Topic 1- Lifestyle, health and risk

Revision notes for the 1st topic of the salters-nuffield edexcel biology textbook

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  • Created by: R_Hall
  • Created on: 09-12-12 16:29


  • Water is a dipolar molecule- the oxygen atom has a slightly negative charge and the hydrogen atoms have a slightly positive charge
  • The opposite charges attract each other, and form hydrogen bonds
  • Water is a solvent (substance dissolve into it)
  • The strong attractions  (cohesion) between the molecules causes them to stick together. This helps water to flow, making it a good transport medium
  • A lot of useful biological substances are ionic (composed of 1 positive atom and 1 negative atom) eg. salt. The opposite charges of the water molecule are attracted to the charges on the ions. The ions will become surrounded by water- dissolved
  • Water has a high specific heat capacity (lots of energy is needed is needed to raise 1cm3 of the water by 1c), lots of energy is needed to break the hydrogen bonds
  • A large energy input causes only a small change- this allows organisms to avoid rapid internal temperature changes, enabling them to maintain a steady temperature
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  • A trigylceride is made up of one glyerol molecule and three fatty acids
  • Fatty acid molecules have long hydrocarbon tails, which are hydrophobic (water hating)- this makes lipids insoluble in water
  • Trigycerides are formed through condensation reactions,where ester bonds join the fatty acids to glycerol. The H atom of glycerol joins to the -OH of the fatty acids, releasing water
  • They are broken up by hydrolysis reactions-a water molecule is added to each ester bond to break it
  • Lipids are unsaturated or saturated, the difference is in the hydrocarbon tail
  • Unsaturated lipids are found in plants. They have double bonds between the c atoms in the hc tail. This causes the chain to kink
  • Saturated lipids are found in animals. They don't have any C=C, just C-C. They are straigth chains
  • Unsaturated fats melt at lower temperatures. The kinks prevent the chains from packing closely together, so weak intermolecular forces mean that little energy is needed to separate
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Why do mammals have a heart and circulation system

  • All cells get energy via aerobic respiration= glucose+ oxygen- ENERGY- carbon dioxide+ water
  • In single-celled organisms, the materials can diffuse directly into the cell across the cell membrane. The diffusion rate is quick as the diffusion path is short
  • Multicellular organisms cannot use direct diffusion, it would be too slow because of the large distances that need to be covered
  • Multicellular organisms have mass transport systems. The raw materials are carried from exchange organs to cells, and metabolic waste is removed
  • Blood is used by mammals as transport system
  • Birds and mammals have double circulatory systems- blood passes through the heart twice during one complete cycle of the body. This gives the blood returning from the lungs an extra boost by the heart, and reduces circulation time
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Blood Vessels and Adaptations

  • Blood vessel walls contain collagen (strong and durable) and elastic fibres (stretch
  • Veins- Take blood back to the heart. Large lumen and very little elastic or muscle tissue. Have valves to prevent backflow. Blood flow assisted by contraction of surrounding muscles
  • Arteries- Carry blood from heart to body. Smaller lumen, have very thick muscular and elastic wall to cope with high pressure blood. The endothelium (lining) is folded, so it can expand to cope with pressure
  • Capillaries- Metabolic exchange occurs between cells and capillaries. The networks of capillaries (capillary beds) increase surface area for exchange. Only 1 cell thick- speeds up diffusion
  • The left ventricle is thicker than right- needs to contract powerfully to push blood around whole body
  • Ventricles are thicker than atria- have to push blood around body, not just into ventricles
  • Values (Atrioventricular and Semi-Lunar) prevent backflow
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Cardiac Cycle

  • Atrial systole
  • The ventricles are relaxed. The atria contract, decreasing the volume of the chamber and increasing pressure. The blood is forced into the ventricles (slight increase in pressure and volume) through the open AV valves
  • Ventricular systole
  • Atria relax. The ventricles contract (decreasing volume) and the pressure increases. Pressure higher than in atria, so AV valves close. Pressure also higher than in aorta/pulmonary artery, which forces S-L valves open and blood is forced into arteries
  • Diastole
  • Ventricles and atria relax. Higher pressure in aorta/pulmonary artery, so S-L close to prevent backflow. Atria fill due to high pressure in vena cava/pulmonary vein- increases pressure. Ventricles relax- pressure falls- AV valves open. Blood falls into atria and process starts again
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Atherosclerosis and Clotting

  • Atherosclerosis- The hardening of arteries
  • The endothelium of the artery is damaged due to high pressure. An inflammatory response is triggered- WBC's move into artery wall and accumulate chemicals to form an atheroma. Calcium salts and fibrous tissue build up and form a hard plaque. This blocks the artery, restricts blood flow and blood pressure increases
  • Atherosclerosis narrows blood vessels- causes heart to be starved of oxygen (angina pain) and heart cells die- heart attack or myocardial infarction. If supply of blood to brain is reduced a stroke happens
  • Blood clots (thrombosis)
  • Platelets stick to the damaged wall of blood vessel and form a platelet plug. The contact causes a cascade of chemical reactions- thromoboplastin is releases, prothrombin is converted into the insoluble thrombin- fibrinogen is converted into the protein fibrin. The strands form a mesh to trap blood cells
  • Deep vein thrombosis is the formation of a blood clot in a vein deep inside the body
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Perception of Risk

  • Risk- the probability of occurrence of some unwanted event or outcome
  • Working out risk of dying from an illness- people who died from disease/ total population x 100= %
  • Probability= total population/ people who died
  • People often overestimate risk because the risk is involuntary, unnatural, unfamiliar, dreaded or unfair
  • Risks can be underestimated as the effect may take place too far in the future for a person to take immediate action (eg. the risk of smokers developing lung cancer)
  • Average probability/ % does not take into account risk factors that increase the chance of a harmful outcome, eg. there is a 1 in 600 risk of having a fatal heart attack, but someone who is overweight and inactive will have a higher risk
  • A correlation is a link between a factor and an outcome. Lots of data is needed to prove a correlation is true
  • A causation is where a factor is proven to cause an outcome
  • A null hypothesis is where you assume that there is no difference between a experimental and control group
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  • Large scale studies are used to find risk factors for common diseases. 2 common designs are-
  • Cohort studies- where a group of people are followed to see who develops the disease- takes a long time, so can be expensive
  • Case-control studies- a group of people with the disease are compared with a group who don't have it
  • The 1st major cohort study into CVD started in 1948, aiming to identify risk factors (the Framingham Heart Study)
  • The control group for a case-control study should be a representation of the population. One of the first was conducted in the 1950's to determine a link between smoking and lung cancer
  • A good study should 1. have a clear hypothesis or aim, to produce valid/reliable results 2. have a representative sample, without selection bias 3. produce valid data (good measurements) 4. have a method which collects reliable results (can be repeated and have concurrent data) 5. have a large enough sample
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Risk Factors for CVD

  • Lifestyle factors
  • Diet- a diet high in saturated fats increases risk. Increases cholesterol levels- which increases atheroma formation- which can lead to blood clots- which can cause heart attacks or strokes
  • High blood pressure- this increases the risk of damage to artery walls- increases risk of atheroma formation- CVD. Excessive alcohol, stress and salt raise blood pressure
  • Smoking- CO in smoke binds to haemoglobin and reduces the O2 transported in blood and therefore available to tissues. The heart muscle is starved -> heart attack, brain starved -> stroke
  • Nicotine makes platelets stickier- blood clots and smoking reduces antioxidants in blood- more artery wall damage and more atheroma
  • Inactivity- increases blood pressure
  • Factors beyond control
  • Genetics- some people inherit alleles that increase risk
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Blood Pressure

  • Elevated blood pressure (hypertension) increases the likelihood of atherosclerosis occurring
  • The systolic pressure is the highest artery pressure when the ventricles have contracted and blood is forced into arteries, the diastolic pressure is the lowest artery pressure when the ventricles are relaxed
  • A sphygmomanometer measures blood pressure
  • Contact between blood and walls of blood vessel causes friction and impedes blood flow- peripheral resistance
  • Elastic recoil of arteries maintains high blood pressure
  • If smooth muscle of artery wall contracts and constrict- bp raised (also resistance)
  • A sign of high bp is oedema, where fluid builds up in tissue causing swelling
  • At the arterial end of the capillary, blood is under pressure. This forces fluid and small molecules in plasma out through the leaky capillary walls into intercellular spaces, forming tissue fluid
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Cholesterol and LDL's

  • Cholesterol is a short lipid molecule, a vital component of cell membranes and production of sex hormones. But there are concerned that a high blood cholesterol level is bad
  • In order to be transported, insoluble cholesterol is combined with proteins to form soluble lipoproteins
  • Low-density lipoproteins (LDL's)- the main cholesterol carrier. Made from saturated trigylcerides, protein and cholesterol. Circulate in the bloodstream and bind to receptor sites on membrane before uptake. Excess LDL's overload receptor sites -> high blood cholesterol -> deposited in artery walls forming atheroma
  • High-density lipoproteins (HDL's)- HDL's have a high % of protein- higher density. Made when unsaturated triglycerides combine with protein and cholesterol. Transport cholesterol from body to liver for breakdown. Lowers blood cholesterol
  • Many studies provide evidence for a positive correlation between fat consumption and CHD mortality rates. However, there is some conflicting evidence
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Diet and Energy

  • The SI unit for energy is the Joule (J), and 4.18 joules= 1 calorie
  • The energy needed to for essential body processes in the basal metabolic rate (BMR)
  • BMR is higher in males, younger people, heavier people and more active people
  • If you eat fewer calories than you use, you will have a negative energy balance- energy stored in the body will be used and you will you lose weight
  • If you eat more calories than you use, you will have a positive energy balance- additional energy will be stored in the body as fat and you will put on weight
  • Body mass index (BMI) is a conventionally used method of classifying body weight relative to a person's height. BMI= body mass/ height 2 (squared)
  • Hip-to-waist-ratio is a better measurement of obesity than BMI and shows an association with risk of heart disease (as it measures the amount of abdominal fat). It is calculated by dividing waist circumference by hip circumference
  • Obesity increases risk of CHD and stroke. The greater the amount of fat that you carry (esp. abdominal) the greater the risk to your heart
  • Obesity raises bp and blood lipid levels
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Carbohydrates 1

  • Monosaccharides
  • Monosaccharides are single sugar units- general formula (CH20)n
  • Glucose, galactose and fructose are hexose sugars- have a ring structure of 5 carbons and an oxygen, with the 6th carbon above or below the ring
  • Glucose- the sugar used by cells in respiration- can be absorbed and transported in bloodstream
  • Galactose- occurs in diet as part of the disaccharide lactose (milk)
  • Fructose- occurs naturally in fruit, honey and vegetable. Helps with seed dispersal (animals attracted to it)
  • Disaccharides
  • Two monosaccharies make a disaccharide via a condensation reaction (make water. The bond that forms between monosaccharides is known as a glycosidic bond/link. Bond broken when water added- hydrolysis
  • Sucrose- glucose+ fructose, form in which sugar transported in plants
  • Maltose- glucose+ glucose, formed when amylose breaks down. Found in germinating seeds
  • Lactose- galactose+glucose, sugar in milk
  • Monosaccharides cause blood sugar to rocket when eaten- di- and poly- more sustained
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Carbohydrates 2

  • Polysaccharides
  • Made up of several sugar monomers. 2 main types- starch (in plants) and glycogen (in animals), they are both nearly insoluble and are not sweet-tasting
  • Both act as energy storage molecules. They are compact molecules with low solubility in water- they don't affect conc. of water in cytoplasm or affect osmotic balance
  • Starch is a mix of amylose and amylopectin molecules
  • Amylose is a straight chain with 1,4 glycosidic links- causes it to be a spiral
  • Amylopectin has side branches, with 1,6 links holding side branched onto chain
  • Starch is a source of energy in our diet
  • Glycogen is a polymer composed of numerous side branches, which can be rapidly hydrolysed to give easy access to stored energy. Humans store glycogen in liver and muscles
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Reducing Risk of CVD

  • Statins- Lower cholesterol (LDL's), therefore decrease risk of atherosclerosis. However, evidence shows that statin treatment increases risk of death from non-vascular causes, but risk small compared to benefits
  • Anti-coagulants- Reduces platelet stickiness and stops cascade of chemical reactions (Aspirin). Warfarin affects the synthesis of clotting factors- prevents embolism and thrombosis. However, can increase the risk of serious bleeding
  • Antihypertensives- reduce blood pressure :
  • Diuretics- Increase volume of urine produced and lowers cardiac input and bp. However, dehydrates body and causes less oxygen to be in body- dizziness, muscle cramp
  • ACE Inhibitors- Inhibits anginotensin II, stops vasoconstriction of vessels, more dilation= less resistance. However
  • Calcium Channel Blockers- Block movement of calcium in muscles, causes vasodilation of blood vessels and decreases bp. However, if the dosage is wrong, then it could affect heart contraction
  • A diet to protect against CVD- balanced energy, reduced sat. fats, more polyunsat. fats, less cholesterol, less salt, more oily fish, more non-starch polysaccharides, more fruit and veg
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