DP Biology SL B1.1 Carbohydrates and Lipids

DP Biology SL B1.1 Carbohydrates and Lipids - Full notes

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DP Biology SL | B1.1 Carbohydrates and Lipids

DP BIOLOGY · THEME B: FORM AND FUNCTION

B1.1

Carbohydrates and Lipids

Full notes for SL · IB-style

Contents

1	Carbon and the diversity of biological molecules
2	Condensation and hydrolysis
3	Monosaccharides and disaccharides
4	Polysaccharides: starch, glycogen and cellulose
5	Glycoproteins and cell recognition
6	Lipids: triglycerides and fatty acids
7	Phospholipids and steroids
8	Carbon: the basis of organic molecules
9	Condensation and hydrolysis
10	Monosaccharides: structure
11	Properties of glucose
12	Polysaccharides: starch, glycogen and cellulose
13	Cellulose and its strength
14	Glycoproteins and cell recognition
15	Lipids: hydrophobic molecules
16	Triglycerides: structure and formation
17	Saturated and unsaturated fatty acids
18	Triglycerides as energy stores
19	Phospholipids and membranes
20	Steroids
21	Tests for biological molecules
22	Mixed review: worked problems
23	Additional exam-style practice
24	Carbohydrates and lipids in diet and health
25	Common misconceptions and links
26	Exam-style question with markscheme
27	Check your understanding
28	Summary and topic map

These are full teaching notes. Read each section in order, try the Think about it question before you read on, and do every Quick check before moving to the next section.

Before you start

Rate yourself on each statement now, and again after you've worked through the notes. Shade R (not yet), A (getting there) or G (confident).

I can…	R	A	G
explain why carbon can form so many different compounds
explain condensation and hydrolysis reactions
describe the structure and roles of glucose, ribose and disaccharides
relate the structures of starch, glycogen and cellulose to their functions
explain the role of glycoproteins in cell recognition
describe triglycerides and explain saturated, monounsaturated and polyunsaturated fatty acids
explain why lipids are good energy stores and insulators
describe phospholipids and steroids

There is no additional HL content in this subtopic. SL and HL students study the same material.

Guiding questions

How do the structures of carbohydrates and lipids relate to their functions in living organisms? Why do organisms store energy in different forms?

How this topic is examined

B1.1 is examined through molecular diagrams (glucose, triglycerides, phospholipids), comparison questions (starch vs glycogen vs cellulose) and data on energy storage. You should be able to draw alpha-glucose and recognise ribose and beta-glucose.

Answers score well when they link a structural feature to its function: branching to rapid release, straight chains to tensile strength, hydrophobic tails to membrane formation.

Command term	What the examiner wants
State / Identify	a brief answer with no explanation needed
Outline	a brief account or summary
Describe	a detailed account, including trends or features, without reasons
Explain	a detailed account including causes, reasons or mechanisms
Distinguish / Compare and contrast	give the differences (and similarities), point by point
Calculate	a numerical answer with working and units
Deduce / Suggest	reach a conclusion from data; propose a reasonable explanation
Evaluate / Discuss	weigh strengths and limitations and reach a judgement

How to use these notes

Each section teaches one part of the syllabus in full. You'll see these boxes throughout; each has one job:

Box	What it's for
Think about it	a question to get you thinking before a section; the answer comes in the section
Key point	the one idea you must not forget
Common mistake	an error examiners see every year, and how to avoid it
In the real world	where the biology shows up outside the classroom
Try this	something quick you can do yourself to test the idea
Worked example	full solutions with IB-style marks (M1 method, A1 answer, R1 reasoning)
Quick check	short questions to test yourself at the end of each section

1 Carbon and the diversity of biological molecules

Carbon forms four bonds, chains and rings.

Think about it

Why is life on Earth based on carbon rather than on another common element such as silicon or oxygen?

Carbon atoms can form four covalent bonds, with other carbon atoms and with hydrogen, oxygen, nitrogen, phosphorus and sulfur. They can form long chains, branched chains and rings, with single or double bonds. This allows an almost unlimited variety of stable molecules, from small sugars to huge proteins and DNA.

The main groups of carbon compounds in living things are carbohydrates, lipids, proteins and nucleic acids. Large molecules (macromolecules) are often polymers: chains of repeating subunits called monomers.

Quick check

1. How many covalent bonds can a carbon atom form?

2. Define polymer.

Answers: 1. four 2. a large molecule made of many repeating monomers

2 Condensation and hydrolysis

Water out to build; water in to break.

