Question
The image represents the structure of the enzyme Rubisco from common pea (Pisum sativum).
(a) State one function of Rubisco. [1]
(b) State a role of the active site of an enzyme. [1]
(c) State the genus of the plant where this Rubisco is found. [1]
(d) Outline one factor that could affect the activity of Rubisco. [2]
▶️Answer/Explanation
Ans:
a
a. enzyme involved in photosynthesis/carbon fixation/Calvin cycle OR speeds up chemical reactions in photosynthesis
b. carboxylation of RuBP
c. production of carbohydrate in photosynthesis
d. addition of carbon dioxide to form glucose (in Calvin cycle) Either photosynthesis or carbon fixation must be mentioned
b site to which substrate binds OR catalytic site Give credit for the lock and key
analogy
c Pisum
d
a. name of factor
b. how it affects rate of reaction Example answer: temperature as the temperature increases the rate of reaction increases until it reaches a maximum and then decreases rapidly Accept answers in a graph.
Question
The equation below shows the production of glucose and galactose from lactose.
Glucose and galactose are examples of monosaccharides. State one other example of a monosaccharide.
There are several different types of carbohydrate. State which type of carbohydrate lactose is.
State the type of chemical reaction that occurs when lactose is digested into glucose and galactose.
Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of reaction is highest at 48°C. In food processing, lactase is used at a much lower temperature, often at 5°C. Suggest reasons for using lactase at relatively low temperatures.
fructose/ribose/deoxyribose/ribulose/other monosaccharides apart from glucose and galactose
▶️Answer/Explanation
Ans:
a. fructose/ribose/deoxyribose/ribulose/other monosaccharides apart from glucose and galactose
b (ii)dlisaccharide
$\mathrm{b}$ (ii)hydrolysis
less denaturation / enzymes last longer at lower temperatures;
lower energy costs / less energy to achieve $5^{\circ} \mathrm{C}$ compared to $48^{\circ} \mathrm{C}$;
reduces bacterial growth / reduces (milk) spoilage;
to form products more slowly / to control rate of reaction;
Question
a. Outline the role of hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides.
b. Describe the use of biotechnology in the production of lactose-free milk.[6]
c. Explain the importance of enzymes to human digestion.[8]
▶️Answer/Explanation
Ans:
Markscheme
a. monosaccharides are single sugars and disaccharides are two sugars and polysaccharides are multiple sugars; hydrolysis is the addition of water to split a molecule into smaller fragments;
$-\mathrm{OH}$ and $-\mathrm{H}$ are added to the fragments;
disaccharides are split/digested into two single sugars;
polysaccharides are broken/digested into smaller fragments (e.g. diasaccharides); process depends on enzyme control (in organisms);
b.
a particular yeast (growing in natural milk) contains lactase;
biotechnology companies can grow/culture the yeast;
lactase (an enzyme) is extracted from the yeast;
natural milk contains lactose/milk sugar;
when added directly to milk, lactase converts lactose into simpler forms;
same effect when milk is passed past immobilized (on surface or beads) lactase;
simpler forms of sugar (glucose and galactose) are easily absorbed (in the small intestine);
a commercial market exists for lactose-free milk / lactose-free milk is example of biotechnology’s economic impact;
some people are lactose intolerant/cannot digest lactose in milk/have lost lactase activity in intestinal cells;
consuming lactose-free milk allows lactose intolerant people to be nourished by milk without discomfort (abdominal cramps and diarrhoea);
many Asians are lactose intolerant whereas less common among other groups (northern Europeans and some Africans);
biotechnology produced in one part of world is more useful in another;
food must be in a small enough form to leave the gut and enter the bloodstream;
physical breakdown is not enough / chemical breakdown is necessary; enzymes are required for the chemical breakdown of food;
c.
