1. Exam Q Flashcards
1
Q
A
2
Q
(ii) With reference to the structure and properties of water molecules, explain why water is often referred to as the universal solvent. [4]
A
(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)
3
Q
A
4
Q
The concentration of phosphate ions was found to be very low in this pond water. Name three compounds that contain phosphate. [2]
A
All 3 correct = 2 marks, 2 or 1 correct = 1 mark (2)
amino acids/protein
ATP
nucleic acids
chlorophyll
5
Q
A
6
Q
A
7
Q
A
8
Q
A
9
Q
A
10
Q
v) add
Reasons why A is an efficient storage molecule
A
- (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)
11
Q
A
(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)
12
Q
A
13
Q
A
- (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
14
Q
A
15
Q
A
16
Q
A
17
Q
A
18
Q
A
- the higher the concentration of protein, the darker the colour
19
Q
- 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.
A
(semi-quantitative) gives an approximation/estimate of the concentration
does not provide actual values
20
Q
A
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
21
Q
A
22
Q
A
23
Q
A
24
Q
(c) Describe how you would test a food sample for the presence of protein. [2]
A
add Biuret reagent/sodium hydroxide followed by dilute copper sulfate (1)
colour change from pale blue to purple/lilac (1)
25
GPT
(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.
26
GPT
(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.
27
GPT
(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!
28
GPT
(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]
29
GPT
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]
30
GPT
(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]
31
GPT
(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]
32
33
34
35
36
37
38
There's no 3′ OH left.
No new phosphodiester bond can form.
Chain elongation stops.
39
40
41
42
43
44
45
46
47
48
49
50
51
52
52
52
53
53
54
55
56
57
57
57
58
59
60
61
62
62
63
64
65
66
67
