🌱 Foundation Pathway
Build confidence with scaffolded explanations, visual aids, word banks, and guided activities. Perfect for grades 4-5 or if you need extra support.
⚡ Core Pathway
Master the essential content for grades 5-6. Clear explanations with retrieval practice and exam-style questions.
💡 Extended Pathway
Push for grades 7-8 with deeper explanations, application questions, and extended writing practice.
⭐ Challenge Pathway
Aim for grades 8-9 with complex scenarios, evaluation questions, and synoptic links.
Chemical Elements in Biological Molecules
2.7What you need to learn: The three main food groups (carbohydrates, proteins, and lipids) are made from different chemical elements. Your job is to remember which elements are in each one!
"CHO" for carbs and lipids, "CHON" for proteins
All three contain Carbon, Hydrogen, and Oxygen. Proteins have an extra letter - N for Nitrogen! This is your key fact for the exam.
🍞 Carbohydrates
- Carbon ✓
- Hydrogen ✓
- Oxygen ✓
Examples: bread, pasta, sugar
🥩 Proteins
- Carbon ✓
- Hydrogen ✓
- Oxygen ✓
- Nitrogen ⭐ EXTRA!
Examples: meat, fish, eggs
🧈 Lipids (Fats)
- Carbon ✓
- Hydrogen ✓
- Oxygen ✓
Examples: butter, oil, cheese
❓ Quick Check 1: Which element is found in proteins but NOT in carbohydrates?
❓ Quick Check 2: A molecule contains carbon, hydrogen, oxygen, and nitrogen. What type of molecule is it?
✅ True or False?
📝 Complete the sentences (use the word bank):
1. All biological molecules contain the elements , , and .
2. The element is only found in .
🔗 Match each molecule to its elements:
Foundation Checkpoint: Can you answer these without looking?
Q1: What elements are found in ALL three food groups?
✓ Model Answer:
Carbon (C), Hydrogen (H), and Oxygen (O)
Q2: What extra element do proteins contain?
✓ Model Answer:
Nitrogen (N)
Q3: A scientist finds nitrogen in a food sample. What type of food molecule must be present?
✓ Model Answer:
Protein (because only proteins contain nitrogen)
All biological molecules contain the elements carbon (C), hydrogen (H), and oxygen (O). Proteins additionally contain nitrogen (N), which is essential for forming amino acids.
| Molecule | Elements Present | Key Feature |
|---|---|---|
| Carbohydrates | C, H, O | H:O ratio usually 2:1 |
| Proteins | C, H, O, N | Contains nitrogen (sometimes sulfur) |
| Lipids | C, H, O | Much more C and H than O |
Common question: "Which element is found in proteins but not in carbohydrates?" Answer: nitrogen. Some proteins also contain sulfur, but you only need to know nitrogen for this specification.
⚡ Quick Fire Retrieval
❓ A food sample is analysed and found to contain 53% carbon, 7% hydrogen, 23% oxygen, and 17% nitrogen. What type of molecule is present?
❓ Which statement about biological molecules is correct?
📝 Exam Question (2 marks): State two differences between the elemental composition of carbohydrates and proteins.
Mark Scheme (2 marks)
- Proteins contain nitrogen / carbohydrates do not (1)
- Proteins may contain sulfur / carbohydrates do not (1)
- Carbohydrates have H:O ratio of 2:1 / proteins do not (1)
Core Checkpoint: Test Your Recall
Q: Explain how you could identify that a food sample contains protein just by looking at its elemental analysis.
✓ Model Answer:
If the analysis shows the presence of nitrogen, the sample must contain protein. This is because proteins are the only biological molecules that contain nitrogen (as part of amino acids).
The elemental composition of biological molecules determines their chemical properties and biological functions.
| Molecule | Elements | Why These Elements? |
|---|---|---|
| Carbohydrates | C, H, O | C-H bonds store energy; O allows hydrogen bonding |
| Proteins | C, H, O, N (+ sometimes S) | N is essential in amino group (-NH₂); S forms disulfide bridges |
| Lipids | C, H, O (less O) | High C:H ratio = high energy density; low O = hydrophobic |
❓ Why do lipids release more energy per gram than carbohydrates during respiration?
❓ What is the role of nitrogen in protein molecules?
📝 Exam Question (4 marks): Compare the elemental composition of carbohydrates and lipids and explain how this affects their role as energy storage molecules.
Mark Scheme (4 marks)
- Both contain C, H, O (1)
- Lipids have proportionally less oxygen / higher C:H ratio (1)
- More C-H bonds means more bonds to be oxidised (1)
- Lipids release more energy per gram / ~37 kJ vs ~17 kJ (1)
- Lipids are better for long-term energy storage / more compact (1)
Extended Checkpoint
Q: Some proteins also contain sulfur. What role does sulfur play in protein structure?
✓ Model Answer:
Sulfur atoms can form disulfide bridges (S-S bonds) between different parts of the protein chain. These covalent bonds help stabilise the tertiary (3D) structure of the protein.
At the molecular level, elemental composition reflects evolutionary optimisation for specific biological functions.
