IB Biology HL – CARBOHYDRATES & LIPIDS (Core Concepts)

1. What are the four macromolecules of life?

Carbohydrates, lipids, proteins, nucleic acids.

2. What do all macromolecules contain?

Carbon atoms.

3. Why are carbon-based molecules stable?

Carbon forms strong covalent bonds.

4. Why can carbon form diverse structures?

It can form four bonds (single/double), allowing rings, branches, and long chains.

5. Why do double bonds limit carbon bonding?

Double bonds are stronger and reduce the number of atoms carbon can bind.

6. What reaction forms polymers from monomers?

Condensation.

7. What does condensation release?

water

8. What reaction breaks polymers into monomers?

Hydrolysis.

9. What does hydrolysis require?

Water.

10. Why is hydrolysis important?

Digestion (energy release) and recycling monomers.

11. Do condensation reactions require energy?

Yes — ATP input.

12. What are monosaccharides?

Single sugar units (e.g., glucose, fructose).

13. Why is glucose biologically important?

Small, soluble, stable, easily transported, primary energy source.

14. What are the three major polysaccharides?

Cellulose, starch, glycogen.

15. Which polysaccharides store energy?

Starch and glycogen.

16. What is cellulose’s function?

Structural support in plant cell walls.

17. What are the two forms of starch?

Amylose (unbranched) and amylopectin (branched).

18. What bonds does amylose have?

1→4 glycosidic bonds.

19. What bonds does amylopectin have?

1→4 and 1→6 glycosidic bonds.

20. How does glycogen compare to amylopectin?

More highly branched.

21. What type of glucose forms starch and glycogen?

Alpha‑glucose.

22. What type of glucose forms cellulose?

Beta‑glucose.

23. Why is every second glucose inverted in cellulose?

Allows hydrogen bonding between chains.

24. What properties do cellulose fibers have?

High tensile strength, high pressure resistance.

25. Why is cellulose insoluble?

Large, tightly packed fibers.

26. What are glycoproteins?

Proteins with attached carbohydrates.

27. Where are glycoproteins found?

Cell membranes (extracellular side).

28. What is their function?

Cell‑cell recognition and communication.

29. How do glycoproteins relate to blood groups?

Different carbohydrate patterns determine A, B, AB, O types.

30. Why are lipids hydrophobic?

Non‑polar; do not dissolve in water.

31. What are the two IB‑relevant lipids?

Triglycerides and phospholipids.

32. What forms a triglyceride?

Glycerol + 3 fatty acids.

33. What bonds form in triglycerides?

Ester bonds (via condensation).

34. What forms a phospholipid?

Glycerol + 2 fatty acids + phosphate group.

35. Why are phospholipids amphipathic?

Hydrophilic head + hydrophobic tails.

36. What structure do phospholipids form in water?

Bilayer

37. What is a saturated fatty acid?

No double bonds; straight chain.

38. What is a monounsaturated fatty acid?

One double bond; bent chain.

39. What is a polyunsaturated fatty acid?

Multiple double bonds; bent chain.

40. What is a cis fatty acid?

Hydrogens on same side → bend.

41. What is a trans fatty acid?

Hydrogens on opposite sides → straight.

42. Which fatty acids pack tightly?

Saturated and trans.

43. Which fatty acids have high melting points?

Saturated and trans.

44. Why are triglycerides good for long‑term energy storage?

~2× more energy per gram than carbohydrates.

45. Why do triglycerides provide insulation?

Hydrophobic → poor heat conduction.

46. Why do triglycerides act as shock absorbers?

Stored in adipose tissue; cushion organs.

47. What is the structure of steroids?

Fused carbon rings.

48. Why can steroids pass through membranes easily?

Hydrophobic nature.