3.3 Carbohydrates

Question 1

Name the elements found in carbohydrates

Answer 1

C, H and O

Question 2

Describe the properties of alpha glucose

Answer 2

• small and water soluble - easily transported in the bloodstream
• complimentary shape to antiport for co- transport for absorption in gut
• complimentary shape to enzymes for glycolysis - respiratory substrate

Question 3

What type of bond forms when monosaccharides react?

Answer 3

1,4 or 1,6 glycosidic bonds
• 2 monomers = 1 chemical bond = disaccharide
• multiple monomers = many chemical bonds = polysaccharides

Question 4

Name 3 disaccharides and how they form

Answer 4

• Maltose : glucose + glucose
• sucrose : glucose + fructose
• lactose : glucose + galactose
all have the molecular formula C12H22O11

Question 5

Describe the structure and functions of starch

Answer 5

• storage polymer of alpha glucose
• insoluble = no osmotic effect on cells
• large = does not diffuse out of cells
• made from amylose
- 1,4 glycosidic bonds
- helix with intermolecular H- bonds = compact
• also made from amylopectin
- 1,4 and 1,6 glycosidic bonds
- branches = many terminal ends for hydrolysis into glucose

Question 6

Describe the structure and functions of glycogen

Answer 6

• main storage polymer of alpha glucose in animal cells
• 1,4 glycosidic & 1,6 glycosidic bonds
• branched = many terminal ends for hydrolysis
• insoluble = no osmotic effect and does not diffuse out of cells
• compact

Question 7

Describe the structure and functions of cellulose

Answer 7

• polymer of beta glucose gives rigidity to plant cell walls - prevents bursting under tugor pressure, holds stem up
• 1,4 glycosidic bonds
• straight chain , unbranched molecule
• alternate glucose molecules are rotated 180°
• H- bond cross links between parallel strands form microfibrils - high tensile strength
• due to inversion of beta glucose molecules- many hydrogen bonds form between the long chains giving cellulose its strength

Question 8

How do triglycerides form?

Answer 8

Condensation reaction between 1 molecule of glycerol and 3 fatty acids which forms ester bonds

Question 9

Name the features of saturated fatty acids

Answer 9

• contain only single bonds
• straight chain molecules have many contact points
• higher melting points = solid at room temperature
• found in animal fats

Question 10

Name the features of unsaturated fatty acids

Answer 10

• contain C= C double bonds
• lower melting points = liquid at room temperature
• found in plant oils

Question 11

Relate the structure of triglycerides to their functions

Answer 11

• high energy: mass ratio = high calorific value from oxidation ( energy storage )
• insoluble hydrocarbon chain = no effect on water potential of cells and used for water proofing
• slow conductor of heat = thermal insulation
• less dense than water

Question 12

Why does cellulose have high tensile strength?

Answer 12

Allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure

Question 13

What do the cellulose fibres help with?

Answer 13

The fibres and other molecules eg. Lignin found in the cell wall forms a matrix which increases the strength of the cell walls

Question 14

Are cellulose fibres permeable , if yes explain why ?

Answer 14

Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane

Question 15

Where in the body is there a high concentration of glycogen?

Answer 15

Liver and muscle cells have a high concentration of glycogen present as visible granules as the cellular respiration rate is high in these cells

Question 16

How is starch stored in plants?

Answer 16

•Starch is the storage polysaccharide of plants
• it’s stored as granules in plastids such as amylopasts and chloroplasts
• plastids are membrane bound organelles they are found in plant cells

Question 17

How are disaccharides and polysaccharides formed?

Answer 17

When two hydroxyl groups ( OH ) on different saccharides interact to form a strong covalent bond called a glycosidic bond

Question 18

How is a glycosidic bond broken?

Answer 18

•when water is added in hydrolysis
• disaccharides and polysaccharides are broken down in hydrolysis reactions

Question 19

What is a condensation reaction?

Answer 19

When two molecules join together via the formation of a new chemical bond with a molecule of water being released in the process

Question 20

Why does the fact that starch is insoluble in water make good for storage ?

Answer 20

As starch is insoluble it doesn’t cause water to enter the cells via osmosis which would make them swell up - this makes it good for storage