T1: Carbohydrates and Food tests

Question 1

what is a carbohydrate?

Answer 1

made from C,H,O
many monosaccharides joined together

Question 2

common monosaccharides

Answer 2

glucose, galactose, fructose

Question 3

what makes maltose?

Answer 3

glucose and glucose

Question 4

what makes lactose?

Answer 4

glucose and galactose

Question 5

what makes sucrose?

Answer 5

glucose and fructose

Question 6

common disaccharides

Answer 6

maltose, lactose, sucrose

formed by the condensation of 2 monosaccharides forming a glycosidic bond

Question 7

define polysaccharide

Answer 7

polymer formed by the condensation of more than two monosaccharides

e:g starch,glycogen and cellulose

Question 8

polysaccharide(s) of alpha glucose

Answer 8

starch and glycogen

Question 9

polysaccharide of beta glucose

Answer 9

cellulose

Question 10

two isomers of glucose are…

Answer 10

alpha glucose + beta glucose

ABBA
alpha has OH below
beta has OH above

Question 11

how to draw glucose

Answer 11

hexagonal shape with overlapping lines
H then HO on left
O in top right of hexagon

Question 12

what is starch made from?

Answer 12

two polysaccharides of alpha glucose
amylose + amylopectin

Question 13

describe amylose

Answer 13

long unbranched chain with alpha 1,4 glycosidic bonds

the angles of the glycosidic bonds give it a coiled structure SO its compact for energy storage

Question 14

describe amylopectin

Answer 14

branched chain of alpha glucose with many side branches
has both alpha 1,4 AND 1,6 glycosidic bonds

side branches allow enzymes to hydrolyse the glycosidic bonds easily SO glucose can be released quickly

Question 15

starch structure and function

Answer 15

large insoluble molecule SO osmotically inactive

large molecule SO cant cross the cell surface membrane and leave the cell

coiled AND branched SO compact for energy storage

branched SO glucose is easily hydrolysed for respiration

Question 16

describe glycogen

Answer 16

many branches but NOT coiled
has more branches than amylopectin

many branches so fast release of glucose + compact

Question 17

describe cellulose

Answer 17

long unbranched chains of beta glucose linked by hydrogen bonds to form microfibrils

Question 18

cellulose structure and function

Answer 18

long straight chains of beta glucose FORM strong microfibrils (provide support for cells)

hydrogen bonding between chains provides rigidity and strength

Question 19

what does cellulose do in plant cell walls?

Answer 19

prevents them from bursting when water enters by osmosis

Question 20

what are the colour changes for Benedicts test for sugars?

Answer 20

blue
green
yellow
orange
brick red

traffic lights + blue n yelllow

Question 21

what are the reducing sugars?

Answer 21

galactose
fructose
maltose
glucose

Question 22

describe Benedicts test for reducing sugars

Answer 22

add Benedicts reagent to sample
heat in a boiling water bath for 5 minutes
if +ve colored ppt forms

Question 23

what are the non reducing sugar(s)?

Answer 23

sucrose

Question 24

describe Benedicts test for non reducing sugars

Answer 24

get new sample + add HCl
heat in a boiling water bath for 5 minutes
neutralise by adding alkali
add Benedicts reagent and heat again

if +ve colored ppt forms
if stays blue no sugars are present

Question 25

describe the starch test

Answer 25

add a few drops of iodine in KI

if +ve then orange to blue/black

Question 26

describe the Biuret test for proteins

Answer 26

add a few drops of NaOH (makes sol alkaline)
add some copper (II) sulfate solution

if +ve blue to lilac

Question 27

describe the lipid test

Answer 27

grind food sample
add ethanol AND shake
add mix to water

if +ve a milky emulsion forms