Leaving Cert Ordinary Level Biology: Nutrition & Biomolecules Revision Notes

1. Chapter Overview

This chapter explains why organisms need food and how food is built from biological molecules. It covers carbohydrates, lipids, proteins, vitamins, minerals and water. It also links nutrients to energy, growth, repair, metabolism and deficiency diseases.

ExamsLogic Big Idea: Food is not only fuel. It also provides raw materials for growth, repair, cell structures, enzymes, antibodies, hormones and healthy body function.

2. Learning Outcomes

I can state the main functions of food.
I can name the six common elements found in food.
I can identify important trace elements.
I can describe carbohydrates, lipids and proteins.
I can distinguish between monosaccharides, disaccharides and polysaccharides.
I can describe triglycerides, phospholipids, amino acids and peptide bonds.
I can explain structural and metabolic roles of biomolecules.
I can describe the sources, functions and deficiency disorders of vitamins C and D.
I can explain the importance of minerals and water.

3. Function of Food

Organisms need food for energy, growth, repair and metabolism.

Function	Explanation	Example
Energy	Food is broken down during respiration to release energy.	Glucose is used in respiration.
Growth	Food provides raw materials to make new cells and tissues.	Proteins help build body tissues.
Repair	Food helps replace or repair damaged cells and tissues.	Amino acids repair muscle tissue.
Metabolism	Food provides substances needed for chemical reactions in cells.	Vitamins and minerals help enzymes work properly.

Examiner Tip: If asked why organisms need food, do not write “for energy” only. Include growth, repair and metabolism when marks allow.

4. Elements in Food

The six common elements in biological molecules can be remembered as CHONPS.

Element group	Elements	Importance
Six common elements	Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur	Build carbohydrates, lipids, proteins and many other cell substances.
Trace elements	Iron, copper, zinc, manganese, fluorine	Needed in small amounts for healthy body function.

Memory Aid: CHONPS = Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur.

5. Carbohydrates

Carbohydrates contain carbon, hydrogen and oxygen. They are important sources of energy and may also have storage or structural roles.

Type	Structure	Examples	Role
Monosaccharide	One sugar unit.	Glucose.	Immediate energy source.
Disaccharide	Two sugar units joined.	Sucrose, lactose, maltose.	Energy source.
Polysaccharide	Many sugar units joined.	Starch, glycogen, cellulose.	Storage or structure.

Examiner Trap: Carbohydrates are not just sugar. Starch, glycogen and cellulose are also carbohydrates.

6. Lipids

Lipids include fats and oils. They are insoluble in water and are important for long-term energy storage, insulation, protection and cell membranes.

Lipid type	Structure	Function
Triglyceride	Glycerol joined to three fatty acids.	Energy storage, insulation and protection.
Phospholipid	Phosphate head and two fatty acid tails.	Main component of cell membranes.

Source of lipids	Examples
Animal sources	Butter, cheese, meat fat, oily fish.
Plant sources	Olive oil, sunflower oil, nuts, seeds, avocado.

Examiner Tip: Triglycerides are mainly used for energy storage. Phospholipids are mainly used in cell membranes.

7. Proteins

Proteins are made from amino acids. Amino acids are joined by peptide bonds to form long chains that fold into specific shapes.

Feature	Meaning
Amino acid	Building block of proteins.
Peptide bond	Bond joining amino acids together.
Protein shape	The folded structure that allows a protein to perform its function.

Protein role	Example
Structural role	Muscle proteins and proteins in cell structures.
Metabolic / active role	Enzymes, antibodies and hormones.

Examiner Trap: Protein shape is important. If the shape changes, the protein may stop working properly.

8. Structural and Metabolic Roles of Biomolecules

Role type	Explanation	Examples
Structural role	Biomolecules form parts of cells and organisms.	Cellulose in plant cell walls, phospholipids in membranes, proteins in tissues.
Metabolic / active role	Biomolecules control or carry out life processes.	Enzymes, antibodies, hormones.

Simple difference: Structural molecules help build the organism. Metabolic molecules help control or carry out biological reactions and processes.

9. Vitamins

Vitamins are needed in small amounts for healthy metabolism. Vitamin C is water-soluble. Vitamin D is fat-soluble.

Vitamin	Type	Sources	Function	Deficiency disorder
Vitamin C	Water-soluble	Citrus fruits, berries, vegetables.	Healthy connective tissue and wound healing.	Scurvy.
Vitamin D	Fat-soluble	Sunlight exposure, oily fish, eggs, fortified foods.	Helps calcium absorption and bone formation.	Rickets.

Student Common Mistake:
❌ Vitamin C deficiency causes rickets.
✅ Vitamin C deficiency causes scurvy. Vitamin D deficiency causes rickets.

10. Minerals and Water

Minerals in Animals

Mineral	Role	Deficiency issue
Calcium	Needed for bones, teeth, muscle function and blood clotting.	Weak bones / poor bone development.
Iron	Needed to make haemoglobin in red blood cells.	Anaemia.

Minerals in Plants

Mineral	Role in plants
Magnesium	Needed to make chlorophyll.
Calcium	Important for cell wall formation and plant growth.

Water

Water is an important biological solvent. Many biological substances dissolve in water, allowing transport and chemical reactions to occur.

Medium for metabolic reactions.
Transports dissolved substances.
Helps regulate temperature.
Supports cells and tissues.

