Topic 1A- Biological Molecules (Carbohydrates)

Question 1

What are polymers

Answer 1

Large, complex molecules composed of long chains of repeating monomers joined together by chemical bonds.

Question 2

What are monomers

Answer 2

Single repeating units from which all polymers are made.

Question 3

Give 3 examples of monomers

Answer 3

Monosaccharides, amino acids and nucleotides.

Question 4

What is the monomer that makes up carbohydrates

Answer 4

Monosaccharides

Question 5

What elements are all carbohydrates made up of

Answer 5

Carbon, hydrogen and oxygen.

Question 6

Give 3 examples of monosaccharides

Answer 6

Glucose, fructose and galactose.

Question 7

What shape of sugar is glucose?

Answer 7

A hexose sugar

Question 8

What is a hexose sugar?

Answer 8

A monosaccharide with 6 carbon atoms in each molecule.

Question 9

What are the isomers of glucose

Answer 9

Alpha glucose and beta glucose.

Question 10

What are isomers

Answer 10

Molecules with the same molecular formula as each other, but with different structures.

Question 11

What is the difference between alpha glucose and beta glucose

Answer 11

The H and OH groups are inverted

Question 12

What is the structure of alpha glucose

Answer 12

Question 13

What is the structure of beta glucose

Question 14

What is the structure of beta glucose

Question 15

What is the reaction called that joins two monosaccharides together and what does this reaction include?

Answer 15

Condensation reaction - two molecules join together with the formation of a new chemical bond, and a water molecule is released when the bond is formed.

Question 16

What bond is formed between two monosaccharides when a molecule of water is released during condensation reactions

Answer 16

Glycosidic bond

Question 17

What is the name for two monosaccharides joined together

Answer 17

Disaccharide

Question 18

Give 3 examples of monosaccharides

Answer 18

Glucose
Fructose
Galactose

Question 19

Give 3 examples of disaccharides

Answer 19

Maltose
Lactose
Sucrose

Question 20

How is maltose formed

Answer 20

The condensation of two glucose molecules

Question 21

How are sucrose molecules made

Answer 21

The condensation of a glucose molecule and fructose molecule

Question 22

How is a lactose molecule made

Answer 22

The condensation of a glucose and galactose molecule

Question 23

What is the reaction called that breaks polymers apart and what happens in it?

Answer 23

Hydrolysis, and a water molecule is added which breaks the glycosidic bond between the monomers, separating them.

Question 24

Give all the reducing sugars

Answer 24

All monosaccharides (glucose, fructose, galactose)

Most disaccharides (Maltose, Lactose)

Question 25

Outline the test for reducing sugars

Answer 25

1) You add Benedict’s reagents (which is blue) to a sample and heat it in a water bath to 95°C. Wait for 5 minutes.

2) If a reducing sugar is present (therefore the test positive), a coloured precipitate will form. If the test is negative, the solution will remain blue.

Question 26

Outline the test for non-reducing sugars

Answer 26

1) If the result of the reducing sugars is negative, there could still be a non-reducing sugar present. To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides.

2) You do this by getting a new sample of the solution, adding dilute hydrochloric acid and carefully heating it in a water bath that’s been brought to boil.

3) You then neutralise it with with sodium hydrogencarbonate.

4) Then just carry out the Benedict’s test as you would for reducing sugars.

5) If the test’s positive, it will form a coloured precipitate (because there are now reducing sugars), and if it’s negative there are no sugars (either reducing or non-reducing.

Question 27

How is a polysaccharide formed

Answer 27

It’s formed when more than two monosaccharides are joined together by condensation reactions.

Question 28

What is the main function of starch

Answer 28

plants store excess glucose as starch (when a plant needs more glucose for energy, it breaks down the starch to release glucose.)

Question 29

What are the two polysaccharides that make up starch

Answer 29

Amylose
Amylopectin

Question 30

Describe the structure of Amylopectin and how each feature allows it to fulfil it’s function

Answer 30

-Polysaccharide- polymer of alpha glucose. Stores glucose which can be hydrolysed and broken down during respiration.

-Long, branched chains of alpha glucose (These branches mean there are more ends from which the enzymes can easily hydrolyse the glucose molecules for quick energy release)

-Contains 1,4 and 1,6 glycosidic bonds which causes the branches to occur

-Very large, which means it can’t fit through the partially permeable membrane, so stays where it’s formed

-It’s insoluble which means it doesn’t effect the water potential (so doesn’t cause water to enter the cell by osmosis-which would cause it to swell)

All of this makes it good for both storage and quick energy release.