Monomers are joined by condensation reactions: two molecules bond together and a molecule of water is released. These are anabolic reactions, requiring energy, usually from ATP, and catalysed by enzymes.

Polymers are broken down by hydrolysis reactions: a molecule of water is used to break the bond between monomers. Digestion is mainly hydrolysis: enzymes such as amylase break starch into maltose by hydrolysis.

The same principle applies to all biological polymers: glucose units into starch (glycosidic bonds), amino acids into proteins (peptide bonds), nucleotides into nucleic acids (phosphodiester bonds), and fatty acids with glycerol into triglycerides (ester bonds).

Figure 1. Condensation builds polymers; hydrolysis breaks them.

Common mistake

Saying hydrolysis 'releases water'. Hydrolysis uses water; condensation releases it.

Quick check

1. What is released in a condensation reaction?

2. Give an example of hydrolysis in the body.

Answers: 1. water 2. digestion of starch by amylase

3 Monosaccharides and disaccharides

Simple sugars are soluble, sweet energy sources.

Monosaccharides are single sugar units. Glucose (C₆H₁₂O₆) is a hexose (six carbons) and the main respiratory substrate in cells. Ribose is a pentose (five carbons) found in RNA and ATP. Glucose exists in two forms, alpha-glucose and beta-glucose, which differ in the position of the –OH group on carbon 1: below the ring in alpha, above it in beta. This small difference has large effects on the polymers they form.

Glucose is soluble (polar –OH groups form hydrogen bonds with water), so it is easily transported in blood and sap, and it is stable. Its oxidation in respiration releases energy to make ATP.

Disaccharides are formed when two monosaccharides join by a condensation reaction, forming a glycosidic bond: maltose (glucose + glucose), sucrose (glucose + fructose; the form in which plants transport sugar) and lactose (glucose + galactose; milk sugar).

Figure 2. Alpha- and beta-glucose differ only in the position of the –OH group on carbon 1.

Quick check

1. Name the bond formed between two monosaccharides.

2. Which disaccharide is transported in phloem?

3. How do alpha- and beta-glucose differ?

Answers: 1. glycosidic bond 2. sucrose 3. position of the –OH on carbon 1

4 Polysaccharides: starch, glycogen and cellulose

Three glucose polymers, three very different jobs.

Polysaccharides are long chains of monosaccharides joined by glycosidic bonds. Being large, they are insoluble or only slightly soluble, so they do not affect the water potential of cells (D2.3), which makes them suitable for storage.

Starch is the energy store of plants. It has two components: amylose, an unbranched chain of alpha-glucose joined by 1,4 bonds that coils into a helix (compact), and amylopectin, a branched chain with 1,6 bonds at branch points. Starch is stored in granules in chloroplasts and in storage organs such as potato tubers.

Glycogen is the energy store of animals and fungi, found in liver and muscle cells. It is like amylopectin but more highly branched. The many branch ends allow enzymes to add or remove glucose rapidly at many points at once, so glucose can be released quickly when needed, for example during exercise.

Cellulose is the main structural component of plant cell walls. It is made of beta-glucose. Because every other beta-glucose is flipped, the chains are straight, not coiled. Parallel chains form many hydrogen bonds with each other, grouping into microfibrils with very high tensile strength. Cellulose walls resist the pressure of water inside the cell (turgor). Most animals cannot digest cellulose because they lack the enzyme cellulase.

Feature	Starch (amylose / amylopectin)	Glycogen	Cellulose
Monomer	alpha-glucose	alpha-glucose	beta-glucose
Bonds	1,4 (and 1,6 in amylopectin)	1,4 and many 1,6	1,4
Shape	helix / branched	highly branched	straight chains, microfibrils
Function	energy store in plants	energy store in animals and fungi	structural: plant cell walls
Key property	compact, insoluble	rapid glucose release	high tensile strength

Key point

Structure fits function: branching gives rapid release (glycogen); coiling gives compact storage (amylose); straight hydrogen-bonded chains give strength (cellulose).

Quick check

1. Why are polysaccharides suitable for storage?

2. Why can glycogen release glucose quickly?

3. Why does cellulose have high tensile strength?

Answers: 1. insoluble: no effect on water potential; compact 2. many branch ends for enzymes to act on 3. straight chains held by many hydrogen bonds in microfibrils

5 Glycoproteins and cell recognition

Sugar chains on the cell surface act as identity tags.

