Year 12 - Carbs and Lipids

Question 1

Explain 3 ways starch molecules are adapted for their function in plant cells.

Answer 1

• Insoluble so doesn’t impact water potential
• Helical so compact
• Large molecule so can’t leave the cell

Question 2

Describe how the structure of glycogen is related to its function.

Answer 2

• Helical so compact
• Polymer of glucose so easily hydrolysed
• Branched so more ends for faster hydrolysis
• Glucose so provides respiratory substrates for energy
• Insoluble so does not impact water potential

Question 3

Explain how the structure of cellulose relates to its function

Answer 3

• Long straight unbranched chains of beta glucose
• Joined by H bonds
• Form microfibrils
• Many weak H bonds strong in large numbers
• Provides strength to the cell wall

Question 4

Compare and contrast the structure and properties of triglycerides and phospholipids.

Answer 4

• Both contain ester bonds
• Both contain glycerol
• Fatty acids on both may be saturated or unsaturated
• Both insoluble in water
• Both contain C, H and O whereas phospholipds contain P
• Triglycerides have 3 fatty acids whereas Phospholipids have 2 fatty acids and a phosphate group
• Triglycerides are hydrophobic whereas fatty acids have hydrophobic and hydrophillic regions.
• Phosolipids form micelles whereas triglycerides don’t

Question 5

How do you make a calibration curve for a reducing sugar and use it to find an unknown concentration?

Answer 5

• Make several known concentration of name sugar
• Carry out benedicts test on each sample
• Use colorimeter to measure absorbance of light in each sample
• Plot calibration curve with concentration on X axis and absorbance on Y axis
• Find the concentration of unknown using the calibration curve

Question 6

What is a monomer?

Answer 6

Monomers are small identical or similar molecules which can be condensed to make larger molecules called polymers.

Question 7

What is a polymer?

Answer 7

Polymers are large molecules made from condensing 3 or more​
identical or similar monomers together.

Question 8

What is an unsaturated fatty acid

Answer 8

Has double bonds in C chain

Question 9

Why do phospholipids form a bilayer but triglycerides do not

Answer 9

• Phospholipid has two hydrophobic fatty acid tails and a hydrophilic phosphate head ​
• Triglycerides have three hydrophobic fatty acid tails only. ​
• The hydrophilic phosphate group on phospholipids attracts water to either side of the bilayer.

Question 10

Describe the emulsion test

Answer 10

• Crush sample to release lipid
• Add ethanol and shake
• Add water and shake
• Forms a cloudy white emulsion (if present)