3.1.2.4 Polysaccharides structure and function and the starch test

Question 1

How is the structure of cellulose suited to its function?

Answer 1

• β-Glucose molecules can form long straight chains
• Parallel chains of cellulose form hydrogen bond ‘cross links’ which add strength
• Cellulose is arranged into microfibrils and then fibres, which add yet more strength

Question 2

Which type of bond forms between adjacent α-glucose molecules in glycogen?

Answer 2

α 1-4 glycosidic bonds

Question 3

Unbranched starch (amylose) coils into a…

Answer 3

compact helix structure

Question 4

What test is described below:

Place 2 cm3 of the sample being tested into a test tube

Add 2 drops of iodine solution

A blue black colouration indicates a positive result

Answer 4

The test for starch

Question 5

Identify the polysaccharide

Answer 5

Starch (amylose)

Question 6

Identify the polysaccharide

Answer 6

Starch (amylopectin)

Question 7

What form does starch take within plant cells?

Answer 7

Starch grains

Question 8

Which type of bond forms between branching α-glucose molecules in glycogen?

Answer 8

α 1-6 glycosidic bonds

Question 9

Which type of bond forms between unbranched starch (amylose) molecules?

Answer 9

α 1-4 glycosidic bonds

Question 10

Identify the polysaccharide

Answer 10

Cellulose

Question 11

How is glycogen different to starch?

Answer 11

Glycogen has many more branches

Question 12

Identify the polysaccharide

Answer 12

Glycogen (more branches than starch)

Question 13

Which type of organism contains starch?

Answer 13

Plants

Question 14

What form does glycogen take in cells?

Answer 14

granules within muscle and liver cells

Question 15

What type of reaction occurs when monosaccharides join?

Answer 15

Condensation reaction

Question 16

How would you test for starch?

Answer 16

1. Place 2 cm3 of the sample being tested into a test tube
2. Add 2 drops of iodine solution
3. A blue black colouration indicates a positive result

Question 17

Cellulose microfibrils are grouped are arranged in parallel groups called…

Answer 17

fibres

Question 18

Which monosaccharide is cellulose made from?

Answer 18

β-Glucose

Question 19

How does the structure of glycogen make it suited to its function?

Answer 19

• It is insoluble so does not cause water to move into the cell via osmosis
• It is large so does not diffuse out of animal cells
• It is compact
• It forms α-Glucose when hydrolysed for respiration
• Many more branches than starch allow α-Glucose to be released faster from glycogen

Question 21

What is the function of glycogen?

Answer 21

an energy store for animal and bacterial cells

Question 22

The coiled helix structure of unbranched starch (amylose) is held in place by…

Answer 22

hydrogen bonds

Question 23

What is the function of cellulose?

Answer 23

• Cellulose is a major component of plant cell walls and provides rigidity to plant cells
• Stops plant cells bursting when water enters

Question 24

How are parallel chains of cellulose held together?

Answer 24

hydrogen bonds

Question 25

What structure does cellulose take?

Answer 25

Long unbranched chains that run parallel to each other

Question 26

Which type of bond forms between branched starch (amylopectin) molecules?

Answer 26

α 1-6 glycosidic bonds

Question 27

Which type of monosaccharide is starch made from?

Answer 27

α-Glucose

Question 28

Which type of bonds join β-Glucose molecules when they form cellulose?

Answer 28

β 1-4 glycosidic bonds

Question 29

Cellulose chains are arranged in parallel groups called….

Answer 29

microfibrils

Question 30

Why does glycogen require more branches than starch?

Answer 30

Animal cells require more energy to function

Question 31

How does the structure of starch make it suited to its function?

Answer 31

• It is insoluble so does not cause water to move into the cell via osmosis
• It is large so does not diffuse out of plant cells
• It is compact
• It forms α-Glucose when hydrolysed for respiration
• Many branches allow α-Glucose to be released fast

Question 32

Name the 3 types of polysaccharide

Answer 32

Starch (amylose and amylopectin)

Glycogen

Cellulose

Question 33

What is the main function of starch?

Answer 33

energy storage in plant cells

Question 34

Describe the structure of glycogen

Answer 34

POLYMER of alpha glucose

joined by glycosidic bonds

branched structure

Question 35

How does glycogen act as a source of energy?

Answer 35

branched chains are HYDROLYSED

into glucose

used in respiration

Question 36

Which type of monosaccharide is glycogen made from?

Answer 36

α-Glucose

Question 37

monosaccharides and disaccharides taste sweet.

the lactose-free milk made after hydrolysis with lactase tastes sweeter than the cows milk containing lactose.

suggest why?

Answer 37

• lactose hydrolysed to a-glucose and galactose
• so more sugar molecules
• sugars produced sweeter than lactose

Question 38

give ways in which the structure of starch is similar to cellulose?

Answer 38

• both contain glucose / C,H,O
• both are polysaccharides

Question 39

give 2 ways in which the structure of starch is different from cellulose?

Answer 39

• starch made from a-glucose, cellulose made from B-glucose
• starch branched, cellulose straight

Question 40

in humans, the enzyme maltase breaks down maltose to glucose. this takes place at normal body temperature.

explain why maltase:

• only breaks down maltose
• allows this reaction to take place at normal body temperature

Answer 40

• tertiary structure
• means active site complementary to maltase
• so enzyme can mould to fit substrate
• enzyme is catalyst/ lowers activation energy
• by forming E-SC