Edexcel iGCSE Biology-2.7 identify chemical elements- Study Notes- New Syllabus
Edexcel iGCSE Biology-2.7 identify chemical elements- Study Notes- New syllabus
Edexcel iGCSE Biology-2.7 identify chemical elements- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
2.7 identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)
Chemical Elements in Carbohydrates, Proteins & Lipids
📝 Introduction
- All living organisms are made from chemical substances called biological molecules.
- These molecules are built from a small number of chemical elements.
- The three main biological molecules are:
- Carbohydrates
- Proteins
- Lipids (fats and oils)
- Each molecule contains a specific combination of elements.
- The elements present help determine the structure and function of the molecule.
Common Chemical Elements in Living Organisms
| Symbol | Element |
|---|---|
| C | Carbon |
| H | Hydrogen |
| O | Oxygen |
| N | Nitrogen |
| S | Sulfur |
🍞 Carbohydrates
What are Carbohydrates?
- Carbohydrates are organic molecules mainly used as an energy source.
- They are one of the most important food groups.
- Plants produce carbohydrates during photosynthesis.
- Animals obtain carbohydrates by eating plants or other animals.
Elements Present in Carbohydrates
Carbohydrates contain:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
General Ratio
In most carbohydrates, the elements occur in the ratio:
- 1 Carbon : 2 Hydrogen : 1 Oxygen
Example: Glucose
Formula: C₆H₁₂O₆
This contains:
- 6 Carbon atoms
- 12 Hydrogen atoms
- 6 Oxygen atoms
Ratio: 6 : 12 : 6
Simplified: 1 : 2 : 1
Functions of Carbohydrates
⚡ Source of Energy
- Main fuel for respiration.
- Broken down to release energy for cell activities.
🌱 Energy Storage in Plants
- Excess glucose is stored as starch.
🏃 Energy Storage in Animals
- Excess glucose is stored as glycogen.
🧱 Structural Role
- Cellulose forms plant cell walls.
Examples of Carbohydrates
| Carbohydrate | Function |
|---|---|
| Glucose | Immediate energy source |
| Starch | Energy storage in plants |
| Glycogen | Energy storage in animals |
| Cellulose | Plant cell walls |
🍗 Proteins
What are Proteins?
- Proteins are large, complex molecules.
- They are made from smaller units called amino acids.
- Different amino acids join together to form different proteins.
- Proteins are essential for growth and maintenance of the body.
Elements Present in Proteins
Proteins contain:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
Many proteins also contain:
- Sulfur (S)
Why is Nitrogen Important?
- Nitrogen is found in amino acids.
- Since proteins are made of amino acids, proteins always contain nitrogen.
- This is the main feature that distinguishes proteins from carbohydrates and lipids.
Key Point
Proteins = CHON
Carbohydrates and lipids do not contain nitrogen.
Sulfur in Proteins
- Some amino acids contain sulfur.
Examples:
- Cysteine
- Methionine
Therefore, some proteins contain sulfur as well.
Functions of Proteins
- Growth – Needed to build new cells and tissues.
- Repair – Repair damaged tissues.
- Enzymes – Most enzymes are proteins. Enzymes speed up chemical reactions.
- Hormones – Some hormones are proteins.
- Antibodies – Protect the body against pathogens.
- Muscle Formation – Muscle fibres are largely made of proteins.
Examples of Proteins
| Protein | Function |
|---|---|
| Enzymes | Speed up reactions |
| Insulin | Controls blood glucose |
| Antibodies | Defence against disease |
| Keratin | Hair and nails |
| Haemoglobin | Oxygen transport |
🥑 Lipids (Fats and Oils)
What are Lipids?
- Lipids include fats and oils.
- They are important energy-storage molecules.
- Lipids are found in plant and animal cells.
Elements Present in Lipids
Lipids contain:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
These are the same elements found in carbohydrates.
Important Difference from Carbohydrates
Although both contain C, H and O:
| Carbohydrates | Lipids |
|---|---|
| Contain relatively more oxygen. | Contain much less oxygen. |
| Often show a 1 : 2 : 1 ratio. | Contain a higher proportion of carbon and hydrogen. |
Because of this: Lipids contain more stored chemical energy.
Functions of Lipids
- Long-Term Energy Storage – Main energy store in animals.
- Insulation – Fat under the skin reduces heat loss.
- Protection – Surrounds and cushions organs.
- Cell Membranes – Phospholipids form cell membranes.
- Waterproofing – Some lipids help prevent water loss.
Examples of Lipids
| Lipid | Function |
|---|---|
| Fat | Energy storage |
| Oil | Energy storage |
| Wax | Waterproofing |
| Phospholipid | Cell membranes |
Difference between carbohydrates and lipids:
| Carbohydrates | Lipids |
|---|---|
| More oxygen | Less oxygen |
| 1:2:1 ratio | No fixed ratio |
| Quick energy source | Long-term energy store |
📊 Summary Table
| Molecule | Elements Present | Main Functions |
|---|---|---|
| Carbohydrates | C, H, O | Energy source, storage, plant structure |
| Proteins | C, H, O, N (+S) | Growth, repair, enzymes, hormones |
| Lipids | C, H, O (low oxygen) | Energy storage, insulation, membranes |
🧠 Key Points
- Carbohydrates contain Carbon, Hydrogen and Oxygen (CHO).
- Proteins contain Carbon, Hydrogen, Oxygen and Nitrogen (CHON).
- Some proteins also contain Sulfur.
- Lipids contain Carbon, Hydrogen and Oxygen (CHO).
- Lipids contain less oxygen than carbohydrates.
- Nitrogen is the main element that makes proteins different from carbohydrates and lipids.
- Lipids store more energy than carbohydrates because they contain a higher proportion of carbon and hydrogen.
⚡ Quick Recap
✔ All biological molecules contain carbon.
✔ Carbohydrates = CHO.
✔ Proteins = CHON (+S).
✔ Lipids = CHO (low oxygen).
✔ Carbohydrates are mainly used for energy.
✔ Proteins are needed for growth, repair and enzymes.
✔ Lipids are used for energy storage, insulation and cell membranes.
✔ Nitrogen is found in proteins but not in carbohydrates or lipids.
✔ Lipids contain less oxygen than carbohydrates.