IB Biology · Theme B: Form and function · SL and HL
B1.1 Carbohydrates and lipids
A one-page summary of B1.1 Carbohydrates and lipids, the key terms to know, and sample exam questions with answers. For the full lesson, open the illustrated revision slides or practise in the app.
Guiding questions
In what ways do variations in form allow diversity of function in carbohydrates and lipids?
How do carbohydrates and lipids compare as energy storage compounds?
What B1.1 covers
Carbon and macromolecules
- B1.1.1Carbon builds diverse compounds
- B1.1.1 · Nature of scienceSI prefixes: an international agreement
- B1.1.2Condensation builds polymers
- B1.1.3Digestion by hydrolysis
Carbohydrates
- B1.1.4Monosaccharides: pentoses and hexoses
- B1.1.4Glucose: properties and use
- B1.1.5Starch and glycogen: energy stores
- B1.1.5Why coils and branches suit storage
- B1.1.6Cellulose: a structural polysaccharide
- B1.1.7Glycoproteins and cell recognition
Lipids
- B1.1.8Lipids are hydrophobic
- B1.1.9Triglycerides and phospholipids
- B1.1.10Saturated and unsaturated fatty acids
- B1.1.10Double bonds lower the melting point
- B1.1.11Adipose tissue: store and insulator
- B1.1.12Phospholipid bilayers
- B1.1.13Recognising steroids
- B1.1.13Steroids cross membranes
B1.1 Carbohydrates and lipids: summary
Carbon and polymers
- Carbon: up to 4 covalent bonds; chains, branches, rings.
- Condensation builds polymers (water out); hydrolysis breaks them (water in).
Monosaccharides
- Pentoses 5 C, hexoses 6 C: count every carbon.
- Glucose: soluble, transportable, stable, high energy yield.
Polysaccharides
- Starch and glycogen: coiled and branched α-glucose; compact, insoluble stores.
- Cellulose: alternating β-glucose; H-bonded microfibrils, strong.
Glycoproteins and lipids
- Carbohydrate markers on cells, e.g. ABO antigens.
- Lipids: fats, oils, waxes, steroids; hydrophobic.
Fats
- Triglyceride = glycerol + 3 fatty acids (ester bonds); phospholipid has a phosphate.
- More C=C, lower melting point; plants store oils, endotherms fats.
Membranes and steroids
- Amphipathic phospholipids form bilayers in water.
- Steroids (four fused rings) are non-polar and cross the bilayer.
Key terms
- Condensation
- joins two monomers with a covalent bond, releasing water.
- Hydrolysis
- splits a bond between monomers by adding water.
- Digestion
- breakdown of large insoluble polymers into small soluble monomers.
- Monosaccharide
- a single sugar unit, such as glucose or ribose.
- Polysaccharide
- a polymer of monosaccharides, such as starch or cellulose.
- Glycoprotein
- a protein with carbohydrate chains attached.
- Lipid
- dissolves in non-polar solvents, only sparingly in water.
- Triglyceride
- glycerol linked to three fatty acids by ester bonds.
- Amphipathic
- having both a hydrophilic part and a hydrophobic part.
- Steroid
- a lipid with four fused carbon rings.
Sample exam questions
Three of the 40 multiple-choice questions for B1.1. Try each one before opening the answer.
Question 1. What is the maximum number of covalent bonds that a carbon atom can form?
- Two
- Four
- Six
- Eight
Show the answer
Answer: B. Carbon has four electrons in its outer shell, so it can form up to four covalent bonds.
Question 2. What happens when two α-glucose molecules join in a condensation reaction?
- Water is released and a glycosidic bond forms.
- Water is used up and a glycosidic bond forms.
- Water is released and a peptide bond forms.
- Water is used up and an ester bond forms.
Show the answer
Answer: A. The –OH on carbon 1 of one glucose and an H from carbon 4 of the other leave as water, and an α-1,4 glycosidic bond forms, giving maltose.
Question 3. Which of these are formed by condensation reactions? I. Polypeptides II. Triglycerides III. Nucleic acids
- I only
- I and II only
- II and III only
- I, II and III
Show the answer
Answer: D. Polypeptides, nucleic acids and triglycerides are all formed by condensation reactions that release water, although triglycerides are not polymers.
Linking questions
Questions that connect B1.1 to other parts of the course, the kind that come up in Paper 2.
- The solvent properties of water (A1.1) are essential for the transport of glucose in blood plasma. How does the polarity of glucose enable its dissolution and transport? (see A1.1)
- How does the structure of phospholipids, introduced in B1.1, underpin the formation and selective permeability of cell membranes? (see B2.1)
- Protein channels and pumps embedded in the phospholipid bilayer are responsible for membrane transport. How do the properties of amino acid R-groups determine whether a protein region sits within the hydrophobic core of the membrane or faces the aqueous environment? (see B1.2, B2.1)
- During prolonged starvation, the body shifts from carbohydrate metabolism to lipid metabolism. Explain how this shift relates to the different energy-storage roles of glycogen and adipose tissue, and why it is a survival adaptation. (see C1.2)
Practise B1.1
This whole lesson is free: notes, quiz, data questions and exam-style papers, with markschemes. No payment needed.