Bonding

Question 1

How do hydrogen bonds form between water molecules ?

Answer 1

Intermolecular attraction.

Slightly positive charged atom (hydrogen) bonded with a slightly negatively barged atom (oxygen).

Question 2

State 7 biologically important properties of water .

Answer 2

• high specific heat capacity
• high specific heat of vaporisation
• incompressible
• density
• metabolite
• surface tension and cohesion
• solvent

Question 3

Incompressible

Answer 3

Provides turgidity in plant cells

Question 4

Why does ice float on water and explain the importance for organisms?

Answer 4

Ice is less dense than water so it floats and acts as an insulating layer to prevent heat loss therefore aquatic organisms don’t freeze, therefore water acts as a habitat. Hydrogen bonds hold the water molecules in fixed positions further away from each other.

Question 5

Why is water being a solvent important for organisms?

Answer 5

• molecules, ions and minerals can be dissolved in water and transported in living things.
• due to water being polar, the positive and negative charger atoms are attracted the the molecules of the solvent causing them to cluster around the solvent .

Question 6

High specific latent heat and vaporisation?

Answer 6

SLH
• lots of energy is required to break bonds, not increase the le Eric energy of water molecules.
• acts as a buffer so it can resist fluctuations in temperature to maintain optimum temperature.

LHV
• coolant, water evaporates from skin and not loosing a lot of water

Question 7

Define a monomer, examples?

Answer 7

Monomer is a single unit of a polymer
• amino acids
• monosaccharides
• nucleotides

Question 8

Define a polymer, examples ?

Answer 8

Many monomers
• polysaccharides
• proteins
• dna/rna

Question 9

Describe a condensation reaction with examples?

Answer 9

When to molecules are chemically joined together with the removal of water.
• results in a glycosidic bond
• water is a product

Question 10

Describe a hydrolysis reaction with examples ?

Answer 10

A water molecules breaks a chemical bond betweeen 2 molecules to make separate monomers
• peptide bonds in proteins
• ester bonds in fatty acids
• glycerol in lipids

Question 11

Name the elements found in carbohydrates, lipids, proteins and nucleic acids

Answer 11

Carbohydrates - C, H, O
Lipids - C, H, O
Proteins - C, H, O, N, S
Nucleic acids - C, H, O, N, P

Question 12

Why are polysaccharides a good energy store?

Answer 12

• glycogen and starch are compact so there is more space in cells.
• polysaccharides hold glucose in chains so they can be snipped off via hydrolysis when needed for respiration.

•polysaccharides are less soluable than monosaccharides. Some hydrogen bonds are hidden inside away inside from the molecule.
> if glucose dissolved in the cytoplasm, the water potential of the cell would reduce and excess water would come in (flaccid).

Question 13

3 disaccharides and how they form.

Answer 13

Maltose > 2 alpha glucose
Sucrose > glucose + fructose
Lactose > glucose + galactose

Question 14

Describe the structure and functions of starch.

Answer 14

• Starch is made up of two polysaccharides: amylose and amylopectin
• starch grains in chloroplast and storage organs

• easily broken to release glucose in respiration

• less soluble than glucose
> larger molecule
> hydroxyl groups are hidden inside the coil

Question 15

Structure of amylose

Answer 15

• alpha glucose monomers
• 1,4 glycosidic bond
• long coiled with helix chains stabilising the hydrogen bonds ( doesn’t affect water potential of the cell)

Question 16

Structure of amylopectin

Answer 16

• alpha glucose
• 1,4 and 1,6 glycosidic bond
• coils similar to amylose
• branches out every 25-40 subunits

Question 17

Describe the structure and function of glycogen

Answer 17

• alpha glucose
• 1,4 and 1,6 glycosidic bond
> 1,4 linked chains are shorter and more branched than amylopectin, making it more compact than starch.
> 1,4 are highly branched so it can be hydrolysed into glucose very quickly due to lots of branches for enzymes to attach. ( insoluble)
• forms granules in the liver and muscle cells

Question 18

Describe the structure and the function of cellulose .

