VCAA Biology How are biochemical pathways regulated?

The fermentation process that produces bioethanol also produces carbon dioxide ($CO_2$) as a byproduct, so bioethanol is not the only product.

Microorganisms, such as yeast or specific bacteria, are essential to carry out the fermentation step that converts sugars into bioethanol.

The production of bioethanol involves multiple biochemical steps, each requiring specific, different enzymes (e.g., cellulase to break down cellulose, and various enzymes for fermentation).

Incorrect. The stroma is the fluid-filled space inside the chloroplast where the light-independent reactions (Calvin cycle) take place, not the light-dependent ones.

Incorrect. Mitochondria are the organelles responsible for cellular respiration and ATP production from glucose, not photosynthesis.

Incorrect. Although chloroplasts have an inner membrane, the light-dependent reactions specifically occur on the thylakoid membranes suspended within the chloroplast.

NADH is an input to the electron transport chain, not an output, as it gets oxidized to NAD$^+$. Additionally, water is a byproduct formed when oxygen accepts electrons, not an energy donor.

Oxygen is an input (the final electron acceptor), not an output. Its role is to pull electrons down the chain and combine with hydrogen ions to form water, not to accept energy from ATP.

NADP$^+$ is an electron carrier involved in photosynthesis, not the cellular respiration electron transport chain. Furthermore, oxygen is an input to this process, not an output.

A competitive inhibitor binds to the active site of the enzyme (ATP synthase), not to the product (ATP).

Inhibiting ATP synthase prevents the conversion of ADP to ATP, which would actually increase the amount of ADP present, not reduce it.

Competitive inhibitors bind directly to the active site of an enzyme. Inhibitors that bind to an allosteric site are known as non-competitive inhibitors.

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.

Temperature increases to an optimum and then decreases due to enzyme denaturation, which is a different trend from carbon dioxide concentration, which simply plateaus.

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.

ATP and NADPH (not NADH) are produced during the light-dependent stage in the thylakoid membranes, and they are transported to the stroma for the light-independent stage.

Photosynthesis utilizes NADPH, not NADH. Furthermore, the light-dependent stage produces ATP and NADPH, rather than ADP.

The Krebs cycle is a stage of cellular respiration that occurs in the mitochondria, not a part of photosynthesis.

While carbon dioxide is required for photosynthesis, reducing leaf overlap primarily serves to maximize light exposure rather than directly increasing gas exchange.

Glucose is a product synthesized during photosynthesis, not a reactant that the plant absorbs from its environment.

Oxygen is a byproduct of photosynthesis, not a reactant that needs to be absorbed to increase the rate of the process.

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.

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.

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.

Enzymes are highly specific to their substrates. Because cellular respiration and photosynthesis involve different chemical reactions and substrates, they require different specific enzymes.

The rate of a biochemical reaction is directly affected by enzyme concentration. Increasing enzyme concentration will increase the reaction rate, provided there is excess substrate available.

Decreasing the temperature below the optimal level reduces kinetic energy and slows down the reaction rate, but it does not cause enzymes to denature. Denaturation is typically caused by high temperatures or extreme pH changes.

The Calvin cycle produces sugar (specifically G3P, which forms glucose) rather than consuming it. Its actual inputs are $CO_2$, ATP, and NADPH.

While sometimes called the dark reactions, the Calvin cycle actually occurs mostly during the day because it relies on the ATP and NADPH continuously generated by the light-dependent reactions.

The Calvin cycle does not require high humidity to function. However, very low humidity might cause a plant to close its stomata, indirectly slowing the cycle by restricting $CO_2$ intake.

Oxygen is a byproduct of the light-dependent reactions, not a reactant in the light-independent reactions. Additionally, photosynthesis uses NADPH, not NADH.

Oxygen is produced during the light-dependent reactions, not used in the light-independent reactions. Also, the cycle consumes ATP rather than ADP to build sugars.

While carbon dioxide and ATP are correct inputs, the light-independent reactions use NADPH as a reducing agent, whereas NADH is primarily involved in cellular respiration.