Diet and Nutrition — Edexcel IGCSE Biology Year 10: Study Notes

Diet and Nutrition – Edexcel IGCSE Biology (Year 10) Study Notes

2.24 Balanced diet and key nutrients

  • A balanced diet should include appropriate proportions of:
    • Carbohydrate
    • Protein
    • Lipid (fats and oils)
    • Vitamins
    • Minerals
    • Water
    • Dietary fibre
  • The purpose is to provide all essential nutrients in the right amounts for health, growth, and energy.

2.25 Sources and functions of nutrients

  • Carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, mineral ions calcium and iron, water, and dietary fibre are components of the diet.
  • Water and dietary fibre are important non-nutrient components for health (water is not a nutrient per se, but essential).
  • The N in MRS H GREN is nutrition.
    • Nutrition provides:
    • Energy for respiration
    • Material for growth and repair (growth and cell division)
    • Support for immune system to fight disease and maintain health
    • Social and cultural aspects of food and eating

The NRS H GREN mnemonic (nutrition) and its implications

  • N = Nutrition
  • R = Related to growth and repair
  • S = Source of energy
  • H = Health and immune function
  • GREN = Growth, respiration, energy, nutrients
  • Practical implications:
    • Nutrition supplies energy via cellular respiration
    • Nutrition provides materials for growth and tissue repair
    • Adequate nutrition supports immune function
    • Food has social and cultural significance

The Balanced Diet – definition and categorization

  • Define the term “balanced diet.”
  • Scientists classify a balanced diet into 5 groups.
  • Students should shade foods: macronutrients in BLUE and micronutrients in RED (conceptual guidance for creating a summary on A3).
  • Table outline to fill (Headings):
    • Food Component
    • Main Function in the Body
    • Good Food Sources
  • Components to consider (example entries):
    1. Carbohydrates: a) Sugars b) Starches c) Dietary Fibre
    • Main Function: provide energy, support digestion (fibre) and regulate blood sugar
    • Good Sources: bread, rice, pasta, potatoes, fruits, vegetables, cereals
    1. Protein
    • Main Function: growth and repair of tissues, enzymes, antibodies
    • Good Sources: meat, fish, eggs, dairy, beans, lentils, tofu, nuts
    1. Lipids (Fats and Oils)
    • Main Function: concentrated energy source, insulation, cell membranes, fat-soluble vitamin absorption
    • Good Sources: butter, oils, fatty fish, nuts, seeds
    1. Vitamins
    • Main Function: various roles (metabolism, immunity, vision, bone health, etc.)
    • Good Sources: fruits, vegetables, dairy, fortified foods
    1. Minerals
    • Main Function: bone health, oxygen transport, fluid balance, enzyme function
    • Good Sources: dairy (calcium), leafy greens (calcium), meat and fortified cereals (iron)

2.26 Energy requirements and pregnancy

  • Energy requirements vary with:
    • Activity levels
    • Age
    • Pregnancy (increased energy needs)
  • Energetic needs can be investigated and measured via calorimetry and dietary assessment.

2.33B Investigating energy content in a food sample

  • You can measure energy content by calorimetry (burning food) and relating heat transfer to water temperature rise.
  • The method involves calculating energy released per unit mass of food.

2.7 Elements present in macromolecules

  • carbohydrates, proteins, and lipids contain the following elements:
    • Carbohydrates: C, H, O
    • Proteins: C, H, O, N (and sometimes S in some amino acids)
    • Lipids: C, H, O

2.8 Structure of macromolecules

  • Macromolecules are large molecules built from smaller subunits:
    • Carbohydrates: starch and glycogen from simple sugars (monosaccharides)
    • Proteins: amino acids
    • Lipids: fatty acids and glycerol
  • Key concept: monomers are linked to form polymers; digestion breaks the bonds to release monomers for absorption.

2.9 Food tests – presence of glucose, starch, protein, and fat

  • You will investigate foods for:
    • Glucose (reducing sugar test, e.g., Benedict’s test)
    • Starch (Iodine test)
    • Protein (Biuret test)
    • Fat (Emulsion test)
  • Always include a CONTROL TEST: a test tube of water only with no nutrients to compare results.