❓ A student claims that "lipids are better energy storage molecules than carbohydrates in all situations." Evaluate this claim.
📝 Challenge Question (6 marks): Explain why lipids contain proportionally less oxygen than carbohydrates, and analyse how this affects their role as energy storage molecules. Include reference to the chemical processes involved in energy release.
Mark Scheme (6 marks)
- Lipids have a high proportion of C-H bonds relative to C-O bonds (1)
- This means lipids are more 'reduced' than carbohydrates (1)
- More energy is released when C-H bonds are oxidised (1)
- Lipids release ~37 kJ/g vs ~17 kJ/g for carbohydrates (1)
- Lipids are hydrophobic so don't require water for storage / don't attract water (1)
- This makes lipids more efficient / compact for long-term energy storage (1)
📝 Synoptic Challenge (6 marks): Migratory birds store fat before long flights, while sprinters rely on carbohydrate stores. Explain the biological advantages of each energy storage strategy for these different activities.
Mark Scheme (6 marks)
- Fat stores more energy per gram / more energy dense (1)
- Fat is lighter than equivalent carbohydrate storage / important for flight (1)
- Long flights need sustained energy over many hours (1)
- Carbohydrates can be broken down faster / quicker ATP release (1)
- Sprinting requires rapid burst of energy / short duration (1)
- Glycogen in muscles can be accessed immediately / without transport (1)
Challenge Checkpoint
Q: Why might the elemental composition of organisms be considered evidence for common ancestry?
✓ Model Answer:
All living organisms use the same basic elements (C, H, O, N) to build their biological molecules. The universal use of carbon-based molecules (carbohydrates, proteins, lipids, nucleic acids) across all life forms suggests all organisms evolved from a common ancestor that used these same biochemical building blocks.
Structure: From Small Units to Large Molecules
2.8Think of LEGO: Large biological molecules are built by joining small building blocks together. Just like you can build a big LEGO model from small bricks!
Large molecules = "Polymers" | Small units = "Monomers"
"Poly" means many, "mono" means one. So a polymer is made of many monomers joined together!
| Large Molecule | Building Blocks | Example Foods |
|---|---|---|
| 🍞 Starch | Simple sugars (glucose) | Bread, pasta, potatoes |
| 🥩 Proteins | Amino acids | Meat, fish, eggs, beans |
| 🧈 Lipids (fats) | Fatty acids + Glycerol | Butter, oil, cheese |
❓ Quick Check 1: What are proteins made from?
❓ Quick Check 2: Starch is made by joining many _____ molecules together.
❓ Quick Check 3: Lipids are made from fatty acids and...
✅ True or False?
📝 Complete the sentences (use the word bank):
1. Proteins are made from joined together.
2. Starch is made from many molecules.
3. Lipids are made from and .
🔗 Match the large molecule to its building blocks:
Small building blocks join together to make large molecules
Foundation Checkpoint: Test Yourself!
Q1: What are the building blocks of proteins called?
✓ Model Answer:
Amino acids
Q2: What two things make up a lipid molecule?
✓ Model Answer:
Fatty acids and glycerol
Q3: What is the difference between starch and glycogen?
✓ Model Answer:
Starch is found in plants, glycogen is found in animals. Both are made from glucose.
Large biological molecules are polymers - chains of smaller repeating units called monomers.
| Polymer | Monomers | Found In |
|---|---|---|
| Starch | Glucose | Plants (energy storage) |
| Glycogen | Glucose | Animals (liver, muscles) |
| Proteins | Amino acids | All living cells |
| Lipids (triglycerides) | 3 fatty acids + 1 glycerol | Cell membranes, fat stores |
Condensation Reaction
A chemical reaction that joins monomers together, releasing a molecule of water each time a bond forms.
Hydrolysis Reaction
The reverse of condensation - water is added to break bonds and split polymers into monomers. This happens during digestion.
⚡ Quick Fire Retrieval
❓ During a condensation reaction, what is released when two monomers join?
❓ Which statement about hydrolysis is correct?
📝 Exam Question (3 marks): Describe how starch molecules are formed from glucose.
Mark Scheme (3 marks)
- Many glucose molecules join together (1)
- By condensation reactions (1)
- Water is released/removed for each bond formed (1)
Core Checkpoint
Q: Explain the difference between condensation and hydrolysis reactions.
✓ Model Answer:
Condensation reactions join monomers together to form polymers, releasing water. Hydrolysis reactions break polymers apart into monomers, using water. They are opposite reactions - condensation builds up molecules while hydrolysis breaks them down.
The type of bond formed depends on which monomers are joining together.
| Polymer | Monomers | Bond Type | Structural Features |
|---|---|---|---|
| Starch (amylose) | α-glucose | Glycosidic (1-4) | Unbranched helix |
| Starch (amylopectin) | α-glucose | Glycosidic (1-4, 1-6) | Branched |
| Glycogen | α-glucose | Glycosidic (1-4, 1-6) | Highly branched |
| Proteins | 20 amino acids | Peptide | Folds into 3D shapes |
| Triglycerides | 1 glycerol + 3 fatty acids | Ester | Long hydrocarbon tails |
❓ Why is glycogen more branched than starch?
