1.2 carbohydrates

Question 1

3 groups

Answer 1

Monosaccharides - monomers from which larger carbohydrates are made

Disaccharides - formed by the condensation of 2 monosaccharides

Polysaccharides - formed by the condensation of many monosaccharides

Question 2

Monosaccharides and disaccharides

Answer 2

Simple carbohydrates (sugars)

Question 3

Monosaccharides

Answer 3

Monomers from which larger carbohydrates are made.

E.g. glucose, fructose and galactose

Question 4

Glucose + glucose

Glucose + fructose

Glucose + galactose

Answer 4

Maltose

Sucrose

Lactose

Question 5

Maltose

Sucrose

Lactose

Answer 5

Glucose + glucose

Glucose + fructose

Glucose + galactose

Question 6

Condensation reaction between 2 monosaccharides

Answer 6

Forms a glycosidic bond

Question 7

Isomer

Answer 7

Same molecular formula but differently arranged atoms

OH group is below C1 on a-glucose, but above C1 in b-glucose

Question 8

Polysaccharides

Answer 8

E.g. starch, glycogen and cellulose

Question 9

Glycogen

Answer 9

Used as energy store in animal cells

Polysaccharide of a-glucose with C1-C4 and C1-C6 glycosidic bonds so, branched

Question 10

Structure of glycogen related to function

Answer 10

Branched, can be rapidly hydrolysed to release glucose for respiration to provide energy

Large so can’t leave cell

Insoluble in water so water potential of cell isn’t affected

Question 11

Starch

Answer 11

Acts as energy store in plant cells

Polysaccharide of a-glucose

Mixture of amylose and amylopectin

Amylose has C1-C4 glycosidic bonds so in unbranched, whilst amylopectin has C1-C4 and C1-C6 glycosidic bonds so is branched

Question 12

Structure of starch related to function

Answer 12

Helical so compact for storage in cell

Large molecule so can’t leave cell

Insoluble in water so doesn’t affect water potential

Question 13

Cellulose

Answer 13

Provides strength and structural support to plant cell walls

Formed by condensation of B-glucose

Question 14

Structure of cellulose related to function

Answer 14

Every other beta-glucose molecule is inverted in a long, straight, unbranched chain

Many hydrogen bonds link parallel strands to form microfibrils

H bonds strong in high numbers

Provides strength and structural support to plant cell walls

Question 15

Test for reducing sugars

Answer 15

Benedicts test

1. Add benedicts reagent
2. Heat in a boiling water bath
3. Positive = green/yellow/orange/red

Question 16

Test for non-reducing sugars

Answer 16

Benedicts

1. Add a few drops of dilute HCl (hydrolysed sugar into its constituent reducing sugars)
2. Heat in a boiling water bath
3. Neutralise with sodium bicarbonate
4. Add benedicts reagent and heat again
5. Non-reducing sugar present = green/yellow/orange/red

Question 17

Reducing sugar

Answer 17

All monosaccharides e.g. glucose

Some disaccharides e.g. maltose/lactose

Question 18

Non-reducing sugar

Answer 18

No monosaccharides

Some disaccharides e.g. sucrose

Question 19

Determining glucose concentration

Answer 19

1. Perform a dilution series of glucose solutions of known concentrations
2. Perform benedicts test on each sample (heat with benedicts solution, use same amount of solution for each test, use excess benedicts, remove precipitate by filtering)
3. Using a colorimeter, measure absorbance of each sample and plot a calibration curve
4. Repeat with unknown sample (find absorbance), and use graph to determine glucose concentration

Question 20

Test for starch

Answer 20

Iodine test

1. Add iodine dissolved in potassium iodide to solution and shake/stir
2. Blue-black colour = present