Carbohydrates, Lipids & Water

Question 1

what are organic molecules? (2)

Answer 1

molecules with carbon-carbon and carbon-hydrogen bonds

they’re typically found in living organisms

Question 2

define monomers

Answer 2

small, repeating units from which larger molecules called polymers are made

Question 3

define polymers

Answer 3

molecules made from a large number of monomers (3 or more) joined together

Question 4

how are monomers joined together to create polymers? (3)

Answer 4

a condensation reaction
- joins two molecules (“monomers”) together with the formation of a chemical bond
- involves the removal of a water molecule

Question 5

how can monomers be split again? (3)

Answer 5

a hydrolysis reaction
- breaks a chemical bond between two molecules (“monomers”)
- involves the use of a water molecule

Question 6

what are carbohydrates?

Answer 6

a diverse group of organic molecules that range from simple monosaccharides to complex monosaccharides

Question 7

what are monosaccharides?
examples: (3)

Answer 7

the monomers from which all large carbohydrates are made

• glucose
• galactose
• fructose

Question 8

how can monosaccharides be joined together? (2)

Answer 8

a condensation reaction
- joins two together through the formation of a glycosidic bond

two monosaccharides = DISACCHARIDE
three monosaccharides = POLYSACCHARIDE

Question 9

name three disaccharides

Answer 9

• maltose
• lactose
• sucrose

Question 10

name three polysaccharides

Answer 10

• starch
• glycogen
• cellulose

Question 11

(alpha) glucose + (alpha) glucose =

Answer 11

maltose

Question 12

(alpha) glucose + galactose =

Answer 12

lactose

Question 13

(alpha) glucose + fructose =

Answer 13

sucrose

Question 14

what are polysaccharides? (3)

Answer 14

a polymer made from joining many monosaccharides together via condensation reactions

• large molecules that don’t pass the cell membrane
• insoluble in water, so doesn’t affect water osmosis

Question 15

structure and function of: STARCH (4)

Answer 15

storage molecule in plants

made from alpha glucose

branched ; alpha (1-4) glycosidic bonds and alpha (1-6) glycosidic bonds
- more ends available to be broken off for energy

helical ; more compact
- more glucose can be stored in less space

Question 16

structure and function of: glycogen (6)

Answer 16

storage molecule in animals

polymer of alpha glucose

branched ; alpha (1-4) glycosidic bonds and alpha (1-6) glycosidic bonds

helical ; more compact
- more glucose can be stored in one place

insoluble

large molecule ; can’t diffuse out of cells

Question 17

what are the differences between starch and glycogen? (3)

Answer 17

animals have a higher metabolic demand than plants (they respire more)

so glycogen, compared to starch, has:
#1: shorter chains
#2: a higher amount of branches
#3: larger surface area

Question 18

structure and function of: cellulose (6)

Answer 18

structural molecule in plants

polymer of beta glucose

long, straight chains ; beta (1-4) glycosidic bonds

chains can be joined together by weak hydrogen bonds, which become strong when there’s lots of them

this forms microfibrils
- which can then be further wound together to make cellulose fibres
- provide rigidity and strength

Question 19

what are lipids? (5)

Answer 19

a varied group of molecules that share the following features:

• contain carbon, hydrogen, oxygen
• proportion of hydrogen to oxygen is less than carbohydrates
• insoluble in water
• soluble in organic solvents like alcohol and acetone

Question 20

what is the main role of lipids?

Answer 20

they’re the main component of the cell surface membrane and membrane-bound organelles

Question 21

what are the remaining four roles of lipids? (4)

Answer 21

SOURCE OF ENERGY
- provide twice as much energy as the same mass of carbohydrates when they’re oxidised

INSULATION
- when stored under the skin, it helps animals retain body heat
- electrical insulators; make up the myelin sheath
PROTECTION
- the heart and the kidneys have a layer of fat to protect them

WATERPROOFING

Question 22

what are the two groups of lipids?