❓ What type of bond joins amino acids together in proteins?
📝 Exam Question (4 marks): Compare the structure of amylose and glycogen and explain how their structures relate to their functions.
Mark Scheme (4 marks)
- Both made from α-glucose / joined by glycosidic bonds (1)
- Amylose is unbranched helix / glycogen is highly branched (1)
- Branching in glycogen provides more end points for enzyme action (1)
- Allows faster glucose release for animal metabolism/activity (1)
The structural diversity of biological molecules reflects their evolutionary optimisation for specific functions.
📝 Challenge Question (6 marks): Compare the structure and function of starch and glycogen as energy storage molecules. Explain how their structural differences relate to the metabolic needs of plants and animals.
Mark Scheme (6 marks)
- Both made from α-glucose monomers joined by glycosidic bonds (1)
- Starch: amylose (unbranched helix) + amylopectin (slightly branched) (1)
- Glycogen is highly branched with many terminal glucose molecules (1)
- Animals have higher metabolic rates / need rapid glucose release during activity (1)
- More branches = more ends where enzymes can act simultaneously (1)
- Plants don't need rapid glucose release as they don't move / have lower metabolic demands (1)
📝 Evaluation Question (6 marks): Evaluate the statement: "The diversity of protein functions is due to the diversity of amino acid sequences."
Mark Scheme (6 marks)
- Statement is largely correct - sequence determines primary structure (1)
- 20 different amino acids allow huge variety of sequences (1)
- However, function also depends on how protein folds (tertiary structure) (1)
- Same sequence can fold differently in different conditions (1)
- Post-translational modifications also affect function (1)
- Interactions with other molecules/proteins contribute to function (1)
Food Tests Practical
2.9What you need to know: There are 4 food tests you must learn. For each one, remember the reagent (chemical used) and the colour change that shows a positive result!
"Benedict's goes Brick red for sugar"
"Iodine turns Inky black-blue for starch"
"Biuret goes Blue to Purple for Protein"
"Emulsion test = milky white for fat"
| Test For | Reagent Used | Positive Result | Negative Result |
|---|---|---|---|
| 🍬 Reducing sugars (glucose) | Benedict's solution + heat | Brick red/orange | Stays blue |
| 🍞 Starch | Iodine solution | Blue-black | Stays orange-brown |
| 🥩 Protein | Biuret reagent | Purple/lilac | Stays blue |
| 🧈 Lipids (fats) | Ethanol + water | Cloudy white emulsion | Stays clear |
❓ Quick Check 1: What colour does Benedict's solution turn when glucose is present?
❓ Quick Check 2: Which test requires heating?
❓ Quick Check 3: What does iodine solution test for?
❓ Quick Check 4: A Biuret test turns purple. What food molecule is present?
✅ True or False?
🔗 Match each test to the correct positive result:
📝 Complete the sentences (use the word bank):
1. To test for glucose, add solution and heat. A positive result is .
2. To test for starch, add solution. A positive result is .
3. To test for protein, add reagent. No heating is needed.
Foundation Checkpoint: Can you recall all 4 tests?
Q1: A student tests a food sample and it turns blue-black. What molecule is present and what test was used?
✓ Model Answer:
Starch is present. The iodine test was used.
Q2: How would you test if milk contains protein?
✓ Model Answer:
Add Biuret reagent to the milk. If protein is present, it will turn purple/lilac.
Q3: Why must Benedict's test be heated?
✓ Model Answer:
The reaction requires heat energy to work. Without heating, the colour change won't happen even if glucose is present.
Food tests allow us to identify the presence of specific nutrients. Each test uses a specific reagent that changes colour in the presence of the target molecule.
| Nutrient | Reagent | Method | Positive Result |
|---|---|---|---|
| Reducing sugars | Benedict's | Add reagent, heat in water bath | Blue → brick red/orange |
| Starch | Iodine | Add drops of iodine solution | Orange-brown → blue-black |
| Protein | Biuret | Add reagent (no heating) | Blue → purple/lilac |
| Lipids | Ethanol + water | Dissolve in ethanol, add water | Cloudy white emulsion |
For Benedict's test, the colour change is gradual: blue → green → yellow → orange → brick red. More sugar = more red!
⚡ Quick Fire Retrieval
❓ A student tests a solution with Benedict's reagent. After heating, it turns green. What does this indicate?
❓ Why does the emulsion test not require heating?
📝 Exam Question (3 marks): Describe how you would test a food sample for the presence of starch.
Mark Scheme (3 marks)
- Add iodine solution to the food sample (1)
- If starch is present, the colour changes from orange-brown (1)
- To blue-black (1)
Core Checkpoint
Q: A student performs Benedict's test and the solution stays blue. What conclusions can be drawn?
✓ Model Answer:
No reducing sugar (glucose) is present in the sample. The test is negative. However, non-reducing sugars like sucrose might still be present - these would require further testing with acid hydrolysis.
Understanding the chemistry behind food tests helps explain why they work.
❓ Why does iodine turn blue-black with starch but not with glucose?
📝 Exam Question (4 marks): Explain the chemistry behind Benedict's test, including why heating is required.
