1.4->1.5 Starch, glycogen, cellulose and lipids

Question 1

Test for starch

Answer 1

1. Place 2cm3 of sample being tested into a test tube
2. Add two drops of yellow iodine solution(potassium iodide) and shake or stir
3. Presence of starch is indicated by blue-black coloration

Question 2

Starch

Answer 2

made up of chains of alpha glucose monosaccharides linked by glycosidic bonds
chains may be branched or unbranched(wound in tight coil that makes molecule compact)
found in many parts of the plant in small grains and storage organs e.g. potato tubers but never animals
major energy source

Question 3

5 ways starch is adapted to energy storage

Answer 3

1. insoluble so doesn’t affect water potential so water isn’t drawn into cells by osmosis
2. doesn’t diffuse out of cells because it’s large and insoluble
3. compact, so a lot can be stored in a small space
4. when hydrolysed it forms a-glucose, which is easily transported and used in respiration
5. branched form has many ends, where enzymes act on simultaneously meaning glucose monomers are released very rapidly

Question 4

Glycogen

Answer 4

found in animals and bacteria but never plant cells
similair to starch but has shorter chains and is more likely to be branched
major carbohydrate storage product
stored in small granules in muscles and liver

Question 5

4 ways glycogen is adapted to energy storage

Answer 5

1. is insoluble and therefore doesn’t draw water into cells by osmosis
2. doesn’t diffuse out of cells because it’s insoluble
3. compact, so a lot can be stored in a small space
4. more highly branched than starch, so has more ends that can be acted on simultaneously by enzymes. So more rapidly broken down to form glucose monomer, which are used in respiration(animals have higher metabolic rate and respiratory rate than plants)

Question 6

3 functions of cellulose

Answer 6

1. provides rigidity to plant cells by being major component in cell wall
2. prevents cell from bursting as water enters by osmosis- exerts inward pressure that stops further influx of water, making plant cells turgid and push against one another
3. Maintains stems and leaves in turgid state so they can provide maximum SA for photosynthesis

Question 7

3 ways structure of cellulose is suited to function

Answer 7

1. made up of beta glucose so forms long, straight unbranched chains
2. chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength
3. the molecules group to form microfibrils which are grouped to form fibres which provides more strength

Question 7

4 lipid characteristics

Answer 7

1. contain carbon, hydrogen and oxygen
2. proportion of O2 to C to H is smaller than in carbs
3. insoluble in water
4. soluble in organic solvents e.g. alcohols and acetone

Question 8

5 lipid roles

Answer 8

1. cell membranes
2. source of energy
3. waterproofing
4. insulation
5. protection

Question 9

Fats

Answer 9

made up of unsaturated fatty acids
solid at room temp(10-20)

Question 10

Oils

Answer 10

made up of saturated fatty acids
oils are liquid at room temp(10-20)

Question 11

Lipid source of energy

Answer 11

when oxidised, lipids provide more than double the energy as same mass of carbs, and it releases valuable water

Question 12

Lipid waterproofing

Answer 12

insoluble in water
both plants and insects have waxy, lipid cuticles that conserve water
mammals produce oily secretion from sebaceous glands in skin

Question 13

Lipid insulation

Answer 13

fats are slow conductors of heat
when stored underneath body surface, helps retain body heat
also act as electrical insulators in the myelin sheath around nerve cells

Question 14

Lipids in cell membrane

Answer 14

phospholipids contribute to flexibility of membranes and transfer of lipd-soluble substances across them

Question 15

Lipid proterction

Answer 15

fat is often stored around delicate organs e.g. kidney

Question 16

Triglyceride

Answer 16

three fatty acids combined with glycerol
each fatty acid forms an ester bond with glycerol in condensation reaction
difference in properties come from variations in fatty acids

Question 17

Fatty acids

Answer 17

70 different types
all have carboxyl group(- COOH) and a hydrocarbon chain attacted
hydrophobic- repels water

Question 18

Saturated fatty acid

Answer 18

no carbon-carbon double bonds
all carbon atoms are linked to possible amount of hydrogen atoms

Question 19

Mono-unsaturated fatty acid

Answer 19

single carbon-carbon double bond present

Question 20

Polyunsaturated fatty acid

Answer 20

more than one double bond between two carbons present
double bonds cause molecule to bend
so they can’t be packed closely together, making them liquid at room temp(oils)

Question 21

4 ways triglyceride’s structure is linked to properties

Answer 21

1. Have high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so is excellent energy source
2. low mass to energy ratio, so good storage molecules because much energy can be stored in small volume(reduces mass animals have to carry to move around)
3. insoluble in water because they are large, non-polar molecules so storage does not affect osmosis or water potential in cells
4. high ratio of hydrogen atoms means they release water when oxidised so provide an important source

Question 22

Phospholipids

Answer 22

made up of two fatty acids, a phosphate molecule and glycerol
phosphate molecules are hydrophilic- attracts water

is polar(made up of two ends that behave differently)
- hydrophilic head which interacts with water(is attracted) but not with fat
- hydrophobic tail- orients itself away from water but readily mixes with fat

Question 23

3 ways strutcure of phospholipids are related to their properties

Answer 23

1. is a polar molecule which means that in an aqueous environment, they form a bilayer within cell-surface membranes, so a hydrophobic barrier is formed between inside and outside of cell
2. hydrophobic phosphate head help to hold at surface of cell-surface membrane
3. structure allows them to form glycolipids by combining with carbs within cell-surface membrane

Question 24

Test for lipids

Answer 24

1. Take completely dry and grease-free test tube
2. add 2cm3 of sample being tested, add 5cm3 of ethanol
3. shake tube thoroughly to dissolve any lipid in sample
4. add 5cm3 of water and shake gently
   5 a milky white emulsion indicates presence of lipid(light passing through emulsion is refracted as it passes from oil to water droplets)
5. As control, repeat with just water instead of sample and final solution should stay clear