Unit 1: Lifestyle, Transport, Genes and Health

Unit 1 — Complete A Level and AS source — IAL Edexcel Modular Revision Notes & Topical Questions

5 min read 12 parts Lesson 1 of 7 Unit quiz

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Unit 1 — Complete A Level and AS source notes — IAL EDEXCEL MODULAR notes: Summarise the key ideas of Unit 1: water, carbohydrates, lipids, proteins, nucleic acids, the circulatory system and the evaluation of health risks.Water — it is a dipole, with a weak negative charge on ox…

Condensation
Hydrolysis
Benedict's test
Iodine test
Emulsion test
Biuret test

Part 1 of 10Water and biological polymers

Water

Water it is a dipole, with a weak negative charge on oxygen and a weak positive charge on hydrogen, so molecules form hydrogen bonds.
It is an excellent solvent for ions and polar molecules such as glucose and amino acids, so it transports dissolved substances in blood.
It is liquid over a wide temperature range and has a high specific heat capacity, which buffers temperature change.

Condensation

Condensation joining of monomers with loss of water.

Hydrolysis

Hydrolysis breaking of bonds by adding water.

Molecule	Monomer and bond	Function
Starch (amylose)	Alpha-glucose, 1,4 glycosidic	Compact energy store in plants
Glycogen and amylopectin	Alpha-glucose, 1,4 and 1,6 glycosidic	Branched, so glucose is released rapidly
Triglyceride	Glycerol + 3 fatty acids, ester bonds	Energy store and insulation
Protein	Amino acids, peptide bonds	Enzymes, haemoglobin, collagen

Part 2 of 10Biochemical tests and enzymes

Benedict's test

Benedict's test it detects reducing sugars by a colour change from blue towards brick-red.

Iodine test

Iodine test it detects starch as a blue-black colour.

Emulsion test

Emulsion test it detects lipids.

Biuret test

Biuret test it detects protein as a purple colour.

Enzymes

Enzymes they lower activation energy, and the protein's 3D shape determines function.

Part 3 of 10Nucleic acids and genes

Nucleotide

Nucleotide it is a pentose sugar, a phosphate group and a nitrogenous base.

Phosphodiester bonds

Phosphodiester bonds they link nucleotides in a sugar-phosphate backbone formed by condensation.

DNA

DNA it is a double helix of two antiparallel strands joined by hydrogen bonds between complementary bases, A with T and C with G.

RNA

RNA it is usually single-stranded, shorter, and contains ribose and uracil.
mRNA carries the code, tRNA carries amino acids and rRNA forms ribosomes.

Genetic code

Genetic code it is a triplet code that is degenerate and non-overlapping.

Protein synthesis

Protein synthesis transcription makes mRNA and translation makes the polypeptide, with amino acids joined by peptide bonds.

Part 4 of 10Inheritance and screening

Genetic cross

Genetic cross a Punnett square for two carriers (Ff × Ff) gives a 1 in 4 chance of an affected (ff) child in cystic fibrosis.

Genetic screening

Genetic screening it includes carrier testing, prenatal testing and preimplantation genetic diagnosis.
- (amniocentesis and chorionic villus sampling)

Ethical issues

Ethical issues they include miscarriage risk, abortion decisions, false results and discrimination.

Part 5 of 10The circulatory system

1Need for mass transport

Need for mass transport large organisms have a small surface area to volume ratio and long diffusion distances.

2Double circulation

Double circulation humans have a closed system in which blood passes through the heart twice per circuit, to the lungs (pulmonary) and to the body (systemic).

3Cardiac cycle

Cardiac cycle atrial systole, ventricular systole and diastole.
Atrioventricular valves close when ventricular pressure exceeds atrial pressure.
Semilunar valves close at the start of diastole when ventricular pressure falls below arterial pressure, preventing backflow.

4Cardiac output

Cardiac output stroke volume × heart rate.

5Vessels

Vessels arteries have thick walls with elastic fibres that stretch and recoil to maintain pressure, veins have valves and capillaries have walls one cell thick for exchange.

6Blood clotting

Blood clotting thrombin converts soluble fibrinogen to insoluble fibrin.

