1.2 carbohydrates

Question 1

What elements are all carbohydrates made from?

Answer 1

carbon, hydrogen and oxygen

Question 2

What are 3 examples of hexose monosaccharides?

Answer 2

glucose, fructose and galactose
they all have the molecular formula C6H12O6

Question 3

What are 3 examples of disaccharides?

Answer 3

sucrose, lactose, maltose
they all have the molecular formula C12H22O11

Question 4

What are the features of monosaccharides?

Answer 4

They are small, soluble and sweet
They are used as an energy store in respiration

Question 5

In what form are carbohydrates transported in the blood?

Answer 5

As monosaccharides

Question 6

Why are glucose molecules soluble in water?

Answer 6

As they are polar so hydrogen bonds can form in between the hydroxyl group and the water molecule

Question 7

What are the two isomers of glucose?

Answer 7

alpha and beta

Question 8

What is the rule for remembering alpha vs beta

Answer 8

Alpha below beta above

Question 9

What type of sugar is glucose?

Answer 9

Hexose sugar

Question 10

How can glucose be described.

Answer 10

Hydrophillic

Question 11

What is an example of a pentose sugar?

Answer 11

Ribose

Question 12

What is a disachharide?

Answer 12

Two monosaccharides bonded together by a glycosidic bond by a condensation reaction

Question 13

What makes up sucrose?

Answer 13

glucose and fructose

Question 14

What makes up lactose?

Answer 14

glucose and galactose

Question 15

What are the three examples of polysaccharides?

Answer 15

starch, glycogen and cellulose

Question 16

What monosaccharides are starch made up of?

Answer 16

Alpha glucose

Question 17

What energy store is glucose made up of?

Answer 17

Chemical energy which can be released during photosynthesis

Question 18

How is glucose produced in plant cells?

Answer 18

using light energy trapped during photosynthesis

Question 19

Why do plants store glucose as starch?

Answer 19

• glucose is soluble so a large amount of dissolved glucose can cause water to move into the cell by osmosis
• this effects the cells water potential
• to stop this cells store glucose as starch as it is unsoluble

Question 20

What two polymers does starch consist of?

Answer 20

Amylose and amylopectin

Question 21

What is the structure of amylose?

Answer 21

• It is a long, unbranched chain which twists into compact a helix structure (coiled)
• it is joined by 1,4 glycosidic bonds

Question 22

How is amylose suited for its function?

Answer 22

Since it is compact its good for storage as you can fit more into a small space

Question 23

How do polysaccharides convert to monosaccharides?

Answer 23

The polymer is broken down through hydrolysis by the addition of a water molecule.

Question 24

What is the structure of amylopectin?

Answer 24

-It is joined by 1,4 and 1,6 glycosidic bonds which causes it to branch every 25-30 molecules
-since it is branched it causes more rapid hydrolysis

Question 25

What are the key features of starch?

Answer 25

• It is insoluble: doesnt effect the water potential of the cell
• It cant diffuse out of the cell: stays where it is stored
• Rapid hydrolysis: enzymes act at the end of the molecule, since amylopectin is branched there are more ends to act on

Question 26

What is the major carbohydrate storage molecule found in animal cells?

Answer 26

Glycogen

Question 27

What is the structure of glycogen?

Answer 27

• it is made up of alpha glucose molecules
• it consists of 1,4 1,6 glycosidic bonds
• it is very heavily branched which allows more rapid hydrolysis
• important as animals require more energy than plants : constantlly moving

Question 28

What are the key features of glycogen?

Answer 28

• heavily branched
• occurs in animals : made from the excess taken in which hasnt been used up in respiration
  -mainly stored in liver and muscle cells : removes toxins and movement respectively
• it is too large to diffuse out of cells

Question 29

What is the role of cellulose?

Answer 29

• major part of the cell wall in plants
• provides structural strength in plants : prevents bursting if excess water is taken in

Question 30

What is cellulose a polymer of?

Answer 30

beta glucose

Question 31

What is the structure of cellulose?

Answer 31

• every other beta glucose molecule is inverted
• this forms a 1,4 glycosidic bonds
• straight, long chains lie parallel to eachother : unbranched
• hydrogen bonds form between neighbouring chains

Question 32

Why are the hydrogen bonds strong?

Answer 32

• weak by themselves
• many form between chains making them strong

Question 33

What happens when cellulose chains group together?

Answer 33

• they create microfibrils
• microfibrils group together to form macrofibrils
• these form a cellulose fibre

Question 34

Describe the benedicts test for reducing sugars

Answer 34

• add an equal volume of benedicts reagent to a sample
• heat the mixture in a water bath at 100* for 5 minutes
• for a positive result there is a colour change from blue to orange/brick red precipitate

Question 35

Describe the benedicts test for non reducing sugars.

Answer 35

• negative result benedicts reagent stays blue
• hydrolyse non-reducing sugars (e.g sucrose) into their monomers by adding 1cm^3 of HCl which will break the glycosidic bond
• heat in a water bath for 5 minutes
• neutralise the mixture using sodium carbonate solution
• proceed with the benedicts test for reducing sugars

Question 36

Describe the test for starch

Answer 36

• add iodine solution
• positive test : orange –> blue/black

Question 37

How could a colorimeter be used to give qualitative results for the presence of sugars and starch?

Answer 37

• make standard solutions with known concerntrations
• record absorbance or % transmission values
• plot calibration curve : absorbance (y axis), concentration (x axis)
• record absorbtion values of unknown samples and use calibration curve to read off concentration