Understanding biochemistry is like having a toolkit for analysing life...
Biology350 views·Updated 23 Jun 2026·2 pagesAS Level Biology 1.1: KEY Topics Explained - WJEC
Kat bert@katbert
1
of 2
Biochemical Tests and Water Properties
You'll need to master four key biochemical tests for your exams. Starch turns blue-black with iodine solution, whilst proteins change from blue to purple with biuret reagent. For lipids, mix with ethanol then water - a cloudy emulsion means lipids are present.
Reducing sugars create a colour spectrum with Benedict's reagent, from blue (no sugar) through green, yellow, orange to brick-red (loads of sugar). Non-reducing sugars need boiling with hydrochloric acid first to break them down.
Water's unique properties make life possible. Its high surface tension creates habitats, whilst high specific heat capacity keeps cellular conditions stable. The fact that ice floats protects aquatic life underneath, and water's cohesive properties allow it to be pulled up through plant stems.
Quick Tip: Remember the acronym CHILIS for water properties - Colourless, High surface tension, High latent heat, High specific heat, Ice floats, Liquid at room temp, Strong cohesion!
2
of 2
Protein Structure and Lipid Functions
Protein structure has four levels you must understand. Primary structure is simply the amino acid sequence, whilst secondary structure involves hydrogen bonding creating repeating patterns like alpha-helices. Tertiary structure gives the final 3D shape through various bonds and interactions.
Globular proteins fold into spherical shapes and dissolve in water (like haemoglobin), whereas fibrous proteins remain long and parallel, usually insoluble (like collagen). Quaternary structure involves multiple polypeptide chains working together.
Lipids serve three main functions: insulation, energy storage, and protection. Triglycerides combine glycerol with three fatty acids, whilst phospholipids have just two fatty acids plus a phosphate group, creating molecules with hydrophilic heads and hydrophobic tails.
Exam Focus: Van der Waals forces occur because electrons move constantly, creating temporary positive and negative areas that help molecules stick together - this often appears in extended response questions!
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Biology350 views·Updated 23 Jun 2026·2 pagesAS Level Biology 1.1: KEY Topics Explained - WJEC
Kat bert@katbert
Understanding biochemistry is like having a toolkit for analysing life itself - these fundamental tests and molecular structures form the backbone of A-level Biology. From identifying what's in your food to understanding how proteins fold, these concepts will pop up...
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Biochemical Tests and Water Properties
You'll need to master four key biochemical tests for your exams. Starch turns blue-black with iodine solution, whilst proteins change from blue to purple with biuret reagent. For lipids, mix with ethanol then water - a cloudy emulsion means lipids are present.
Reducing sugars create a colour spectrum with Benedict's reagent, from blue (no sugar) through green, yellow, orange to brick-red (loads of sugar). Non-reducing sugars need boiling with hydrochloric acid first to break them down.
Water's unique properties make life possible. Its high surface tension creates habitats, whilst high specific heat capacity keeps cellular conditions stable. The fact that ice floats protects aquatic life underneath, and water's cohesive properties allow it to be pulled up through plant stems.
Quick Tip: Remember the acronym CHILIS for water properties - Colourless, High surface tension, High latent heat, High specific heat, Ice floats, Liquid at room temp, Strong cohesion!
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Protein Structure and Lipid Functions
Protein structure has four levels you must understand. Primary structure is simply the amino acid sequence, whilst secondary structure involves hydrogen bonding creating repeating patterns like alpha-helices. Tertiary structure gives the final 3D shape through various bonds and interactions.
Globular proteins fold into spherical shapes and dissolve in water (like haemoglobin), whereas fibrous proteins remain long and parallel, usually insoluble (like collagen). Quaternary structure involves multiple polypeptide chains working together.
Lipids serve three main functions: insulation, energy storage, and protection. Triglycerides combine glycerol with three fatty acids, whilst phospholipids have just two fatty acids plus a phosphate group, creating molecules with hydrophilic heads and hydrophobic tails.
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