Mark Scheme (4 marks)
- Reducing sugars have free aldehyde/ketone groups (1)
- These reduce copper(II) ions to copper(I) ions (1)
- Copper(I) oxide precipitate is brick red/orange (1)
- Heating provides activation energy for the reduction reaction (1)
At the highest level, you should be able to design experiments and evaluate their limitations.
📝 Challenge Question (6 marks): A student wants to compare the sugar content of different fruit juices using Benedict's test. Design an experiment that would allow semi-quantitative comparison, and discuss the limitations of using Benedict's test for this purpose.
Mark Scheme (6 marks)
- Use equal volumes of each juice sample (1)
- Add equal volumes of Benedict's solution (1)
- Heat for same time at same temperature (1)
- Compare final colours to a colour chart/standards (1)
- Limitation: only detects reducing sugars, not sucrose (1)
- Limitation: subjective colour comparison / not precise (1)
- Alternative: use colorimeter for quantitative measurement (1)
Enzymes as Biological Catalysts
2.10What is an enzyme? Enzymes are special proteins that speed up chemical reactions in living things. Without enzymes, reactions would be too slow for life!
The enzyme is the LOCK, the substrate is the KEY
Just like only the right key fits a lock, only the right substrate fits into an enzyme's active site. This is why enzymes are SPECIFIC - each enzyme only works on one type of molecule!
Active Site
The special area on an enzyme where the substrate fits. It has a unique shape that only matches one substrate.
Substrate
The molecule that the enzyme works on (the thing being broken down or joined together).
• Enzymes are biological catalysts
• Enzymes speed up reactions without being used up
• Enzymes are proteins
• Enzymes are specific (one enzyme = one reaction)
❓ Quick Check 1: What type of molecule are enzymes?
❓ Quick Check 2: What is the name of the area where the substrate fits into an enzyme?
❓ Quick Check 3: Why are enzymes described as "specific"?
✅ True or False?
📝 Complete the sentences (use the word bank):
1. Enzymes are biological s that speed up reactions.
2. All enzymes are made of .
3. The molecule that an enzyme works on is called the .
4. The substrate fits into the enzyme's .
🔗 Match the terms to their meanings:
Foundation Checkpoint: Can you answer these?
Q1: What is a catalyst?
✓ Model Answer:
A catalyst is a substance that speeds up a chemical reaction without being used up itself.
Q2: Why do enzymes only work on one type of substrate?
✓ Model Answer:
The active site has a specific shape that only matches one substrate shape - like a lock and key.
Enzymes are biological catalysts - proteins that speed up metabolic reactions without being used up. Each enzyme has a specific 3D shape with an active site that only fits one substrate.
• The enzyme's active site has a complementary shape to the substrate
• Substrate binds to active site → enzyme-substrate complex forms
• Reaction occurs → products released → enzyme unchanged
Use the word "complementary" not "same shape" when describing how substrate fits active site. The shapes fit together like jigsaw pieces.
⚡ Quick Fire Retrieval
❓ What forms when a substrate binds to an enzyme?
❓ Why can an enzyme catalyse the same reaction many times?
📝 Exam Question (3 marks): Describe the lock and key model of enzyme action.
Mark Scheme (3 marks)
- Substrate has complementary shape to active site (1)
- Substrate binds to active site / forms enzyme-substrate complex (1)
- Products released / enzyme unchanged / can be reused (1)
Enzymes lower the activation energy required for reactions, allowing them to proceed at body temperature. The induced fit model provides a more accurate description than lock and key.
• Active site shape changes slightly when substrate binds
• Enzyme "moulds" around the substrate
• This puts strain on bonds in substrate, helping the reaction
• Explains why enzymes can have some flexibility
Activation Energy
The minimum energy required to start a chemical reaction. Enzymes lower this barrier, allowing reactions to occur faster at lower temperatures.
❓ How do enzymes speed up reactions?
📝 Exam Question (4 marks): Compare the lock and key model with the induced fit model of enzyme action.
Mark Scheme (4 marks)
- Lock and key: active site is rigid/fixed shape (1)
- Induced fit: active site changes shape when substrate binds (1)
- Induced fit is more accurate / explains flexibility (1)
- Induced fit explains how binding can strain substrate bonds (1)
At the highest level, consider how enzyme structure relates to function and how catalytic mechanisms work at the molecular level.
📝 Challenge Question (6 marks): Explain how the tertiary structure of an enzyme is essential for its function, and discuss what happens when this structure is disrupted.
Mark Scheme (6 marks)
- Tertiary structure = 3D folding of polypeptide chain (1)
- Creates the specific shape of the active site (1)
- Active site shape is complementary to substrate (1)
- Disruption (by heat/pH) = denaturation (1)
- Active site shape changes permanently (1)
- Substrate can no longer bind / enzyme loses function (1)
Effects of Temperature and pH on Enzymes
2.11-2.13Key idea: Enzymes work best at their "favourite" temperature and pH. Too hot or too cold, too acidic or too alkaline - and they stop working!
Not too hot, not too cold, not too acidic, not too alkaline - JUST RIGHT!
