Biological Molecules - Carbohydrates (2.1.2)

Question 1

What is the structure of the two forms of glucose called?

Answer 1

Ring structure.

Question 2

Picture / draw the two types of glucose structures.

Answer 2

Question 3

Glucose is the main energy source in animals and plants.

Explain how its structure is related to its function.

Answer 3

Highly soluble making it easily transported around the body.

Its chemical bonds store lots of energy.

Question 4

Picture / draw the structure of ribose.

Answer 4

Question 5

Describe the process of polysaccharide formation?

Answer 5

A hydrogen atom (from one hydroxyl group) on one monosaccharide bonds to a hydroxyl group on the other, releasing a molecule of water.

Question 6

What are three disaccharides and what are they each formed from?

Answer 6

Maltose
a-glucose + a-glucose

Sucrose
a-glucose + fructose

Lactose
a-glucose / b-glucose + galactose

Question 7

Describe the structure of amylose and its relation to its function.

Answer 7

Long unbranched chains of a-glucose.

Glycosidic bonds give it a coiled structure.

Compact, making it good for storage.

Question 8

Describe the structure of amylopectin and its relation to its function.

Answer 8

Long branched chains of a-glucose.

Side branches allow enzymes to get to the glycosidic bonds more easily.

Glucose can be released quickly.

Question 9

Explain the structure of glycogen.

Answer 9

Many side branches allow for the quick breakdown of glycosidic bonds and the release of glucose.

Very compact molecule making it good for storage.

Question 10

Explain the structure of a cellulose molecule.

Answer 10

Long unbranched chains of beta-glucose forming cellulose chains.

Hydrogen bonds between cellulose chains form strong fibres called microfibrils.

Question 11

What test do you use to detect the presence of starch?

Answer 11

Iodine test.

Question 12

What are the steps for testing for starch?

Answer 12

Add iodine in potassium iodide solution to the test sample.

Question 13

What is the process for testing for the presence of reducing sugars?

Answer 13

Add Benedict’s reagent to a sample and heat in a water bath that has been brought to the boil.

Question 14

What does a positive and negative result look like after performing a Benedict’s test?

Answer 14

Positive - Yellow > Orange > Brick red

Negative - Stays Blue

Question 15

What are the steps for testing for non-reducing sugars?

Answer 15

Take a new sample of the test solution and add dilute hydrochloric acid.

Heat in a water bath that has been brought to the boil.

Neutralise with sodium hydrogencarbonate.

This process breaks the sample down into a monosaccharide.

Carry out the Benedict’s test again.

Question 16

What other test, apart from Benedict’s test can be used to test for glucose?

Answer 16

Test strips

Question 17

How do you create known concentrations of glucose?

Answer 17

Question 18

What are the steps for using a colorimeter for determining the concentration of a sample?

Answer 18

Do Benedict’s test on each solution, plus a negative control.

Remove any precipitate by centrifuge, or by leaving it for 24 hours and waiting for it to settle.

Switch on the colorimeter and allow 5 minutes for it to stabilise.

Use a red filter

Add distilled water to a cuvette so it is three-quarters full, place it into the machine

Zero the machine

Add test samples to clean cuvettes and measure the readings

Question 19

Explain how a glucose biosensor works

Answer 19

The enzyme glucose oxidase catalyses the oxidation of glucose at the electrodes.

An electrical charge is created which is converted to an electrical signal by electrodes.

The signal is processed to work out the initial glucose concentration.