Carbs And Lipids

Question 1

Give 4 ways in which the structure of starch is similar to cellulose

Answer 1

• Both are polymers
• Both contain carbon hydrogen and oxygen
• Both contain glycosidic bonds
• Both have 1-4 links

Question 2

Give ways in which the structure of starch is different to cellulose

Answer 2

• Starch contains A-glucose, has 1-6 bonds, branched chains, glucose monomers are the same way up, No H-bonds between molecules, no microfibrils

WHEREAS

• Cellulose has B-glucose, no 1-6 bonds, unbranched chains, every other B-glucose monomer is inverted, has microfibrils, has H-bonds between molecules

Question 3

Other than energy storage, state two advantages to a mammal of having fat in its tissues

Answer 3

• Insulation
• Protection of organs

Question 4

Cotton is a plant fibre used to make cloth Explain how cellulose gives cotton its strength

Answer 4

• Many hydrogen bonds form between cellulose molecules to form microfibrils
• cellulose fibres and other molecules form a matrix

Question 5

Similarities and differences between structures of starch and glycogen

Answer 5

SIMILARITIES
• Both are made of Alpha-glucose
• Both are branched molecules
• Both have 1,4 glycosidic bonds and 1,6 glycosidic bonds

DIFFERENCES
• Glycogen more highly branched
• Starch made up of amylose and amylopectin polysaccharides

Question 6

Describe how the student could separate a mixture of monosaccharides in solution

Answer 6

•Paper chromatography
• A spot of the solution is placed on chromatography paper and the paper is suspended in a solvent
• Larger molecules will move slower on the paper
• The original mixture to separate out into different spot/bands

Question 7

Colorimeter would be used over a comparison done by eye to eye because

Answer 7

• Because it provides a quantitative measurement

Question 8

Advantages of storing food as starch rather than sugar are

Answer 8

• Starch is compact
• Starch is insoluble so doesn’t affect water potential
• Starch is easily broken down when needed

Question 9

What does qualitative mean?

Answer 9

The test shoes the presence of the sample, not how much sample is present

Question 10

Define the term unsaturated fatty acid (3)

Answer 10

• Long hydrocarbon chains
• With a carboxylic group
• At least 1 carbon to carbon double bond within the hydrocarbon chain

Question 11

Using your knowledge of the structure of triglycerides, explain why the solution goes cloudy

Answer 11

• Triglycerides are non-polar molecules
• Therefore they are hydrophobic molecules
• Triglycerides form micelles in water,which causes the cloudy appearance

Question 12

Phospholipids can form cell membranes because

Answer 12

• Phospholipids have a polar head group/phosphate group
• Phosphate group can form hydrogen bonds with water
• Fatty acids are hidden from water
• Phospholipids form a bilayer

Question 13

Describe and explain the function of micelles

Answer 13

STRUCTURE
• spherical arrangement of phospholipids in water
• Hydrophilic heads around the edge/hydrophobic tails in the middle
FUNCTION
• aft as emulsifiers
• can transport hydrophilic or hydrophobic contents across membranes

Question 14

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.

Answer 14

Compact/occupies small space/tightly packed;

Question 15

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

Answer 15

1. Insoluble;
2. Don’t affect water potential;
   OR
3. Helical;
   Accept form spirals
4. Compact;
   OR
5. Large molecule;
6. Cannot leave cell.

Question 16

The structure of cellulose is related to its role in plant cell walls. Explain how

Answer 16

Long/straight/unbranched chains of b-glucose
(Joined by) hydrogen bonds;
Form (micro)fibrils/(macro)fibrils;
Provide rigidity/strength/support;

Question 17

Hydrogen bonds are important in cellulose molecules. Explain why

Answer 17

1. Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
2. Providing strength/rigidity (to cellulose/cell wall);
3. Hydrogen bonds strong in large numbers;

Question 18

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

Answer 18

1. Add Benedict’s;
2. Heat;
3. Red/orange/yellow/green
   (shows reducing sugar
   present);

Question 19

Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.

Answer 19

1) Lactose has a different shape / structure;
2) Does not fit / bind to active site of enzyme / sucrase;

Question 20

Describe how a triglyceride is formed

Answer 20

One glycerol and 3 fatty acids
Condensation reactions and removal of 3 water molecules
ester bonds formed

Question 21

Explain how digestion of starch in the gut (small intestine) leads to an increase in the concentration of glucose in the blood. Details of co-transport are not required.

Answer 21

Hydrolysed by enzymes / hydrolysed by amylase / maltase;

If named enzyme given, it must relate to the correct substrate

2. Produces glucose (in the gut);
3. Small enough to cross the gut wall (into the blood) / monomers / monosaccharides (can) cross the gut wall (into the blood);

Accept cell membranes / epithelium / cells for ‘gut wall’

Question 22

Suggest a method you could use to estimate the concentration of glucose in several different solutions that all turned brick red with Benedict’s reagent in 3 minutes.

Answer 22

time how long it took to go brick red
weigh precipitate
dilute glucose samples

Question 23

Describe how structure of glycogen is related to its function

Answer 23

Helical so compact
Polymer of glucose so easily hydrolysed
Branched so larger SA so more ends for faster hydrolysis
Insoluble so doesn’t affect water potential

Question 24

Suggest a method other than colorimetry that can be used to measure quantity of reducing sugar in solution

Answer 24

Filter and dry precipitate
Find mass

Question 25

Use of a colorimeter improves repeatability of the results. Why

Answer 25

Quantitive
Standardises the method

Question 26

Arrangement of phospholipids in cell surface membrane

Answer 26

Bilayer
Hydrophobic fatty acid tails point away from water
Hydrophilic phosphate heads attracted to water

Question 27

Describe how ester bond is formed in a phospholipid molecule

Answer 27

Condensation reaction between glycerol and fatty acid.

Question 28

State and explain a property of water that helps to prevent temperature increase

Answer 28

High specific heat capacity
Buffers changes in temperature

Question 29

Test for presence of a lipid

Answer 29

Crush grind sample
Add ethanol and shake then add water and shake
White milky emulsion

Question 30

Give one similarity and 2 differences between the membrane structure shown and fluid-mosaic

Answer 30

Both have phospholipid bilayer
Both have proteins

DIFFERENCES
No channel proteins whereas fluid mosaic does
Cholesterol not present whereas present in fluid mosaic