Question

Mitochondria a. are involved in cellular respiration. b. break down ATP to release energy for cells. c. contain hemoglobin and cristae. d. have a convoluted outer membrane. e. All of these are correct.

Short answer

The correct statement about mitochondria is: a. Mitochondria are involved in cellular respiration.

Step-by-step solution

Read and understand the statements

Read each of the statements given in the exercise, and try to recall what you know about the structure and function of mitochondria.

Evaluate Statement a

Statement a says mitochondria are involved in cellular respiration. This is a correct statement, as mitochondria are known as the "powerhouse" of the cell. They are responsible for cellular respiration and producing ATP, the cell's energy currency.

Evaluate Statement b

Statement b says mitochondria break down ATP to release energy for cells. This statement is incorrect: while mitochondria produce ATP through cellular respiration, they do not directly break down ATP themselves. Instead, ATP is broken down elsewhere in the cell to release energy for cellular processes.

Evaluate Statement c

Statement c says mitochondria contain hemoglobin and cristae. This statement is partially correct: mitochondria do contain cristae, which are folds in the inner membrane where the production of ATP occurs. However, mitochondria do not contain hemoglobin, as that is a protein found in red blood cells.

Evaluate Statement d

Statement d says mitochondria have a convoluted outer membrane. This statement is incorrect, as it is the inner membrane of mitochondria that is convoluted, forming the cristae mentioned in Statement c. The outer membrane is relatively smooth and porous, allowing for the movement of small molecules.

Evaluate Statement e

Statement e says that all of these statements are correct. Since we have found that some of the statements are incorrect or only partially correct (b, c, and d), Statement e is incorrect.

Choose the correct statement

Based on our evaluation in Steps 2 through 6, the only fully correct statement about mitochondria is Statement a: mitochondria are involved in cellular respiration.

Key concepts

Understanding Cellular Respiration

Cellular respiration is a fundamental biological process wherein cells convert nutrients into energy, which is vital for sustaining life. At its core, cellular respiration is about extracting energy from food molecules like glucose and converting it into a more usable form, adenosine triphosphate (ATP).

This complex procedure takes place in multiple stages, with the first being glycolysis, happening in the cell's cytoplasm, where glucose is split into two molecules of pyruvate. Subsequent steps, including the Krebs cycle and the electron transport chain, occur inside mitochondria.

It's in these mitochondrial steps where the majority of ATP is generated, through a process known as oxidative phosphorylation. During this process, electrons are transferred across the mitochondrial membranes, creating a proton gradient that drives the synthesis of ATP. A noteworthy point for students is that oxygen is essential for the final steps of this sequence – giving it the name aerobic respiration.

ATP Production: The Cell's Energy Currency

ATP is akin to the currency of the cell, and mitochondria could be likened to a bank where this currency is manufactured. This molecule stands for adenosine triphosphate and serves as the primary energy carrier in all living cells. The real magic of ATP lies in its structure, which contains three phosphate groups.

When energy is required, ATP is broken down into adenosine diphosphate (ADP) and a free phosphate molecule, and this reaction releases energy that can be harnessed by the cell. While mitochondria are not the location for the breakdown of ATP (as per the incorrect textbook statement b), they are indeed where ATP is synthesized from ADP and inorganic phosphate, primarily on the inner mitochondrial membrane's cristae through a complex enzyme called ATP synthase. Understanding the cycle of ATP production and consumption is essential to grasp the continuous energy flow within a cell.

Mitochondrial Structure: Powerhouse Design

Visualize the mitochondrion as a specialized cellular power plant with a very distinctive architecture. It possesses a double-membrane structure; an outer membrane that encases the organelle and an inner membrane that folds into structures known as cristae, mentioned in the Step 4 solution.

The inner membrane's folds significantly increase the surface area, which is critical for the enzymes involved in ATP production. Contrary to the statement in the textbook, the outer membrane is not convoluted but smooth and contains proteins called porins, making it permeable to ions and small proteins.

Inside the inner membrane lies the mitochondrial matrix where the Krebs cycle takes place. This compartment contains enzymes, mitochondrial DNA, and ribosomes, all necessary for mitochondrial function. As for hemoglobin, which is incorrectly associated with mitochondria in the textbook exercise, it is actually a component of red blood cells, responsible for oxygen transport, not tied to the mitochondrial function. Proper understanding of the mitochondrial structure aids in comprehending its role in ATP production and cellular respiration.