1. Exam Q

Question 1

Answer 1

Question 2

(ii) With reference to the structure and properties of water molecules, explain why water is often referred to as the universal solvent. [4]

Answer 2

(ii) water molecules are polar/uneven distribution of charge (1)
Hδ+ attracted to particles with +ve charge/Oδ- attracted to particles with -ve charge (1)
bonds in substance break (1)
substance dissolves (1)

Question 3

Answer 3

Question 4

The concentration of phosphate ions was found to be very low in this pond water. Name three compounds that contain phosphate. [2]

Answer 4

All 3 correct = 2 marks, 2 or 1 correct = 1 mark (2)
amino acids/protein
ATP
nucleic acids
chlorophyll

Question 5

Answer 5

Question 6

Answer 6

Question 7

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

v) add
Reasons why A is an efficient storage molecule

Answer 10

1. (a) (i) A amylose (1)
   B amylopectin (1)

   (ii)	C	glycogen (1)
           storage of glucose (1)
   
   (iii)	glucose + α/alpha (1)
   
   (iv)	name + form		glucose  + β/beta (1)
       location in plant cell	cell wall (1)
       bond Z			β / beta glycosidic (1)
       bond W		hydrogen bond (1)
   	 
   (v)	(A coils up) due to the formation of hydrogen bonds (1)
   
       (storage) any 2 (x1) from
       compact (1)
       easy to add or remove glucose molecules (1)
       insoluble (1)
       no osmotic effect (1)

Question 11

Answer 11

(b) (i) contains nitrogen (1)
carbohydrates only contain carbon, hydrogen and oxygen (1)
(ii) many monomers/small molecules joined together to make a large molecule/chain (1)
(iii) Any 3 (x1) from:
alternate monosaccharides inverted by 180o (1)
hydrogen bonds can cross link molecules (1)
to form microfibrils (1)
with high tensile strength (1)

Question 13

Answer 13

2. (a) (i) colour perception is subjective/
   not everyone sees a colour in the same way
   (ii) can only give an approximation of the concentration/
   does not give actual values(b) (i) 0.4 mol dm-3

   (ii)	with an absorbance of 0.1 concentration could be 0 or 0.05
   
   (iii)	could be more than one reducing sugar in a food
       all would produce a positive result with Benedict’s reagent

Question 14

Answer 14

Question 15

Answer 15

Question 16

Answer 16

Question 17

Answer 17

Question 18

Answer 18

1. the higher the concentration of protein, the darker the colour

Question 19

2. The Biuret test for protein can only provide semi-quantitative data about the concentration of protein. Explain what is meant by the term semi-quantitative.

Answer 19

(semi-quantitative) gives an approximation/estimate of the concentration
does not provide actual values

Question 20

Answer 20

perception of colour is subjective
different people interpret a colour change differently

at very low concentrations of protein the colour change is very small
may not be enough to register as a positive result

starting colour is pale blue and low concentration of protein produces a very pale 	lilac/purple colour
may not be enough of colour change to see a difference in colour

Question 21

Answer 21

Question 22

Answer 22

Question 23

Answer 23

Question 24

(c) Describe how you would test a food sample for the presence of protein. [2]

Answer 24

add Biuret reagent/sodium hydroxide followed by dilute copper sulfate (1)
colour change from pale blue to purple/lilac (1)

Question 25

GPT

Answer 25

(i) Name the type of bonds labelled A and B.
A: Covalent bond (between the oxygen and hydrogen within a single water molecule).
B: Hydrogen bond (between the hydrogen of one molecule and the oxygen of another).
(ii) Explain how charges on the hydrogen atoms enable the formation of bond A.
Hydrogen atoms in a water molecule have a partial positive charge (δ+), while the oxygen atom has a partial negative charge (δ−). This results in a polar covalent bond within the water molecule.
(iii) Explain how the properties of water molecules enable water to:
Act as a universal solvent:
Water molecules are polar, so they can surround and interact with other polar or charged substances, breaking them apart into ions or molecules and dissolving them.

Have a high specific heat capacity:
Hydrogen bonds between water molecules require a significant amount of energy to break. This allows water to absorb and store heat without large changes in temperature.

(iv) Liquid water is transparent. Why is this important to plants living in aquatic habitats?
Transparency allows sunlight to pass through the water, enabling photosynthesis to occur in aquatic plants and algae.

Question 26

GPT

Answer 26

(b) (i) Complete the diagram to show the reaction involved in converting this disaccharide to its component monosaccharides.
Add a water molecule (H₂O) above the reaction arrow to indicate hydrolysis.
Split the glycosidic bond between the glucose and galactose units to show the two separate monosaccharides.
(ii) Name the following:
The name of the reaction that breaks down lactose:
Hydrolysis.

The name and type of bond broken during this reaction:
Glycosidic bond (a covalent bond).

The monosaccharides released when lactose is broken down:
Glucose and galactose.

(iii) Lactose is a reducing sugar. Describe how you would test for the presence of a reducing sugar in a sample of food.
Add Benedict’s reagent to the food sample.
Heat the mixture in a water bath.
Observe the color change: a positive test for reducing sugar will produce a precipitate that changes from blue to green, yellow, orange, or brick-red, depending on the concentration of reducing sugar.

Question 27

GPT

Answer 27

(a) (i) Answers:
Increase the strength of teeth and bones: Calcium ions (Ca²⁺)
Are needed to form some amino acids: Nitrate ions (NO₃⁻)
Are essential for photosynthesis: Magnesium ions (Mg²⁺)
(a) (ii) Answer:
One function of iron in the human body: Iron is essential for the formation of hemoglobin, which transports oxygen in the blood.

(b) (i) Diagram Instructions:
Draw a phospholipid molecule with the following features:

Hydrophilic head: Represented as a circle, labeled as “phosphate group” or “polar head.”
Hydrophobic tails: Two tails extending from the head, labeled as “fatty acid tails” or “non-polar tails.”
Label the hydrophilic head as water-attracting and the hydrophobic tails as water-repelling. Let me know if you need a detailed drawing for clarity!

Question 28

GPT

Answer 28

(ii) Elements in triglycerides:

Carbon, hydrogen, oxygen [1]
(iii) Three uses of triglycerides:

Long-term energy storage. [1]
Thermal insulation. [1]
Buoyancy or organ protection.
(iv) Naming parts:

X: Glycerol [1]
Y: Fatty acids [1]
Z: Ester bond [1]

Question 29

GPT

Answer 29

Question 3
(a)
(i) Identifications:

Acidic region: Carboxyl group (COOH) [1]
Nitrate essential: Amino group (NH₂) [1]
Contains sulfur: R group [1]
(ii) Differences:

Proteins contain nitrogen and sometimes sulfur, absent in carbohydrates and lipids. [2]

Question 30

GPT

Answer 30

(b)
(i) Highest structure:

Quaternary, as insulin has multiple polypeptide chains linked together. [1]
(ii) Secondary structure:

Alpha helices or beta-pleated sheets, stabilized by hydrogen bonds. [2]
(iii) Consequences of missing bond:

Insulin cannot maintain its 3D structure, leading to loss of functionality. [2]

Question 31

GPT

Answer 31

(c)
(i) Diagram:

Show two amino acids joined by a peptide bond, with water as a byproduct. [2]
(ii) Naming:

Bond: Peptide bond [1]
Reaction: Condensation reaction [1]
(d)
(i) Protein test:

Add Biuret reagent to food. Positive result: purple color indicates proteins. [3]
(ii) Semi-quantitative explanation:

The intensity of the purple color gives an approximate concentration of protein. [2]