Part 6 of 10Cardiovascular disease and risk

Atherosclerosis

Atherosclerosis an atheroma, a deposit of cholesterol, fibres and white cells, forms beneath the artery endothelium.
Thrombosis then occurs when a clot blocks the artery.

Lipoproteins

LDL carries cholesterol to tissues and raises risk, and HDL carries it back to the liver.

Risk reduction

Risk reduction a diet low in saturated fat, exercise and not smoking, and where needed statins, which reduce LDL by inhibiting an enzyme in the liver.

Dietary antioxidants

Dietary antioxidants they are linked with reduced CVD risk, though the evidence is inconclusive.

Obesity indicators

BMI and waist-to-hip ratio.

Part 7 of 10Health, risk and data

Health, risk and data

Correlation and causation

Correlation and causation a correlation does not prove that one factor causes another,
- and causal evidence needs a plausible mechanism and repeated studies.

Study design

Study design large random samples, controlled variables and statistical tests give valid and reliable data.

Perception of risk

Perception of risk people often over- or underestimate actual risks.

Part 8 of 10Surface area and diffusion

Fick's law
- rate of diffusion is proportional to surface area × concentration difference ÷ thickness of the exchange surface.
- If the diffusion distance halves and the surface area doubles, the rate increases four times.

Part 9 of 10More from the specification

1Mammalian cardiac cycle and pressure changes

Atrial systole forces blood into relaxed ventricles;
- ventricular systole elevates chamber pressure, closing atrioventricular valves and opening semilunar valves.

2Effect of caffeine on Daphnia heart rate

In biological bioassays, exposing transparent Daphnia to increasing concentrations of caffeine significantly elevates heart rate through neurochemical stimulation.

3Arterial endothelium and atherosclerosis

Damage to arterial endothelial linings triggers inflammatory responses,
leading to plaque atheroma formation, lumen narrowing,
and elevated cardiovascular risk.

4Atrium

Upper chamber receiving blood.

5Coronary artery

Artery supplying the heart muscle with oxygen and glucose.

Part 10 of 10More on this topic

1Benedict's test for reducing sugars

Benedict's test for reducing sugars heat the sample with excess Benedict's reagent in a boiling water bath.
Colour changes from blue through green, yellow and orange to brick-red as reducing sugar concentration rises.
Copper(II) ions are reduced to insoluble copper(I) oxide, forming a precipitate.

Saying haemoglobin picks up more oxygen in tissues when CO₂ is high — high CO₂ lowers its affinity, so oxygen is released.

Concluding a correlation proves a cause — causal claims need a mechanism and repeated evidence.

4Non-reducing sugars

Non-reducing sugars they give no colour change, so first boil with dilute hydrochloric acid to hydrolyse the glycosidic bond.
Neutralise with sodium hydrogencarbonate and make slightly alkaline, then repeat Benedict's test.
A brick-red precipitate then shows a non-reducing sugar was present.

5Bohr effect

Bohr effect high CO₂ lowers blood pH, so haemoglobin has a lower affinity for oxygen and the curve shifts right.
Oxygen is released more readily in respiring tissues.

6Fetal haemoglobin

Fetal haemoglobin it has a higher affinity for oxygen, so the curve is to the left and the fetus takes oxygen from the mother at the placenta.

Key terms

Term	Meaning
Dipole	A molecule with an uneven distribution of charge, such as water.
Condensation	Joining of monomers with loss of water.
Nucleotide	Monomer of nucleic acids made of a pentose sugar, phosphate and base.
Atheroma	Deposit of cholesterol, fibres and white cells beneath the artery endothelium.
Statins	Drugs that lower blood LDL cholesterol by inhibiting a liver enzyme.
Cardiac output	Stroke volume multiplied by heart rate.

Avoid these mistakes

Using surface area and surface area to volume ratio interchangeably — larger organisms have a larger area but a smaller ratio.

Stating that a correlation shows one factor causes the other.

Describing water as a non-polar molecule — it is a dipole.

Saying statins reduce cholesterol absorption in the gut — they inhibit an enzyme in the liver.

Last updated: 18 October 2026