Question

The oxygen required by cellular respiration becomes part of which molecule? a. ATP b. \(\mathrm{H}_{2} \mathrm{O}\) c. pyruvate \(\mathrm{d} . \mathrm{CO}_{2}\)

Short answer

The oxygen required by cellular respiration ultimately becomes part of the water (H2O) molecule during the electron transport chain. Therefore, the correct answer is option b. H2O.

Step-by-step solution

Understand Cellular Respiration

Cellular respiration is a process used by cells to break down glucose into usable energy in the form of ATP. This process occurs in three main stages: glycolysis, the Krebs cycle (citric acid cycle), and the electron transport chain.

Analyze the Role of Oxygen in Cellular Respiration

Oxygen plays a crucial role in the final stage of cellular respiration - the electron transport chain (ETC). During this stage, electrons are transported through a series of protein complexes, ultimately combining with oxygen to produce water (H2O). This final reaction is essential for the entire process, as it allows for the regeneration of NAD+ and FAD, which are then used in earlier stages of cellular respiration.

Identify the Molecule with Oxygen

Now that we know oxygen is involved in the electron transport chain stage of cellular respiration to produce water (H2O), we can eliminate the other options: a. ATP - Oxygen is not a part of the ATP molecule. c. Pyruvate - Oxygen is not a part of the pyruvate molecule. d. CO2 - Although oxygen is a part of the CO2 molecule, it is not where the oxygen required for cellular respiration ends up.

Choose the Correct Option

After analyzing the role of oxygen in cellular respiration and examining the given options, we can conclude that oxygen ends up as a part of the following molecule: b. H2O (Water) So, the correct answer is option b. H2O.

Key concepts

Glycolysis

In the fascinating journey of transforming glucose into energy, the first step we encounter is glycolysis. Think of glycolysis as the warm-up phase where the glucose molecule, a 6-carbon sugar, is split into two 3-carbon molecules called pyruvate. This process occurs in the cytoplasm of the cell and doesn’t require oxygen, which is why it’s termed anaerobic.

During glycolysis, a little bit of ATP is produced, but more importantly, the stage sets the stage for the subsequent steps. NAD+ molecules gain electrons from glucose, becoming NADH, which will later carry these electrons to the electron transport chain for further energy extraction. In terms of improving students' understanding of this concept, it's useful to visualize glycolysis as a priming step – it prepares the carbon structures and harvests some energy investments for the heavy lifting to come in later stages.

Krebs cycle

After glycolysis, we dive into the Krebs cycle, also known as the citric acid cycle. Here, the narrative unfolds within the mitochondria, where the pyruvate is ushered into a series of chemical reactions that extract electrons and produce carbon dioxide as a byproduct.

Each turn of the Krebs cycle results in the further breakdown of carbon molecules, the production of ATP, and the creation of NADH and FADH₂. These latter two molecules are like buckets brimming with high-energy electrons, ready to be tipped into the next stage. It's like a ride at an amusement park for electrons with numerous stops where carbon dioxide hops off, and high-energy electron pairs board the ride.

Electron Transport Chain

The electron transport chain (ETC) represents the thrilling climax of cellular respiration. Situated within the inner mitochondrial membrane, the ETC is a series of proteins that act as electron shuttles. Here, electrons from NADH and FADH₂ are passed like a hot potato from one protein complex to the next.

With each handoff, energy is released and used to pump hydrogen ions across the membrane, creating a gradient. It's akin to pumping air into a balloon – the higher the pressure, the more potential energy there is. At the end of this chain, oxygen waits patiently, ready to catch these electrons and, along with some hydrogen ions, forms water – the molecule of life.

ATP Production

Now, let's talk about the endgame – ATP production. This mesmerizing finale happens through a process called oxidative phosphorylation. Due to the gradient established by the ETC, hydrogen ions rush back into the mitochondrial matrix through an enzyme called ATP synthase.

This flow is akin to water turning a waterwheel; it harnesses the energy to attach a phosphate group to ADP, creating ATP – the cell's energy currency. In total, a single glucose molecule can yield a bountiful supply of around 30-32 ATP molecules through cellular respiration. This wealth of ATP then powers myriad cellular activities, from muscle contraction to the firing of neurons, illustrating the importance of efficiently understanding and harnessing the power held in the molecular bonds of glucose.