Image: Why eat?

Because we're hungry? Not necessarily. But biologically speaking…we eat to get energy. The food we eat is broken down, the glucose extracted, and that energy is converted into ATP.

Cellular Respiration

What happens to the energy stored in glucose during photosynthesis? How do living things make use of this stored energy? The answer is cellular respiration. This process releases the energy in glucose to make ATP (adenosine triphosphate), the molecule that powers all the work of cells.

Stages of Cellular Respiration

Cellular respiration involves many chemical reactions. The reactions can be summed up in this equation:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Chemical Energy (in ATP)

The reactions of cellular respiration can be grouped into three stages: glycolysis (stage 1), the Krebs cycle, also called the citric acid cycle (stage 2), and electron transport (stage 3). Figurebelow gives an overview of these three stages, which are further discussed in the concepts that follow. Glycolysis occurs in the cytosol of the cell and does not require oxygen, whereas the Krebs cycle and electron transport occur in the mitochondria and do require oxygen.

Image: Cellular respiration takes place in the stages shown here. The process begins with a molecule of glucose, which has six carbon atoms. What happens to each of these atoms of carbon?

Structure of the Mitochondrion: Key to Aerobic Respiration

The structure of the mitochondrion is key to the process of aerobic (in the presence of oxygen) cellular respiration, especially the Krebs cycle and electron transport. A diagram of a mitochondrion is shown in Figure below.

Image: The structure of a mitochondrion is defined by an inner and outer membrane. This structure plays an important role in aerobic respiration.

As you can see from Figure above, a mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is called the intermembrane space. The space enclosed by the inner membrane is called the matrix. The second stage of cellular respiration, the Krebs cycle, takes place in the matrix. The third stage, electron transport, takes place on the inner membrane.

Overview of Cell Respiration (Video)

Summary

Cellular respiration takes the energy stored in glucose and transfers it to ATP.
Cellular respiration has three stages: glycolysis: the Krebs cycle and electron transport.
The inner and outer membranes of the mitochondrion play an important roles in aerobic respiration.

Review

Define cellular respiration.
What are the three stages of cellular respiration?
Describe the structure of the mitochondrion and discuss the importance of this structure in cellular respiration.
Assume that a new species of organism has been discovered. Scientists have observed its cells under a microscope and determined that they lack mitochondria. What type of cellular respiration would you predict that the new species uses? Explain your prediction.
When you exhale onto a cold window pane, water vapor in your breath condenses on the glass. Where does the water vapor come from?

____________________________________________________________________________

Image: In the presence of oxygen. Why?

Oxygen is made by trees and other plants during photosynthesis. We know that we need oxygen to live. But why? This oxygen is an essential component for the optimal production of usable energy - which occurs through cellular respiration.

Cellular Respiration-Advanced

You know that humans deprived of oxygen for more than a few minutes will quickly become unconscious and die. Breathing, also known as respiration, is essential for human life, because the body cannot store oxygen for later use as it does food. The mammalian respiratory system, shown in Figure below features a diaphragm, trachea, and a thin membrane whose surface area is equivalent to the size of a handball court - all for efficient oxygen intake. Other forms of life employ different types of respiratory organs: fish and aquatic amphibians and insects flaunt gills, spiders and scorpions develop "book lungs," and terrestrial insects use an elaborate network of tubes called tracheae, which open via spiracles, as shown in Figure below. A constant supply of oxygen gas is clearly important to life. However, do you know why you need oxygen?

Image: (left) The human respiratory system is only part of the story of respiration. Diaphragm, lungs, and trachea take air deep into the body and provide oxygen gas to the bloodstream. The fate of that oxygen is the story of cellular respiration. (center) Spiracles in this Cluentius Sphinx (Neococytius cluentius) caterpillar connect to a system of internal tubes (tracheae), which carry oxygen throughout the animal's body. (right) Gills in this alpine newt larva, Ichthyosaura alpestris, bring blood close to an extensive surface area so that the newt can absorb dissolved oxygen gas from its watery habitat.

Many people would answer that oxygen is needed to make carbon dioxide, the gas exhaled or released by each of the respiratory systems listed above. However, CO₂ is a waste product. But a waste product of what?

There must be more to this story than just gas exchange with the environment. To begin to appreciate the role of oxygen inside your body, think about when your breathing rate increases: climbing a steep slope, running a race, or skating a shift in a hockey game. Respiration rate correlates with energy use, and that correlation reflects the link between oxygen and energy metabolism. For this reason, the chemical process inside your cells that consume oxygen to produce usable energy is known as cellular respiration. During this process, energy is converted from glucose, in the presence of oxygen, into numerous ATP molecules. The glucose, of course, comes from the food you eat. In biological terms, you do not eat because you are hungry, you eat to get energy. Other heterotrophic organisms also acquire glucose from other organisms, whereas autotrophic organisms make their own glucose, mostly through photosynthesis.

Though cellular respiration can occur anaerobically without oxygen, the process is much more efficient under aerobic conditions, in the presence of oxygen. And what exactly is the role of oxygen? Oxygen is the final electron acceptor of the electron transport chain in the final step of cellular respiration. Oxygen combines with electrons and hydrogen ions to produce water.

Summary

Respiration is the exchange of gases between the body and the outside air.
Cellular respiration is the cellular process which transfers chemical energy from glucose to ATP.
Oxygen is essential to have efficient cellular respiration; most organisms need oxygen for a single purpose: to release energy from food for use by cells.

Review

Why do nearly all organisms die without a constant supply of oxygen?
Describe the difference between respiration and cellular respiration.
What is the role of oxygen in cellular respiration?
Which is most efficient, aerobic respiration or anaerobic respiration?

Additional videos for study:

Cell Respiration and the Mighty Mitochondria (Video) Cellular Respiration and the Mighty Mitochondria

Cell respiration- Pulteney Science (Video) Cellular Respiration Explained

Overview of Cell respiration - Khan Academy (Video) Overview of cellular respiration | Cellular respiration | Biology | Khan Academy

Introduction to Cellular respiration- Khan Academy (Video) Introduction to cellular respiration | Cellular respiration | Biology | Khan Academy

ATP & Respiration- Crash course (Video) ATP & Respiration: Crash Course Biology #7

Cell Respiration- Bozeman (Video)Cellular Respiration

Content modified from ck-12

https://www.ck12.org/biology/Cellular-Respiration/lesson/Cellular-Respiration-BIO/ and

https://www.ck12.org/biology/Cellular-Respiration/lesson/Cellular-Respiration-Advanced-BIO-ADV/

Except as expressly otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with theCreative Commons Attribution – Non-Commerical 3.0 Unported (CC BY-NC) License ( http://creativecommons.org/licenses/by-nc/3.0/) , as amended and updated by Creative Commons from time to time (the “CC BY-NC License”).

If you wish to download the contents of this page as a printable pdf, click here Cellular-Respiration.pdf

If you wish to download the contents of this page as a printable pdf, click here Cellular-Respiration-Advanced-BIO-ADV.pdf