Pearson Edexcel International GCSE Biology 4BI1: Nutrition – Revision Notes

For full explanations and worked examples, use the nutrition study guide. These notes are for the final weeks.

They cover sub-topic 2(e) Nutrition of the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3 (September 2024): statements 2.18–2.33B. The qualification is untiered. Only 2.33B, the food energy practical, is in bold with a B reference, so it is Paper 2 only; the rest can appear on either paper.

Course links: 4BI1 Biology hub, printable checklist, nutrition practice questions and all free 10-minute diagnostics. Enzyme action, temperature and pH are in the cell structure revision notes.

Flowering plants

2.18–2.19 Photosynthesis

• Photosynthesis converts light energy into chemical energy (in glucose).
• Chlorophyll, in chloroplasts, absorbs the light.
• It supplies the energy at the start of nearly every food chain, and releases oxygen.

Equation	Form
Word	carbon dioxide + water → glucose + oxygen (light, chlorophyll)
Symbol	6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Raw materials: carbon dioxide (from the air, through stomata) and water (from the soil, through xylem). Products: glucose and oxygen.

2.20 Limiting factors

Factor	Why it affects the rate	Shape of graph
Light intensity	Supplies the energy	Rises, then levels off
Carbon dioxide concentration	Raw material	Rises, then levels off
Temperature	Enzymes control the reactions	Rises to an optimum, then falls steeply

Method: naming the limiting factor from a graph

1. Find the part of the curve you are asked about.
2. If the line is still rising as the x-axis factor increases, that factor is limiting.
3. If the line is flat, the x-axis factor is not limiting. Name one of the other two factors.
4. If another curve at a higher level of a second factor sits above it, that second factor was limiting on the lower curve’s flat part.

2.21 Leaf adaptations

Structure	Adaptation
Large surface area	Absorbs more light
Thin	Short diffusion path for carbon dioxide
Transparent cuticle and upper epidermis	Let light through to the mesophyll
Palisade mesophyll	Most chloroplasts; near the upper surface
Spongy mesophyll	Air spaces for gas diffusion
Stomata and guard cells	Let carbon dioxide in
Xylem / phloem	Bring water in / take sugars away

2.22 Mineral ions

Ion	Needed for	If short
Magnesium	Making chlorophyll	Yellow leaves, less photosynthesis
Nitrate	Making amino acids (then proteins)	Poor growth

2.23 Practicals in steps

Oxygen from pondweed

1. Pondweed in water with sodium hydrogencarbonate.
2. Lamp at a set distance; heat shield to keep temperature steady.
3. Let the plant adjust, then count bubbles per minute or measure gas volume.
4. Repeat at each distance; calculate the mean.
5. Test the gas: it relights a glowing splint.

Starch test on a leaf

1. Boiling water: kills the leaf, makes cells permeable.
2. Hot ethanol (flame off): removes chlorophyll.
3. Warm water: softens the leaf.
4. Iodine: blue-black means starch.

Requirement experiments (destarch first, about 48 hours in the dark)

Requirement	Set-up	Result
Light	Part of leaf covered with foil	Covered part: no starch
Carbon dioxide	Soda lime with the plant; control without	Soda lime plant: no starch
Chlorophyll	Variegated leaf	White parts: no starch

Humans

2.24–2.25 Balanced diet

A balanced diet has carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre in appropriate proportions.

Nutrient	Source	Function
Carbohydrate	Rice, bread, potatoes	Energy
Protein	Meat, fish, beans	Growth, repair, enzymes
Lipid	Oils, butter, nuts	Energy store, insulation, membranes
Vitamin A	Liver, carrots	Vision in dim light, healthy skin
Vitamin C	Citrus fruit	Healthy skin and gums (prevents scurvy)
Vitamin D	Oily fish; skin in sunlight	Calcium absorption, bones (prevents rickets)
Calcium	Milk, cheese	Bones, teeth, blood clotting
Iron	Red meat, spinach	Haemoglobin (prevents anaemia)
Water	Drinks	Solvent, transport, cooling
Fibre	Vegetables, wholegrain	Bulk for peristalsis, prevents constipation

2.26 Energy requirements

• Higher with more activity (more respiration in muscles).
• Varies with age: high for size while growing; often lower in old age.
• Higher in pregnancy: growth of fetus and placenta, extra mass to carry.

2.27–2.28 Alimentary canal

Order: mouth → oesophagus → stomach → duodenum → ileum → colon → rectum → anus. The pancreas releases enzymes into the duodenum; the liver makes bile.

Region	Key job
Mouth	Chewing; salivary amylase
Oesophagus	Peristalsis to stomach
Stomach	Churning; protease; acid kills bacteria
Duodenum	Pancreatic enzymes and bile added
Ileum	Digestion finished; absorption
Colon	Water absorbed
Rectum	Faeces stored

Peristalsis: waves of muscle contraction and relaxation. Circular muscle contracts behind the food and relaxes in front of it.