The "just right" conditions are called the OPTIMUM temperature and OPTIMUM pH.
Optimum Temperature
The temperature at which an enzyme works fastest. For human enzymes, this is usually around 37°C (body temperature).
Denaturation
When an enzyme's shape is permanently changed (by too much heat or extreme pH), so the substrate no longer fits. The enzyme stops working forever!
🥶 Too cold: Enzyme works slowly (molecules move slowly)
✅ Optimum (37°C): Enzyme works fastest
🔥 Too hot: Enzyme denatures - shape changes permanently, stops working
❓ Quick Check 1: What is the optimum temperature for most human enzymes?
❓ Quick Check 2: What happens to an enzyme when it denatures?
❓ Quick Check 3: Why do enzymes work slowly at low temperatures?
❓ Quick Check 4: Pepsin (stomach enzyme) works best at pH 2. What type of conditions does it prefer?
✅ True or False?
📝 Complete the sentences:
1. The temperature at which an enzyme works best is called the temperature.
2. Most human enzymes work best at .
3. At low temperatures, enzymes work .
4. When an enzyme , its changes shape.
Foundation Checkpoint: Test Yourself!
Q1: What does "optimum" mean when talking about enzymes?
✓ Model Answer:
Optimum means the best or ideal conditions where the enzyme works fastest.
Q2: Why can't a denatured enzyme work anymore?
✓ Model Answer:
The active site has changed shape permanently, so the substrate can no longer fit into it.
Q3: Why does enzyme activity increase as temperature rises (before the optimum)?
✓ Model Answer:
Higher temperature gives molecules more kinetic energy, so they move faster and collide more often. More collisions between enzyme and substrate means more reactions.
Enzyme activity is affected by temperature and pH. Each enzyme has an optimum where it works fastest.
| Condition | Effect on Enzyme Activity | Explanation |
|---|---|---|
| Low temperature | Slow activity | Less kinetic energy, fewer collisions |
| Optimum temperature | Maximum activity | Maximum collision rate, enzyme intact |
| High temperature | Activity drops to zero | Enzyme denatures, active site changes shape |
| Extreme pH | Activity drops | Enzyme denatures, active site changes shape |
Different enzymes have different optimum pH values:
• Pepsin (stomach): pH 2 (acidic)
• Salivary amylase: pH 7 (neutral)
• Pancreatic enzymes: pH 8-9 (alkaline)
⚡ Quick Fire Retrieval
❓ A graph of enzyme activity against temperature shows a peak at 40°C. What can you conclude?
📝 Exam Question (3 marks): Explain why enzyme activity decreases at temperatures above the optimum.
Mark Scheme (3 marks)
- High temperature causes enzyme to denature (1)
- The active site changes shape (1)
- Substrate can no longer fit / no enzyme-substrate complex forms (1)
Core Checkpoint
Q: Describe how you would investigate the effect of temperature on enzyme activity.
✓ Model Answer:
Set up water baths at different temperatures (e.g., 20, 30, 40, 50, 60°C). Add enzyme and substrate to test tubes and place in each water bath. Time how long it takes for the reaction to complete (e.g., starch to disappear using iodine test). Repeat at each temperature. Plot a graph of reaction rate against temperature.
The relationship between temperature and enzyme activity can be explained using collision theory and molecular interactions.
• High temperatures break hydrogen bonds and ionic bonds in the enzyme
• These bonds maintain the tertiary structure (3D shape)
• When broken, the active site loses its specific shape
• This is usually irreversible
❓ Which bonds are broken during denaturation?
📝 Exam Question (4 marks): Explain the effect of pH on enzyme activity at the molecular level.
Mark Scheme (4 marks)
- pH affects the ionisation of amino acid R groups (1)
- This affects ionic bonds / hydrogen bonds holding the tertiary structure (1)
- At extreme pH, these bonds break (1)
- Active site shape changes / enzyme denatures (1)
📝 Challenge Question (6 marks): A student investigated the effect of temperature on amylase activity. The results showed maximum activity at 37°C, but some activity remained at 60°C. Explain these results and evaluate the experimental design.
Mark Scheme (6 marks)
- 37°C is the optimum temperature for human amylase (1)
- Activity remaining at 60°C suggests not all enzyme denatured (1)
- Denaturation is a gradual process / some molecules denature before others (1)
- Possible error: enzyme may not have equilibrated to water bath temperature (1)
- Improvement: allow time for temperature equilibration before mixing (1)
- Should control pH / substrate concentration / enzyme concentration (1)
📝 Synoptic Question (6 marks): Explain why bacteria living in hot springs have enzymes with different temperature optima compared to human enzymes, and discuss the implications for biotechnology.
Mark Scheme (6 marks)
- Hot spring bacteria have evolved / adapted to high temperatures (1)
- Their enzymes have more stable tertiary structures (1)
- Stronger bonds (e.g., more disulfide bridges) resist denaturation (1)
- These enzymes are useful in industrial processes requiring high temperatures (1)
- Example: Taq polymerase used in PCR (1)
- High temperatures can kill contaminating bacteria / speed up reactions (1)
Components of a Balanced Diet
2.24-2.25What is a balanced diet? A diet that contains all the nutrients your body needs in the right amounts. There are 7 things you need to remember!
