▶️ Answer/Explanation
(a)
Function of the cell: This pancreatic cell secretes digestive enzymes, which are proteins, into the small intestine.
Relevant organelles and their roles:
- Nucleus:
a. Contains genes that are transcribed to mRNA for enzyme production. - Rough Endoplasmic Reticulum (RER):
b. Has ribosomes on its surface that synthesize proteins (digestive enzymes) from mRNA instructions. - Mitochondria:
c. Produces ATP, supplying energy needed for protein synthesis and secretion. - Golgi Apparatus:
d. Modifies and packages enzymes into vesicles. - Vesicles:
e. Transport enzymes to the plasma membrane for secretion via exocytosis.
(b) (i) Lipase catalyzes the hydrolysis (breakdown) of lipids/triglycerides into fatty acids and glycerol.
(ii) Protease
Markscheme:
(a)
a. genes for digestive enzymes are transcribed in the nucleus;
b. rough ER/ribosomes produces/synthesizes enzymes/proteins;
c. mitochondrion produces ATP to provide energy for protein/enzyme production;
d. Golgi apparatus/body processes enzymes/proteins
OR
Golgi apparatus/body packages enzymes into vesicles;
e. vesicles carry enzymes to (plasma) membrane
OR
vesicles secrete enzymes by exocytosis;
(b)
(i) digestion/hydrolysis/break down of lipids/fats/triglycerides (into fatty acids and glycerol);
(ii) amylase / endopeptidase / trypsin / trypsinogen / protease;
▶️ Answer/Explanation
(a)
- Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the enzyme responsible for carbon fixation in the Calvin cycle of photosynthesis.
- It catalyzes the carboxylation of RuBP (ribulose bisphosphate) by CO₂, leading to the production of organic molecules (e.g., glucose).
(b)
- The active site is the region of an enzyme where the substrate binds and the reaction is catalyzed.
- It provides a specific shape that matches the substrate (lock and key model).
(c)
The species is Pisum sativum, so the genus is: Pisum
(d)
- Factor name and effect on enzyme activity must be included.
- Example:
- Temperature – as temperature increases, enzyme activity increases up to an optimum point, then decreases rapidly due to denaturation.
Markscheme:
(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.
▶️ Answer/Explanation
a.
- Example: Fructose
b(i).
Lactose is a disaccharide
(It is made of two monosaccharides: glucose and galactose)
b(ii).
This is a hydrolysis reaction
(Water is used to break the glycosidic bond between the two monosaccharides)
c.
Enzymes are more stable at low temperatures, so:
- Less denaturation occurs → enzymes last longer.
- Lower energy costs in industry compared to heating to 48°C.
- Reduces bacterial growth and spoilage (especially in dairy products like milk).
- Allows better control of the rate of reaction and product formation.
Markscheme:
a. Other examples of monosaccharides:
- Fructose
- Ribose
- Deoxyribose
- Ribulose
- Other monosaccharides apart from glucose and galactose
b (i). Type of carbohydrate lactose is:
- Disaccharide
b (ii). Type of chemical reaction:
- Hydrolysis
c. Reasons for using lactase at low temperatures (5°C):
- 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 the rate of reaction.
▶️ Answer/Explanation
a.
- Monosaccharides are single sugar units; disaccharides consist of two monosaccharides; polysaccharides are long chains of monosaccharides.
- Hydrolysis involves the addition of water to break bonds between sugar units.
- This reaction adds -OH and -H to the fragments (from water).
- Disaccharides are broken into two monosaccharides (e.g., lactose → glucose + galactose).
- Polysaccharides are broken into disaccharides or monosaccharides.
- These reactions are enzyme-controlled in living organisms.
b.
- Certain yeast species naturally produce the enzyme lactase.
- These yeasts are cultured using biotechnology to extract lactase enzyme.
- Lactase is added to milk to hydrolyze lactose into glucose and galactose.
- Alternatively, milk is passed over immobilized lactase enzymes.
- The resulting lactose-free milk is easier to digest for lactose-intolerant individuals.
- Lactose-free milk reduces symptoms like bloating, cramps, and diarrhea.
- Biotechnology allows industrial-scale production of lactose-free milk, especially in populations with high lactose intolerance (e.g., many Asians).
- It provides both a health benefit and an economic opportunity.
c.
- Enzymes act as biological catalysts, increasing the speed of digestion.
- They allow reactions to occur at normal body temperature.
- Enzymes are specific to substrates (e.g., amylase for starch).
- Digestion involves sequential steps, e.g., proteins → peptides → amino acids.
- Different enzymes work in specific environments (e.g., low pH in the stomach for pepsin).
- Enzymes like:
- Amylase breaks carbohydrates → monosaccharides
- Protease breaks proteins → amino acids
- Lipase breaks fats → fatty acids and glycerol
- Enzymes optimize nutrient absorption by converting macromolecules into absorbable units.
