Biology ISA: Glucose in Solutions

Carbohydrate Structure

Monosaccharides - Glucose, Fructose, Galactose
Basic monomer unit - sugar
Soluble, sweet-tasting
Formula = (CH2O)n

Disaccharides - Maltose, Sucrose, Lactose
Pair of monosaccharides joined by glycosidic bond
Glycosidic bond formed by removal of 1 molecule water
Can be separated into constituent monosaccharides by hydrolysis
Addition of 1 molecule water
O forms between OH and HO

Polysaccharides - Starch, Cellulose, Glycogen
Held together by glycosidic bonds, formed by condensation reactions
Large, insoluble, suitable for storage or support
Polymers

Test for Reducing Sugars (sugar that can donate electrons to another chemical)

• Place 2cm3 of liquid form of food sample in test tube (grind up with water if not)
• Add equal volume of Benedict's Reagent (alkaline solution of copper sulphate)
• Heat in a gently boiling water bath for five minutes
• Brick red precipitate of copper oxide should form

If there is a negative result and the solution remains blue...

Test for Non-Reducing Sugars (do not donate electrons)

• Place 2cm ground up food sample with 2cm dilute HCl acid
• This hydrolyses the disaccharide into its constituent monosaccharides
• Add sodium hydrogencarbonate to neutralise the solution as Benedict's does not work in alkaline conditions
• Test with pH paper 
• Re-test with Benedict's Reagent, add 2cm and heat for 5 minutes in a gently boiling waterbath
• If it now turns brick red, a non-reducing sugar is present

TEST = SEMI-QUANTITATIVE 

Relies on colour changes to estimate amount of reducing sugar in a sample

Absorption in the Small Intestine

Diffusion in Absorption

Net movement of molecules from high to low conc
Carbohydrates digested continually
Higher conc of glucose in SI than blood = concentration gradient
Blood constantly circulated = glucose absorbed, constantly removed by cells for respiration, maintains concentration gradient

Villi contract and relax muscles to mix SI contents
When glucose is absorbed from food adjacent to villi, new glucose-rich food replaces it
Maintains concentration gradient, allows diffusion to continue 

Villi

Finger-like projections in SI walls, thin walls with rich capillary network on one…