C-arbs, A-mino acids (protein), M-inerals, P-roteins... V-itamins, W-ater, F-ats (lipids)
Or try: "Come And Meet Paul's Very Weird Family" = Carbs, And, Minerals, Proteins, Vitamins, Water, Fats
| Nutrient | Function | Good Sources |
|---|---|---|
| 🍞 Carbohydrates | Energy | Bread, pasta, rice, potatoes |
| 🥩 Proteins | Growth and repair | Meat, fish, eggs, beans |
| 🧈 Lipids (fats) | Energy, insulation, cell membranes | Butter, oil, cheese, nuts |
| 💊 Vitamins | Keep body working properly | Fruits, vegetables |
| �ite🪨 Minerals | Various (bones, blood, etc.) | Meat, vegetables, dairy |
| 💧 Water | All chemical reactions | Drinks, foods |
| 🌾 Fibre | Helps food move through gut | Wholegrain, fruit, vegetables |
• Vitamin C: Healthy skin, prevents scurvy
• Vitamin D: Strong bones, works with calcium
• Calcium: Strong bones and teeth
• Iron: Makes haemoglobin (red blood cells)
❓ Quick Check 1: What is the main function of carbohydrates?
❓ Quick Check 2: What is the main function of protein?
❓ Quick Check 3: Which mineral is needed to make haemoglobin?
❓ Quick Check 4: What disease is caused by lack of vitamin C?
✅ True or False?
🔗 Match each deficiency to its disease:
📝 Complete the sentences:
1. Carbohydrates and lipids provide .
2. Proteins are needed for and repair.
3. and are both needed for strong bones.
4. is needed to make haemoglobin in red blood cells.
Foundation Checkpoint
Q1: Name the 7 components of a balanced diet.
✓ Model Answer:
Carbohydrates, proteins, lipids (fats), vitamins, minerals, water, fibre
Q2: A person has soft, weak bones. What might they be lacking in their diet?
✓ Model Answer:
Calcium and/or Vitamin D (both are needed for strong bones)
A balanced diet provides all nutrients in the correct proportions for good health.
| Nutrient | Source | Function | Deficiency Disease |
|---|---|---|---|
| Vitamin A | Liver, carrots, eggs | Good vision, healthy skin | Night blindness |
| Vitamin C | Citrus fruits, peppers | Healthy connective tissue | Scurvy |
| Vitamin D | Sunlight, oily fish, eggs | Calcium absorption | Rickets |
| Calcium | Dairy, green vegetables | Strong bones and teeth | Rickets, osteoporosis |
| Iron | Red meat, spinach, beans | Haemoglobin production | Anaemia |
⚡ Quick Fire Retrieval
📝 Exam Question (3 marks): Explain why a person who does not eat any dairy products might develop weak bones.
Mark Scheme (3 marks)
- Dairy is a source of calcium (1)
- Calcium is needed for strong bones (1)
- Lack of calcium leads to weak bones / rickets / osteoporosis (1)
• Age (teenagers need more for growth)
• Gender (males typically need more)
• Activity level (athletes need more)
• Pregnancy (extra energy for baby's growth)
• Climate (cold environments need more for warmth)
📝 Exam Question (4 marks): Explain why a pregnant woman needs more iron in her diet than a non-pregnant woman of the same age.
Mark Scheme (4 marks)
- Iron is needed to make haemoglobin (1)
- Pregnant woman has increased blood volume (1)
- Needs to supply oxygen to developing fetus (1)
- Fetus needs iron for its own blood cells (1)
📝 Challenge Question (6 marks): A vegetarian athlete is planning their diet. Discuss the nutritional challenges they might face and how they could address them while maintaining peak performance.
Mark Scheme (6 marks)
- May lack complete proteins / need to combine plant proteins (1)
- Iron absorption lower from plant sources / may need supplements (1)
- Athletes need more protein for muscle repair (1)
- Can get protein from eggs, dairy, beans, lentils, tofu (1)
- Need high carbohydrate intake for energy during training (1)
- May need B12 supplements if vegan (1)
Structure of the Digestive System
2.27-2.28What is the digestive system? It's a long tube (about 9 metres!) that runs from your mouth to your anus. Food travels through it and gets broken down so nutrients can be absorbed into your blood.
Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → (Colon) → Anus
| Organ | What Happens Here |
|---|---|
| 👄 Mouth | Food is chewed (mechanical digestion) and mixed with saliva containing amylase |
| 🔽 Oesophagus | Food tube - pushes food to stomach by peristalsis |
| 🫃 Stomach | Churns food, adds acid and pepsin (protein digestion begins) |
| ➰ Small intestine | Most digestion and absorption happens here |
| 🔄 Large intestine | Absorbs water from undigested food |
| 📦 Rectum | Stores faeces |
| 🚽 Anus | Faeces leave the body (egestion) |
Peristalsis
The squeezing action of muscles in the gut wall that pushes food along. Muscles contract behind the food and relax in front of it - like squeezing toothpaste from a tube!