Question 31

Describe the structure of Amylose and how this is useful to it’s function

Answer 31

-Polymer of Alpha Glucose

• Long, unbranched chain of alpha glucose (this alpha glucose can later be broken down for energy)

-Joined together by 1,4 glycosidic bonds which causes the alpha glucose molecules to be at angles angles to each other, causing a coiled structure (this makes it compact, therefore it’s good for storage as you can fit more glucose into a small space)

-Very large which means it can’t fit through the partially permeable membrane, so stays where it’s formed,

-(it’s soluble in water)

-This all makes it very good for storage.

Question 32

What is the test for starch? Outline this test.

Answer 32

Iodine test

-add iodine dissolved in potassium iodide solution to the test sample.

-If there is starch present, the sample changes from browny-orange to a dark, blue-black colour.

Question 33

What is the main function of glycogen?

Answer 33

It’s the main energy storage material in animals

Question 34

Describe the structure of glycogen and how the features help it to complete it’s function

Answer 34

-Polymer of Alpha Glucose.

-Formed by many long branched chains of alpha glucose (more branches than amylose, which allows for even quicker hydrolysis of the glucose molecules off the ends of the branches and therefore quicker energy release)

-Joined together by 1,4 and 1,6 glycosidic bonds which causes branches.

-Very compact molecule, which means it can store a lot of glucose in a small space and therefore is very good for storage

-Very large, which means it can’t pass through the partially permeable membranes and therefore stays where it’s formed

-Insoluble, so doesn’t effect the water potential of cells and cause lots of water to enter the cell which would make it swell.

-All if these features make it very good for storage and quick release

Question 35

Describe the structure of Cellulose and how this helps it to carry out it’s function

Answer 35

1) It’s function is to strengthen cell walls

2) It’s a polymer of beta glucose, which benefits the plant because many animals are unable to digest beta glucose and therefore they are discouraged from eating the plant.

3) Cellulose is made of long, unbranched chains of beta glucose. Every other beta glucose molecule is inverted and they are held together by 1,4 glycosidic bonds. (This causes the straight, unbranched structure)

4) lots of these chains are joined together by lots of hydrogen bonds (together they are very strong) and this forms microfibrils. Lots of these microfibrils join together to form fibres

5) the fibres then cross over each other to create mechanical strength in the cell walls.

Question 36

What are the words for tests to do with human judgement and tests to do with numbers

Answer 36

Human judgement= qualitative
Numbers= quantitative

Question 37

Outline two quantitative tests to messure the amount of reducing sugars and give 5 control variables

Answer 37

METHOD 1: USING A COLOURIMETER:
1) First, produce a dilution series of known concentrations of glucose solutions

2) Add Benedict’s solution to each one and heat to 95° in a water bath for 5 minutes.

3) Calibrate the colourimeter by measuring the absorbance of a sample of distilled water first, then measure the absorbance of each solution. (The higher the absorbance, the more reducing sugar present). Then test your unknown sample.

4) plot a calibration curve of absorbance on the y axis and the concentration on the x axis, drawing a curve of besy fit.You can use this line to estimate the concentration of reducing sugar in the sample

METHOD 2: MEASURING PRECIPITATE:
1) Complete the Benedict’s test for reducing sugars on the sample
2) filter the sample and dry the precipitate
3) find the mass using a balance. The bigger the mass, the more sugar is present.

FOR EACH METHOD, ADHERE TO THESE CONTROL VARIABLES:
1) volume of Benedict’s solution
2) concentration of Benedict’s solution
3) volume of sample tested
4) temperature in the water bath
5) duration of heating

Question 38

Outline how you can test which monosaccharides are in a monosaccharide mixture.

Answer 38

Chromatography:
1) first stain the monosaccharide sample. Place a spot of this sample on the line drawn in pencil at the bottom of the chromatography paper.

2) place spots of standard solutions of different known monosaccharides on the line beside the sample.

3) lower the paper into a beaker with the solvent, and wait for the solvent to travel up the paper.

4) analyse the chromatogram. If the mixture contains a monosaccharide, it will match up to the height of the known sample of that known monosaccharide.