Examiner Tip: Water is often called a biological solvent because many substances dissolve in it and can be transported or used in reactions.

11. Common Student Mistakes

Thinking carbohydrates only mean sweet sugars.
Forgetting starch, glycogen and cellulose are polysaccharides.
Confusing triglycerides and phospholipids.
Forgetting proteins are made from amino acids.
Writing that peptide bonds join sugars instead of amino acids.
Mixing up scurvy and rickets.
Forgetting magnesium is needed for chlorophyll in plants.
Explaining water only as something organisms drink, without mentioning its solvent role.

12. Examiner Traps

Trap 1: CHONPS must be written accurately: carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.

Trap 2: Benedict's test detects reducing sugars, not all carbohydrates. This links to the practical work.

Trap 3: Triglycerides and phospholipids are both lipids but have different roles.

Trap 4: Vitamin C → scurvy. Vitamin D → rickets.

Trap 5: Iron is needed for haemoglobin, while magnesium is needed for chlorophyll.

13. Examiner Secrets

Secret 1: For protein questions, always mention amino acids and peptide bonds.

Secret 2: For vitamin questions, include source, function and deficiency disorder.

Secret 3: For mineral questions, separate animal roles from plant roles.

Secret 4: For water questions, use the word solvent.

14. Section A: Multiple Choice Practice

Which group shows the six common elements in food?
A. CHONPS B. CHONK C. CHOPF D. COPS
Which molecule is made from amino acids?
A. Starch B. Protein C. Lipid D. Vitamin D
Which vitamin deficiency causes scurvy?
A. Vitamin A B. Vitamin C C. Vitamin D D. Vitamin K
Which mineral is needed to make haemoglobin?
A. Calcium B. Iron C. Magnesium D. Fluorine
Which biomolecule forms the main structure of cell membranes?
A. Phospholipid B. Starch C. Glucose D. Vitamin C

15. Section B: Structured Practice Questions

State four functions of food. [4 marks]
Name the six common elements found in food. [6 marks]
Distinguish between monosaccharides, disaccharides and polysaccharides. [6 marks]
Describe the structure and function of a triglyceride. [4 marks]
Explain why the shape of a protein is important. [3 marks]
Give the source, function and deficiency disorder of vitamin C. [4 marks]
State the role of iron in animals and magnesium in plants. [4 marks]
Explain why water is important in living organisms. [4 marks]

16. Mark Scheme Answers

Section A:
1. A   2. B   3. B   4. B   5. A

Section B:

Q1. Energy [1]; growth [1]; repair [1]; metabolism [1].

Q2. Carbon [1]; hydrogen [1]; oxygen [1]; nitrogen [1]; phosphorus [1]; sulfur [1].

Q3. Monosaccharide = one sugar unit [2]; disaccharide = two sugar units [2]; polysaccharide = many sugar units [2].

Q4. Glycerol [1]; joined to three fatty acids [1]; energy storage [1]; insulation/protection [1].

Q5. Shape determines function [1]; active/binding role depends on shape [1]; changed shape may stop protein working [1].

Q6. Citrus fruits/vegetables [1]; connective tissue/wound healing [1]; deficiency causes scurvy [2].

Q7. Iron needed for haemoglobin/red blood cells [2]; magnesium needed for chlorophyll [2].

Q8. Solvent [1]; transport [1]; medium for reactions [1]; temperature regulation/support [1].

17. Quick Revision Card

Food functions: Energy, growth, repair, metabolism.
CHONPS: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.
Carbohydrates: Mono-, di- and polysaccharides.
Triglyceride: Glycerol + three fatty acids.
Phospholipid: Cell membrane component.
Protein: Amino acids joined by peptide bonds.
Vitamin C: Deficiency causes scurvy.
Vitamin D: Deficiency causes rickets.
Iron: Needed for haemoglobin.
Magnesium: Needed for chlorophyll.
Water: Biological solvent.

18. Interactive Simulator: Biomolecule Detective

Identify the Biomolecule or Nutrient

Clue: This molecule is made of amino acids joined by peptide bonds.

Examiner Feedback

Ready

Choose the nutrient or biomolecule group that matches the clue.

Score: 0/0

19. Mastery Checklist

I can state the functions of food.
I can name CHONPS and important trace elements.
I can distinguish mono-, di- and polysaccharides.
I can describe triglycerides and phospholipids.
I can explain proteins as amino acid chains joined by peptide bonds.
I can distinguish structural and metabolic roles of biomolecules.
I can describe vitamin C and vitamin D sources, functions and deficiencies.
I can explain the roles of calcium, iron, magnesium and water.
I can answer OL exam questions on nutrition and biomolecules.

Leaving Cert Ordinary Level Biology

Subtopics Covered

What This Pack Includes

1. Chapter Overview

2. Learning Outcomes

3. Function of Food

4. Elements in Food

5. Carbohydrates

6. Lipids

7. Proteins

8. Structural and Metabolic Roles of Biomolecules

9. Vitamins

10. Minerals and Water

Minerals in Animals

Minerals in Plants

Water

11. Common Student Mistakes

12. Examiner Traps

13. Examiner Secrets

14. Section A: Multiple Choice Practice

15. Section B: Structured Practice Questions

16. Mark Scheme Answers

17. Quick Revision Card

18. Interactive Simulator: Biomolecule Detective

Identify the Biomolecule or Nutrient

Examiner Feedback

19. Mastery Checklist