VCAA Biology How are biochemical pathways regulated?
4 sample questions with marking guides and sample answers
ATP synthase is an enzyme that is used in the formation of ATP.
A competitive inhibitor to ATP synthase is introduced into a cell.
The competitive inhibitor would initially
bind to the active site of ATP, blocking it from binding to ATP synthase.
reduce the number of ADP molecules available for moving cellular energy.
bind to the allosteric site of ATP synthase, preventing ADP from binding.
cause more ADP molecules to be present in the cell.
Reveal Answer
bind to the active site of ATP, blocking it from binding to ATP synthase.
A competitive inhibitor binds to the active site of the enzyme (ATP synthase), not to the product (ATP).
reduce the number of ADP molecules available for moving cellular energy.
Inhibiting ATP synthase prevents the conversion of ADP to ATP, which would actually increase the amount of ADP present, not reduce it.
bind to the allosteric site of ATP synthase, preventing ADP from binding.
Competitive inhibitors bind directly to the active site of an enzyme. Inhibitors that bind to an allosteric site are known as non-competitive inhibitors.
cause more ADP molecules to be present in the cell.
By inhibiting ATP synthase, the enzyme can no longer convert ADP and inorganic phosphate into ATP, leading to an initial accumulation of ADP molecules in the cell.
Three factors that affect the rate of photosynthesis in plants are stated below:
- Factor 1 – light intensity
- Factor 2 – carbon dioxide concentration
- Factor 3 – temperature
Scientific data consistently shows specific trends for each factor when other variables are controlled.
Graphs were plotted showing the rate of photosynthesis against an increasing change in each factor.
If plotted over a large range, which of the following would show graphs with the same trend?
factors 1 and 2
factors 1 and 3
factors 2 and 3
factors 1, 2 and 3
Reveal Answer
factors 1 and 2
Both light intensity and carbon dioxide concentration show the same trend: the rate of photosynthesis increases initially and then plateaus when another factor becomes limiting.
factors 1 and 3
Temperature shows a different trend than light intensity; it increases to an optimum point and then rapidly decreases as enzymes denature, whereas light intensity plateaus.
factors 2 and 3
Temperature increases to an optimum and then decreases due to enzyme denaturation, which is a different trend from carbon dioxide concentration, which simply plateaus.
factors 1, 2 and 3
Temperature has a distinct peak and decline curve due to enzyme denaturation, which differs from the plateauing curves of light intensity and carbon dioxide concentration.
During cellular respiration
cells will consistently yield 36 or 38 molecules of ATP from each molecule of glucose.
there is a difference between the theoretical and actual ATP yields when cells break down glucose.
ATP is not produced in the cells in the roots of plants as these cells have no glucose source.
C4 plants consistently produce more ATP from each glucose molecule compared to C3 plants.
Reveal Answer
cells will consistently yield 36 or 38 molecules of ATP from each molecule of glucose.
While 36 to 38 ATP is often taught as the theoretical maximum yield per glucose molecule, cells rarely achieve this consistently due to proton leakage and the energy costs of transporting molecules into the mitochondria.
there is a difference between the theoretical and actual ATP yields when cells break down glucose.
The actual ATP yield (typically around 30-32 ATP) is lower than the theoretical maximum (36-38 ATP) because the proton gradient is also used to drive other transport processes, and some protons leak across the inner mitochondrial membrane.
ATP is not produced in the cells in the roots of plants as these cells have no glucose source.
Plant root cells actively perform cellular respiration to produce ATP. They receive the necessary glucose (transported as sucrose) from the photosynthetic leaves via the plant's phloem.
C4 plants consistently produce more ATP from each glucose molecule compared to C3 plants.
C3 and C4 designations refer to different photosynthetic pathways for carbon fixation, not cellular respiration. Both types of plants use the same general cellular respiration pathways to break down glucose.
A student notices that many plants grow in a way that reduces the overlap of their leaves.
This adaptation allows a faster rate of photosynthesis in the plants as the plants can absorb more
carbon dioxide into the bundle sheath cells.
glucose through the mesophyll cell wall.
oxygen from the air.
light on the grana.
Reveal Answer
carbon dioxide into the bundle sheath cells.
While carbon dioxide is required for photosynthesis, reducing leaf overlap primarily serves to maximize light exposure rather than directly increasing gas exchange.
glucose through the mesophyll cell wall.
Glucose is a product synthesized during photosynthesis, not a reactant that the plant absorbs from its environment.
oxygen from the air.
Oxygen is a byproduct of photosynthesis, not a reactant that needs to be absorbed to increase the rate of the process.
light on the grana.
Reducing leaf overlap maximizes the surface area exposed to sunlight, allowing more light to be absorbed by the chlorophyll located in the grana of the chloroplasts.