3.1.2 monosaccharaids, disaccharides and polysaccharides

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A-Level Biology Flashcards on 3.1.2 monosaccharaids, disaccharides and polysaccharides , created by d s on 10/09/2015.

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Question Answer
Name the three types of carbohydrates: Monosaccharaides disaccharides Polysaccharides
Name three monosaccharaides: glucose, fructose and galactose.
What bond joins two monosaccharaides? Glycosidic bond
What does a-glucose look like?
What does b-glucose look like?
Which carbohydrates are reducing sugars? All monosaccharaides are reducing sugars and maltose (a disaccharide) is a reducing sugar.
What is a reducing sugar? A sugar that can donate an electron to another chemical.
What is the test for reducing sugars? Benedict's Test Benedict's reagent is added to the sample and heated. If a reducing sugar is present then a red precipitate of copper oxide is formed.
What happens when disaccharides are hydrolysed? They break the glycosidic bond and release their monomers.
Which two monomers make maltose? glucose + glucose = maltose
Which two monomers make sucrose? Glucose + fructose = sucrose
What two monomers make lactose? glucose + galactose = lactose
What is the test for non-reducing sugars? Add HCL to hydrolyse the disaccharides into their monomers. Then add Benedict's reagent - only maltose will form a red precipitate as it is the only reducing one.
What properties of polysaccharides make them useful for storage and structural purposes? large insoluble molecule
Where is starch found? In plants, often as microscopic grains.
Describe the structure of starch? Unbranched chain of a-glucose joined by glycosidic bonds. It forms a helix structure which makes it compact.
Which features of starch make it suitable as a storage molecule? *Insoluble-doesn't affect water potential *Large and insoluble- cannot diffuse across membranes. *Compact- a lot can be stored in a small space. *Easily converted back to a-glucose.
What is the test for starch? Iodine changes from yellow to blue-black.
Where is glycogen found? In animals and bacteria.
Where is glycogen often stored? In the liver and muscles.
Describe the structure of glycogen: Short chain of a-glucose with extensive branching
What features make glycogen suited to its role? *Insoluble: doesn't affect water potential *Compact *Highly branched: so enzymes easily attach and broken down into a-glucose quicker.
Where is cellulose found? In plant cell walls
Describe the structure of cellulose: Long, straight, unbranched chain of b-glucose that are parallel. Allowing hydrogen bonds to form between the chains. B-glucose is similar to a-glucose just the OH and H are inverted on the first carbon.
What is the function of cellulose in plants? Cellulose group to make microfibrils, these then group to from fibres, which reinforce strength.
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