Carbohydrates - Mono And Disaccharides

Question 1

What are some examples of monomers?

Answer 1

Monosaccharides, amino acids and nucleotides

Question 2

What elements are found in carbohydrates?

Answer 2

Carbon, hydrogen and oxygen

Question 3

What is the ratio of hydrogen to oxygen atoms in a carbohydrate?

Answer 3

Hydrogen:Oxygen
2:1

Question 4

What 3 groups can carbohydrates be classified into?

Answer 4

Monosaccharides, disaccharides and polysaccharides

Question 5

What are some features of monosaccharides and disaccharides?

Answer 5

Small
Soluble
Easy to transport
Sweet tasting

Question 6

What are uses of monosaccharides?

Answer 6

Respiration to provide energy
Growth during formation of larger carboydrates

Question 7

What are examples of monosaccharides?

Answer 7

Glucose
Fructose
Galactose

Question 8

What type of sugar are monosaccharides?

Answer 8

Reducing

Question 9

What are the two isomers of glucose and how are they different?

Answer 9

Alpha glucose and beta glucose

Alpha has hydroxyl groups on the same side and beta has them on different sides

Question 10

How is a disaccharide formed?

Answer 10

When two monosaccharides are joined together by a glycosidic bond formed from a condensation reaction

Question 11

What by-product is always made with disaccharides?

Answer 11

Water

Question 12

How are maltose, sucrose and lactose formed?

Answer 12

Glucose+glucose->maltose + water
Glucose + fructose -> sucrose+water
Glucose+galactose->lactose+water

Question 13

What is the formula of a disaccharide?

Answer 13

C12H22O11

Question 14

How can disaccharides be hydrolysed?

Answer 14

Hearing with an acid or by an enzyme

Question 15

What is the non reducing sugar to know?

Answer 15

Sucrose

Question 16

What test is used for testing for reducing sugars??

Answer 16

Benedict’s test

Question 17

How do you do the Benedict’s test?

Answer 17

1- A small amount of the sample is placed in a test tube with the same volume of Benedict’s solution
2-This is heated to 95oC in a water bath
3- A brick red or orange precipitate is a positive result
4- Benedict’s remains blue for a negative result

Question 18

What type of test is the Benedict’s test for reducing sugars??

Answer 18

Qualitative - it doesn’t allow you to compare results from different samples

Question 19

What would a more intense result indicate? (Qualitative test)

Answer 19

A higher concentration of reducing sugar is present in the solution

Question 20

What is useful about the semi-quantitative Benedict’s test?

Answer 20

Allows you to compare concentrations of reducing sugar in different solutions/samples

Question 21

What is bad about the semi-quantitative Benedict’s test?

Answer 21

It is subjective and may be difficult to judge the colour

Question 22

What must be done to control variables in semi-quantitative Benedict’s test?

Answer 22

Standardised - by using same volume of Benedict’s solution, same volume of the sample solutions and the samples must be heated for same period of time at the same temperature

Question 23

What is the colour scale from lowest to highest concentration of reducing sugar for the semi-quantitative Benedict’s test?

Answer 23

Blue - no reducing
Green/yellow ppt- low conc
Orange red ppt- medium conc
Brick red- high conc

Question 24

What is the Quantitative Benedict’s test used for?

Answer 24

To obtain numerical data to compare the concentrations of reducing sugar in different samples or to find the concentration of an unknown sample

Question 25

What are the steps of the Quantitative Benedict's test?

Answer 25

1- Perform the Benedict's test on reducing sugar solution of known conc 2-Control variables standardised, add same vol of sugar solution and same vol of Benedict's and heat in water bath for same time at same temp 3-Use a colourimeter to measure absorbance of each of the known solutions 4-Plot a graph of known conc (x) against absorbance (y). This is a calibration curve, add a line of best fit. 5-Repeat Benedict's test with unknown sample 6-Use absorbance value of unknown to read of the calibration curve to find its conc

Question 26

What are the steps of the test for a non-reducing sugar?

Answer 26

1-Take a small sample and heat in a 95oc water bath with Benedict's solution to confirm a negative result 2-Hydrolyse another sample of the sucrose by heating in a 95oc water bath with dilute acid like HCl 3-When cooled, neutralise the acid with an alkali like NaOH 4-Add the same conc of Benedict's solution and heat in a 95oc water bath 5-A positive brick red colour indicates that a non-reducing sugar was originally present.