• Digestion = breaking down large food molecules into small ones
• Absorption = small molecules passing through gut wall into blood
• Egestion = removing undigested waste (faeces) from the body
❓ Quick Check 1: Where does most absorption of nutrients happen?
❓ Quick Check 2: What is the name of the muscular action that moves food through the gut?
❓ Quick Check 3: What is absorbed in the large intestine?
✅ True or False?
📝 Complete the sentences:
1. Food travels from the mouth to the stomach through the .
2. The produces acid and churns food.
3. Most absorption happens in the .
4. The large intestine absorbs .
Foundation Checkpoint
Q1: Put these in order from mouth to anus: large intestine, stomach, oesophagus, small intestine
✓ Model Answer:
Oesophagus → Stomach → Small intestine → Large intestine
Q2: Describe how peristalsis moves food through the gut.
✓ Model Answer:
Muscles in the gut wall contract behind the food and relax in front of it. This pushes the food forwards in a wave-like motion.
The alimentary canal is a continuous tube from mouth to anus. Each region is adapted for its specific function.
| Region | Function | Key Features |
|---|---|---|
| Mouth | Mechanical + chemical digestion | Teeth, tongue, salivary amylase |
| Oesophagus | Transport | Muscular wall for peristalsis |
| Stomach | Protein digestion begins | HCl, pepsin, churning |
| Small intestine | Complete digestion + absorption | Villi, enzymes, bile |
| Large intestine | Water absorption | No villi |
| Rectum/Anus | Storage and egestion | Sphincter muscles |
Peristalsis involves TWO types of muscle:
• Circular muscles contract behind the food (squeezes it)
• Longitudinal muscles contract ahead (shortens the tube)
⚡ Quick Fire Retrieval
📝 Exam Question (3 marks): Describe how peristalsis moves food through the alimentary canal.
Mark Scheme (3 marks)
- Circular muscles contract behind the food (1)
- Longitudinal muscles contract in front of the food (1)
- This creates a wave of contraction that pushes food along (1)
• Thick muscular wall for churning
• Gastric glands produce HCl (kills bacteria, provides optimum pH for pepsin)
• Gastric glands produce pepsin (protease)
• Mucus lining protects stomach wall from acid and enzymes
📝 Exam Question (4 marks): Explain how the stomach is adapted for its functions in digestion.
Mark Scheme (4 marks)
- Muscular wall for churning / mechanical digestion (1)
- Produces hydrochloric acid / kills bacteria / optimum pH for pepsin (1)
- Produces pepsin / protease for protein digestion (1)
- Mucus protects stomach wall from acid / self-digestion (1)
📝 Challenge Question (6 marks): Explain how the stomach is protected from digesting itself, and discuss what might happen if these protective mechanisms fail.
Mark Scheme (6 marks)
- Mucus forms a protective barrier on stomach lining (1)
- Mucus is alkaline / neutralises acid at the surface (1)
- Epithelial cells are constantly replaced (1)
- Pepsin is secreted as inactive pepsinogen (1)
- If protection fails: acid damages stomach wall / ulcer forms (1)
- Ulcers can cause bleeding / pain / perforation (1)
Digestive Enzymes
2.29Why do we need to digest food? Large food molecules are too big to pass through the gut wall into the blood. Enzymes break them into smaller molecules that can be absorbed!
Amylase breaks down starch (amyl- relates to starch)
Protease breaks down protein
Lipase breaks down lipids (fats)
| Enzyme | Breaks Down | Products |
|---|---|---|
| Amylase | Starch | Maltose → Glucose |
| Protease (pepsin, trypsin) | Protein | Amino acids |
| Lipase | Lipids (fats) | Fatty acids + glycerol |
• Amylase: Salivary glands (mouth) and pancreas
• Protease: Stomach (pepsin) and pancreas (trypsin)
• Lipase: Pancreas
❓ Quick Check 1: What enzyme breaks down starch?
❓ Quick Check 2: What are the products of lipid digestion?
❓ Quick Check 3: What are proteins broken down into?
✅ True or False?
🔗 Match each enzyme to what it digests:
Foundation Checkpoint
Q1: Name the three main types of digestive enzyme and what each one digests.
✓ Model Answer:
Amylase digests starch. Protease digests protein. Lipase digests lipids (fats).
Q2: Where is amylase produced in the body?
✓ Model Answer:
Salivary glands (in the mouth) and the pancreas.
| Enzyme | Substrate | Products | Where Produced |
|---|---|---|---|
| Amylase | Starch | Maltose | Salivary glands, pancreas |
| Maltase | Maltose | Glucose | Small intestine |
| Pepsin | Protein | Polypeptides | Stomach |
| Trypsin | Protein | Amino acids | Pancreas |
| Lipase | Lipids | Fatty acids + glycerol | Pancreas |
1. Amylase breaks starch → maltose (disaccharide)
2. Maltase breaks maltose → glucose (monosaccharide)
⚡ Quick Fire Retrieval
• Pepsin: pH 2 (acidic stomach)
• Salivary amylase: pH 7 (neutral mouth)
• Pancreatic enzymes: pH 8-9 (alkaline duodenum)
📝 Exam Question (4 marks): Explain why salivary amylase stops working when food reaches the stomach.
