What you need to know
- 1.2disaccharideA sugar made of two monosaccharides joined by a glycosidic bond, such as maltose, sucrose or lactose. structure and carbohydrate roles.
- 1.4Glycosidic bonds, condensationA reaction that joins two molecules with a covalent bond and releases a molecule of water. and hydrolysisA reaction that breaks a covalent bond using a molecule of water..
This is a new Scholar Lab activity under the textbook’s navigation heading; it does not reproduce the textbook feature.
By the end, you should be able to…
- Transfer familiar carbohydrate ideas to a new sugar.
- Separate formula from bonding arrangement.
Build your understanding
The information you need
Trehalose is a disaccharideA sugar made of two monosaccharides joined by a glycosidic bond, such as maltose, sucrose or lactose. made from two glucoseA hexose (six-carbon) monosaccharide, C₆H₁₂O₆. It is the main respiratory substrate. units. For this activity, you are told that its glycosidic linkage differs from the one in maltoseA disaccharide of two α-glucose molecules joined by a 1,4 glycosidic bond. and that trehalose is non-reducing. These are supplied facts for application, not extra named sugars to memorise for Topic 1.
Apply the familiar chemistry
Joining two C₆H₁₂O₆ molecules by a condensationA reaction that joins two molecules with a covalent bond and releases a molecule of water. reaction removes H₂O, giving C₁₂H₂₂O₁₁. hydrolysisA reaction that breaks a covalent bond using a molecule of water. reverses the bond formation and produces two glucose molecules. Having the same molecular formula as maltose does not require the same arrangement of atoms.
Make a testable prediction
A negative Benedict’s result before hydrolysis does not mean a sample contains no carbohydrate. If hydrolysis releases glucose, an appropriately prepared hydrolysed sample could give a positive reducing-sugar test. Compare with controls rather than assuming all disaccharides behave identically.
Make your reasoning visible
Use the supplied information
The challenge is applying condensationA reaction that joins two molecules with a covalent bond and releases a molecule of water. and hydrolysisA reaction that breaks a covalent bond using a molecule of water., not recalling an unfamiliar sugar.
Avoid overinterpreting a negative test
A reducing-sugar test does not detect every carbohydrate.
Avoid this misconception
The claim: Two sugars with the same molecular formula must have the same properties.
The correction: Different bonding arrangements can change enzyme recognition and test behaviour.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Write the molecular formula of the disaccharide formed from two glucose molecules by one condensation reaction.
Show suggested answer
C₁₂H₂₂O₁₁: add the glucose formulae and subtract H₂O.
Practice question
Retrieval and explanation · suggested answer
Predict the products of complete trehalose hydrolysis from the information supplied.
Show suggested answer
Two glucose molecules per trehalose molecule; water is used to break the glycosidic bond.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
An enzyme hydrolyses maltose but not trehalose. Both contain two glucose units. Suggest a molecular explanation.
Show a hint
Think about the arrangement recognised by an active site.
Explore the reasoning
The different glycosidic arrangements give different molecular shapes and interactions. Trehalose may not bind productively at the enzyme’s active site.
Recall this lesson
Lesson recall questions
Question 1 of 5: Distinguish a monosaccharide used for immediate energy release from a polysaccharide used for storage.
Saccharides and energy stores
Practice question
Retrieval and explanation · suggested answer
Distinguish a monosaccharide used for immediate energy release from a polysaccharide used for storage.
Lesson: 1A 3: Carbohydrates 2: Polysaccharides
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
A name is not a structure
1A · Thinking Bigger: TrehaloseFlyBase’s chemical entry identifies trehalose by its structure and links to chemical databases. Researchers need precise chemical identity when comparing experiments. For a food chemist, a familiar-sounding name…Specification 1.2(i) · 1.4Read & use the scienceClose article
Why this matters
FlyBase’s chemical entry identifies trehalose by its structure and links to chemical databases. Researchers need precise chemical identity when comparing experiments. For a food chemist, a familiar-sounding name is not enough to predict digestion. Two sugars can contain the same kinds of atom yet arrange their bonds differently. Whether a particular enzyme hydrolyses them depends on that arrangement and on its active site. Trehalose offers a useful unfamiliar case: apply the supplied structural evidence instead of guessing from an ending such as “-ose”. This is also why a claim about one sugar cannot automatically be transferred to every other sugar.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
Why is “a glucose-based sugar” too vague for a reproducible experiment?
Explore a possible response
It does not identify whether the sample is glucose, a particular disaccharide or a polymer, nor the linkages or concentration.
Explore the source
- FlyBase: trehaloseFlyBase
What are endurance athletes actually storing?
1A · Carbohydrates 2: PolysaccharidesCarbohydrate loading in endurance sport is about changing the availability of stored fuel, not filling muscles with a pool of free glucose. Research on exercise performance has investigated…Specification 1.2(i) · 1.2(ii) · 1.4Read & use the scienceClose article
Why this matters
Carbohydrate loading in endurance sport is about changing the availability of stored fuel, not filling muscles with a pool of free glucose. Research on exercise performance has investigated muscle glycogen and how its availability relates to prolonged activity. Glycogen is a branched polymer: storing many glucose units in large molecules reduces the number of freely dissolved particles compared with storing the same units separately. Its structure also provides many ends from which units can be mobilised. This explains why molecular architecture matters to a sporting practice, while leaving training, event length and individual responses as additional variables.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.2(ii) be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
Why would storing an equivalent number of glucose units as free glucose create a different osmotic problem from storing them as glycogen?
Explore a possible response
Many separate glucose molecules exert a larger effect on water potential than far fewer polymer molecules; more water would tend to enter. This is a qualitative comparison, not a claim that glycogen stores contain no water.