2.29 Enzymes

Enzyme	Substrate	Product	Made by / acts in
Amylase	Starch	Maltose	Salivary glands, pancreas
Maltase	Maltose	Glucose	Lining of small intestine
Protease	Protein	Amino acids	Stomach, pancreas, small intestine
Lipase	Lipid	Fatty acids + glycerol	Pancreas; acts in small intestine

2.30–2.31 Bile

• Made in the liver, stored in the gall bladder, released into the duodenum.
• Alkaline: neutralises stomach acid, giving the right pH for enzymes in the small intestine.
• Emulsifies lipids: large drops → small droplets → larger surface area for lipase.
• Not an enzyme. It does not break bonds.

2.32 Villus

Feature	Benefit
Many villi and microvilli; long ileum	Large surface area
Wall one cell thick	Short diffusion distance
Capillary network	Removes glucose and amino acids; keeps concentration gradient
Lacteal	Absorbs fatty acids and glycerol

2.33B Energy in food (Paper 2 only)

Quantity	Formula
Energy released (J)	mass of water (g) × 4.2 × temperature rise (°C)
Energy per gram (J/g)	energy released ÷ mass of food (g)

1 cm³ of water has a mass of 1 g. Divide J by 1000 for kJ. The measured value is too low because of heat loss and incomplete burning.

Small worked reminders

Linking a structure to its function. For an “explain” mark, name the feature, then say what it does, then say why that helps. For example: “The villi have a dense capillary network (feature), which carries absorbed glucose away quickly (what it does), so a steep concentration gradient is kept and diffusion stays fast (why it helps).”

Reading a carbon dioxide curve. If raising carbon dioxide from 0.02% to 0.06% raises the rate, but raising it from 0.10% to 0.14% does not, then carbon dioxide was limiting at low concentration but not at high concentration. At high concentration, light intensity or temperature is limiting.

Controlled variables in the pondweed practical. When light is the independent variable, keep carbon dioxide (same amount of sodium hydrogencarbonate), temperature (heat shield) and the type and length of pondweed the same.

Must-know distinctions

• Amylase vs maltase: amylase makes maltose; maltase makes glucose.
• Bile vs lipase: bile emulsifies (physical); lipase digests (chemical).
• Liver vs gall bladder: liver makes bile; gall bladder stores it.
• Magnesium vs nitrate: chlorophyll vs amino acids.
• Digestion vs absorption: breaking down vs taking into the blood.
• Light vs temperature curves: light levels off; temperature has an optimum and then falls.

Quick self-test

1. Write the balanced symbol equation for photosynthesis.
2. What energy change happens in photosynthesis?
3. Which ion does a plant need to make chlorophyll?
4. Why is a plant kept in the dark for 48 hours before a starch experiment?
5. Why is ethanol heated in a water bath and not over a flame?
6. Name the vitamin that helps the body absorb calcium.
7. Why does a pregnant woman need more energy?
8. Which enzyme breaks maltose into glucose?
9. Give two jobs of bile.
10. What does the lacteal absorb?
11. A 0.60 g food sample raises the temperature of 30 cm³ of water by 15 °C. Calculate the energy released per gram, in kJ/g.
12. On a rate against temperature graph, why does the rate fall above the optimum?

Answers

1. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
2. Light energy → chemical energy (in glucose).
3. Magnesium.
4. To use up stored starch, so any starch found was made during the experiment.
5. Ethanol is flammable.
6. Vitamin D.
7. For the growth of the fetus and placenta and to carry the extra mass.
8. Maltase.
9. Neutralises stomach acid; emulsifies lipids.
10. Fatty acids and glycerol.
11. 30 × 4.2 × 15 = 1890 J; 1890 ÷ 0.60 = 3150 J/g = 3.15 kJ/g.
12. The enzymes’ active sites change shape, so the reactions slow down.

Where marks are usually lost

• Writing “sunlight” as a reactant in the word equation; light goes over the arrow, not as a substance.
• Unbalanced symbol equations, such as 6O instead of 6O₂.
• Naming the x-axis factor as limiting on the flat part of a graph.
• Saying high temperature “kills” the enzymes rather than changing the shape of the active site.
• Giving “makes chlorophyll” for nitrate or “makes protein” for magnesium.
• Defining a balanced diet without “in the right proportions”.
• Saying bile is made in the gall bladder, or that bile digests fat.
• Saying amylase produces glucose.
• Describing villi as only “having a large surface area” when the question asks for three adaptations.
• In 2.33B, forgetting to divide by the mass of food, or mixing up J and kJ.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1), Specification, Issue 3, September 2024, published by Pearson Education Limited. Topic 2: Structures and functions in living organisms, sub-topic (e) Nutrition, statements 2.18–2.33B.