enzymes increase the rate of digestion;
enzymes are biological catalysts;
enzymes allow digestion to occur at body temperature;
enzymatic digestion is a sequential process e.g. from protein to peptide to amino acid;
specific location for each reaction with specific conditions/environments e.g. stomach high acidity;
most enzymes work extracellularly / some enzymes work intracellularly;
variations in $\mathrm{pH}$ throughout digestive tract promote the activity of different digestive enzymes / different enzymes have different optimal pHs;
amylases digest carbohydrate to monosaccharides;
proteases digest proteins to amino acids;
lipases digest fats to fatty acids and glycerol;
Question
a. Distinguish between ventilation, gas exchange and cell respiration.[4]
b. Outline the process of aerobic respiration.[6]
c. Respiration and other processes in cells involve enzymes. Explain the factors that can affect enzymes.[8]
▶️Answer/Explanation
Markscheme
a. ventilation is moving air into and out of lungs/inhalation and exhalation; involves (respiratory) muscle activity; gas exchange involves movement of carbon dioxide and oxygen; between alveoli and blood (in capillaries) / between blood (in capillaries) and cells; cell respiration is the release of energy from organic molecules/glucose; (aerobic) cell respiration occurs in mitochondria; To award [4 max] responses must address ventilation, gas exchange and cell respiration.
b. during glycolysis glucose is partially oxidized in the cytoplasm; (small amount/yield of) ATP produced; (two) pyruvate formed by glycolysis; pyruvate absorbed into/broken down in the mitochondrion; requires oxygen; carbon dioxide is produced; water is produced; large amount/yield of energy/ATP molecules (per glucose molecule);
c. collisions between enzyme/active site and substrate;enzyme activity increases as temperature rises; more frequent collisions at higher temperatures; each enzyme has an optimum temperature / enzymes have optimal temperatures; high temperatures (above optimum) denature enzymes; each enzyme has an optimum $\mathrm{pH}$ / enzymes have optimal $\mathrm{pHs}$;
increase or decrease from optimum $\mathrm{pH}$ decreases rate of reaction/activity; extreme $\mathrm{pH}$ alters/denatures the tertiary/ $3 \mathrm{D}$ protein/enzyme structure;
increasing substrate concentration increases the rate of reaction; higher substrate concentration increases chance of collision;
until plateau;when all active sites are busy; Accept clearly annotated graph.
Question
a. Outline the role of condensation and hydrolysis in metabolic reactions involving carbohydrates.[4]
b. Metabolic reactions are catalysed by enzymes. Explain how enzymes catalyse reactions and how a change in pH could affect this.[8]
c. Describe the digestion of food in the human digestive system. $[6]$
▶️Answer/Explanation
Ans:
a. condensation is joining together molecules with the release of water;
(in general) two monosaccharides join to form a disaccharide / many mono-saccharides/disaccharides form polysaccharides;
example; (eg. two glucose from maltose)
hydrolysis is the breaking down of molecules with the addition of water;
(in general) disaccharides break into monosaccharides / polysaccharides break into disaccharides/monosaccharides;
example; (eg. maltose forms two glucose)
b. enzymes speed up the rate of chemical reactions;
lock and key model;
substrate fits into active site;
enzyme-substrate specificity;
enzymes work best at optimal $\mathrm{pH} /$ different enzymes have different optimal pHs;
increase/decrease from optimum $\mathrm{pH}$ decreases activity;
change in $\mathrm{pH}$ changes structure/charge of active site;
changing three-dimensional structure of enzyme/protein;
not allowing substrate to fit in active site;
enzymes can be denatured if change is extreme;
denaturing is loss of its biological properties;
sketch graph showing $\mathrm{pH}$ versus enzyme activity;
c. chewing food makes smaller particles/increases surface area of food;
starch digestion (begins) in the mouth/by saliva/(salivary) amylase/ptyalin;
digestion of proteins in stomach;
acid condition in stomach provides optimum $\mathrm{pH}$ for enzymes;
stomach muscle contraction causes mechanical digestion;
enzymes in small intestine complete digestion;
alkaline condition in small intestine provides optimum $\mathrm{pH}$ for enzymes;
bile salts help to emulsify fats;
example of amylase with source, substrate and products;
example of protease with source, substrate and products;
example of lipase with source, substrate and products;