Glycoproteins are proteins with carbohydrate chains attached. In the plasma membrane, the carbohydrate chains project from the outer surface. They act as recognition markers, allowing cells to identify each other, and as receptors.

The ABO blood group system is a clear example. All people have a basic carbohydrate chain (antigen O) on red blood cell glycoproteins. People with blood group A have an extra sugar (N-acetylgalactosamine) added; group B have a different sugar (galactose); group AB have both; group O have neither. The immune system recognizes foreign antigens, which is why blood transfusions must be matched.

Blood group	Antigens on red cells	Antibodies in plasma	Can receive from
A	A	anti-B	A, O
B	B	anti-A	B, O
AB	A and B	none	A, B, AB, O
O	neither	anti-A and anti-B	O only

Quick check

1. What are glycoproteins?

2. Why can people with blood group O donate to all groups?

Answers: 1. proteins with carbohydrate chains attached 2. their red cells carry no A or B antigens

6 Lipids: triglycerides and fatty acids

Hydrophobic molecules for long-term energy storage and insulation.

Lipids are a diverse group of substances that are hydrophobic: insoluble in water but soluble in non-polar solvents. They include fats, oils, waxes, phospholipids and steroids.

Triglycerides are formed by condensation of one glycerol molecule with three fatty acids, forming three ester bonds and releasing three molecules of water. Fats are triglycerides that are solid at room temperature; oils are liquid.

A fatty acid is a hydrocarbon chain with a carboxyl group at one end. Saturated fatty acids have only single bonds between carbons; the chains are straight and pack closely, so saturated fats (mostly from animals) are solid at room temperature. Unsaturated fatty acids have one (monounsaturated) or more (polyunsaturated) C=C double bonds. Cis double bonds put a kink in the chain, so molecules pack loosely and form oils, liquid at room temperature (mostly from plants). Trans fats have straight chains despite a double bond; they are produced artificially and are linked to heart disease.

6.1 Lipids as energy stores and insulators

Lipids are excellent long-term energy stores. They release about twice as much energy per gram as carbohydrates (about 37 kJ g⁻¹ compared with 17 kJ g⁻¹) because they contain more C–H bonds and less oxygen. Being insoluble, they are stored without water, so they are compact and light: an important advantage for animals that move.

Adipose tissue also provides thermal insulation under the skin of mammals (for example the thick blubber of seals and whales), as lipids conduct heat poorly, and protects organs from physical damage.

Energy storage	Carbohydrate (glycogen)	Lipid (triglyceride)
Energy per gram	about 17 kJ	about 37 kJ
Solubility	slightly soluble; stored with water	insoluble; stored without water
Speed of release	rapid	slow
Use	short-term store	long-term store

WORKED EXAMPLE 1 Energy storage comparison

A migrating bird needs 740 kJ of stored energy for a flight. Calculate the mass of fat and the mass of glycogen needed, and explain the advantage of storing fat.

Solution

Fat: 740 ÷ 37 = 20 gA1

Glycogen: 740 ÷ 17 = 43.5 g (plus associated water, several times heavier in practice)A1

Fat stores the same energy in less than half the mass, so the bird is lighter in flightR1

Quick check

1. What molecules form a triglyceride?

2. Why are unsaturated oils liquid at room temperature?

3. Why do lipids store more energy per gram than carbohydrates?

Answers: 1. glycerol and three fatty acids 2. cis double bonds kink chains so they pack loosely 3. more C–H bonds, less oxygen

7 Phospholipids and steroids

Phospholipids build membranes; steroids act as hormones.

A phospholipid is like a triglyceride, but one fatty acid is replaced by a phosphate group. The phosphate head is hydrophilic; the two fatty acid tails are hydrophobic. A molecule with both properties is amphipathic.

In water, phospholipids spontaneously form a bilayer, with hydrophilic heads facing the water on both sides and hydrophobic tails facing inwards, away from water. This bilayer is the basic structure of all cell membranes (B2.1). It is a barrier to ions and polar molecules, which cannot easily cross the hydrophobic core.

Steroids are lipids with a structure of four fused carbon rings. Cholesterol is a steroid found in animal membranes, where it regulates fluidity. Steroid hormones, such as oestradiol, testosterone and progesterone, are made from cholesterol. Because they are hydrophobic, steroid hormones can pass through plasma membranes and act on receptors inside cells (C2.1).

Figure 3. A phospholipid bilayer: hydrophilic heads face water on both sides; hydrophobic tails face inward.

