12.1 CARBOHYDRATES

Question 1

WHAT IA A MONOMER?

Answer 1

Small identical or similar molecules which can be condensed (joined or inked together) to make larger molecules called polymers

EXAMPLES- Amino Acids, Monosaccharides and nucleotides

Question 2

POLYMER

Answer 2

They are large molecules from joining many ( 3 or more) identical or similar monomers together.

EXAMPLES - DNA, RNA, starch and haemoglobin

Question 3

HOW A BOND IS FORM?

Answer 3

A condensation reaction joins the 2 molecules together with the formation of a chemical bond and involves the elimination of a molecule of water. This is catalysed by an enzyme. H2O is removed.

Question 4

common monosaccharides

Answer 4

glucose, galactose and fructose

Question 5

Disaccharides and example

Answer 5

Disaccharides (dimer) are formed by condensation of 2 monosaccharides
Eg. Maltose, Lactose
and Sucrose

Question 6

Maltose

Answer 6

2 Alpha glucose

Question 7

Lactose

Answer 7

Alpha glucose + Galactose

Question 8

Sucrose

Answer 8

Alpha Glucose + Fructose

Question 9

condensation equation

Answer 9

C6H12O6 + C6H12O6 ——→ C12H22O11 + H2O

Question 10

Reducing sugar test

Answer 10

Add (equal volume/ 2cm^3) Benedict’s solution and heat

A coloured changed from Blue to green/yellow/orange/red
precipitate indicates the presence of a reducing sugar If there is NO CHANGE in colour there could be a non-reducing sugar present.

Question 11

Describe how a student would show the of reducing sugars were present in solution

Answer 11

Add equal volumes of Benedict’s solution;

Heat to 95°C

Red/orange/
yellow/green precipitate (shows reducing sugar is present)

Question 12

Non-reducing sugar test

Answer 12

1. Heat a sample with acid for a few minutes to hydrolyse the glycosidic bond then neutralise the solution with an alkali. Acid = HCL Alkali = Sodium hydrogen carbonate
2. Heat again with Benedict’s reagent
3. Brick red precipitate shows a positive result ( for non resulting sugar)

Question 13

Unknown conc of sugars

Answer 13

Benedict test (semi-quantitive) test for sugars as it only gives you an idea if sugars are present due to the colours but not the concentration.

colorimeter is quantitive as it measures that intensity of light passing through the solution/sample.

Increasing the amount of sugars increase the mass of the precipitate.

Question 14

Standardising the method

Answer 14

Samples should always be shaken before testing

Zero the colorimeter before use (with a control)

Use the same filter throughout

Use same volume for each reading

Question 15

TO DETERMINE CONC OF UNKNOWN SOLUTION

Answer 15

Make up several known conc of maltose/ glucose/ maltose/ lactose/ fructose

Carry out the Benedict’s test on each sample

Take readings of absorbance/transmission using a colorimeter

Plot readings to produce a graph called a calibration curve with

X axis —> concentration of named sugar/ mol dm-3

Y axis ^^ absorbance/transmission /

AU/%

Draw the line of best fit

Question 16

TRiglycerides

Answer 16

• Make from one molecule of glycerol to 3 fatty acids joined by ester bonds.
• It’s not a polymer as it’s not make from the same/similar monomers.
• They are commonly found in food
• Conducts heat slowly
• Stored around delicate organs to protect them

Question 17

Saturated

Answer 17

fatty acids don’t have double bonds between carbon atoms within the hydrocarbon chain.

Question 18

Unsaturated

Answer 18

fatty acids have double bonds between carbon atoms within the hydrocarbon chain.

Question 19

Test for lipids

Answer 19

1. Crush/grind sample (if needed)
2. Mix with ethanol and shake
3. Then add water
4. Forms a cloudy white emulsion if lipid is present.

Question 20

PHOSPHOLIPIDS

Answer 20

Similar to triglycerides but one of the fatty acids is replaced by a phosphate group

The tails are 2 fatty acid tails - non-polar (no charge) and hydrophobic (hate water)

The phosphate group (PO4^3-) is hydrophilic , is polar and has a negative charge

Question 21

STARCH

Answer 21

1:4 and 1:6 glycosidic bonds

Branched chain of alpha glucose/coiled into a helix

Structure is compact so it’s good for storage and it takes up less space

Insoluble so it doesn’t affect water potential (osmosis)

LARGE so it’s doesn’t diffuse out of cell

Provides a large surface area for rapid hydrolysis and respiration

Question 22

GLYCOGEN

Answer 22

ONLY FOUND IN ANIMAL CELLS

similar to starch but:

• it has shorter chains
• More highly branched
• Larger surface area

Stored in muscles and liver

short chains lead to glycogen to be more rapidly hydrolysed into glucose for respiration

Animals require glycogen to be hydrolysed into glucose faster than plants can hydrolyse starch

It’s insoluble like starch

Question 23

CELLULOSE

Answer 23

Beta glucose are joined through condensation And are flipped 180 degrees one after each one AND FORM 1-4 B-GLYCOSIDIC BONDS

They form long straight unbranched chains

Form microfibrils or macro-fibrils which provide support and strength to place cells as the cell wall are made from cellulose.

Formed by many weak hydrogen bonds between OH groups and adjacent H from another unbranched cellulose molecules to form microfibrils/ macro-fibrils.

Question 24

Why starch has a spiral shape? Why is it’s shape important for its function in cells.

Answer 24

It is compact/occupies small space/ tightly packed

Question 25

Explain one way in which starch molecules are adapted for their function in plant cells

Answer 25

1. It’s insoluble so doesn’t affect water potential
2. Helical SO COMPACT
3. Large so molecules can’t leave cell