QCAA Biology Alternative Sequence Exchange of nutrients and wastes
8 sample questions with marking guides and sample answers
Which reaction is catalysed by amylase enzymes?
starch maltose
proteins amino acids
lactose glucose and galactose
triglycerides free fatty acids and glycerol
Reveal Answer
starch maltose
Amylase is the specific enzyme responsible for breaking down complex carbohydrates like starch into simpler sugars such as maltose.
proteins amino acids
The breakdown of proteins into amino acids is catalyzed by protease enzymes, such as pepsin or trypsin, rather than amylase.
lactose glucose and galactose
The digestion of the disaccharide lactose into glucose and galactose is catalyzed by the enzyme lactase, not amylase.
triglycerides free fatty acids and glycerol
The hydrolysis of triglycerides into free fatty acids and glycerol is catalyzed by lipase enzymes, not amylase.
Intestinal microvilli are
absorptive epithelial cells in the large intestine.
folds in the small intestine that are lined with blood and lymphatic vessels.
extensions of the intestinal surface cells that are specialised for absorption.
motile extensions of the intestine that help move food through both intestines.
Reveal Answer
absorptive epithelial cells in the large intestine.
Microvilli are subcellular structures, not entire cells, and they are primarily found on the epithelial cells of the small intestine rather than the large intestine.
folds in the small intestine that are lined with blood and lymphatic vessels.
This describes villi, which are larger, multicellular folds in the intestinal lining. Microvilli are microscopic projections on the surface of individual cells.
extensions of the intestinal surface cells that are specialised for absorption.
Microvilli are tiny, finger-like projections on the apical surface of intestinal epithelial cells that significantly increase the surface area available for nutrient absorption.
motile extensions of the intestine that help move food through both intestines.
Microvilli are non-motile structures designed for absorption, unlike cilia which are motile. Food is moved through the intestines by muscular contractions called peristalsis.
The main nitrogenous waste excreted by mammals in urine is
ammonia.
ornithine.
uric acid.
urea.
Reveal Answer
ammonia.
Incorrect. Ammonia is highly toxic and is primarily excreted by aquatic animals, whereas mammals convert it into a less toxic substance before excretion.
ornithine.
Incorrect. Ornithine is an amino acid involved in the urea cycle to help process nitrogenous waste, but it is not the waste product itself.
uric acid.
Incorrect. Uric acid is the primary nitrogenous waste excreted by birds, reptiles, and insects to conserve water, not mammals.
urea.
Correct. Mammals convert toxic ammonia into urea in the liver, which is highly soluble and less toxic, making it the primary nitrogenous waste excreted in their urine.
The diffusion of ions between nephrons and capillaries in the kidney is efficient because
capillaries have thin walls.
nephrons have large diameters.
ion concentrations are isotonic.
capillaries have low blood pressure.
Reveal Answer
capillaries have thin walls.
Thin capillary walls, which are only one cell thick, minimize the distance ions must travel, thereby maximizing the rate and efficiency of diffusion.
nephrons have large diameters.
A larger diameter would decrease the surface area-to-volume ratio, which would actually make diffusion less efficient.
ion concentrations are isotonic.
Diffusion requires a concentration gradient to occur. If the solutions were isotonic (equal in concentration), there would be no net movement of ions.
capillaries have low blood pressure.
While capillary pressure affects bulk flow and filtration, diffusion is driven by concentration gradients and short distances, not low blood pressure. Furthermore, glomerular capillaries in the kidney actually have relatively high pressure to facilitate filtration.
Explain how a change in the metabolic activity of an organism could affect its enzyme function.
Reveal Answer
Increase in metabolic activity (e.g. due to illness or exercise) can increase body temperature. Enzymes are essential proteins to cell function with a specific range of conditions (e.g. temperature) when they function best. Deviations beyond that range in temperature affect the enzyme’s ability to interact with the substrate, preventing the catalysis of reactions essential for cell function.
| Descriptor | Marks |
|---|---|
Explains a relevant factor changing as a result of metabolic function | 1 |
Explains the specific role of enzymes (catalysis) | 1 |
Explains what effect factor change has on enzyme function | 1 |
The active site of an enzyme consists of
lipids.
amino acids.
nucleic acids.
carbohydrates.