Quick check

1. Why are phospholipids amphipathic?

2. Why do phospholipids form bilayers in water?

3. Name two steroid hormones.

Answers: 1. hydrophilic phosphate head, hydrophobic tails 2. hydrophobic tails avoid water; heads face water 3. oestradiol, testosterone, progesterone

8 Carbon: the basis of organic molecules

Four bonds, endless variety.

Carbon can form four covalent bonds, single or double, with other carbon atoms and with H, O, N and S. This allows chains, branches and rings, giving an enormous variety of stable molecules: carbohydrates, lipids, proteins and nucleic acids.

WORKED EXAMPLE 2 Carbon bonding (standard)

Explain why carbon is suited to forming the backbone of biological molecules.

Solution

Forms four covalent bondsR1

Can form chains, rings and branches of any lengthR1

9 Condensation and hydrolysis

Building and breaking polymers.

Condensation joins monomers by removing water, forming a covalent bond (glycosidic in carbohydrates, ester in lipids, peptide in proteins). Hydrolysis breaks these bonds by adding water. Digestion is hydrolysis; synthesis of polymers is condensation.

WORKED EXAMPLE 3 Disaccharide (standard)

Write a word equation for the formation of sucrose.

Solution

glucose + fructose → sucrose + waterA1

Condensation forming a glycosidic bondA1

Quick check

1. How many water molecules are released when 100 glucose molecules form a straight chain of amylose?

Answers: 1. 99

10 Monosaccharides: structure

α- and β-glucose.

Glucose (C6H12O6) exists as a ring in water. In α-glucose, the OH on carbon 1 is below the ring; in β-glucose, it is above. This small difference changes the polymers formed. Other monosaccharides include fructose, galactose and ribose.

WORKED EXAMPLE 4 Isomers (standard)

Distinguish α-glucose from β-glucose.

Solution

Position of the OH group on C1: below the ring (α) or above (β)R1

Quick check

1. Name a five-carbon monosaccharide in RNA.

Answers: 1. ribose

11 Properties of glucose

Soluble and transportable.

Glucose is soluble (polar OH groups form hydrogen bonds with water), so it is easily transported in blood and sap. It is a small molecule that diffuses easily and is chemically stable but releases energy in respiration.

WORKED EXAMPLE 5 Transport (standard)

Explain why glucose is transported in blood plasma but not stored as glucose.

Solution

Soluble: easily transportedR1

Storing it would affect water potential (osmotic problems); stored as insoluble glycogenR1

12 Polysaccharides: starch, glycogen and cellulose

Structure and function.

Polysaccharide	Monomer	Bonds	Structure	Function
amylose	α-glucose	1,4	unbranched helix	energy storage in plants
amylopectin	α-glucose	1,4 and 1,6	branched	energy storage in plants
glycogen	α-glucose	1,4 and 1,6	highly branched	energy storage in animals and fungi
cellulose	β-glucose	1,4	straight chains, alternate inverted	structural (cell walls)

WORKED EXAMPLE 6 Glycogen (exam level)

Explain how the structure of glycogen suits its function.

Solution

Highly branched: many ends for rapid hydrolysis to glucoseR1

Compact and insoluble: does not affect water potentialR1

13 Cellulose and its strength

Microfibrils.

In cellulose, every second β-glucose is inverted, producing straight chains. Hydrogen bonds between parallel chains form microfibrils with great tensile strength, which make plant cell walls strong enough to resist turgor pressure.

WORKED EXAMPLE 7 Strength (standard)

Explain why cellulose is strong.

Solution

Straight chains lie parallelR1

Many hydrogen bonds between chains form microfibrilsR1

14 Glycoproteins and cell recognition

Sugar tags on cell surfaces.

Glycoproteins have carbohydrate chains attached to membrane proteins. They act in cell–cell recognition, as receptors, and as antigens. The ABO blood groups are determined by different carbohydrate chains on red blood cell glycoproteins.

WORKED EXAMPLE 8 Blood groups (standard)

Explain why a person with blood group A cannot receive group B blood.

Solution

Their plasma contains anti-B antibodiesR1

These recognize the B antigen and cause agglutinationR1

Quick check

1. Which blood group is the universal donor for red cells?

Answers: 1. O (no A or B antigens)

15 Lipids: hydrophobic molecules

Fats, oils, phospholipids, steroids.

Lipids are a diverse group of mostly non-polar, hydrophobic molecules, soluble in non-polar solvents. They include triglycerides (fats and oils), phospholipids, steroids (cholesterol, sex hormones) and waxes.

