Chemical and Physical Basis of Life — A/L Biology

What must I remember about Chemical and Physical Basis of Life?

• Water's unique life-supporting properties derive from polarity and extensive hydrogen bonding: high specific heat capacity, high heat of vaporization, cohesion/adhesion, and lower density as ice.
• Carbohydrates are polyhydroxy aldehydes or ketones: Monosaccharides (glucose, fructose, ribose); Disaccharides with glycosidic bonds (maltose: α-1,4; sucrose: α-1,2; lactose: β-1,4); Polysaccharides (starch, glycogen, cellulose).
• Lipids are hydrophobic macromolecules: Triglycerides (glycerol + 3 fatty acids linked by ester bonds), Phospholipids (amphipathic membrane components), and Steroids (four fused carbon rings).
• Proteins are polymers of amino acids joined by peptide bonds: Four levels of structure — Primary (amino acid sequence), Secondary (α-helix, β-pleated sheet via H-bonds), Tertiary (3D folding via disulfide, ionic, hydrophobic interactions), Quaternary (multiple polypeptide subunits).
• Nucleic acids (DNA and RNA) are polymers of nucleotides composed of a pentose sugar, phosphate group, and nitrogenous base (purines: A, G; pyrimidines: C, T, U) joined by 3',5'-phosphodiester bonds.

Test yourself (1 minute)

1. Biochemical tests identification

   Starch = Iodine test (blue-black); Reducing sugars = Benedict's test (brick-red precipitate); Proteins = Biuret test (purple/violet); Lipids = Sudan III / Ethanol emulsion test.

2. DNA vs RNA structural distinctions

   DNA has deoxyribose, thymine (A-T, G-C), double-stranded double helix; RNA has ribose, uracil (A-U, G-C), single-stranded.

3. Enzyme action principles

   Protein catalysts that lower activation energy without altering free energy change (ΔG); sensitive to pH, temperature, substrate concentration, and competitive/non-competitive inhibitors.

Practise Chemical and Physical Basis of Life questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 1

What should I study first?

Next in the syllabus

Where does Chemical and Physical Basis of Life fit in the syllabus?

Year 1 · Term 1