1.1 + 1.2 - Carbohydrates Flashcards
What is a monomer? (1)
- A monomer is a smaller/repeating unit/molecule from which larger molecules/polymers are made from
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar. (3)
- Heat with acid and neutralise
‘accept boil/water bath for heat’
‘accept named alkali for neutralise’
‘accept named examples eg HCl and NaHCO3’ - Heat with Benedict’s (solution)
- Red precipitate/colour
Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule. (2)
- Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers)
- Cellulose molecule has a straight chain and glycogen is branched
- Cellulose molecule has a straight chain and glycogen is coiled
- Glycogen has 1,4 and 1,6 glycosidic bonds and cellulose has only 1,4- glycosidic bonds
Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage molecule. (2)
- Insoluble in water, so doesn’t affect water potential
- Branched /coiled / (α-) helix, so makes molecule compact
- Branched/coiled / (α-) helix so can fit many (molecules) in a small area
- Polymer of (α-) glucose so provides glucose for respiration
- Branched/more ends for fast breakdown/enzyme action
- Large (molecule) so it can’t cross the cell membrane
Describe the structure of glycogen. (2)
- Polysaccharide of α-glucose
- Polymer of α-glucose
- Joined by glycosidic bonds / branched structure
Suggest how glycogen acts as a source of energy. (2)
- Hydrolysed to glucose
- Glucose used in respiration
Name the monomers from which a maltose molecule is made. (1)
- Glucose (and glucose)
Name the type of chemical bond that joins the two monomers to form maltose. (1)
- Glycosidic
Explain one way in which starch molecules are adapted for their function in plant cells. (2)
- Insoluble
- Don’t affect water potential
or - Helical
- Compact
or - Large molecule
- Cannot leave cell
Explain how cellulose molecules are adapted for their function in plant cells. (3)
- Long and straight chains
- Become linked together by many hydrogen bonds to form fibrils
- Provide strength (to cell wall)
Name the monomer present in
(i) Cellulose
(ii) Starch
- Cellulose = beta glucose
- Starch = alpha glucose
Cotton is a plant fibre used to make cloth. Explain how cellulose gives cotton it strength (2)
- The many hydrogen bonds found between the parallel chains of microfibrils
- Cellulose fibres and other molecules (eg. lignin) found in the cell wall form a matrix
A laboratory assistant added Benedict’s reagent to a solution of sucrose in a test tube and applied heat. Predict and explain the results. (1)
- No colour change because sucrose is a non-reducing / not a reducing sugar
List two similarities and two differences between the structures of starch and glycogen. (4)
Similarities:
- Both are made of the same monomer, alpha glucose
- Both are branched molecules
- Both contain 1,4 glycosidic bonds and 1,6 glycosidic bonds
Differences:
- Starch is made up of amylose and amylopectin polysaccharides
- Glycogen is more highly branched than starch (amylopectin)
- Glycogen has more terminal ends than starch
Glucose is converted into starch for storage within plant cells, describe the reaction that takes place for this to occur. (3)
- In a condensation reaction
- That forms glycosidic bonds (between monomers)
- Chains are formed with 1,4 links/bonds
- Branches are formed with 1,6 links/bonds
- Water is produced as a by-product
