1.2 Diet & Health — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

Section 1 of 8Diet & Health

Essential knowledge

Energy input comes from carbohydrate, fat and protein; output includes BMR and physical activity. Intake greater than output leads to weight gain; less leads to weight loss.

Obesity indicators include BMI and waist-to-hip ratio; obesity is a risk factor for CVD, type 2 diabetes and high blood pressure.

Monosaccharides (glucose, fructose, galactose) join by glycosidic bonds to form disaccharides (maltose and lactose by 1,4 bonds; sucrose by a 1,2 bond).

Amylose is an unbranched helix of α-glucose (1,4 bonds) – compact; amylopectin is branched (1,4 and 1,6) – many ends for enzymes; glycogen is more branched – rapid release for animals.

Triglycerides are formed by condensation between glycerol and three fatty acids forming ester bonds; saturated chains are straight, unsaturated chains are kinked by C=C bonds.

Cholesterol is made in the liver and needed for membranes and steroid hormones; it travels in blood as lipoproteins.

Diets high in saturated fat raise blood LDL, which increases atheroma formation; diets higher in polyunsaturated fat raise HDL and lower LDL.

Plant stanols and statins reduce blood LDL; high salt intake raises blood pressure.

Vitamin C content can be found by titrating a food sample into DCPIP (blue) until it decolourises; more vitamin C means less sample needed.

Good epidemiological studies use large random samples, controls, matched groups, reliable measures and consider confounding variables.

Scientific claims are validated by peer review, replication and publication; media reports can over-simplify risk.

α and β glucose

Monosaccharides are classed by carbon number

triose (3C), pentose (5C, e.g. ribose) and hexose (6C, e.g. glucose).
In α-glucose the OH on carbon 1 points below the ring;
- in β-glucose it points above.
Glucose is soluble, so it is easily transported, and its bonds store energy.

Sucrose bond

Maltose (glucose + glucose) and lactose (glucose + galactose) contain 1,4 glycosidic bonds, but sucrose (glucose + fructose) is joined by a 1,2 glycosidic bond. Disaccharides are soluble and sweet because their many OH groups hydrogen bond with water.

Fatty acid structure

A fatty acid has a carboxyl group (–COOH) at one end of a hydrocarbon chain (R group), written RCOOH. In unsaturated fats, cis double bonds (H atoms on the same side) are metabolised by enzymes, while trans fats cannot fit enzyme active sites and are linked to heart disease.

LDL receptors

Cells take up LDL by binding it to LDL receptors on their membranes. When LDL is in excess these receptors become saturated/blocked, so blood cholesterol rises. The LDL:HDL ratio matters more than either alone; a high ratio (e.g. above about 5:1) indicates raised CVD risk.

Antihypertensives

Antihypertensives lower blood pressure, reducing endothelial damage and so atheroma risk.

Beta blockers stop heart rate rising, vasodilators widen blood vessels,
and diuretics reduce Na⁺ reabsorption in the kidney, lowering blood volume.
- (and therefore water)
Risks include dizziness, fainting and kidney problems.

Statins

Statins inhibit a liver enzyme needed to make cholesterol, so blood LDL falls and atheroma formation is reduced. Side effects can include muscle pain, liver damage and digestive upset, and they may encourage people to neglect lifestyle changes.

Anticoagulants

Anticoagulants (e.g. warfarin) reduce blood clotting, lowering the risk of thrombosis blocking a vessel. Platelet inhibitors (e.g. aspirin) are a type that stop platelets clumping together. The main risk of both is excessive bleeding, e.g. internal bleeding or bruising.

Perception of risk

Risk is the probability that a harmful event will happen. People often overestimate risks that are dramatic, unfamiliar or heavily reported in the media, and underestimate risks they know little about, have never experienced, or whose harm is delayed (e.g. effects of a poor diet).

Vitamin C calibration curve

To find vitamin C in an unknown juice, first titrate a series of known vitamin C concentrations (made by serial dilution) against a fixed volume of DCPIP.

Plot volume needed to decolourise against concentration;
- this calibration curve lets you read off the concentration of each juice.
Keep shaking time constant; DCPIP is an irritant.

Error bars & significance

When comparing two groups, if standard deviation (or error) bars overlap, the difference is probably not significant and could be due to chance; if they do not overlap, the difference is likely significant. Conclusions should only apply to the population sampled.

Section 2 of 8Process & sequence

1

Identify dependent and independent variables and a clear hypothesis (e.g. higher saturated fat intake increases CVD risk).

2

Use a large, representative sample chosen randomly, matched for other risk factors (age, sex, smoking).

3

Control or record confounding variables; use a control group.

4

Collect data over a long enough period with valid, reliable measurements (e.g. blood cholesterol, BMI).

5

Analyse using statistics to test for a significant correlation; state whether it is positive or negative.

6

Evaluate: check for bias, peer review, replication and a plausible mechanism before claiming causation.

DCPIP titration for vitamin Cwrite these steps in this order; each step is a marking point.

1

Pipette a fixed volume (1 cm³) of 1% DCPIP into a test tube.

2

Add a standard vitamin C solution from a burette dropwise, shaking, until blue colour just disappears; record volume.

