(3.1.2) carbohydrates

Question 1

what are carbohydrates?

Answer 1

molecules composed of carbon, hydrogen and oxygen.

Question 2

what are monosaccharides?

Answer 2

monosaccharides are the monomers from which larger carbohydrates are made.

Question 3

what are examples of monosaccharides?

Answer 3

glucose, galactose and fructose.

Question 4

what are isomers?

Answer 4

molecules with the same chemical formula but different arrangement of atoms and different properties.

(e.g. glucose has alpha-glucose and beta-glucose)

Question 5

how are disaccharides formed?

Answer 5

by two monosaccharides chemically joined together by a condensation reaction, forming a glycosidic bond between the hydroxyl groups.

Question 6

how can disaccharides break up?

Answer 6

by undergoing a hydrolysis reaction, which breaks the glycosidic bond and restores the original monosaccharides.

Question 7

what are examples of disaccharides?

Answer 7

• maltose (two alpha-glucose)
• sucrose (glucose + fructose)
• lactose (glucose + galactose)

Question 8

what are polysaccharides?

Answer 8

long, complex carbohydrates made of many monosaccharides chemically linked together by condensation reactions.

Question 9

what are examples of polysaccharides?

Answer 9

• glycogen, starch (alpha-glucose polymers)
• cellulose (straight-chained beta-glucose polymer).

Question 10

what are properties of glycogen?

Answer 10

• larger number of side branches providing lots of ends which can be easily hydrolysed to release glucose for respiration
• large and compact which maximises the amount of energy stored, and won’t affect the cell water potential

Question 11

what are properties of starch?

Answer 11

• amylose is coiled which makes it very compact for more energy to be stored
• amylopectin is branched which provides lots of ends which can be easily hydrolysed to release glucose for respiration
• large + insoluble so it will not affect cell water potential

Question 12

what are properties of cellulose?

Answer 12

• microfibrils held by hydrogen bonds which form strong cross linkages to provide strength to structure
• exerts inward pressure that stops the inflex of water, keeping cells rigid to maximise surface area for photosynthesis

Question 13

how do you test for reducing sugars?

Answer 13

1. add excess benedict’s to the test solution
2. boil the mixture

blue > green/yellow/orange/red (if reducing sugar is present)

Question 14

how do you test for non-reducing sugars?

Answer 14

1. need a negative result for reducing sugars
2. add hydrochloric acid and heat
3. neutralise the acid with sodium hydroxide
4. add benedict’s regent and boil

red precipitate if non-reducing sugar is initially present