1.5-LIPIDS

Question 1

Lipids is a varied group of substances but what characteristics do they share? (4)

Answer 1

contain carbon, hydrogen and oxygen

proportion of oxygen to carbon and hydrogen smaller than in carbohydrates

insoluble in water

soluble in organic solvents i.e. alcohols and acetone

Question 2

What are the main groups of lipids?

Answer 2

triglycerides (fats and oils)

phospholipids

Question 3

Where is one of the roles of lipids?

Answer 3

in the cell membrane (cell-surface membranes and membranes around organelles)

Question 4

What does phospholipids contribute to?

Answer 4

the flexibility of membranes and the transfer of lipid-soluble substances across them

Question 5

What is a role of lipids? (1)

Answer 5

source of energy

when oxidised, lipids provide more than twice the energy as the mass of carbohydrates and release valuable water

Question 6

What is a role of lipids? (2)

Answer 6

waterproofing
lipids are insoluble in water and so useful as waterproofing. both plants ans insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in skin

Question 7

What is a role of lipids? (3)

Answer 7

insulation
fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. also act as electrical insulators in myelin sheath around nerve cells

Question 8

What is a role of lipids? (4)

Answer 8

protection

fat is often stored around delicate organs i.e. kidneys

Question 9

What is the state of fats and oils at room temperature (10-20℃)?

Answer 9

fats are solid

oils are liquid

Question 10

Why are triglycerides so called?

Answer 10

as they have three (tri) fatty acids combined with glycerol (glyceride)

Question 11

What does each fatty acid form?

Answer 11

forms an ester bond with glycerol in a condensation reaction

Question 12

What does the hydrolysis of a triglyceride produce?

Answer 12

produces glycerol and three fatty acids

Question 13

What is the same in all triglycerides?

Answer 13

the glycerol molecule

Question 14

Where does the difference in the properties of different fats and oils come from?

Answer 14

variation in the fatty acids

Question 15

How many fatty acids are there?

Answer 15

over 70 different fatty acids

Question 16

What do all the fatty acis have?

Answer 16

a carboxyl (-COOH) group with a hydrocarbon chain attached

Question 17

What is the fatty acid known as if this chain had no carbon-carbon double bond?

Answer 17

describes as saturated, because all the carbon atoms are linked to the max no. of hydrogen atoms

Question 18

What is it called when there is a single double bond?

Answer 18

mono-unsaturated

Question 19

What is it called if more than one double bond is present?

Answer 19

polyunsaturated

Question 20

What does it mean for triglycerides to have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms?

Answer 20

an excellent source of energy

Question 21

What does it mean for triglycerides to have low mass to energy ratio?

Answer 21

makes them good storage molecules because much energy can be stored in a small volume

Question 22

How is triglycerides being good storage molecules especially beneficial in animals?

Answer 22

as it reduces the mass they have to carry as they move around

Question 23

What property do triglycerides have by being large, non-polar molecules?

Answer 23

insoluble in water

Question 24

What does triglycerides being insoluble in water mean?

Answer 24

their storage does not affect osmosis in cells or the water potential of them

Question 25

What happens due to triglycerides having a high ratio of hydrogen to oxygen atoms?

Answer 25

release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts.

Question 26

What are phospholipids similar to?

Answer 26

lipids

Question 27

How are phospholipids different to lipids?

Answer 27

one of the fatty acid molecules is replaced by a phosphate molecule

Question 28

Do fatty acids repel or attract water?

Answer 28

repel water (are hydrophobic)

Question 29

Do phosphate molecules repel or attract water?

Answer 29

attract water (are hydrophilic)

Question 30

What two parts is a phospholipid made up of?

Answer 30

a hydrophilic ‘head’

a hydrophobic ‘head’

Question 31

What does the hydrophilic ‘head’ do?

Answer 31

interacts with water ( attracted to it) but not with fat

Question 32

What does the hydrophobid ‘head’ do?

Answer 32

orients itself away from water but mixes readily with fat

Question 33

What are molecules that have two ends (poles) that behave differently said to be?

Answer 33

polar

Question 34

What does them being polar mean?

Answer 34

when these polar phospholipid molecules are placed in water they position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible

Question 35

What makes phospholipids polar molecules?

Answer 35

having a hydrophilic phosphate head and a hydrophobic tail of two fatty acids

Question 36

What does phospholipids being polar molecules mean?

Answer 36

in an aqueous environment phospholipids molecules form a bilayer within cell-surface membranes

Question 37

What does the bilayer within cell-surface membranes result in ?

Answer 37

a hydrophobic barrier is formed between the inside and outside of a cell

Question 38

What do the hydrophilic phosphate ‘heads’ of phospholipids molecules do?

Answer 38

help to hold at the surface of the cell-surface membrane

Question 39

What does the phospholipid structure allow them to form?

Answer 39

glycolipids by combining with carbohydrates within the cell-surface membrane

Question 40

Why are these glycolipids important?

Answer 40

in cell recognition

Question 41

What is the cloudy colour due to in test for lipids?

Answer 41

any lipid in the sample being finely dispersed in the water to form an emulsion

Question 42

What happens to light passing through this emulsion?

Answer 42

it is refracted as it passes from oil droplets to water droplets, making it appear cloudy