3

Repeat with each food/juice sample, keeping DCPIP volume and concentration constant.

4

Repeat three times and calculate a mean for each sample.

5

Calculate mass of vitamin C per cm³ of sample by comparison with the standard.

Section 3 of 8Compare

Starch (amylose, amylopectin) and glycogen
Feature	Amylose	Amylopectin	Glycogen
Found in	Plants	Plants	Animals (liver, muscle)
Monomer	α-glucose	α-glucose	α-glucose
Bonds	1,4 glycosidic only	1,4 and 1,6 glycosidic	1,4 and many more 1,6 glycosidic
Shape	Unbranched helix, compact	Branched	Highly branched, compact
Consequence	Stores many glucose in small space	Many ends for fast hydrolysis	Very fast glucose release for active animals

All are insoluble so do not affect water potential of cells.

LDL vs HDL
Feature	LDL	HDL
Main lipid	Saturated fat	Unsaturated fat
Density	Lower (less protein)	Higher (more protein)
Cholesterol carried	Liver → tissues	Tissues → liver
Effect on CVD risk	Increases	Decreases

Section 4 of 8Worked examples

Worked examples

A man of mass 95 kg is 1.80 m tall. Calculate his BMI and classify it.

BMI = 95 ÷ 1.80² = 95 ÷ 3.24 = 29.3 kg m^-2 (3 s.f.): overweight (25–29.9).

1.0 cm³ DCPIP was decolourised by 2.5 cm³ of 1.0 mg cm^-3 vitamin C standard, and by 10.0 cm³ of orange juice. Calculate vitamin C concentration in the juice.

Mass vitamin C to decolourise 1 cm³ DCPIP = 2.5 × 1.0 = 2.5 mg.
- Juice concentration = 2.5 mg ÷ 10.0 cm³ = 0.25 mg cm^-3.

Gain of about 0.97 kg

A person takes in 11 500 kJ per day; BMR is 7 200 kJ and activity uses 3 100 kJ. Calculate the daily energy balance and predict the change in mass over 30 days (1 kg of fat stores about 37 000 kJ).

Output = 7200 + 3100 = 10 300 kJ.
- Balance = 11 500 − 10 300 = +1200 kJ day^-1.
- Over 30 days = 36 000 kJ;
  - ÷ 37 000 = gain of about 0.97 kg (2 s.f.).

Section 5 of 8Keep going

Diet & Health Edexcel A Level Biology SNAB: what to do next

These Diet & Health Edexcel A Level Biology SNAB notes covered the key ideas, worked examples and exam technique for this topic. Check your Diet & Health Edexcel A Level Biology SNAB understanding with the practice questions below, then reread any Diet & Health Edexcel A Level Biology SNAB point you were unsure about before moving on.

Diet & Health Edexcel A Level Biology SNAB: revision checklist

1

Revise the main Diet & Health Edexcel A Level Biology SNAB definitions until you can write them from memory.

2

Practise Diet & Health Edexcel A Level Biology SNAB exam questions under timed conditions.

3

Link each Diet & Health Edexcel A Level Biology SNAB idea to a diagram or a worked example.

4

List the common Diet & Health Edexcel A Level Biology SNAB mistakes and how to avoid them.

5

Explain one Diet & Health Edexcel A Level Biology SNAB idea out loud as if teaching a friend.

6

Summarise Diet & Health Edexcel A Level Biology SNAB in five key points on a revision card.

7

Check which command words appear most often in Diet & Health Edexcel A Level Biology SNAB questions.

1

Practice: Diet & Health Edexcel A Level Biology SNAB practice questions

2

Previous lesson: 2.2 Inheritance — 9BI0 Notes

3

Next lesson: 3.1 Cell Structure & Organisation — 9BI0 Notes

4

Course: Edexcel A Level Biology A (snab) 9BI₀ — all units

5

Official syllabus: Pearson Edexcel A Levels

Section 6 of 8Key terms

Section 7 of 8Command terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Section 8 of 8Exam technique

Keywords the mark scheme looks for in this lesson

Energy budget · Basal metabolic rate (BMR) · Monosaccharide · Disaccharide · Polysaccharide · Glycosidic bond · Condensation reaction · Hydrolysis · Triglyceride · Saturated fatty acid · Unsaturated fatty acid · Low-density lipoprotein (LDL) · High-density lipoprotein (HDL) · Correlation vs causation

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

1

Use specification keywords exactly (e.g. enzyme–substrate complex, active site, complementary).

2Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

3Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

4

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

5Avoid vague words

“it”, “stuff”, “goes up”, “energy is made”. Name the substance and the process.

6

Extended (6-mark) responses are marked on content AND a logical, linked line of reasoning.

Words to avoid

1

fats are bad cholesterolLDL, carrying cholesterol to tissues, is associated with increased atheroma.

2

glucose molecules are joined by hydrolysisjoined by condensation forming a glycosidic bond, releasing water.

3

saturated fats have no double bonds so are solid because they are heavystraight chains pack closely, raising melting point.

4

the study proves diet causes heart diseasethe data show a correlation; a causal mechanism must also be shown.

5

glycogen is branched so it stores morebranching gives many ends so enzymes can hydrolyse it rapidly.