top of page

Lesson Notes

Chemical Basis of Life

Grade

10

Term

1

This guide breaks down the essential information you need to master the first topic for your exam.

1. Short Notes: Core Concepts

A. The Main Building Blocks (Bio-molecules) All living things are made of four main types of organic compounds:

  1. Carbohydrates: Main source of quick energy.

  2. Proteins: For building, repair, and controlling reactions.

  3. Lipids (Fats & Oils): For long-term energy storage and insulation.

  4. Nucleic Acids: The "blueprint" of life (genetic information).

B. Key Elements

  • The most common elements in these molecules are Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N).

  • Mnemonic: Remember "CHON".

C. Deep Dive into Bio-molecules

Bio-molecule

Elements

Building Block (Monomer)

Key Functions & Facts

Food Examples

Carbohydrates

C, H, O

Monosaccharides (e.g., Glucose)

- Main energy source. <br> - Monosaccharides: Simple sugars. <br> - Disaccharides: Two sugars (e.g., Sucrose). <br> - Polysaccharides: Complex carbs (e.g., Starch in plants, Glycogen in animals, Cellulose in plant walls).

Rice, Bread, Potatoes, Sugar, Fruits

Proteins

C, H, O, N (sometimes S)

Amino Acids

- Building body structures (muscles, hair). <br> - Enzymes: Biological catalysts that speed up reactions. <br> - Antibodies for immunity.

Meat, Fish, Eggs, Lentils (Dhal), Beans

Lipids

C, H, O

Fatty Acids & Glycerol

- Store energy long-term. <br> - Insulate the body to keep it warm. <br> - Form cell membranes. <br> - Protect organs. <br> - Do not dissolve in water.

Coconut Oil, Butter, Ghee, Nuts, Avocado

Nucleic Acids

C, H, O, N, P

Nucleotides

- DNA: Stores genetic info. <br> - RNA: Helps build proteins. <br> - Controls all cell activities.

Found in all living cells (not a "food group").

D. Essential Inorganic Compounds

  • Water (H₂O): The most important! It's the "Universal Solvent" where chemical reactions happen, it transports substances, and helps control body temperature.

  • Minerals: Inorganic elements needed for health (e.g., Calcium for bones, Iron for blood).

  • Vitamins: Organic compounds needed in small amounts (e.g., Vitamin C for gums, Vitamin D for bones).

2. Tips & Tricks for the Exam

  • Mnemonic for Food Tests: To remember the tests, try "I Bring Beer Pong" -> Iodine, Benedict's, Biuret, Paper (for fats/lipids).

  • Identify the "-ose": Words ending in -ose (glucose, sucrose, lactose) are almost always sugars (carbohydrates).

  • Enzymes are Proteins: This is a key link. If a question mentions a "biological catalyst," the answer is an enzyme, which is a protein.

  • Draw a Concept Map: Connect the four main bio-molecules with their functions and food sources. Visual aids help memory.

3. Important Points & Common Exam Questions

  • Food Tests are Crucial: You must know the food tests, the reagents used, and the colour change for a positive result. This is a guaranteed question area.

Test For

Reagent(s) Used

Positive Result (Colour Change)

Starch

Iodine Solution

Blue-Black

Glucose (Reducing Sugar)

Benedict's Solution + Heat

Brick-Red Precipitate

Protein

Biuret Solution (NaOH + CuSO₄)

Purple / Violet

Lipids (Fats)

Sudan III <br> or Emulsion Test (Ethanol + Water)

Red Globules <br> or Milky-White Emulsion

  • Deficiency Diseases: Be prepared to link a mineral or vitamin to its deficiency disease.

    • Iron deficiency causes Anemia.

    • Iodine deficiency causes Goitre.

    • Vitamin C deficiency causes Scurvy (bleeding gums).

    • Vitamin D deficiency causes Rickets (weak bones in children).

  • Functions of Water: Expect questions on why water is essential for life. Key points: excellent solvent, high specific heat capacity (prevents rapid temperature changes), and helps in transport.

  • Cellulose vs. Starch: Both are polysaccharides made of glucose, but humans can digest starch for energy, while we cannot digest cellulose (it acts as dietary fiber).

වියාචනය (Disclaimer)

Idasara Academy ඉගෙනුම් සම්පත් නිර්මාණය කර ඇත්තේ සිසුන්ට මගපෙන්වීම, පුහුණුව සහ අධ්‍යයන උපායමාර්ග ලබාදී සහයෝගය දැක්වීමටය.

කෙසේ වෙතත්, සියලුම විභාග සහ නිල අවශ්‍යතා සඳහා, සිසුන් අනිවාර්යයෙන්ම ශ්‍රී ලංකා අධ්‍යාපන අමාත්‍යාංශයේ, අධ්‍යාපන ප්‍රකාශන දෙපාර්තමේන්තුව විසින් ප්‍රකාශයට පත් කරන ලද නිල පෙළපොත් සහ සම්පත් පරිශීලනය කළ යුතුය.

ජාතික විභාග සඳහා අන්තර්ගතයේ නිල බලය ලත් මූලාශ්‍රය වනුයේ රජය විසින් නිකුත් කරනු ලබන මෙම ප්‍රකාශනයි.

bottom of page