1.4 Chemicals of Life

• Composition, properties and functions of carbohydrates, lipids and proteins
• Vitamins, mineral salts and water
• Food tests for carbohydrates, lipids, proteins and vitamin C
• Enzymes and their properties
• Factors affecting enzyme activity

• describe the composition, properties and functions of the chemicals of life
• investigate the presence of carbohydrates, lipids, proteins and vitamin C in food
• investigate the presence of enzymes in living tissues
• determine factors affecting enzymatic reactions in cells
• appreciate the importance of chemical components in cells

“What are living things actually made of?”

The titles are open to everyone. Reading a lesson needs an account — sign in or create one.

1. The chemicals of life
   40 min · 2 practice tasks · quiz
   What organisms are built from, and how to test for each.
2. Enzymes
   40 min · 2 practice tasks · quiz
   The proteins that make reactions possible at body temperature, and what stops them.
3. What carbohydrates are made of
   40 min · 1 practice tasks · quiz
   Carbohydrates contain carbon, hydrogen and oxygen, with hydrogen and oxygen in the same 2:1 ratio as water.
4. Simple sugars: mono and disaccharides
   40 min · 1 practice tasks · quiz
   Glucose, fructose and galactose are single units; maltose, sucrose and lactose are pairs joined by condensation.
5. Starch, glycogen and cellulose
   40 min · 1 practice tasks · quiz
   Three polymers of glucose: a plant store, an animal store, and the fibre of cell walls.
6. What carbohydrates do in the body
   40 min · 1 practice tasks · quiz
   Glucose fuels respiration; starch and glycogen store energy; cellulose is fibre; excess carbohydrate becomes fat.
7. Amino acids and peptide bonds
   40 min · 1 practice tasks · quiz
   Proteins are built from amino acids joined by peptide bonds; nitrogen is the element that sets them apart.
8. How a protein gets its shape
   40 min · 1 practice tasks · quiz
   Sequence folds into helix or sheet, then into a 3D shape; globular proteins do jobs, fibrous proteins are cables.
9. What proteins do
   40 min · 1 practice tasks · quiz
   Growth, repair, enzymes, transport, defence, hormones and, only when desperate, energy.
10. How a lipid is built
    40 min · 1 practice tasks · quiz
    A triglyceride is glycerol plus three fatty acids; saturated tails pack as fats, unsaturated tails stay liquid as oils.
11. Types and functions of lipids
    40 min · 1 practice tasks · quiz
    Fats, oils, phospholipids, steroids and waxes: energy store, insulation, membranes and waterproofing.
12. Nucleic acids: DNA and RNA
    40 min · 1 practice tasks · quiz
    DNA stores the instructions for proteins; RNA carries those instructions. Both are chains of nucleotides.
13. Why water is an unusual molecule
    40 min · 1 practice tasks · quiz
    Water is polar, so it forms hydrogen bonds: that is why it is a solvent, resists temperature change, and is cohesive.
14. What water does in living things
    40 min · 1 practice tasks · quiz
    Water is the solvent, transport medium, reactant, coolant and turgor support of organisms - and dehydration is quickly dangerous.
15. Vitamins: small doses, large effects
    40 min · 1 practice tasks · quiz
    Vitamins are organic compounds needed in small amounts; they are classed as water-soluble or fat-soluble.
16. Vitamins on a Kenyan plate
    40 min · 1 practice tasks · quiz
    Local sources of A, C, D and B vitamins, why milling and boiling lose them, and how DCPIP tests for vitamin C.
17. Mineral salts the body cannot skip
    40 min · 1 practice tasks · quiz
    Minerals are inorganic ions. Macro ones (Ca, P, Na, K, Mg) are needed in larger amounts; micro ones (Fe, I, Zn, F) in traces.
18. Iron, iodine, calcium and fluoride in Kenya
    40 min · 1 practice tasks · quiz
    Anaemia, goitre, rickets and dental fluorosis are mineral problems with local causes and local public-health answers.
19. Testing for starch with iodine
    40 min · 1 practice tasks · quiz
    Iodine solution turns blue-black with starch. The method, the control, and what Kenyan foods actually do.
20. Benedict's test for reducing sugar
    40 min · 1 practice tasks · quiz
    Heat with Benedict's solution: blue through green, yellow and orange to brick red. Sucrose needs acid hydrolysis first.
21. The Biuret test for protein
    40 min · 1 practice tasks · quiz
    Sodium hydroxide then copper sulphate: blue to purple. Do not confuse it with Benedict's.
22. Testing for lipids
    40 min · 1 practice tasks · quiz
    A translucent spot on paper, or a white emulsion when ethanol then water is added. Ethanol is flammable - no flames.
23. A balanced diet
    40 min · 1 practice tasks · quiz
    Enough of all seven classes for age, sex, work and climate - not ugali alone, and not energy alone.
24. Kwashiorkor and marasmus
    40 min · 1 practice tasks · quiz
    Two faces of protein-energy malnutrition still seen in drought, displacement and poor weaning in Kenya.
25. Deficiency diseases still seen in Kenya
    40 min · 1 practice tasks · quiz
    Night blindness, anaemia, goitre, rickets, scurvy and pellagra - signs, missing chemical, and the public-health reply.
26. Lock and key: why enzymes are specific
    40 min · 1 practice tasks · quiz
    The active site fits one substrate. Products leave; the enzyme is unchanged. Heat or pH that warps the site ends the reaction.
27. Temperature and the rate of enzyme reactions
    40 min · 1 practice tasks · quiz
    Rate rises with collisions up to an optimum, then falls steeply as the enzyme denatures. Cooling is reversible; boiling is not.
28. pH, substrate and enzyme concentration
    40 min · 1 practice tasks · quiz
    Each enzyme has an optimum pH. Extra substrate only helps until sites are full; extra enzyme raises rate if substrate is waiting.