Practical and revision notes (general guidance)

  • DA textbook pages 48–53 (and the Triple Textbook pages 58–61) provide detailed revision notes and experimental procedures for food tests.
  • For energy tests, refer to page 54 (DA) for more on food tests; page 58 (Triple text) for 2.7 and 2.8 concepts.

Carbohydrates

  • Carbohydrate is a key energy source; it makes up about 1% of body mass in terms of carbohydrate content but is crucial for energy production via respiration.
  • Starch is stored in plants; plants make starch from glucose via photosynthesis.
  • Glycogen is the storage carbohydrate in animals (found in liver and muscle) and is structurally similar to starch but not identical.
  • Carbohydrates are built from monomers called monosaccharides (simple sugars). Simple sugars are usually sweet; starch is not.
  • The chemical elements that make up starch and simple sugars are C, H, and O.
  • Cellulose is found in plant cell walls and is known as dietary fibre (roughage). Fibre is important for digestive health.

Proteins

  • Proteins account for about 18% of body mass and are needed for all cells.
  • Three detailed reasons we need protein:
    • Growth and tissue repair (muscle, organs, enzymes)
    • Production of enzymes and some hormones
    • Immune system function (antibodies) and transport molecules
  • 3 vegan protein sources (examples): lentils, beans, tofu (others include chickpeas, quinoa, nuts, seeds, tempeh).
  • Proteins are large insoluble macromolecules made of amino acid monomers that are soluble.
  • Elements in proteins and amino acids: C, H, O, N (and sometimes S).
  • Essential vs non-essential amino acids:
    • Essential amino acids must be obtained from the diet (cannot be synthesized by the body)
    • Non-essential amino acids can be synthesized by the body
  • Deficient means deficient in a nutrient, leading to inadequate intake or absorption.
  • Consequences of a diet deficient in protein may include stunted growth, impaired tissue repair, decreased immune function, and reduced muscle mass.

Lipids

  • Lipids include fats and oils; animal fat is solid at room temperature; plant oils are usually liquid.
  • Lipids make up around 10% of body mass.
  • Two reasons we need lipids in the diet:
    • Concentrated energy source and insulation
    • Help absorb fat-soluble vitamins (A, D, E, K) and contribute to cell membrane structure
  • Saturated fats vs. unsaturated fats: saturated fats have no double bonds between carbon atoms (typically solid at room temperature); unsaturated fats have one or more double bonds (usually liquid at room temperature).
  • When consumed in excess, cholesterol and saturated fat are thought to be unhealthy (risk factors for cardiovascular disease).
  • Lipids are macromolecules built from smaller monomers: three fatty acids and glycerol (triglycerides).
  • Elements in lipids: C, H, O (and sometimes P in phospholipids, though not specified in the transcript).

Vitamins and Minerals

  • Vitamin / Mineral | Good Food Source | Function in Body | Deficiency Disease
    • Iron: sources include red meat, fortified cereals. Function: oxygen transport (hemoglobin). Deficiency: iron-deficiency anaemia.
    • Calcium: dairy, leafy greens. Function: bone and teeth health, nerve/muscle function. Deficiency: rickets (children), osteopenia/osteoporosis (adults).
    • Vitamin C: citrus fruits, peppers. Function: collagen synthesis, wound healing, immune support. Deficiency: scurvy.
    • Vitamin A: liver, carrots, dairy. Function: vision, immune function, skin health. Deficiency: night blindness.
    • Vitamin D: fortified foods, sunlight exposure. Function: calcium absorption and bone health. Deficiency: rickets in children, osteomalacia in adults.
  • Water plays a major role in cytoplasm and blood plasma.
    • In cytoplasm and plasma, water acts as a solvent, medium for reactions, and transport medium.
    • Water in joints acts as a lubricant and cushion.

Water

  • Water is not a nutrient per se but is essential for life and a major component in cells and blood plasma.
  • Importance in cytoplasm and plasma: solvent, reaction medium, transport medium.
  • Water in joints functions as a lubricating lubricant.

Digestion and macromolecules

  • The three main macromolecules in our diet are:
    • Starch (large insoluble carbohydrate)
    • Cellulose (large insoluble carbohydrate) – fibre
    • Proteins
    • Lipids – fats and oils
  • These larger macromolecules are called macromolecules or macronutrients.
  • Digestive system works to break the bonds between monomers so they can be absorbed as soluble monomers into the bloodstream.
  • The detailed digestion and absorption will be studied in Year 10 (read ahead to DA pages 58–61).

