Carbohydrates

Question 1

Functions of carbohydrates

Answer 1

Energy source (eg. glucose)
Store of energy (eg. starch and glycogen)
Structural units (eg. cellulose in plants and chitin in insects)

Question 2

Glycosidic bond

Answer 2

A bond formed by two monosaccharides via condensation reaction

Question 3

Monosaccharides

Answer 3

Have a backbone of single bonded carbon atoms, with one double bonded with oxygen to form a carbonyl group

Question 4

General formula of a monosaccharide

Answer 4

(CH2O)n ->where n is a number between 3 and 7

Question 5

Draw the structure of a beta glucose

Question 6

Draw the structure of a alpha glucose molecule

Question 7

Draw the structure of ribose

Question 8

Draw the structure of deoxyribose

Question 9

Hexose sugars

Answer 9

Alpha and beta glucose
have 6 carbon atoms

Question 10

Pentose sugars

Answer 10

ribose and deoxyribose
have 5 carbon atoms

Question 11

Maltose equation

Answer 11

α-glucose + α-glucose

Question 12

Sucrose equation

Answer 12

α-glucose + fructose

Question 13

Lactose equation

Answer 13

α-glucose + β-galactose

Question 14

Cellobiose equation

Answer 14

β-glucose + β-glucose

Question 15

What happens when the α/β-glucose joins to form disaccharides

Answer 15

A condensation reaction occurs to form a glycosidic bond. 2 hydroxyl (-OH) groups line up next to each other and a water molecule is removed, leaving an oxygen atom as a link

Question 16

How are disaccharides broken into monosaccharides

Answer 16

Hydrolysis
Water provides a hydroxyl group (-OH) and hydrogen group (H), helping glycosidic bonds to break

Question 17

Homopolysaccharides

Answer 17

Polysaccharides made solely of one type of monosaccharide (eg strach)

Question 18

Heteropolysaccharide

Answer 18

Polysaccharides made up of more than one type of monomer (eg hyaluronic acid)

Question 19

Where do plants store energy

Answer 19

starch in chloroplasts and membrane bound starch grains

Question 20

where do humans store energy

Answer 20

glycogen in liver and muscle cells

Question 21

Why does starch and glycogen act as good stores of monosaccharides

Answer 21

-> compact- don’t occupy a large amount of space and are dense
-> hold glucose molecules in chains which can easily be ‘snipped off,’ by hydrolysis for respiration
-> branched (amylose)/unbranched (amylopectin and glycogen) chains- branched chains are more compact so many glucose molecules can be snipped off by hydrolysis when lots of energy is required quickly

Question 22

Structure of Amylose (plants)

long chain of α-glucose molecules with 1,4 glycosidic bonds

Answer 22

coils into spiral shape, held in shape by Hydrogen bonds
Hydroxyl groups are placed inside coil, making molecule less soluble

Question 23

Structure of amylopectin (plants)

Glycosidic bonds between carbons 1-4 and additional branches of 1-6 bonds -> alpha glucose

Answer 23

Coils into spiral shape held together by hydrogen bonds
Has branches emerging from spiral

Question 24

Structure of Glycogen (animals)

Glycosidic bonds between carbons 1-4, branches formed by 1-6 bonds -> alpha glucose

Answer 24

1-4 bonded chain is smaller than amylopectin
less tendency to coil
more branches, more compact
easier to remove monomer units

Question 25

Cellulose

Answer 25

Tough, insoluble, fibrous substance homopolysaccharide made up of long chains of β-glucose molecules, bonded through condensation to form glycosidic bonds

Question 26

Structure of cellulose

Question 27

How are cell walls formed

Answer 27

60-70 cellulose chains bind to form microfibils, which bundle to form macrofibils with up to 400 microfibils- these are embedded in pectins to form cell walls

Question 28

Why are β-glucose molecules flipped 180 degrees in cellulose chains

Answer 28

To prevent the chains from spiralling allow formation of hydrogen bonds which improves strength and stability

Question 29

Benefits of cellulose for cell walls

Answer 29

-> Macrofibils + microfibils have high tensile strength due to (H) bonds between chains +strong glycosidic bonds -> macrofibils run in all directions, criss-crossing for extra strength -> Glycosidic bonds are less easy to break -> space between macrofibils for water and mineral ions to pass through cell makes cell wall fully permeable

Question 30

Cell wall functions

Answer 30

-> High tensile strength prevents plant cells from bursting when turgid, protecting the cell membrane -> Macrofibil structure can be reinforced for extra support/to make the walls waterproof