1.5 - Lipids

Question 1

Test for lipids (Emulsion test):

Answer 1

1. take a completely dry, grease tube
2. use 2cm^3 of sample and add 5cm^3 of ethanol
3. shake thoroughly to dissolve
4. add 5cm^3 of H2O and gently shake
5. milky white emulsion is present if lipid is present
6. use water instead of sample as control which remains clear

Question 2

Adaptations of phospholipid molecules

Answer 2

• Polar molecules (hydrophilic heads and hydrophobic tails of 2 fatty acid) - in aqeuous environments - phospholipid molecules form a bilayer within the cell-surface membrane and a hydrophobic layer is formed
• Hydrophilic head helps to hold at the surface of the cell-surface membrane
• The structure allows them to form glycolipids by combining with carbohydrates by combining with carbohydrates within the cell-surface membrane

Question 3

Polar molecule definitions

Answer 3

2 ends which react differently

Question 4

What are phospholipids made up of?

Answer 4

Hydrophilic head and hydrophobic tail

Question 5

What are phospholipids?

Answer 5

Similar to triglycerides but one of the fatty acid molecules are replaced by a phosphate molecule whereas fatty acid molecules are hydrophobic and phosphates are hydrophilic

Question 6

Think about the ratio of C-H atoms, mass, water potential and H-O ratio

Structure of triglycerides in relation to their properties

Answer 6

• have a high ratio of energy-storing carbon-hydrogen to carbon atoms which is an excellent store of energy
• low mass: energy - good storage molecules becasue much energy can be stored in a small volume which reduces the mass animals have to carry around
• large non-polar molecules which are insoluble in water and their storage doesn’t affect osmosis in cells or water potential
• high ratio of hydrogen:oxygen atoms - release water when oxidised so they’re an important source for desert-living organisms

Question 7

Polyunsaturated fats

Answer 7

more than one double bond between carbon bonds

Question 8

Mono-saturated fats

Answer 8

one double carbon bond

Question 9

Saturated fat structures

Answer 9

only single carbon bonds

Question 10

Structure of Triglycerides

Answer 10

Question 11

What are triglycerides

Answer 11

Known as tri due to the 3 fatty acids combined with glycerol and each fatty acid forms an ester bon with glycerol in the condensation reaction

Question 12

Role of lipids in protection

Answer 12

stored around delicate organs

Question 13

where is it within the body

Role of lipids in insulation

Answer 13

Fats are slow conductors of heat and when stored beneath the body surface to retain heat - they also act as electrical insulators in the myelin sheath around nerve cells

Question 14

Animals and plants examples

Role of lipids in waterproofing

Answer 14

Lipids are insoluble in water and therefore is waterproofing and both insects and plants have many cuticles that conserve water - mammals instead produce an oily secretrion from the sebaceous glands in the skin

Question 15

Role of lipids as a source of energy

Answer 15

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

Question 16

What property does the cell membrane acquire as a result

Role of lipids in cell membranes

Answer 16

phospholipids contribute to the flexibility of these membranes and transfer of lipid-soluble substances across it

Question 17

Role of lipids and where?

Answer 17

Cell membranes
Source of energy
waterproofing
insulation
protection

Question 18

main group of lipids names

Answer 18

Triglycerides and phospholipids

Question 19

shared characteristics of lipids

Answer 19

• all contain C, H, N, O
• insoluble in water
• soluble in organic solvents such as alcohols and acetone