WORKED EXAMPLE 9 Solubility (standard)

Why are lipids insoluble in water?

Solution

Mostly non-polar hydrocarbon chains cannot form hydrogen bonds with waterR1

16 Triglycerides: structure and formation

Glycerol and three fatty acids.

A triglyceride forms by condensation between one glycerol and three fatty acids, producing three ester bonds and three water molecules. Fatty acids may be saturated (no C=C), monounsaturated (one C=C) or polyunsaturated (several).

WORKED EXAMPLE 10 Formation (standard)

How many water molecules are released when a triglyceride forms?

Solution

3A1

Quick check

1. Name the bond between glycerol and a fatty acid.

Answers: 1. ester bond

17 Saturated and unsaturated fatty acids

Kinks and melting points.

Saturated fatty acids have straight chains that pack closely, so fats rich in them are solid at room temperature. cis-Unsaturated fatty acids have kinks at the C=C bonds, preventing close packing, so oils are liquid. trans-Fats are straight despite a double bond and are linked to heart disease.

WORKED EXAMPLE 11 Melting point (exam level)

Explain why butter is solid but olive oil is liquid at room temperature.

Solution

Butter: mainly saturated fatty acids pack closely: stronger intermolecular forcesR1

Olive oil: mainly cis-unsaturated: kinks prevent close packingR1

18 Triglycerides as energy stores

Compact and insoluble.

Lipids store about twice as much energy per gram (37 kJ g−1) as carbohydrates (17 kJ g−1), are insoluble (no osmotic effect), and adipose tissue also provides thermal insulation (blubber) and protection.

WORKED EXAMPLE 12 Energy storage (standard)

Calculate the mass of glycogen needed to store the same energy as 10 kg of fat.

Solution

10 × 37 = 370 MJM1

370/17 = 21.8 kgA1

In the real world

Migrating birds store fat before long flights; a ruby-throated hummingbird can almost double its mass with fat before crossing the Gulf of Mexico.

Quick check

1. Why do animals store energy mainly as fat rather than glycogen?

Answers: 1. more energy per gram; lighter for mobile animals

19 Phospholipids and membranes

Amphipathic molecules.

A phospholipid has a hydrophilic phosphate head and two hydrophobic fatty acid tails. In water, phospholipids form bilayers with heads facing out and tails in, the basis of all cell membranes.

WORKED EXAMPLE 13 Bilayer (standard)

Explain why phospholipids form a bilayer.

Solution

Heads are hydrophilic and face water on both sidesR1

Tails are hydrophobic and face each other insideR1

20 Steroids

Four fused rings.

Steroids have four fused carbon rings. Cholesterol regulates membrane fluidity and is a precursor for steroid hormones such as testosterone, oestradiol and cortisol. Steroid hormones are lipid-soluble and pass through membranes to bind intracellular receptors.

Quick check

1. Why can steroid hormones enter cells directly?

Answers: 1. they are lipid-soluble and diffuse through the phospholipid bilayer

21 Tests for biological molecules

Laboratory identification.

Molecule	Test	Positive result
starch	iodine solution	orange-brown to blue-black
reducing sugar	Benedict's, heat	blue to green/yellow/brick red
non-reducing sugar	hydrolyse with acid, neutralize, then Benedict's	brick red after hydrolysis
lipid	emulsion test (ethanol then water)	cloudy white emulsion
protein	biuret reagent	blue to purple

WORKED EXAMPLE 14 Non-reducing sugar (standard)

Describe how to test for sucrose.

Solution

Negative Benedict's firstR1

Hydrolyse with dilute HCl, neutralize, repeat Benedict's: brick redR1

22 Mixed review: worked problems

Bringing the ideas together.

WORKED EXAMPLE 15 Mixed problem (exam level)

Compare starch and cellulose.

Solution

Both polymers of glucose linked by 1,4 glycosidic bondsR1

Starch: α-glucose, helical/branched, energy storeR1

Cellulose: β-glucose, straight chains, microfibrils, structuralR1

23 Additional exam-style practice

Paper 1 and Paper 2.

WORKED EXAMPLE 16 Paper 1 question (standard)

Which molecule is a polymer of β-glucose? A. amylose B. glycogen C. cellulose D. sucrose

Solution

CA1

WORKED EXAMPLE 17 Paper 2 question (exam level)

Outline the roles of lipids in organisms.

Solution

Energy storage (triglycerides)R1

Membranes (phospholipids); hormones (steroids)R1

Insulation and protectionR1

24 Carbohydrates and lipids in diet and health

Balance and risks.