Answer 18

• polymer of beta glucose
• 1,4 glycosidic bond ( every other glucose is inverted making it a straight chain and unbranched)
> can only be broken down by a cellulose enzyme which we don’t have . Herbivores have bacteria and protoctists in the gut to break down cellulose)
• hydrogen bonds within the chain to prevent spiralling, giving cellulose its high tensile strength.

Question 19

How do triglycerides form?

Answer 19

Condensation reaction between a glycerol and three fatty acids .

Question 20

Differences between saturated and unsaturated fatty acids.

Answer 20

Saturated; 
• only single bonds 
• straight chain molecules 
• higher melting point- solid at room temperature 
• found in animal fats 

Unsaturated; 
• only double carbon bonds 
• kinked molecules 
• lower melting point - liquid at room temperature 
• found in plant oils

Question 21

Relate the structure of triglycerides to their function

Answer 21

• insoluble - no effect on the water potential of the cell and waterproofing
• slow conductor of heat - thermal insulation e.g stored as adipose tissue in whales acts as a heat insulator
• less dense than water - buoyancy of aquatic animals, fat is less dense than water
• energy source - can be broken down in respiration to release energy in atp. To hydrolyse the water bonds and then the glycerol and fatty acids can be broken down into co2 and h2o.

Question 22

Structure and function of phospholipids.

Answer 22

• same as triglycerides but instead of one fatty acids it’s a hydrophilic phosphate group
• condensation reaction between and oh group and a phosphate molecule and an oh group forms an ester bond.
• forms bilayer in water

Question 23

Are triglycerides and phospholipids monomers?

Answer 23

No they are macromolecules.

Question 24

Describe the structure and function of cholesterol.

Answer 24

• a steroid alcohol
> not fat
> complex.
> dual hydrophobic/ hydrophilic
• adds to the stability of membranes
> hydroxyl group at periphery of membrane.
> keeps membrane fluid at room temperature.
• made in the liver and small intestines
> in bile, cholesterol can stick together to form gallstones.
> in blood, can be deposited in the inner lining in blood vessel cause aesthetic

Question 25

Structure of an amino acid.

Answer 25

Amine group
Carboxyl group
R side group

Question 26

How do polypeptide form?

Answer 26

Condensation reaction between amino acids to form peptide bonds.

Question 27

Primary structure of a protein .

Answer 27

The sequence, number and the type of amino acid in the polypeptide is determines by a sequence of codons on mRNA.

Question 28

Secondary structure of a protein

Answer 28

Hydrogen bonds form between negative charge oxygen atoms attach to each

Question 29

How to test for proteins

Answer 29

Biuret confirms presence of peptide bond.
Positive result blue to purple
Negative result blue

Question 30

Tests for lipids

Answer 30

Ethanol

Positive result milky white emulsion

Question 31

Tests for reducing sugars

Answer 31

Add benedict’s
Heat to 80
Positive orange and red precipitate forms

Question 32

Test for no. Reducing sugar

Answer 32

Obtain negative result from reducing sugar 
Hydrolyse e.g add hcl 
Neutralise using sodium carbonate 
Add benedict’s 
Heat to 80 
Same results

Question 33

Test for starch

Answer 33

Iodine

Positive orange to blue/black

Question 34

Alpha and beta glucose role in the body? And ribose

Answer 34

Alpha; energy source, component of starch and glycogen( energy stores)

Beta; energy source, component of cellulose which provides structural support in cell walls.

Ribose; component of rna, atp and nad .

Question 35

Lipids structure

Answer 35

• macromolecules ( lower amount of oxygen )

* non polar and hydrophobic

Question 36

Esterification

Answer 36

A condensation reaction between the carboxyl group of a fatty acid and the hydroxyl group of a glycerol forming and ester bond and water is released.