carbohydrates

Question 1

state the elements present in carbohydrates

Answer 1

carbon, hydrogen, oxygen

Question 2

state the general formula of carbohydrates

Answer 2

Cx(H2O)y

Question 3

define the term monosaccharide

Answer 3

a monomer, or single unit, that makes a simple sugar

Question 4

define the term disaccharide

Answer 4

two monosaccharides joined together by a condensation reaction

Question 5

define the term polysaccharide

Answer 5

many monosaccharides joined together by a polymerisation reaction

Question 6

define the term pentose sugar

Answer 6

a monosaccharide containing 5 carbons

Question 7

define the term hexose sugar

Answer 7

a monosaccharide containing 6 carbons

Question 8

what is meant by a furanose ring?

Answer 8

a monosaccharide that forms a cyclic ring with 5 members

Question 9

what is meant by a pyranose ring?

Answer 9

a monosaccharide that forms a cyclic ring with 6 members

Question 10

define the term isomer

Answer 10

an isomer has the same chemical formula but a different structural formula and arrangement

Question 11

describe the difference between alpha and beta glucose

Answer 11

the same other than the arrangement of the OH and H group on carbon 1. alpha glucose has the OH group below the carbon whereas beta glucose has the OH above the carbon.
when alpha glucose forms a polysaccharide the chain is helix shaped, whereas beta glucose forms a straight chain.

Question 12

list the properties of ribose

Answer 12

carbons : 5
oxygens: 10
hydrogens: 5 
positioning of OH on carbon 1: above c 
solubility: soluble
polar: yes
hydroxyl groups: yes

Question 13

list the properties of alpha-glucose

Answer 13

carbons: 6
oxygens: 12
hydrogens: 6
positioning of OH on carbon 1: below c
solubility: soluble
polar: yes
hydroxyl groups: yes

Question 14

list three examples of disaccharides and the monomers they are composed of.

Answer 14

sucrose - alpha glucose and fructose
lactose - alpha glucose and galactose
maltose - 2 x alpha glucose

Question 15

state the properties and function of glucose

Answer 15

• small, soluble, a good source of energy, polar

- found in plant sap, human blood and most animal cells

Question 16

state the properties and function of fructose

Answer 16

• soluble, energy source, one of the smallest units

- found in fruits

Question 17

state the properties and function of galactose

Answer 17

• very stable in solution, very similar to glucose

- not normally found in large quantities but forms a part of milk

Question 18

state the properties and function of maltose

Answer 18

• formed by the breakdown of starch, made of two alpha glucose molecules
• found in intestines and germinating seeds

Question 19

state the properties and function of sucrose

Answer 19

• made from glucose and sucrose, good preservative

- found in sugar cane or beat

Question 20

state the properties and function of lactose

Answer 20

• made from glucose and galactase, the beta glycosidic bonds can cause lactose intolerance. difficult to hydrolyse - slow release of energy.
• found in milk

Question 21

describe how the hydrolysis of maltose occurs and why water is needed.

Answer 21

two alpha glucose units are broken at the glycosidic 1-4 bond. water is needed to complete the units of alpha glucose produced.

Question 22

explain why alpha glucose linking forms starch whereas beta glucose forms cellulose.

Answer 22

alpha glucose chains form helix shapes called amylose, alpha glucose also forms branches called amylopectin. these two elements form starch. However when beta glucose forms a chain it forms only straight lines, these are held together by hydrogen bonds to form cellulose microfibrils.

Question 23

name the two different polysaccharides that link together to form starch.

Answer 23

amylose and amylopectin

Question 24

explain why glycosidic bonds are called 1,4 or 1,6

Answer 24

they’re called 1,4 if they occur between carbon 1 of one monosaccharide and carbon 4 of another, and 1,6 when it’s between carbon 1 and carbon 6. you start counting the carbons from the very right carbon in the sugar.

Question 25

explain how to calculate the number of glycosidic bonds in a polysaccharide given the number of monosaccharides within it.

Answer 25

each monosaccharide forms 1 bond except the last one so the formula would be n-1

Question 26

what is the function of starch?

Answer 26

an energy storage product

Question 27

what is the function of cellulose?

Answer 27

structural support for plant cells in the form of the cell wall.

Question 28

what is the function of glycogen?

Answer 28

an energy storage product

Question 29

describe the structure of a cellulose fibre.

Answer 29

• made from straight chains of beta glucose
• the many chains are held together by hydrogen bonds
• chains clump to make microfibrils which in turn from macrofibrils which create cellulose fibres

Question 30

relate the structural properties of starch to its function.

Answer 30

• insoluble: stops the energy source from dissolving and affecting the water potential of the cell.
• small and compact size: lots of energy can be stored in a small area
• bonding: glucose molecules can be broken off from either end to get more energy.
• side chains: amylopectin forms many branches so more glucose molecules can be broken off at once from each chain.

Question 31

relate the structural properties of cellulose to its function.

Answer 31

• insoluble: it holds its shape and remains even in plants living under water.
• size: large with many chains forming a strong mesh
• bonding: resistant to hydrolysis
• no side chains

Question 32

relate the structural properties of glycogen to its function.

Answer 32

• insoluble: doesn’t dissolve/affect water potential. readily available as an energy source
• size: long chains but consists mostly of branches
• bonding: hydrolysed very rapidly due to the large number of side chains caused by many 1,6 glycosidic bonds.
• side chains: lots of side chains increase the number of ends for glucose to be taken off of during respiration.