organisms - Beta glucose (most common in plants) and alpha glucose (most common in animals) Ribose is a monosaccharide containing five carbon atoms, it is a pentose sugar and a component of DNA and RNA. Disaccharides Maltose is a disaccharide formed by condensa on of two glucose molecules Sucrose is a disaccharide formed by condensa on of glucose & fructose Lactose is a disaccharide formed by condensa on of glucose & galactose Polysaccharides Polysaccharides are formed from many glucose units joined together. Glycogen is the main energy storage molecule in animals and is formed from many molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds. It has a large number of side branches meaning that the molecule can be hydrolysed and energy can be https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc released quickly. Moreover, it is a rela vely large, but compact molecule thus maximising the amount of energy it can store. Starch stores energy in plants and it is a mixture of two polysaccharides called amylose and amylopec n: Amylose – amylose is an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds , as a result of that amylose is coiled and thus it is a very compact molecule meaning it can store a lot of energy. Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds , due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly. It is also a compact molecule, although not as compact as amylose. Lipids Lipids are biological molecules which are only soluble in organic solvents such as alcohols. There are two types of lipids: Saturated lipids such as those found in animal fats – saturated lipids don’t contain any carbon-carbon double bonds. Unsaturated lipids which can be found in plants – unsaturated lipids contain carbon-carbon double bonds and melt at lower temperatures than saturated fats. Intermolecular forces are weaker in unsaturated lipids and therefore they have a lower mel ng point The double bonds in unsaturated lipids reduce the strength of these intermolecular forces (as they create a ‘kink’ in the hydrocarbon chain, so molecules cannot pack together as closely). As a result, saturated fats are solid at liquid temperature and unsaturated lipids are liquid at room temperature. Animal fats are normally saturated whereas plant oils are o en unsaturated. Proper es of lipids: Lipids are waterproof because the fa y tail is hydrophobic. Very compact, and be er gram-for-gram energy release than carbohydrates or proteins because more energy is stored in C-O bonds that are hydrolysed. Lipids are non-polar and insoluble in water, therefore they are good for storage - they don’t interfere with the water-based reac ons in the cytoplasm. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Lipids conduct heat slowly therefore they provide thermal insula on. Triglycerides are lipids made of one molecule of glycerol and three fa y acids joined by ester bonds formed in condensa on reac ons. Different fa y acids have different R groups, and some triglycerides contain a mix of different fa y acids. Triglycerides are used as energy reserves in plant and animal cells. In phospholipids, one of the fa y acids of a triglyceride is subs tuted by a phosphate-containing group. Phosphate heads are hydrophilic and the tails are hydrophobic and as a result phospholipids form a bilayer in the cell membrane as heads face watery environments whereas the tails move away from them. High and Low Density Lipoproteins Cholesterol is a soluble lipid made in the body and is transported by proteins in soluble complexes called lipoproteins consis ng of proteins and lipids. There are two types of lipoproteins: High density lipoprotein (‘good’ cholesterol) is formed from unsaturated fats, protein and cholesterol and transports cholesterol from body ssues to the liver where it’s broken down. It reduces the cholesterol levels and reduce the risk of atherosclerosis. Low density lipoprotein (‘bad’ cholesterol) is formed from saturated fats, protein and cholesterol and transports cholesterol from the liver to the blood, thus causing the cholesterol level to increase, hence why it is linked to atherosclerosis. # The propor on of protein is higher in HDL whereas the propor on of cholesterol & fat in HDL is lower. There’s a correla on between high levels of saturated fats and high blood cholesterol as saturated fats are one of the components of low density lipoproteins. However, the link between cholesterol and cardiovascular diseases is causal because cholesterol is involved in plaque forma on. Treatment of CVD There are various types of medical treatments of CVD such as: An coagulants, such as warfarin, reduce the risk of clot forma on. However, they dosage needs to be carefully controlled as taking too much can lead to uncontrolled bleeding. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Sta ns, which reduce blood cholesterol levels by blocking the enzyme which produces cholesterol in the liver. There are various side effects and risks of sta ns such as nausea, inflamma on, diarrhoea and cons pa on. It’s important not to solely rely on sta ns to lower the cholesterol levels – they’re most effec ve when combined with a healthy diet. Platelet inhibitors make platelets less s cky, thus reducing the risk of blood clots and atheroma forma on. Aspirin is a platelet inhibitory drug, however it can cause stomach bleeding as it irritates the stomach lining. An hypertensives, which reduce blood pressure. They include: Beta blockers, which reduce the frequency of heart contrac ons and make them less powerful by blocking response of heart to hormones. However, taking beta blockers might increase risk of diabetes. Diure cs, which increase the volume of urine, thus lowering blood volume and pressure. Possible side effects include nausea, muscle cramps and dizziness. ACE inhibitors reduce blood pressure by blocking the conversion of Angiotensin I to Angiotensin II, which causes arterial constric on. Side effects of ACE inhibitors include dizziness, cough and heart arrhythmia. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc