Topic 1 · Lifestyle, Health and Risk

Topic 1 · Lifestyle, Health and Risk — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

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📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision

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Lesson summary

Lifestyle, Health and Risk — notes: Explain the circulatory system, heart and blood vessels, the cardiac cycle, atherosclerosis and clotting, cardiovascular disease risk factors, data interpretation, treatments, energy budgets, carbohydrates and lipids, and the vitamin C practic…

Small organisms
Large organisms
Mass transport
What it does
Double circulation
Cohesion and adhesion

Section 1 of 32Need for a circulatory system

Need for a circulatory system

Small organisms

Small organisms single cells get oxygen and glucose directly and diffusion distances are short.

Large organisms

Large organisms many layers of cells, diffusion distances too great, high energy needs; exchange surfaces are linked to a mass transport system.
- (digestive system and lungs connected to the circulatory system)

Mass transport

Mass transport bulk movement of gases or liquids in one direction, usually through vessels;
- in mammals the one-way flow of blood carries nutrients and gases to all cells.

What it does

Brings substances quickly between exchange sites.
Maintains diffusion gradients at exchange sites and between cells and their surroundings.
Supplies reactants and removes waste for effective cell activity.

Double circulation

Double circulation pulmonary and systemic circuits.

Section 2 of 32Water in transport

Water

Water the medium for all metabolic reactions and for transporting substances.

Polarity

One oxygen atom shares electrons covalently with two hydrogen atoms.
Sharing is unevenoxygen is weakly negative (δ–) and hydrogen weakly positive (δ+), a dipole, so water is polar.
Hydrogen bonds form between adjacent water molecules;
- they are weak, constantly break and reform, so water flows.

Cohesion and adhesion

Cohesion and adhesion cohesion is attraction between water molecules;
- adhesion is hydrogen bonding to other molecules;
- together water flows easily.

Solvent

Ions (Na⁺, Cl^–) and polar substances (glucose) dissolve.
Water molecules surround charged particlespositive parts attract negative particles, negative parts attract positive ones.
Dissolved solutes are more reactive and metabolites are transported in solution.

Exam tip

Exam tip link structure of water to its transport function.

Section 3 of 32Heart: circulation and structure

Heart: circulation and structure

Circulatory types

Closed
- blood always in vessels.
- Open: blood bathes organs in a body cavity.
Double
- two loops (lungs and body).
- Single: one loop.

Humans

Humans closed double circulation; blood passes through the heart twice per circuit.
Right sidedeoxygenated blood to the lungs (pulmonary circulation).
Left sideoxygenated blood pumped at high pressure round the body (systemic circulation).

Heart

Heart about 300 g, fist-sized, hollow and muscular, in the chest cavity within the pericardium.
- (tough fibrous sac)

Chambers

Chambers two atria (top), two ventricles (bottom); the septum separates left and right so blood does not mix.

Blood supply to the heart

Blood supply to the heart coronary arteries supply the heart muscle.

Diagram note

Diagram note the right side of the heart appears on the left of the diagram.

Section 4 of 32Heart valves and vessels at the heart

Valve	Position
Tricuspid (AV)	Right atrium and right ventricle
Bicuspid (AV)	Left atrium and left ventricle
Pulmonary (semilunar)	Right ventricle and pulmonary artery
Aortic (semilunar)	Left ventricle and aorta

Valve action

Valve action open when pressure behind is greater than in front;
- close when pressure in front is greater;
- keep flow forward and maintain pressure.

Valve tendons (cords)

Valve tendons (cords) attach valves to the heart wall and stop them turning inside out under high pressure.

Vessels in

Vessels in vena cava (from the body) and pulmonary vein (from the lungs).

Vessels out

Vessels out pulmonary artery (to the lungs) and aorta (to the body).

Section 5 of 32Blood vessel types and arteries

Blood vessel types and arteries

Types

Arteriescarry blood away from the heart, usually at high pressure.
Arteriolesbranch from arteries into capillaries.
Capillariesmicroscopic vessels to the cells.
Venulescapillaries to veins.
Veinscarry blood to the heart at low pressure.

Lumen

Lumen narrow in arteries, wider in veins.

Artery wall

Artery wall three layers

Endothelium (tunica intima)one cell thick, smooth to reduce friction, folded to expand under pressure.
Smooth muscle and elastic tissue (tunica media): thick;
- muscle strengthens and can constrict the lumen to divert blood (for example away from the gut in exercise);
- elastic tissue stretches and recoils to even out pressure fluctuations.
Outer wall (tunica adventitia/externa)collagen protects against overstretching.

Features

Features narrow lumen maintains high pressure; a pulse is felt as arteries stretch with each beat.

Section 6 of 32Veins and capillaries

Feature	Veins	Capillaries
Wall	Same layers as arteries but thinner muscle and elastic layers (low pressure)	One layer of endothelial cells (no cell wall); thin and permeable
Lumen	Wide: reduces friction and ensures adequate return speed	Very narrow: red cells pass in single file, slowing flow for more time for diffusion
Valves	Present: prevent backflow	Absent
Pulse	Absent (distance from heart)	Absent
Special features	Flow slower but volume per unit time equals arteries	Pores let plasma leak to form tissue fluid; white cells squeeze through; short diffusion distance; form capillary beds

Exam tip
- pair each structural feature with its effect on function; muscle contracts and elastic tissue recoils.

Section 7 of 32Cardiac cycle: phases

1Cardiac cycle

Cardiac cycle events in one heartbeat;
- contraction is systole, relaxation is diastole;
- the cycles are continuous with no gap.

2Pressure and volume

Pressure and volume contraction reduces chamber volume and increases pressure;
- relaxation increases volume and lowers pressure;
- valves open and close with pressure changes.

Atrial systole

Atrial systole atrial walls contract, volume falls and pressure rises above the ventricles; AV valves open; blood is forced into the ventricles.
- (which are relaxed)

Ventricular systole

Ventricular systole ventricle walls contract;
- pressure exceeds the atria, closing AV valves;
- pressure exceeds the aorta and pulmonary artery, opening semilunar valves;
- blood leaves;
- the relaxed atria begin to fill.

Diastole

Diastole atria and ventricles relax;
- ventricular pressure falls below the arteries so semilunar valves close;
- atria fill via the vena cava and pulmonary vein;
- atrial pressure exceeds ventricular, AV valves open and blood flows passively into the ventricles.

Section 8 of 32Interpreting the cardiac cycle graph

Point	Events
A (end of diastole)	Atrium full; atrial pressure higher than ventricle, so AV valve open
A–B (atrial systole)	Atrium contracts, pressure rises; blood into ventricle; ventricular pressure rises slightly
B	Ventricle contracts; ventricular pressure exceeds atrial; AV valve shuts
C (ventricular systole)	Ventricular pressure exceeds aorta; aortic valve opens; blood forced into aorta
D (start of diastole)	Ventricle empty and relaxing; pressure falls below aorta; aortic valve closes
D–E	Ventricle relaxed, pressure falls; blood flows into the atrium from the pulmonary vein, raising atrial pressure
E	Atrial pressure exceeds ventricular; AV valve opens
After E (late diastole)	Ventricle expands, volume rises and pressure falls; blood flows slowly through AV valve; pressures in both then rise slowly

1Heart rate calculation

Heart rate calculation one cycle 0.7 s gives 1 ÷ 0.7 = 1.43 beats per second; × 60 = 85.7 beats per minute.
- (60 ÷ cycle time)

2Common assessment

Common assessment pressure and volume changes, valve opening and closing, and when blood flows in or out.

Section 9 of 32Practical: heart rate in Daphnia

Practical: heart rate in Daphnia

Factors that affect heart rate

Factors that affect heart rate drugs, caffeine, alcohol, sex, weight, height, temperature, diet, dehydration;
- control all other variables.

Why Daphnia

Why Daphnia small transparent invertebrates, so the heart can be seen under a light microscope.

Apparatus

Apparatus light microscope, cavity slide, Daphnia culture, pipette, caffeine solutions of a range of concentrations, distilled water, stopwatch.

Prepare five caffeine concentrations and a distilled water control (serial dilution can be used).

Put pond water and three drops of distilled water in the cavity slide well.

Transfer a large Daphnia gently with a pipette (a Petri dish can be used instead).

View under low power; the heart is on the dorsal side above the gut, in front of the brood pouch.

Time 20 seconds and count beats (mark dots on paper).

Multiply by three for beats per minute.

Return the Daphnia to the culture; repeat with at least 5 more.

Repeat with each concentration.

Variations

Variations temperature, or 1% ethanol.

Results

Results mean heart rate against caffeine concentration; positive correlation.

Ethics

Daphnia cannot consent or express pain; some regard invertebrates as more ethical than vertebrates.
Handle gently, keep examination short, return promptly.
Avoid extremes of temperature or strong solutions.

Section 10 of 32Atherosclerosis

Atherosclerosis

Atherosclerosis hardening of the arteries;
- progressive;
- starts with damage to the endothelium and an inflammatory response.

Causes of damage

Causes of damage high blood pressure, certain cholesterol, smoking, diabetes, obesity, old age.

The endothelium is damaged.

Inflammation: macrophages accumulate at the site.

Lipids and cholesterol clump with macrophages under the endothelium,

forming fatty streaks (an early sign); platelets add to the deposit.
- (cell fragments involved in clotting)

These accumulate as a plaque called an atheroma.

The atheroma narrows the lumen, restricting flow and raising blood pressure.

Over time it calcifies and hardens, reducing elasticity and further raising blood pressure.

Section 11 of 32Blood clotting (thrombosis)

Purpose

Purpose prevents blood loss and pathogen entry and forms a scab for healing.

Trigger

Trigger a break in skin or mucous membrane releases molecules that start a cascade of reactions involving plasma proteins.

The damaged vessel releases thromboplastin.

Thromboplastin and plasma calcium ions convert soluble prothrombin into the enzyme thrombin.

Thrombin converts soluble fibrinogen into insoluble fibrin.

Fibrin fibres mesh and trap platelets and red blood cells, forming a clot.

Section 12 of 32Clots, stroke, CHD and DVT

1Atheroma and clots

Atheroma and clots a plaque can rupture the endothelium,
- giving a rough surface that triggers thrombosis; the clot can block the artery or dislodge and travel.

2Effect

Effect reduced blood flow lowers oxygen delivery and respiration in cells.

3Stroke

Stroke sudden loss of brain function from disrupted blood flow; a clot blocking brain arteries reduces oxygen, so cells cannot make ATP.
- (ischemic stroke)

4Coronary heart disease

Coronary heart disease atheromas and clots in the coronary arteries.
Reduced oxygen to heart muscle, less respiration and no ATP.
Cells cannot contract, reducing force; cells can die.
Myocardial infarction (heart attack); large areas affected may cause fatal heart failure.

5Heart attack symptoms

Heart attack symptoms chest pain, shortness of breath, sweating.

6Deep vein thrombosis (DVT)

Deep vein thrombosis (DVT) clot in a deep vein, most often in the legs;
- causes include prolonged inactivity, old age, some medications.

Section 13 of 32Cardiovascular disease and risk factors

Cardiovascular disease and risk factors

CVD

CVD conditions of the heart and blood vessels, usually linked with atherosclerosis and thrombosis.

Risk factor

Risk factor linked to higher risk of disease but does not guarantee it; correlation is not always causation.

Types of risk factor

Lifestyle (diet, alcohol).
Substances in the body or environment (air pollution, asbestos).
Genetic predisposition.
Other biological factors (age, sex).

Interaction

Interaction many diseases result from several factors: high-cholesterol diet, lack of exercise and smoking together raise arterial damage.

Control

Control lifestyle factors are partly controllable, though healthy choices are easier for some people (cost, time); age, sex and genetics are not controllable.
- (diet, smoking, alcohol, exercise)

Section 14 of 32Interpreting data on risk factors

1Correlation and causation

Correlation and causation correlation does not prove one variable caused the other;
- other factors influence disease.

2Describing data

Describing data identify trends and quote numbers.
- (oldest group of 80+ has the highest relative risk, 2.4)

3Drawing conclusions

State what the data show about the relationship (association or correlation).
Keep to what the data show; no causal claim from one data set.
Do not extrapolate beyond the study group (ages, mice to humans).

4Validity

Larger samples are more representative.
Valid results measure what was intended and are analysed correctly.
Statistical tests check significance.
Use a control group (for example no drug).
Repeat studies; many studies should agree.
Control other variables.
Researchers should not be biased (for example paid for a result).

Section 15 of 32Worked example: passive smoking and CVD

Data

523 non-smoking partners of smokers;
- relative risk of CVD: 1.00 at 0 cigarettes, 1.23 at 1–19, 1.31 at 20 or more per day.

Describe

Describe risk rises from 1.00 to 1.23 to 1.31 as exposure increases.

Conclude

Conclude an association between exposure to smoke and CVD risk; best not to claim causation from one study.

Validity comments

523 is a fairly small sample.
Only one study; needs replication.
Other risk factors not considered (age, diet, sex, exercise);
- for example smokers are often older, more men smoke, smokers may exercise less.
No statistical test stated, so significance unknown.

Section 16 of 32Conflicting evidence and experimental design

Meta-analysis

Meta-analysis combining similar studies; similar conclusions are needed to accept a finding.

Conflicting evidence

Conflicting evidence shows a different pattern from other evidence;
- more research is needed;
- often a sign that other variables are involved.

Design evaluation

Samplerepresentative, random selection removes bias (friends or gym-goers share lifestyles).
Variables
- more control gives more reliable and valid data;
  - reliable data can be repeated;
  - valid data tests only one independent variable.
Datano bias in collection or analysis.
Controlsa point of comparison.
Repetitionsimilar repeated results are reliable.
Reproduciblerepeating the whole investigation gives the same findings.

Section 17 of 32Perception of risk

1Risk

Risk the chance or probability that a harmful event will occur;
- the statistical chance needs scientific evidence.

2Perceived versus actual risk

Perceived versus actual risk they can differ.

3Overestimated because of

Misleading media information.
Overexposure to information.
Personal experience of the risk.
Unfamiliarity with the event.
Severe harm from the event.

4Underestimated because of

Lack of information.
Misunderstanding of risk factors.
No personal experience.
Unfamiliarity.
Harm that is not immediate.

Section 18 of 32Treatment of CVD

Drug type	How it works
Antihypertensives (beta blockers, vasodilators, diuretics)	Lower blood pressure (hypertension), reducing endothelial damage and so atheromas and thrombosis. Beta blockers prevent increases in heart rate; vasodilators widen vessels; diuretics reduce blood volume by decreasing sodium (and so water) reabsorption in the kidneys
Statins	Block an enzyme in the liver needed to make cholesterol; lower LDL concentration, reducing atheroma risk
Anticoagulants	Reduce blood clotting (coagulation), lowering the risk of thrombosis and blockage
Platelet inhibitors (aspirin)	A type of anticoagulant; prevent platelets clumping together so clots do not form

Best approach

Best approach reduce risk factors; know the four drug types with their benefits and risks.

LDLs

"bad" cholesterol; high levels raise atheroma risk.

Section 19 of 32Energy budgets and diet

Energy needs

Energy needs cells need constant energy from respiration; food stores energy in carbohydrates and lipids.

Energy budget

Energy budget energy input – energy output.
- (energy transferred in growth, movement, reproduction and respiration)

Units

Calorie = kilocalorie; adult about 2 000 kcal (about 8 700 kJ) per day to keep a healthy weight.

Worked example

Worked example intake 12 400 kJ.
School 6 h at 4 kJ/min = 1 440 kJ.
Run 1 h at 17 kJ/min = 1 020 kJ.
Sleep 8 h at 3 kJ/min = 1 440 kJ.
Meals 2 h at 5 kJ/min = 600 kJ.
Output = 4 500 kJ; budget = 12 400 – 4 500 = 7 900 kJ surplus (only the listed activities are counted).

Imbalance

Intake above outputexcess stored as fat, weight gain, possibly overweight and obese.
Intake below outputfat reserves used, weight loss, possibly underweight.