Mark Scheme (4 marks)
- Salivary amylase has optimum pH 7 / neutral (1)
- Stomach has pH 2 / acidic (1)
- Extreme pH causes denaturation (1)
- Active site changes shape / substrate cannot fit (1)
📝 Challenge Question (6 marks): A patient has had their gall bladder removed. Explain how this might affect their ability to digest and absorb lipids, and suggest dietary advice for this patient.
Mark Scheme (6 marks)
- Gall bladder stores and concentrates bile (1)
- Without gall bladder, bile drips continuously / not released in response to fat (1)
- Less bile available for large fatty meals (1)
- Fat not fully emulsified / smaller surface area for lipase (1)
- Advice: eat smaller, more frequent meals (1)
- Reduce fat intake / avoid very fatty foods (1)
The Role of Bile
2.30-2.31Important: Bile is NOT an enzyme! It doesn't digest food, but it helps digestion happen. Think of bile like washing-up liquid for fats!
📍 Made in the LIVER
📦 Stored in the GALL BLADDER
🎯 Released into the SMALL INTESTINE (duodenum)
Function 1: Neutralises acid
Bile is alkaline. It neutralises stomach acid so enzymes in the small intestine can work (they need pH 8-9).
Function 2: Emulsifies fats
Breaks large fat droplets into tiny droplets. This gives a bigger surface area for lipase to work on.
❓ Where is bile produced?
❓ What does "emulsify" mean?
📝 Complete the sentences:
1. Bile is made in the and stored in the .
2. Bile stomach acid.
3. Bile fats to increase surface area for .
Never say bile "digests" fat - it doesn't! Bile emulsifies fat to increase surface area for lipase (the enzyme that actually digests fat).
📝 Exam Question (3 marks): Explain how bile helps in the digestion of lipids.
Mark Scheme (3 marks)
- Bile emulsifies lipids / breaks into small droplets (1)
- Increases surface area (1)
- For lipase to work on / faster digestion (1)
• Bile salts are amphipathic (have hydrophobic and hydrophilic regions)
• Hydrophobic ends embed in fat droplets
• Hydrophilic ends face outward into aqueous solution
• This prevents droplets from rejoining (coalescing)
📝 Challenge Question (6 marks): Explain why bile is described as amphipathic and how this property is essential for its function in lipid digestion.
Mark Scheme (6 marks)
- Amphipathic means having both hydrophobic and hydrophilic regions (1)
- Hydrophobic region interacts with lipid droplets (1)
- Hydrophilic region interacts with aqueous environment (1)
- Bile salts coat lipid droplets (1)
- Prevents droplets from coalescing / keeps them small (1)
- Maximises surface area for lipase action (1)
Adaptations for Absorption
2.32Absorption is when digested food passes from your gut into your blood. The small intestine has special structures called VILLI that are brilliant at this job!
Villus (plural: villi)
Tiny finger-like projections that line the small intestine. They increase the surface area for absorbing nutrients.
1️⃣ Large surface area - finger-like shape + microvilli
2️⃣ Thin walls - only one cell thick (short diffusion distance)
3️⃣ Good blood supply - maintains concentration gradient
4️⃣ Lacteal - absorbs fatty acids and glycerol
❓ What do villi increase?
❓ Why do villi have a good blood supply?
✅ True or False?
Foundation Checkpoint
Q: Name 4 ways villi are adapted for absorption.
✓ Model Answer:
1. Large surface area (finger-like shape + microvilli)
2. Thin walls (one cell thick)
3. Good blood supply (maintains concentration gradient)
4. Lacteal (absorbs fats)
| Adaptation | How It Helps Absorption |
|---|---|
| Villi (finger-like) | Increase surface area |
| Microvilli on cells | Further increase surface area |
| Single cell epithelium | Short diffusion distance |
| Dense capillary network | Maintains concentration gradient |
| Lacteal | Absorbs lipids into lymph |
📝 Exam Question (4 marks): Explain how the structure of a villus is adapted for efficient absorption of nutrients.
Mark Scheme (4 marks)
- Finger-like shape / microvilli increase surface area (1)
- Thin wall / one cell thick for short diffusion distance (1)
- Good blood supply maintains concentration gradient (1)
- Blood carries absorbed nutrients away (1)
• Glucose and amino acids can be absorbed by active transport
• Allows absorption against concentration gradient
• Requires ATP from mitochondria (villi have many mitochondria)
• Ensures complete absorption of nutrients
📝 Challenge Question (6 marks): A patient with coeliac disease has damaged villi. Explain how this would affect their nutrition and why they might become deficient in multiple nutrients.
Mark Scheme (6 marks)
- Damaged villi have reduced surface area (1)
- Less efficient absorption of all nutrients (1)
- Glucose/amino acid absorption reduced (1)
- Fatty acid absorption via lacteal reduced (1)
- Vitamin and mineral absorption also affected (1)
- Could lead to anaemia/osteoporosis/weight loss/fatigue (1)
📋 Specification Checklist
Tick off each point as you feel confident: