Carbohydrates

Question 1

What are monomers?

Answer 1

Smaller units from which larger molecules are made

Question 2

What are polymers?

Answer 2

Molecules made from a large number of similar monomers joined together

Question 3

What is a condensation reaction?

Answer 3

Joins two monomers together by forming a chemical bond and eliminating a water molecule

Question 4

What is hydrolysis?

Answer 4

Breaks a chemical bond between two molecules using a water molecule

Question 5

What elements do carbohydrates contain?

Answer 5

Carbon, hydrogen and oxygen

Question 6

What is the general formula of carbohydrates?

Answer 6

CnH2n0n

Ratio = 2 hydrogen : 1 oxygen

Question 7

How do you number carbons?

Answer 7

Start backwards

Question 8

What are monosaccharides?

Answer 8

The basic molecular units (monomers) of carbohydrates

Question 9

Give some examples of reducing sugars

Answer 9

Glucose, fructose, galactose

Question 10

What is an isomer?

Answer 10

Molecules with the same chemical formula but different structure

Question 11

What are the two isomers of glucose?

Answer 11

Alpha and beta

Question 12

What is the bond formed between monosaccharides (in a condensation reaction) ?

Answer 12

Glycosidic bond

Question 13

Which monosaccharides make up maltose?

Answer 13

Glucose + glucose

Question 14

Which monosaccharides make up sucrose?

Answer 14

Glucose + fructose

Question 15

Which monosaccharides make up lactose?

Answer 15

Glucose + galactose

Question 16

What is a disaccharide?

Answer 16

Two monosaccharides joined together by a glycosidic bond formed in a condensation reaction

Question 17

How can disaccharides be hydrolysed?

Answer 17

Heating with acid or by an enzyme

Question 18

What is the test for reducing sugars?

Answer 18

Benedict’s test
- place small sample of sugar in test tube with same volume of Benedict’s solution
- heat to 95 degrees in a water bath
- brick red/orange colour = positive result
- if it remains blue, no reducing sugar present

Question 19

What is a qualitative test?

Answer 19

Does not allow comparison of results from different samples - simply gives positive or negative result

Question 20

What is a quantitative (Benedict’s) test?

Answer 20

Produces a colour whose intentity depends on the concentration of reducing sugar in a solution

Question 21

How to carry out quantitative Benedict’s test

Answer 21

• perform test on reducing sugars of known concentrations
• control variables standardised
• use calorimeter to measure absorbance of each known solution
• plot graph of known concentrations (x-axis) against absorbance value (y-axis)
• add line of best fit to calibration curve

Question 22

How to test for non-reducing sugars

Answer 22

• confirm negative result with Benedict’s test
• hydrolyse sample of sugar by heating in 95 degrees water bath with dilute acid
• when cooled, neutralise with alkali
• repeat Benedict’s test
• brick-red colour indicates non-reducing sugar present

Question 23

What is a polysaccharide?

Answer 23

Polymers of glucose formed by the joining of glucose molecules (during condensation reactions)

Question 24

What are the characteristics of polysaccharides?

Answer 24

• do not taste sweet
• insoluble in water
• non-reducing
• function as storage or structural molecules

Question 25

What is the function of starch?

Answer 25

Storage

Question 26

Where is starch found?

Answer 26

In the cytoplasm of plant cells

Question 27

What is the structure of starch?

Answer 27

• Long, branched chains of alpha glucose molecules linked by glycosidic bonds
• Helical shape

Question 28

How is the structure of starch related to its function?

Answer 28

• large so cannot cross cell membrane and leave cell
• helical shape = compact store (lots stored in small place)
• branching = large surface area (glucose molecules hydrolysed quickly for respiration)

Question 29

Why is the insolubility of starch useful?

Answer 29

It’s osmotically inactive so does not draw water into a cell which could lead to cell damage

Question 30

How is starch detected?

Answer 30

Iodine test
- add 2-3 drops of iodine solution
- blue/black colour = starch present
- orange/yellow = no starch present

Question 31

What is the function of glycogen?

Answer 31

Storage

Question 32

Where is glycogen found?

Answer 32

In animals (liver and muscle cells)

Question 33

What is the structure of glycogen?

Answer 33

Branched chains of alpha glucose (more branched than starch)

Question 34

How is glycogen suited to its function?

Answer 34

• insoluble meaning osmotically inactive
• branched so hydrolyses rapidly to release glucose for respiration

Question 35

What is the function of cellulose?

Answer 35

Structural support

Question 36

Where is cellulose found?

Answer 36

In the cell wall of plant cells

Question 37

What is the structure of cellulose?

Answer 37

• long, straight chains of (inverted) beta glucose molecules
• crosslinked hydrogen bonds
• microfibrils

Question 38

How is the structure of cellulose suited to its function?

Answer 38

• large number of hydrogen bonds gives strength
• straight chains ‘stacked’ to create cell wall (gives high tensile strength)
• chains of beta glucose strong + rigid (prevents plant cells bursting)

Question 39

What are the two types of starch?

Answer 39

Amylose and Amylopectin

Question 40

What is the structure of amylose?

Answer 40

alpha 1,4 linkage

Question 41

What is the structure of amylopectin?

Answer 41

alpha 1,4 and 1,6 linkage

Question 42

What are the benefits of the structure of amylopectin?

Answer 42

• More branched than amylose due to 1,6 bonds
• Makes it easier for glucose to be released

Question 43

What would be the problem with having excess glucose in cells?

Answer 43

It is soluble and so could disrupt osmosis, leading to cell damage