# Which Statement About Cellular Respiration is True

## 5.nine: Cellular Respiration

##### Bring on the S’mores!

This inviting campfire tin can exist used for both heat and light. Oestrus and light are two forms of free energy that are released when a fuel like wood is burned. The cells of living things too become energy past “burning.” They “burn down” glucose in the process called cellular respiration.

Within every cell of all living things, energy is needed to carry out life processes. Energy is required to break downwardly and build upwards molecules and to transport many molecules across plasma membranes. All of life’southward work needs energy. A lot of energy is also simply lost to the environment as heat. The story of life is a story of free energy flow — its capture, its change of form, its use for work, and its loss every bit rut. Energy, unlike affair, cannot exist recycled, so organisms crave a constant input of energy. Life runs on chemic energy. Where exercise living organisms get this chemical energy?

## Where do organisms get energy from?

The chemical energy that organisms need comes from food. Food consists of organic molecules that store energy in their chemical bonds. Glucose is a simple carbohydrate with the chemic formula $$\mathrm{C_6H_{12}O_6}$$. It stores chemic free energy in a concentrated, stable form. In your body, glucose is the form of energy that is carried in your claret and taken upward by each of your trillions of cells. Cells practice cellular respiration to extract energy from the bonds of glucose and other food molecules. Cells can store the extracted energy in the form of ATP (adenosine triphosphate).

## What is ATP?

Let’south have a closer look at a molecule of ATP, shown in the figure $$\PageIndex{2}$$. Although information technology carries less energy than glucose, its construction is more complex. “A” in ATP refers to the bulk of the molecule – adenosine – a combination of a nitrogenous base and a five-carbon sugar. “T” and “P” betoken the three phosphates, linked by bonds that concord the energy actually used past cells. Usually, simply the outermost bail breaks to release or spend energy for cellular work.

An ATP molecule is like a rechargeable battery: its free energy can be used by the cell when information technology breaks apart into ADP (adenosine diphosphate) and phosphate, and then the “worn-out battery” ADP tin exist recharged using new energy to attach a new phosphate and rebuild ATP. The materials are recyclable, but recall that free energy is not! ADP can be further reduced to AMP (adenosine monophosphate and phosphate, releasing boosted free energy. As with ADT “recharged” to ATP, AMP tin can be recharged to ADP.

How much energy does it cost to do your torso’southward work? A single cell uses near ten million ATP molecules per second and recycles all of its ATP molecules nearly every 20-thirty seconds.

## What Is Cellular Respiration?

Some organisms can make their ain food, whereas others cannot. An
autotroph
is an organism that can produce its own nutrient. The Greek roots of the word
autotroph
mean “self” (auto) “feeder” (troph). Plants are the best-known autotrophs, but others exist, including certain types of leaner and algae. Oceanic algae contribute enormous quantities of food and oxygen to global nutrient chains. Plants are also
photoautotrophs, a blazon of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical free energy in the form of carbohydrates.
Heterotrophs
are organisms incapable of photosynthesis that must therefore obtain free energy and carbon from nutrient by consuming other organisms. The Greek roots of the word
heterotroph
mean “other” (hetero) “feeder” (troph), meaning that their food comes from other organisms. Even if the food organism is another animal, this food traces its origins dorsum to autotrophs and the process of photosynthesis. Humans are heterotrophs, every bit are all animals. Heterotrophs depend on autotrophs, either direct or indirectly.

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Cellular respiration
is the procedure past which individual cells pause down food molecules, such as glucose and release energy. The procedure is similar to burning, although it doesn’t produce light or intense heat as a campfire does. This is because cellular respiration releases the energy in glucose slowly, in many small-scale steps. It uses the free energy that is released to form molecules of ATP, the energy-carrying molecules that cells use to power biochemical processes. Cellular respiration involves many chemical reactions, but they can all be summed up with this chemic equation:

$\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O + Free energy} \nonumber$

where the energy that is released is in chemical energy in ATP (vs. thermal energy every bit heat). The equation above shows that glucose ($$\ce{C6H12O6}$$) and oxygen ($$\ce{O_2}$$) react to grade carbon dioxide ($$\ce{CO_2}$$) and water $$\ce{H_2O}$$, releasing energy in the process. Because oxygen is required for cellular respiration, it is an
aerobic
process.

