carbohydrates

Question 1

general formula of carbohydrates?

Answer 1

Cₓ(H₂O)ᵧ

Question 2

substances that make up carbohydrates

Answer 2

• carbon
• hydrogen
• oxygen

Question 3

definition of monosaccharide

Answer 3

a carbohydrate that cannot be hydrolysed to a simpler carbohydrate

Question 4

general formula of monosaccharide

Answer 4

(CH₂O)ₙ
C6H12O6

Question 5

examples of monosaccharides

Answer 5

• glucose
• fructose
• galactose

Question 6

definition of disaccharide

Answer 6

formed by a condesation reaction between two monosaccharides - one molecule of water is removed from the pair of monosaccharides

Question 7

examples of dissacharides

Answer 7

• maltose - glucose + glucose
• sucrose - glucose + fructose
• lactose - glucose + galactose

Question 8

bond formed between two monosaccharides / bond in disaccharide

Answer 8

glycosidic bond

Question 9

what processes form and breaks glycosidic bonds?

Answer 9

forms - condensation (removes a water molecule)
breaks - hydrolysis (adds a water molecule)

Question 10

definition of polysaccharide

Answer 10

polymer of monosaccharides

Question 11

examples of polysaccharides

Answer 11

• starch - storage polysaccharide in plants
• glycogen - storage polysaccharide in humans
• cellulose - structural polysaccharide in plants

Question 12

formula for starch

Answer 12

C6H12O6 (glucose) - H2O (condensation) =
(C6H10O5)

Question 13

structure of starch

Answer 13

• polymer of glucose
• two components : amylose and amylopectin

Question 14

details of amylose

Answer 14

• straight chain structure with helical shape
• several thousand glucose unit joined by glycosidic bonds

Question 15

details of amylopectin

Answer 15

• compact with highly branched structure
• twice as many glucsose units as amylose.

Question 16

functions of carbohydrates

Answer 16

1] source of energy

2] sucrose is a good transport sugar in the phloem of plants
* very soluble
* chemically unreactive

3] polysaccharides (starch and glycogen) are good storage molecules
* large and insoluble
* compact shapes
* easily hydrolysed into monosaccharides

4] cellulose is a good structural polysaccharide
* good tensile strength
* permeable

5] monosaccharides needed to synthesise:
* dissacharides and polysaccharides
* nucleic acids (RNA, DNA)

Question 17

test for reducing sugars

Answer 17

Benedict’s Test
1. To 2cm³ of the test sample in a test tube, add an equal volume of Benedict’s solution
2. Mix well and place in a boiling water bath for 2 minutes
3. Observe any color change

present: turns green, yellow, brown, red
absent: remains blue

Question 18

test for non reducing sugar

Answer 18

1. To 2cm³ of the test sample in the test tube, add a few drops of HCl.
2. Heat the mixture for 2 mins in a hot water bath
3. After 2 minutes, neutralise the acid by adding sodium hydrogen carbonate until effervescence stops.
4. Carry out Benedict’s test
5. Test will now turn out to be positive as non reducing sugar is broken down into reducing sugars.

Question 19

test for starch

Answer 19

1. Add a few drops of iodine solution to the test sample in a test tube or white tile
2. observe any color change.

present: dark blue
absent: remains brown.