1.3 - Lipids, 1.7 - Water, 1.8 - Inorganic Ions

Question 1

Describe how to test for lipids in a sample

Answer 1

1) Dissolve (solid) sample in ethanol
2) Add an equal volume of water
3) Shake for approximately 1 min
4) if positive, a milky white emulsion forms
The more lipid there is, the more noticeable the milky white colour will be

Question 2

How do triglycerides form?

Answer 2

Through 3 condensation reactions between 1 molecule of glycerol & 3 fatty acids, in which 3 ester bonds are formed, and 3 water molecules are released.

Question 3

What are triglycerides made of?

Answer 3

Triglycerides are composed of 1 molecule of glycerol & 3 fatty acids.

Question 4

Contrast saturated and unsaturated fatty acids.

Answer 4

Saturated contain only single bonds between carbon atoms, whereas unsaturated contain 1+ double bond(s) between carbon atoms.
Saturated is a straight-chain, whereas due to double bonds, unsaturated chain is ‘kinked’ .
Saturated has a higher melting point than unsaturated (s = solid at room temp, u = liquid)
Saturated is found in animal fats whereas unsaturated is found in plant oils.

Question 5

Relate the structure of triglycerides to their functions

Answer 5

• High energy to mass ratio = good for energy storage
• Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing
• Slow conductor of heat = thermal insulation
• Less dense than water = buoyancy of aquatic animals

Question 6

What is a phospholipid composed of?

Answer 6

1 phosphate group
1 glycerol molecule
2 fatty acids

Question 7

What is meant by an ‘amphipatic molecule’?

Answer 7

A molecule having both hydrophobic and hydrophilic regions.

Question 8

Describe the structure and function of phospholipids.

Answer 8

It is an amphipathic molecule, with a glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head.
It forms a phospholipid bilayer in water = component of cell membranes.
Tail can splay outwards = waterproofing.

Question 9

Compare phospholipids and triglycerides.

Answer 9

• Both have glycerol backbone
• Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids.
• Both contain the elements, C. H. O.
• Both formed by condensation reactions.

Question 10

Contrast phospholipids and triglycerides

Answer 10

• Phospholipids contain 2 fatty acids & 1 phosphate group, whereas triglycerides contain 3, and no phosphates
• Phospholipids have a hydrophilic head & hydrophobic tail, whereas the whole of triglycerides is hydrophobic.
• Phospholipids are used primarily in membrane formation, whereas triglycerides are used primarily as an energy storage molecule.

Question 11

Are phospholipids and triglycerides polymers?

Answer 11

No, they are not made from a small repeating unit. They are macromolecules.

Question 12

Why is water a polar molecule?

Answer 12

Oxygen is more electronegative than hydrogen, so attracts the electron density in the covalent bond more strongly.
O has a slightly negative charge therefore, & H has a slightly positive charge

Question 13

State 5 biologically important properties.

Answer 13

• Important metabolite
• Good solvent
• High latent heat of vapourisation
• High specific heat capacity
• Cohesion between water molecules

Question 14

Why is being an important metabolite a useful property of water?

Answer 14

All condensation & hydrolysis reactions require water in order to break or form bonds.

Question 15

Why is water’s high latent heat of vaporisation a useful property?

Answer 15

A lot of energy is required to vaporise water, so organisms can loose water through evaporation to cool down.

Question 16

Why is water’s high specific heat capacity a useful property?

Answer 16

Hydrogen bonds between water absorb lots of energy, so a lot of energy is needed to heat water up. This means that water doesn’t experience rapid heat changes making it a good habitat, and also water inside animals helps to maintain a constant internal body temperature.

Question 17

Why is being polar a useful property of water?

Answer 17

Many important substances are ionic (contain a positively and negatively charged molecule)
As water is polar, its positive end will be attracted to negative molecules and its negative end to positives, meaning that ions will get totally surrounded by water, dissolving them.

Question 18

Why is the strong cohesion between water molecules a useful property?

Answer 18

Cohesion is the attraction between molecules of the same type. Water is cohesive as it is polar.
This helps water to flow, making it good for transporting substances (for example, up xylem vessels in plants)
This also means water has a high surface tension when it’s in contact with air, causing it to form droplets (e.g. sweat), which is a reason some insects can walk on water.

Question 19

What is an ion?

Answer 19

An ion is an (group of) atom that has an electric charge (+ = cation, - = anion)

Question 20

What is an inorganic ion?

Answer 20

An ion which doesn’t contain carbon atoms. (There is a few exceptions)

Question 21

Where are inorganic ions found usually?

Answer 21

In the cytoplasm and extracellular fluid.

Question 22

Give examples of inorganic ions.

Answer 22

Iron ions, hydrogen ions, sodium ions, phosphate ions.

Question 23

Explain the role of hydrogen ions in the body.

Answer 23

pH is calculated based on the concentration of H+ (the more H+ present, the lower (more acidic) the pH)
Hydrogen ions interact with H-bonds & ionic bonds in the tertiary structure of proteins, which can cause them to change shape / denature.

Question 24

Explain the role of iron ions in the body.

Answer 24

Haemoglobin is made of 4 polypeptide chains, each with an Fe 2+ in the centre. Iron ions binds to oxygen and delivers it to respiring cells.
When oxygen is bound Fe 2+ temporarily becomes Fe 3+.

Question 25

Explain the role of sodium ions in the body.

Answer 25

They are involved in co-transport for absorption of glucose & amino acids in the lumen of the gut.
Involved in propagation of action potentials in neurones.

Question 26

Explain the role of phosphate ions in the body.

Answer 26

When PO4 3- is attached to another molecule, its known as a phosphate group.
Phosphate groups are key components of DNA, RNA & ATP.
In ATP, its the bonds between phosphate groups that store energy.
Phosphate groups in DNA & RNA allow nucleotides to join to form polynucleotides.