Complication

Complication not all calories are equal; the body processes foods differently.
- (fats, sugars, sucrose, fructose)

Section 20 of 32Carbohydrates and monosaccharides

Carbohydrates and monosaccharides

Carbon

Carbon carbon atoms form stable covalent bonds in chains, branches and rings; monomers join by polymerisation into polymers.
- (also with O, N, S)

Carbohydrates

Carbohydrates contain C, H and O; three types: monosaccharides, disaccharides, polysaccharides.

Monosaccharides

Monosaccharides simple sugars and monomers.
Triose (3C): glyceraldehyde.
Pentose (5C): ribose.
Hexose (6C): glucose, a ring of carbons 1–5 with carbon 6 above the ring.

Alpha and beta glucose

Alpha and beta glucose differ only in H and OH on carbon 1: alpha has the OH below (H above);
- beta has the OH above (H below).

Function

Function store energy in bonds, released in respiration;
- soluble so easily transported;
- many covalent bonds;
- condense to form larger carbohydrates;
- some form structural fibres.

Section 21 of 32Glycosidic bonds and disaccharides

Glycosidic bond

Glycosidic bond a strong covalent bond formed when two hydroxyl groups on different monosaccharides react, releasing one water (condensation).
OH on carbon 1 and carbon 4: 1,4 bond.
Carbon 1 and carbon 6: 1,6 bond.

Hydrolysis

Hydrolysis adding water breaks the bond.
- (digestion; breakdown of stored carbohydrate in muscle and liver)

Why polymers

Why polymers polysaccharides are insoluble so have little osmotic effect.

Disaccharide	Made from	Bond
Maltose	Glucose + glucose	1,4
Sucrose	Glucose + fructose	1,2
Lactose	Glucose + galactose	1,4

Function
- quick-release energy: easily hydrolysed to monosaccharides and absorbed;
  - many hydroxyl groups hydrogen bond with water, so soluble and sweet.

Section 22 of 32Polysaccharides: starch and glycogen

Polysaccharides: starch and glycogen

Polysaccharides

Polysaccharides many monosaccharides joined by glycosidic bonds; branched or unbranched, straight or coiled.
Branchedfaster breakdown.
Straightstructural (cellulose).
Coiledcompact storage (amylose).

Storage features

Storage features compact and insoluble.
- (no osmotic effect, unlike glucose)

Starch

Starch plant storage polysaccharide, in granules in plastids.
- (amyloplasts store starch grains)
Amylose: unbranched helix of α-glucose with 1,4 bonds; compact.
Amylopectin: branched with 1,4 and 1,6 bonds; many terminal glucose molecules easily hydrolysed or added to.

Glycogen

Glycogen storage polysaccharide of animals and fungi.
More highly branched than amylopectin, with 1,4 and 1,6 bonds.
More terminal glucose for fast storage or release, matching high animal activity.
Compact; liver and muscle cells hold visible granules, enabling a high respiration rate.

Note

Note cellulose is not needed here; know the starch–glycogen differences.

Section 23 of 32Lipids and triglycerides

Lipids and triglycerides

Lipids

Lipids contain C, H and O; non-polar and hydrophobic; roles in energy yield and storage, insulation and hormonal communication.
- (less oxygen than carbohydrates)

Triglycerides

Triglycerides main component of fats and oils; monomers glycerol (an alcohol) and fatty acids.

Fatty acid

Fatty acid hydrocarbon R chain with a methyl end and a carboxyl group (RCOOH).
- (4 to 24 carbons)

Variation

Variation chain length, and saturation.
Saturatedno C=C double bonds, linear unbranched chain (mainly animal fats).
Unsaturatedmono- or polyunsaturated (mainly vegetable oils, with exceptions such as coconut and palm oil).
Cis fatty acids (H on the same side of the double bond) are metabolised by enzymes.
Trans fatty acids (H on opposite sides) cannot form enzyme–substrate complexes, are not metabolised and are linked with coronary heart disease.

Functions

Functions energy storage, insulation, buoyancy, protection.

Section 24 of 32Ester bond formation

Ester bond formation

A hydroxyl (–OH) group of glycerol reacts with the carboxyl (–COOH) group of a fatty acid.

An ester bond forms; this is a condensation reaction (esterification) releasing one water.

Three fatty acids join one glycerol, so three water molecules are released.

Exam tip
- know the triglyceride structure so you can tell saturated from unsaturated.

