Carbohydrates and Lipids

Question 1

Monomers

Answer 1

Small units from which larger molecules are made. They are condensed to form polymers.

Question 2

Polymers

Answer 2

Large molecules made by joining 3 or more identical monomers together

Question 3

Carbohydrates are…

Answer 3

organic molecules which are a source of energy and storage

Question 4

Structure of carbohydrates

Answer 4

Carbon, hydrogen, oxygen in a 1:2:1 ratio

Question 5

Generic formula of carbohydrates

Answer 5

(CH2O)n where n = 3 to 6

Question 6

Monosaccharides

Answer 6

Single sugar monomers joined together. They are the simplest carbohydrates

Question 7

Examples of monosaccharides

Answer 7

glucose, fructose, galactose

Question 8

Why is glucose an important sugar?

Answer 8

It is the building block of larger carbohydrates and main source of energy in respiration

Question 9

Isomers

Answer 9

Molecules that have the same chemical formula but a different structure so the atoms are arranged differently in space

Question 10

Amylose structure and function

Answer 10

(1-4) glycosidic bond which forms long and straight chains of alpha glucose molecules which coil into a helix. This makes the structure compact which means it is good for storage

Question 11

Amylopectin structure and function

Answer 11

Branched chains of alpha glucose molecules.
(1-4) and (1-6) glycosidic bond which provides a large surface area for rapid hydrolysis by enzymes to release glucose for respiration

Question 12

Amylose and amylopectin structure and function

Answer 12

Both are insoluble so doesn’t affect water potential
Both are large which means water cannot diffuse out of cells

Question 13

Glycogen

Answer 13

Found in cells with a high metabolic rate. So in the liver and muscle of animals

Question 14

How is glycogen similar to starch?

Answer 14

Both are insoluble so doesn’t affect water potential or diffuse out of cells

Question 15

How is glycogen different from starch?

Answer 15

Glycogen is more highly branched so release of energy is faster. Glycogen has shorter chains so more rapidly hydrolysed into glucose used in respiration.

Question 16

Why is it important that glucose is rapidly hydrolysed?

Answer 16

Because animals require glycogen being more rapidly hydrolysed into glucose used in respiration as animals do a lot of activities which require more energy

Question 17

Cellulose

Answer 17

Found in plant cell walls and stops the plant cell from bursting when too much water enters by osmosis - makes the cell turgid.

Question 18

Structure of cellulose

Answer 18

Long, straight unbranched chains of beta glucose molecules joined together by condensation reactions. The chains are held together by many weak hydrogen bonds which form cross-links.

Question 19

What happens when cross-links are formed in between chains of cellulose?

Answer 19

The cross-links form microfibrils which are further wound together to form cellulose fibres. This provides strength and it means the cell can resist osmotic pressure and the bonds are difficult to break

Question 20

What happens to every other beta glucose molecule in cellulose?

Answer 20

It rotates horizontally (inverted) 180 degrees

Question 21

Lipids

Answer 21

organic molecules made up of carbon, hydrogen, and oxygen, but unlike carbohydrates, they will not dissolve in water

Question 22

Two types of lipids

Answer 22

triglycerides and phospholipids

Question 23

Triglycerides

Answer 23

Commonly found in food and good source of energy

Question 24

Phospholipids

Answer 24

help to form cell membrane of a cell

Question 25

Structure of a triglyceride

Answer 25

one glycerol molecule and three fatty acids
condensation reaction between glycerol and fatty acid forms an ester bond
can contain saturated and unsaturated fatty acids

Question 26

Why are triglycerides not polymers?

Answer 26

This is because they are not made of the same/similar monomers

Question 27

Triglycerides function

Answer 27

Good stores of energy
Insoluble so storing them does not affect water potential of a cell
High hydrogen to oxygen ratio meaning they are a good source of water when broken down
commonly known as fats and oils

Question 28

Phospholipid structure

Answer 28

One glycerol molecule and 2 fatty acids and one phosphate molecule
condensation reaction to form ester bond
can contain saturated and unsaturated fatty acid

Question 29

Test for reducing sugars

Answer 29

Benedict’s test

Question 30

Describe Benedict’s test for reducing sugars

Answer 30

Add equal volumes of the sugar sample to test tube Add equal volume (2cm3) of benedict’s reagent to sample
Heat sample in a water bath at 95 degrees Celsius
Red precipitate indicates presence of reducing sugar

Question 31

Describe the Benedict’s test for non-reducing sugars.

Answer 31

Observe a negative result in Benedict’s test for reducing sugars
Add an acid (hydrochloric) to sugar sample and heat to 95 degrees Celsius
Neutralise with alkali (sodium hydrogen carbonate)
Add equal volume (2cm3) of Benedict’s solution to sugar solution
Heat again to 95 degrees Celsius
Red/orange/green/yellow precipitate should form

Question 32

Test for Starch

Answer 32

Add 2 drops of potassium iodide solution to your sample
Gently shake the tube
Blue-black indicates indicates presence of starch

Question 33

Test for protein

Answer 33

Add sample to test tube and add biuret solution to test tube
Gently mix
Purple/lilac indicates proteins are present

Question 34

Test for lipids

Answer 34

Add sample to test tube and then add ethanol to test tube
Thoroughly mix or shake to dissolve any lipid
Then add water and shake
Cloudy white emulsion should form if lipids are present

Question 35

Describe how you would produce a calibration curve for a reducing sugar of unknown concentration and use it to obtain results

Answer 35

Make up several known concentrations of of the reducing sugar
Carry out the Benedict’s test on each sample
Use a colorimeter to measure the colour intensity of each solution and plot a calibration curve
Known concentration on the x-axis and absorbance/transmission on the y-axis
Find the concentration of the unknown sample using the calibration curve

Question 36

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

Answer 36

Long straight unbranched chains of beta glucose
Joined by many weak hydrogen bonds which form cross links
Form microfibrils
Provide strength

Question 37

Hydrogen bonds are important in cellulose molecules. Explain why.

Answer 37

Hydrogen bonds hold chains of beta glucose together
Provide strength
Many weak hydrogen bonds provide strength in large numbers

Question 38

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

Answer 38

Insoluble so doesn’t affect water potential
OR
Helical so compact
OR
Large molecule so cannot leave the cell

Question 39

Explain why a buffer solution was added to the amylase-starch mixture.

Answer 39

To maintain pH so that change in pH does not affect the rate of reaction

Question 40

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, to measure quantity of reducing sugar in a solution.

Answer 40

Filter and dry the precipitate
Find the mass

Question 41

Use of a colorimeter would improve repeatability of the student’s results. Give one reason why.

Answer 41

Standardise the method