Problem 12 - Biology Today and Tomorrow Without Physiology

Question

In eukaryotes, aerobic respiration is completed in the _________. a. nucleus b. mitochondrion c. plasma membrane d. cytoplasm

Step-by-Step Solution

Answer

Aerobic respiration is completed in the mitochondrion.

Step 1: Understanding the Question

The question asks where aerobic respiration is completed in eukaryotic cells. It provides four options as possible answers.

Step 2: Review of Aerobic Respiration

Aerobic respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water. In eukaryotic cells, this process involves several stages: glycolysis, the citric acid cycle, and oxidative phosphorylation.

Step 3: Identify Location of Cellular Processes

Glycolysis occurs in the cytoplasm, the citric acid cycle takes place in the mitochondrial matrix, and oxidative phosphorylation occurs on the inner mitochondrial membrane. The complete process of aerobic respiration culminates in the mitochondria.

Step 4: Selecting the Correct Answer

Given the locations of the various stages, aerobic respiration is ultimately completed in the mitochondrion. Thus, the correct choice is (b) mitochondrion.

Key Concepts

Eukaryotic Cells

Eukaryotic cells are complex and highly organized structures that make up many forms of life. Unlike prokaryotic cells, eukaryotic cells have a defined nucleus where the cell's genetic material is housed. These cells are found in plants, animals, fungi, and protists, making them incredibly diverse.

Key features of eukaryotic cells include membrane-bound organelles, which allow for specialized functions and efficiency in cellular processes. These organelles include the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus, among others. The presence of these structures makes eukaryotic cells highly efficient at metabolism, energy production, and overall cellular activities.

One of the most important organelles in eukaryotic cells for energy production is the mitochondrion, which plays a crucial role in aerobic respiration.

Mitochondrion

The mitochondrion is often referred to as the "powerhouse of the cell" due to its vital role in generating energy. It is a small, double-membrane-bound organelle found in the cytoplasm of eukaryotic cells. Mitochondria are unique in that they have their own genetic material and resemble bacteria in their origin, supporting the endosymbiotic theory.

Mitochondria are the site of aerobic respiration, the process that produces adenosine triphosphate (ATP), which is the energy currency of the cell. This organelle has an inner membrane that folds into structures called cristae, increasing the surface area for the reactions involved in ATP production. The enclosed space, known as the matrix, is where the citric acid cycle (also known as the Krebs cycle) occurs.

• This means that the mitochondrion is integral to energy conversion and plays a critical role in enabling cells to perform their functions effectively.

Cellular Respiration Stages

Cellular respiration is a multi-stage process through which cells harvest energy from food molecules, specifically glucose, and convert it into ATP. It consists of three main stages, each occurring in specific areas of the cell:

**1. Glycolysis** occurs in the cytoplasm of cells, breaking down one molecule of glucose into two molecules of pyruvate while producing a small amount of ATP and NADH.

**2. The Citric Acid Cycle** (Krebs cycle) takes place in the mitochondrial matrix. Here, the pyruvate is transformed and oxidized, producing CO2, NADH, and FADH2, while also generating a small amount of ATP.

**3. Oxidative Phosphorylation** occurs on the inner mitochondrial membrane. This stage involves the electron transport chain and chemiosmosis, and it is during this process that the majority of ATP is produced. Electrons from NADH and FADH2 are transferred through a series of proteins, ultimately generating a large amount of ATP. Through these stages, cells efficiently extract energy from nutrients, highlighting the critical role of the mitochondrion in this essential life process.