Diets high in saturated and trans fats raise LDL cholesterol, increasing the risk of atherosclerosis and coronary heart disease. Unsaturated fats (especially omega-3) are linked with lower risk. Excess refined carbohydrate intake is linked to obesity and type 2 diabetes.

Quick check

1. Why are trans-fats considered harmful?

Answers: 1. they raise LDL cholesterol and increase heart disease risk

25 Common misconceptions and links

Students often think…	Actually…
hydrolysis releases water	hydrolysis uses water
starch and cellulose are made of the same glucose	starch uses alpha-glucose; cellulose beta-glucose
all fats are unhealthy	unsaturated (cis) fats are part of a healthy diet; trans fats are harmful
lipids are polymers	triglycerides are not polymers of repeating monomers

How B1.1 connects to the rest of the course

Topic	Connection
A1.1 Water	hydrophilic and hydrophobic substances
B1.2 Proteins	condensation forms peptide bonds
B2.1 Membranes (HL)	phospholipid bilayers
C1.2 Cell respiration	glucose and lipids as respiratory substrates
C2.1 Signalling (HL)	steroid hormones

26 Exam-style question with markscheme

Try this under exam conditions (about 15 minutes) before reading the markscheme.

Figure 4. Energy released by oxidation of three storage molecules.

(a) Calculate how many times more energy per gram triglycerides release than glycogen. [1]

(b) Explain why lipids are used for long-term energy storage in animals. [3]

(d) Explain how the structure of phospholipids allows them to form membranes. [3]

Markscheme

Part	Answer	Marks
(a)	37 ÷ 17 = 2.2	A1
(b)	more energy per gram	R1
	insoluble: stored without water, compact and light	R1
	insulation / protection as extra roles	R1
(c)	glycogen alpha-glucose, cellulose beta-glucose	A1
	glycogen highly branched, cellulose straight	A1
	cellulose forms hydrogen-bonded microfibrils	A1
(d)	hydrophilic heads, hydrophobic tails (amphipathic)	R1
	tails face inward away from water	R1
	spontaneous bilayer formation	R1

Examiner's comments. In (c), the best answers stated the monomer, branching and arrangement for both molecules.

27 Check your understanding

Section A: multiple choice

1. A condensation reaction

A. releases water B. uses water C. breaks polymers D. requires no energy

2. Cellulose is made of

A. alpha-glucose B. fructose C. beta-glucose D. galactose

3. Glycogen is more branched than

A. cellulose B. amylopectin C. amylose D. both

4. A triglyceride contains

A. three glycerols B. a phosphate group C. four carbon rings D. glycerol and three fatty acids

5. A saturated fatty acid has

A. one double bond B. no C=C double bonds C. several double bonds D. a phosphate group

6. Steroid hormones can enter cells because they are

A. hydrophobic B. large C. charged D. proteins

Section B: structured

7. Draw alpha-glucose. [2]

8. Explain how the structure of cellulose relates to its function. [3]

9. Distinguish between saturated and unsaturated fatty acids. [3]

10. Explain the role of glycoproteins in the ABO blood groups. [3]

Answers

1. A 2. C 3. B 4. D 5. B 6. A

7. Hexagon ring with O, C1–OH below the ring, CH₂OH on C5.

8. Beta-glucose; straight chains; hydrogen bonds form microfibrils; tensile strength for cell walls.

9. Saturated: single bonds, straight, solid; unsaturated: C=C, kinks (cis), liquid.

10. Carbohydrate chains on glycoproteins act as antigens; A and B add different sugars; immune recognition.

28 Summary and topic map

Idea	Remember
Carbon	four bonds; chains and rings
Condensation / hydrolysis	water released / water used
Monosaccharides	glucose (alpha, beta), ribose
Disaccharides	maltose, sucrose, lactose; glycosidic bond
Polysaccharides	starch, glycogen (storage); cellulose (structure)
Glycoproteins	recognition; ABO blood groups
Lipids	triglycerides; saturated vs unsaturated; energy and insulation
Phospholipids, steroids	bilayers; hormones

Before the exam, make sure you…

•link each structure to its function
•state alpha or beta glucose for each polysaccharide
•explain energy storage with figures
•draw phospholipid bilayers correctly

Carbohydrates and Lipids on one page

Cover this page with a sheet of paper and try to rebuild it from memory. Whatever you can't recall is what to revise next.

Figure 5. Topic map for Carbohydrates and Lipids.

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