Section 25 of 32Lipids, cholesterol and lipoproteins

Risk factor

Risk factor increases the chance of disease without guaranteeing it;
- incidence is the number of cases in a group in a given time.

Cholesterol

Cholesterol a lipid made in the body; needed for membranes, sex hormones, and bile; transported as lipoproteins.
- (lipid and protein)

Feature	HDL	LDL
Contains	Unsaturated fat, cholesterol, protein	Saturated fat, cholesterol, protein
Role	Move cholesterol from tissues to the liver for recycling or excretion; lower blood cholesterol; help remove cholesterol from plaques	Move cholesterol from the liver into the blood until cells need it; raise blood cholesterol when it is low
Cell receptors	—	Bind to membrane receptors for uptake; excess LDL blocks receptors, raising blood cholesterol
Common label	"Good"	"Bad"

Ratio matters

Ratio matters roughly 3:1 LDL:HDL is thought healthy; above 5:1 raises risk of heart disease.

Other factors

Other factors diet and how cells process lipids.

Section 26 of 32Evaluating lipoprotein and CVD data

1Things to check

Sample size (representative).
Who is in the sample (results apply only to similar people).
A control group.
Control of other variables (age, diet, activity, genetics, secondary smoke exposure).
Statistical significanceoverlapping standard deviations mean no significant difference.

2Example

300 men aged 40 to 80, LDL and HDL measured over 30 weeks against CVD events.
Describeevent rate about 28% with LDL and about 18% with HDL.
Concludeno significant difference because standard deviation bars overlap.
Validitysample small, only men 40–80, smoking, diet and exercise not measured or controlled.

3Evidence linking cholesterol to CVD

A main risk factor named by the British Heart Foundation and NHS.
Statins lowering cholesterol reduce heart disease.
Saturated fat raises LDL and is linked to CVD events.
Lower total cholesterol links to fewer coronary events.
Plaque regression with lipid-lowering therapy.

4Caution

Caution correlation is not causation; a third variable may be involved; say "there is a correlation".
- (alleles affecting fat metabolism)

Section 27 of 32Reducing CVD risk factors

Diet

Diet some studies link saturated fat to CVD risk, others are inconclusive; food labels and traffic-light labels for sugar, saturated fat and salt help informed choices.
- (red high, orange medium, green low)

Obesity

Obesity linked to CVD events; measures:
Waist-to-hip ratio
- waist ÷ hips;
  - should be below 0.86 (women) and 1.0 (men).
BMI = mass (kg) ÷ height² (m²): under 18.5 underweight;
- 18.5–24.9 normal;
- 25–29.9 overweight;
- 30 or more obese.

Smoking

Smoking research led to health warnings, media portrayal as unhealthy, and free support to stop smoking.

Exercise

Exercise inactivity is linked with CVD; campaigns, more school physical education, targeted encouragement.
- (for example teenagers)

Section 28 of 32Practical: vitamin C content

Vitamin C

Vitamin C ascorbic acid, in green vegetables, fruits and potatoes; a good reducing agent, easily oxidised.

Principle

Principle titrate against DCPIP, a blue dye that turns colourless with vitamin C.

Apparatus

Apparatus vitamin C solutions, 1% DCPIP, distilled water, fruit juices, measuring cylinder, pipette, stopwatch, test tubes.

Make about six known vitamin C concentrations (serial dilution).

Put 1 cm³ DCPIP in a test tube.

Add a vitamin C solution drop by drop with a graduated pipette or burette, shaking for the same time after each drop (control variable).

Record the volume added when the solution turns colourless.

Repeat twice more and take the mean.

Repeat for each concentration.

Plot volume needed against concentration to make a calibration curve.

Repeat with fruit juices and read their concentrations from the curve.

Result

Result the volume needed falls as vitamin C concentration rises.

Risk assessment

DCPIP is an irritantavoid skin contact and wear eye protection.

Section 29 of 32Calculating mass of vitamin C

Calculating mass of vitamin C

Basis

1 cm³ of a 1% vitamin C solution contains 10 mg.

Mass needed to decolourise 1 cm³ DCPIP

10 mg × volume of 1% solution used.