Reveal Answer
lipids.
Incorrect. Enzymes are proteins, not lipids. Lipids are primarily involved in energy storage and cell membrane structure, not in forming catalytic active sites.
amino acids.
Correct. Enzymes are proteins, which are made up of folded chains of amino acids. The active site is formed by a specific 3D arrangement of these amino acids that bind to the substrate and catalyze the reaction.
nucleic acids.
Incorrect. Nucleic acids (DNA and RNA) store and transmit genetic information. While a few specialized RNA molecules called ribozymes can act as catalysts, standard enzymes and their active sites are composed of amino acids.
carbohydrates.
Incorrect. Carbohydrates are sugars used for energy and structural support. Although some enzymes have carbohydrate groups attached to them, the actual catalytic active site is made of amino acids.
Identify which factor is most likely to cause an increase in the reaction rate of an enzyme.
the presence of inhibitors
a decrease in temperature
an increase in pH of the solution
an increase in concentration of the substrate
Reveal Answer
the presence of inhibitors
Inhibitors bind to enzymes and decrease their activity, which would lower the reaction rate rather than increase it.
a decrease in temperature
Decreasing temperature lowers the kinetic energy of molecules, resulting in fewer collisions between the enzyme and substrate, thus decreasing the reaction rate.
an increase in pH of the solution
Enzymes have a specific optimal pH. Increasing the pH beyond this optimal level can denature the enzyme and decrease the reaction rate.
an increase in concentration of the substrate
Increasing substrate concentration increases the frequency of collisions with enzyme active sites, leading to a higher reaction rate until all active sites are saturated.
The table shows a comparison of the quantities of water and solutes in the glomerular filtrate of the kidney and the urine over 24 hours.
| Glomerular filtrate | Urine | |
|---|---|---|
| Water (L) | 170 | 1.5 |
| Glucose (g) | 170 | 0 |
| Sodium (g) | 560 | 5 |
| Urea (g) | 51 | 30 |
Explain how selective reabsorption and secretion across nephron membranes contribute to the urine's composition. Reference the data in your response.
Reveal Answer
Most of the water, glucose and sodium is reabsorbed and not excreted in urine, whereas most of the urea is excreted. Sodium is actively reabsorbed from glomerular filtrate to create a concentration gradient. As a result, only 5 g out of 560 g of sodium is excreted.
Water is reabsorbed out of the glomerular filtrate due to the concentration gradient created by the removal of sodium. The table shows that only 1.5 L of water is excreted from a total of 170 L of filtrate.
Nearly half of the urea is reabsorbed during water reabsorption. Of the original 51 g of urea, only 30 g is excreted, and 21 g reabsorbed. There is no glucose present in the urea as all 170 g of glucose is selectively reabsorbed and transported out of filtrate back to the blood via facilitated transport.
| Descriptor | Marks |
|---|---|
Explains the trends in the data | 1 |
Explains active sodium reabsorption | 1 |
Identifies that water reabsorption is due to sodium (salt) concentration gradient | 1 |
Identifies small amount of urea reabsorption with water | 1 |
Explains how glucose is selectively reabsorbed via facilitated transport | 1 |
If urine output for an adult decreases to an average of 30 mL/h, they are most likely dehydrated. Explain the homeostatic mechanisms that regulate the volume of urine produced during dehydration.
Reveal Answer
Antidiuretic hormone (ADH) stimulates water reabsorption by activating the insertion of water channels into kidney tubule membranes.
These channels transport solute-free water through tubular cells and back into blood, leading to a decrease in urine volume and therefore an increase in urine osmolarity.
| Descriptor | Marks |
|---|---|
Explains the role ADH plays in stimulating water channels | 1 |
Identifies that water is transported back to blood or interstitial fluid | 1 |
Identifies increased urine concentration (osmolarity) | 1 |