Markscheme:
a. Role of Hydrolysis in Carbohydrate Relationships
– Monosaccharides are single sugars, 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., disaccharides);
– Process depends on enzyme control (in organisms);
b. Biotechnology in Lactose-Free Milk Production
– 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 (glucose and galactose);
– Same effect when milk is passed past immobilized (on surface or beads) lactase;
– Simpler forms of sugar are easily absorbed (in the small intestine);
– A commercial market exists for lactose-free milk / example of biotechnology’s economic impact;
– Some people are lactose intolerant / cannot digest lactose / lack lactase activity;
– Consuming lactose-free milk avoids discomfort (e.g., abdominal cramps, diarrhea);
– Many Asians are lactose intolerant, while less common in other groups (e.g., northern Europeans);
– Biotechnology produced in one region may be more useful in another;
c. Importance of Enzymes in Human Digestion
– Enzymes increase the rate of digestion;
– Enzymes are biological catalysts;
– Enzymes allow digestion to occur at body temperature;
– Enzymatic digestion is sequential (e.g., protein → peptide → amino acid);
– Specific locations/environments for reactions (e.g., stomach high acidity);
– Most enzymes work extracellularly / some intracellularly;
– Variations in \(\mathrm{pH}\) optimize different digestive enzymes;
– Amylases digest carbohydrates to monosaccharides;
– Proteases digest proteins to amino acids;
– Lipases digest fats to fatty acids and glycerol;
▶️ Answer/Explanation
a.
- Ventilation is the movement of air into and out of the lungs — involves inhalation and exhalation.
- It is driven by respiratory muscle activity, such as the diaphragm and intercostal muscles.
- Gas exchange is the diffusion of oxygen and carbon dioxide:
- Between the alveoli and the blood in lung capillaries, and
- Between the blood and body cells in tissues.
- Cell respiration is the release of energy (in the form of ATP) from organic molecules like glucose.
- Aerobic cell respiration takes place in the mitochondria and requires oxygen.
b.
- Begins with glycolysis in the cytoplasm, where glucose is partially oxidized.
- Produces a small amount of ATP and forms two molecules of pyruvate.
- Pyruvate is transported into the mitochondrion, where it is fully broken down.
- Oxygen is required for the breakdown of pyruvate.
- Carbon dioxide is produced as a waste product.
- Water is also produced.
- Results in a large yield of ATP (approximately 36–38 ATP per glucose molecule).
c.
- Enzyme activity depends on collisions between the enzyme’s active site and its substrate.
- Temperature:
- Activity increases with temperature due to more frequent collisions.
- There is an optimum temperature where the enzyme works best.
- Above the optimum, enzymes become denatured (active site shape changes).
- pH:
- Each enzyme has an optimum pH.
- Deviation from optimum pH reduces activity.
- Extreme pH values can cause denaturation of the enzyme.
- Substrate concentration:
- Increasing substrate increases activity due to more collisions.
- Eventually, a plateau is reached when all enzyme active sites are occupied (enzyme saturation).
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.
▶️ Answer/Explanation
a.
- Condensation reactions involve joining molecules together with the release of water.
- Example: Two monosaccharides (e.g., two glucose) combine to form a disaccharide (e.g., maltose).
- Many monosaccharides can also join to form polysaccharides (e.g., starch, glycogen, cellulose).
- Hydrolysis reactions involve breaking down molecules with the addition of water.
- Disaccharides can be broken down into monosaccharides, and polysaccharides into smaller sugar units.
- Example: Maltose is hydrolyzed to form two glucose molecules.
b.
- Enzymes speed up the rate of chemical reactions by lowering the activation energy.
- They follow the lock and key model — the substrate fits precisely into the enzyme’s active site.
- This results in enzyme-substrate specificity.
- pH affects enzyme activity — each enzyme has an optimal pH where it functions best.
- A change in pH alters the charge and structure of the active site.
- This can reduce or stop enzyme activity by preventing substrate binding.
- Extreme pH changes can denature enzymes, causing loss of function.
- Denaturation involves a change in the enzyme’s three-dimensional shape.
- A graph of enzyme activity vs. pH typically shows a peak at the optimum and a drop on either side.
c.
- Chewing in the mouth increases surface area of food, aiding enzyme action.
- Starch digestion begins in the mouth by salivary amylase (ptyalin), which converts starch to maltose.
- Protein digestion occurs in the stomach, where pepsin breaks proteins into smaller peptides.
- The acidic pH in the stomach (due to HCl) is ideal for pepsin function.
- Mechanical digestion continues via muscle contractions in the stomach wall.
- In the small intestine, digestion is completed by enzymes like:
- Pancreatic amylase: starch → maltose → glucose
- Proteases (e.g., trypsin): proteins → peptides → amino acids
- Lipases: fats → fatty acids + glycerol
- The small intestine has an alkaline pH, which is optimal for most digestive enzymes there.
- Bile salts (from the liver) emulsify fats, increasing surface area for lipase action.
Markscheme:
a.
• Condensation is joining together molecules with the release of water;
• (In general) two monosaccharides join to form a disaccharide / many monosaccharides/disaccharides form polysaccharides;
• Example: (e.g., two glucose form 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: (e.g., 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;