Answer 22

• triglycerides
• phospholipids

Question 23

TRIGLYCERIDES: structure (2)

Answer 23

made from one glycerol and three fatty acid molecules

• joined together via 3 condensation reactions to form ester bonds between the carboxyl group in fatty acids and the hydroxyl group in glycerol

Question 24

TRIGLYCERIDES: features (4)

Answer 24

• hydrophobic (repel water)
• contain a lot of energy due to the high ratio of C-H bonds compared to C-C bonds
• low energy : mass ratio ; makes them good for storage ; can be stored in a small space
• contain a high ratio of H:O ; release water when oxidised and so can be a good water source for desert animals

Question 25

**FATTY ACIDS**: structure (3)

Answer 25

*hydrocarbon chain* ; they either make for a saturated fatty acid or an unsaturated fatty acid - saturated have no double bonds between the carbon atoms within the hydrocarbon chain - unsaturated have double bonds between the carbon atoms

Question 26

**PHOSPHOLIPIDS**: structure (3)

Answer 26

- similar to triglycerides, however there is a phosphate group that replaces one of the fatty acids - the glycerol combines with two fatty acids and one phosphate group - there are only 2 ester bonds within a singular phosphate molecule

Question 27

what are the two parts of a phospholipid?

Answer 27

**hydrophilic phosphate head** - attracted to water; interacts with it - the attraction is caused by the polar nature of the phosphate group **hydrophobic fatty acid tails** - repelled by water; faces away from it - because fatty acids are non-polar

Question 28

why is **water** fundamental to life on earth?

Answer 28

the earliest forms of life are thought to have evolved in water

Question 29

what are the five properties of water? (5)

Answer 29

- it's a **metabolite** - it's a **solvent** - it has a **large specific heat capacity** - it has a **large latent heat of vaporisation** - **cohesion**

Question 30

water as a... **metabolite**

Answer 30

allows water to be involved in metabolic reactions such as condensation and hydrolysis

Question 31

water as a... **solvent** (2)

Answer 31

- allows metabolic reactions to occur - allows the transportation of substances

Question 32

water as having a... **high specific heat capacity** (2)

Answer 32

- 'buffers' changes in temperature - helps mammals to maintain a core temperature despite changes in environmental temperature

Question 33

water as having a... **large latent heat of vaporisation** (2)

Answer 33

- provides a cooling effect - requires a lot of energy to evaporate water and so when evaporation occurs, it takes away this energy from the body which provides the cooling effect.

Question 34

water as being... **cohesive** (2)

Answer 34

- supports the formation of continuous molecules of water - provides surface tension which supports small organisms on the surface of water

Question 35

can triglycerides be classed as polymers?

Answer 35

no because they are not made from monomers with the same or similar structure

Question 36

draw out an alpha glucose molecule

Question 37

list the **three** different tests for a carbohydrate

Answer 37

- benedict's test for reducing sugar - benedict's test for non-reducing sugar - iodine test for starch

Question 38

describe the benedict's test for a reducing sugar (2)

Answer 38

- add equal volumes of benedict's solution and sample to a test tube - heat to 95 degrees

Question 39

what is the result of the benedict's test if a reducing sugar **is** present?

Answer 39

formation of a brick red precipitate

Question 40

why is the benedict's test known as **"semi-quantitative"**?

Answer 40

because the colour of the precipitate indicates an **approximate** concentration

Question 41

describe the benedict's test for a non-reducing sugar (3)

Answer 41

- boil a sample with **hydrochloric acid** for 5 minutes - **neutralise** the solution by adding an alkali - now test as you would for a reducing sugar

Question 42

describe the step by step method for making a **calibration curve** to estimate the unknown concentration of a reducing sugar (6)

Answer 42

- make up **several known concentrations** of a reducing sugar - carry out the **benedict's test** on each of these concentrations - use a colorimeter to **measure the absorbance** - **plot calibration curve** - carry out benedict's test on the sample with an unknown concentration - then measure its absorbance via the colorimeter