Cellular respiration occurs in the cells of all living things, both autotrophs and heterotrophs. All of them catabolize glucose to form ATP. The reactions of cellular respiration tin can exist grouped into three main stages and an intermediate stage:
glycolysis,
Transformation of pyruvate, the
Krebs cycle
(also chosen the citric acid cycle), and
Oxidative Phosphorylation. Effigy $$\PageIndex{3}$$ gives an overview of these three stages, which are also described in detail beneath.

## Glycolysis

The starting time stage of cellular respiration is
glycolysis. This procedure is shown in the top box in Figure $$\PageIndex{3}$$ showing a 6-carbon molecule being broken down into two iii-carbon pyruvate molecules. ATP is produced in this process which takes identify in the cytosol of the cytoplasm.

### Splitting Glucose

The discussion

glycolysis

means “glucose splitting,” which is exactly what happens in this stage. Enzymes split a molecule of glucose into two molecules of pyruvate (also known as pyruvic acid). This occurs in several steps, as shown in figure $$\PageIndex{4}$$. Glucose is commencement dissever into glyceraldehyde 3-phosphate (a molecule containing iii carbons and a phosphate grouping). This procedure uses two ATP. Next, each glyceraldehyde 3-phosphate is converted into pyruvate (a 3-carbon molecule). this produces two iv ATP and 2 NADH.

### Results of Glycolysis

Energy is needed at the start of glycolysis to split the glucose molecule into two pyruvate molecules. These ii molecules get on to stage II of cellular respiration. The free energy to split up glucose is provided by two molecules of ATP. As glycolysis gain, energy is released, and the free energy is used to brand iv molecules of ATP. As a consequence, there is a
net gain of two ATP molecules
during glycolysis. high-free energy electrons are besides transferred to energy-carrying molecules chosen electron carriers through the process
known as reduction. The electron carrier of glycolysis is
. Electrons are transferred to ii NAD+ to produce 2 molecules of NADH. The energy stored in NADH is used in stage Three of cellular respiration to make more ATP. At the end of glycolysis, the following has been produced:
• 2 net molecules of ATP

## Transformation of Pyruvate into Acetyl-CoA

In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are sites of cellular respiration. If oxygen is available, aerobic respiration will go forrard. In mitochondria, pyruvate volition exist transformed into a two-carbon acetyl group (by removing a molecule of carbon dioxide) that will exist picked upwardly by a carrier compound called coenzyme A (CoA), which is made from vitamin B5. The resulting compound is called acetyl CoA and its product is ofttimes called the oxidation or the Transformation of Pyruvate (run into Figure $$\PageIndex{5}$$. Acetyl CoA can be used in a diversity of means past the cell, but its major office is to deliver the acetyl group derived from pyruvate to the side by side pathway step, the Citric Acid Bicycle.

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## Citric Acrid Cycle

Before you read about the last 2 stages of cellular respiration, you lot need to review the construction of the mitochondrion, where these two stages take identify. As you lot can run across from Effigy $$\PageIndex{vi}$$, a mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is chosen the intermembrane space. The space enclosed past the inner membrane is chosen the matrix. The second stage of cellular respiration, the Krebs bike, takes place in the matrix. The third stage, electron send, takes identify on the inner membrane.

Remember that glycolysis produces two molecules of pyruvate (pyruvic acid). Pyruvate, which has three carbon atoms, is split apart and combined with CoA, which stands for coenzyme A. The product of this reaction is acetyl-CoA. These molecules enter the matrix of a mitochondrion, where they starting time the Citric Acid Cycle. The third carbon from pyruvate combines with oxygen to form carbon dioxide, which is released equally a waste product. Loftier-energy electrons are also released and captured in NADH. The reactions that occur next are shown in Figure $$\PageIndex{7}$$.

### Steps of the Citric Acid (Krebs) Cycle

The Citric Acid Cycle begins when acetyl-CoA combines with a iv-carbon molecule chosen OAA (oxaloacetate; see the lower panel of Figure $$\PageIndex{seven}$$). This produces citric acid, which has six carbon atoms. This is why the Krebs cycle is also called the citric acid wheel. After citric acid forms, it goes through a serial of reactions that release energy. This energy is captured in molecules of ATP and electron carriers. The Krebs cycle has two types of energy-carrying electron carriers: NAD+ and FAD. The transfer of electrons to FAD during the Kreb’s Bicycle produces a molecule of FADH2. Carbon dioxide is also released equally a waste material production of these reactions. The concluding step of the Krebs bike regenerates OAA, the molecule that began the Krebs bicycle. This molecule is needed for the next turn through the bike. Two turns are needed because glycolysis produces 2 pyruvate molecules when it splits glucose.