Energy from Food and Energy Balance

  • Energy from food is measured per gram and expressed in different units: Joules per gram (J/g) and Calories per gram (Cal/g) in dietary contexts.
  • The energy store in food is chemical energy.
  • The body transfers the chemical energy stored in food into a chemical energy form used by cells (ATP) via cellular respiration. This is an aerobic process that requires oxygen.
  • The energy released per gram when fully oxidized:
    • Carbohydrate: 17 kJ/g17\ \text{kJ/g}
    • Fat: ≈37−39 kJ/g\approx 37-39\ \text{kJ/g}
  • Daily energy needs depend on factors including age, activity level, and pregnancy status (pregnant women need more energy).
  • Balance energy intake with energy expenditure to maintain body mass and health.

Energy stores and processes in the body

  • The energy store in food is chemical energy.
  • The body converts stored chemical energy into ATP through cellular respiration (aerobic respiration when oxygen is used).
  • The eight characteristics of life include metabolism and respiration (the energy release from food is part of these processes).

Energy from Food – Investigation (Practical Focus)

  • You can measure energy content of food by burning it and heating water.
  • Key facts for calculation:
    • 4.2 J raise 1 g of water by 1°C
    • 1 cm³ of water has mass 1 g
  • Investigation steps outline (summary):
    • Pour 20 cm³ of water into a boiling tube
    • Clamp in stand and measure water temperature
    • Weigh the dry food piece
    • Burn the food and direct heat to the water
    • Record highest temperature rise
    • Repeat with different foods, using fresh water each time
    • Use a control (water only) to compare
  • Calculation for energy content per gram of food:
    • Energy per gram = (T<em>f−T</em>i)×20×4.2m\frac{(T<em>f - T</em>i) \times 20 \times 4.2}{m}
    • Where
    • $T_f$ = final temperature of water
    • $T_i$ = initial temperature of water
    • $m$ = mass of food in grams
  • Conclude and evaluate: consider anomalous results and how to improve the experiment.

Practical steps recap (Methods from Page 14)

  • 1. Pour exactly 20 cm³ of water into a boiling tube.
  • 2. Clamp the tube in a retort stand.
  • 3. Measure and record water temperature.
  • 4. Find mass of dry food.
  • 5. Impale food and hold over Bunsen flame until it burns.
  • 6. Immediately place the burning food under the boiling tube so heat transfers to the water.
  • 7. Determine when the experiment is complete.
  • 8. Stir and record the highest water temperature.
  • 9. Repeat with different foods; use fresh water and same volume of water each time.
    1. Record results in a table and calculate energy content per gram using the formula above.

Extensions and reflective questions

  • Why is it important to have a control test?
  • How do anomalous results arise, and how could you minimize errors in repeated experiments?
  • How does energy balance relate to health and disease (e.g., obesity, malnutrition)?

Connections and practical implications

  • Link nutrition to health outcomes (growth, immunity, disease risk).
  • Understand energy balance and why pregnant individuals require higher energy intake.
  • Recognize how macromolecules are digested and absorbed as monomers for metabolism.
  • Apply calorimetry concepts (heat transfer to water) to estimate energy content in foods.

Quick reference formulas and values

  • Energy per gram (carbohydrate) ≈ 17 kJ/g17\ \text{kJ/g}
  • Energy per gram (fat) ≈ 37−39 kJ/g37-39\ \text{kJ/g}
  • Energy transfer equation in the food-energy experiment:
    • E<em>per gram=(T</em>f−Ti)×20×4.2mE<em>{per\ gram} = \dfrac{(T</em>f - T_i) \times 20 \times 4.2}{m}
    • where $m$ is the mass of food in grams
  • 1 cm³ water ≡ 1 g mass
  • 4.2 J is the energy required to raise 1 g of water by 1°C

Practical study tips

  • Use the 5-group model to categorize foods into macronutrients and micronutrients.
  • Practice predicting results for food tests (glucose, starch, protein, fat) before performing experiments.
  • Create a filled A3 summary with: Food Component, Main Function, and Good Sources for each category (Blue = macronutrients; Red = micronutrients).
  • Review the digestive system basics to understand how large molecules are broken down into absorbable monomers.
  • Relate energy calculations to real-life scenarios (diet planning, pregnancy, activity levels).