### Results of the Citric Acid Cycle

After the second turn through the Citric Acrid Bicycle, the original glucose molecule has been cleaved downward completely. All six of its carbon atoms have combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in a full of 16 energy-carrier molecules. These molecules are:

• two ATP
• 2 FADH$$_2$$
• 6 CO$$_2$$: ii CO$$_2$$ from Transformation of Acetyl CoA and 4 CO$$_2$$ from Citric Acid Cycle.

## Oxidative phosphorylation

Oxidative phosphorylation is the concluding stage of aerobic cellular respiration. There are two substages of oxidative phosphorylation, Electron transport concatenation and Chemiosmosis. In these stages, energy from NADH and FADHtwo, which result from the previous stages of cellular respiration, is used to create ATP.

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### Electron Ship Chain (ETC)

During this phase, high-energy electrons are released from NADH and FADH2, and they move along electron-send chains found in the inner membrane of the mitochondrion. An electron-transport chain is a serial of molecules that transfer electrons from molecule to molecule by chemical reactions. These molecules are found making up the three complexes of the electron ship chain (scarlet structures in the inner membrane in Figure $$\PageIndex{8}$$). Equally electrons flow through these molecules, some of the free energy from the electrons is used to pump hydrogen ions (H+) across the inner membrane, from the matrix into the intermembrane space. This ion transfer creates an electrochemical gradient that drives the synthesis of ATP. The electrons from the final protein of the ETC are gained by the oxygen molecule, and it is reduced to water in the matrix of the mitochondrion.

### Chemiosmosis

The pumping of hydrogen ions beyond the inner membrane creates a greater concentration of these ions in the intermembrane infinite than in the matrix – producing an electrochemical gradient. This gradient causes the ions to menstruation back across the membrane into the matrix, where their concentration is lower. The flow of these ions occurs through a poly peptide circuitous, known as the ATP synthase complex (see blueish structure in the inner membrane in Effigy $$\PageIndex{8}$$. The ATP synthase acts as a aqueduct protein, helping the hydrogen ions across the membrane. The period of protons through ATP synthase is considered chemiosmosis. ATP synthase also acts as an enzyme, forming ATP from ADP and inorganic phosphate. It is the catamenia of hydrogen ions through ATP synthase that gives the energy for ATP synthesis. After passing through the electron-transport concatenation, the low-energy electrons combine with oxygen to grade water.

## How Much ATP?

You lot take seen how the three stages of aerobic respiration utilise the energy in glucose to make ATP. How much ATP is produced in all three stages combined? Glycolysis produces 2 ATP molecules, and the Krebs cycle produces ii more than. Electron transport from the molecules of NADH and FADH2
made from glycolysis, the transformation of pyruvate, and the Krebs wheel creates as many as 32 more ATP molecules. Therefore, a total of upwards to 36 molecules of ATP can be made from only one molecule of glucose in the process of cellular respiration.

## Review

1. What is the purpose of cellular respiration? Provide a concise summary of the process.
2. Describe and explain the construction of ATP (Adenosine Tri-Phosphate).
3. State what happens during glycolysis.
4. Describe the structure of a mitochondrion.
5. Outline the steps of the Krebs cycle.
6. What happens during the electron transport stage of cellular respiration?
7. How many molecules of ATP can be produced from one molecule of glucose during all three stages of cellular respiration combined?
8. Exercise plants undergo cellular respiration? Why or why not?
9. Explain why the process of cellular respiration described in this department is considered aerobic.
10. Name iii energy-carrying molecules involved in cellular respiration.
11. Energy is stored within chemical _________ within a glucose molecule.

12. True or Fake
. During cellular respiration, NADH and ATP are used to brand glucose.

13. True or False
. ATP synthase acts as both an enzyme and a aqueduct protein.

14. Truthful or False
. The carbons from glucose end up in ATP molecules at the finish of cellular respiration.
15. Which stage of aerobic cellular respiration produces the most ATP?

## Which Statement About Cellular Respiration is True

Source: https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/05%3A_Cells/5.09%3A_Cellular_Respiration