Chapter 6: Cellular Respiration and Energy Pathways Flashcards

Comprehensive practice flashcards based on Chapter 6: Cellular Respiration and Energy Pathways, covering mastering concepts, figures, summary, and end-of-chapter review questions.

Why do all organisms need ATP?

To provide the energy that powers the chemical reactions that occur in their cells.

What are the three general pathways used to generate ATP from food?

Aerobic respiration, anaerobic respiration, and fermentation.

Which organisms perform aerobic respiration?

Organisms from all three domains and all eukaryotic kingdoms.

In which types of organisms do anaerobic respiration and fermentation mostly occur?

Mostly in microorganisms.

What are two ways organisms acquire $\text{O}_2$ for their cells?

By direct diffusion across the cell membrane, or through specialized gas exchange organs such as gills or lungs.

Why do plants carry out both photosynthesis and cellular respiration?

Plants use carbohydrates produced in photosynthesis as the energy source for cellular respiration, which generates ATP to power cell activities.

What chemical equation summarizes aerobic respiration?

$$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$$

What is the primary carbohydrate broken down during glycolysis?

Glucose.

Why do the reactions of cellular respiration occur step-by-step instead of all at once?

If the reactions occurred all at once, the sudden release of heat energy would destroy cells.

What are the three main stages of cellular respiration?

Glycolysis, the Krebs cycle, and the electron transport chain.

What occurs during glycolysis?

Glucose is split into two pyruvate molecules, producing ATP and some NADH.

What occurs during the Krebs cycle?

It releases $\text{CO}_2$ and produces additional ATP, NADH, and $\text{FADH}_2$.

What occurs during the electron transport chain stage of cellular respiration?

It uses energy stored in NADH and $\text{FADH}_2$ to create a gradient of hydrogen ions across the inner mitochondrial membrane, which ATP synthase uses to form ATP.

What enzyme uses the hydrogen ion gradient to phosphorylate ADP into ATP?

ATP synthase.

Which cellular organelle produces the majority of ATP in eukaryotic cells?

The mitochondrion.

What are the structural parts of a mitochondrion?

An outer membrane, a highly folded inner membrane, an intermembrane compartment between the two membranes, and an inner fluid called the mitochondrial matrix.

What are cristae in a mitochondrion?

Folds of the inner mitochondrial membrane that house electron transport chain proteins.

Where do the transition step and the Krebs cycle occur in a eukaryotic cell?

In the mitochondrial matrix.

Where is the electron transport chain located in eukaryotic cells?

Embedded in the inner mitochondrial membrane.

Where in a eukaryotic cell does glycolysis take place?

Outside the mitochondrion, in the cell's cytosol.

Does glycolysis require oxygen to function?

No, glycolysis does not require $\text{O}_2$.

How is substrate-level phosphorylation defined?

An enzyme directly transfers a phosphate group from a donor molecule to ADP, forming ATP.

How is chemiosmotic phosphorylation defined?

An electron transport chain creates a gradient of $\text{H}^+$ ions, and ATP synthase uses the potential energy in that gradient to add a phosphate group to ADP.

What is the net gain of ATP and NADH per glucose molecule in glycolysis?

A net gain of 2 ATPs and 2 NADHs.

How many carbon atoms are in pyruvate compared to an acetyl group?

Pyruvate has three carbon atoms; an acetyl group has two.

What happens to the third carbon atom removed from pyruvate during the transition step?

It is released as $\text{CO}_2$.

How does the Krebs cycle begin?

The two-carbon molecule acetyl CoA reacts with a four-carbon molecule to produce citrate.

What happens to citrate during the Krebs cycle?

It is rearranged and oxidized through several intermediate molecules, releasing two $\text{CO}_2$ molecules and storing energy/electrons in ATP, NADH, and $\text{FADH}_2$.

How do electrons from NADH and $\text{FADH}_2$ create a proton gradient in the electron transport chain?

As electrons pass along proteins in the chain, the proteins use their energy to pump hydrogen ions into the intermembrane space.

What is the role of $\text{O}_2$ in the electron transport chain?

$\text{O}_2$ is the final electron acceptor at the end of the electron transport chain.

What molecule is produced when oxygen accepts electrons at the end of the electron transport chain?

Water ($\text{H}_2\text{O}$).

What is the theoretical yield of ATP per glucose molecule in aerobic respiration?

36 ATP molecules.

How many ATP molecules are theoretically yielded by 10 NADH molecules in the electron transport chain?

30 ATP molecules.

How many ATP molecules are theoretically yielded by 2 $\text{FADH}_2$ molecules in the electron transport chain?

4 ATP molecules.

How many total ATP are produced directly by electron transport prior to subtracting shuttle costs?

34 ATP molecules.

What energy cost is subtracted when calculating the net theoretical yield of 36 ATP per glucose?

2 ATP (the cost of moving NADH from glycolysis into the intermembrane space).

What is the actual ATP yield per glucose molecule under real cellular conditions?

About 30 ATP per molecule of glucose.

Why is the actual ATP yield lower than the theoretical yield of 36 ATP?

Protons leak across the inner mitochondrial membrane, and energy is used to move pyruvate and ADP into the mitochondrion.

Where do digested polysaccharides enter the energy-extracting pathways?

They are digested to glucose, which enters at glycolysis.

Give two examples of polysaccharides that are digested to glucose for cellular respiration.

Starch and glycogen.

At which entry points can digested protein products enter energy pathways?

As pyruvate, acetyl CoA, or a Krebs cycle intermediate.

What products are fats digested into before entering respiration pathways?

Glycerol and fatty acids.

How does glycerol enter cellular respiration?

It is converted to pyruvate.

How do fatty acids enter cellular respiration?

They are broken down into acetyl CoA molecules that enter the Krebs cycle.

How does the body store excess calories as fat?

Acetyl CoA molecules are diverted from the Krebs cycle and combined to form fats.

What are three examples of alternative electron acceptors used in anaerobic respiration?

Nitrate, sulfate, and carbon dioxide.

How many ATP molecules per glucose molecule does fermentation produce?

2 ATP molecules (produced during glycolysis).

Do fermentation reactions themselves generate any additional ATP beyond glycolysis?

No, fermentation reactions do not generate any additional ATP.

What is the primary function of fermentation reactions?

To restore $\text{NAD}^+$, which allows glycolysis to continue in the absence of oxygen.

What are two common examples of fermentation pathways?

Alcoholic fermentation and lactic acid fermentation.

What organic end products are produced by alcoholic fermentation?

Ethanol and $\text{CO}_2$.

What organic end product is produced by lactic acid fermentation?

Lactic acid (or lactate).

Which energy pathway is considered the most ancient, and why?

Glycolysis, because virtually all cells possess it, and it does not require $\text{O}_2$, allowing it to arise in an $\text{O}_2$-free environment.

Why must the earliest metabolic pathways on Earth have been anaerobic?

Because life existed before cyanobacteria began releasing $\text{O}_2$ into the atmosphere.

How did mitochondria originate according to endosymbiotic theory?

When ancient host cells engulfed free-living aerobic bacteria capable of using $\text{O}_2$ in energy pathways.

How did chloroplasts originate according to endosymbiotic theory?

When an ancient host cell engulfed photosynthetic cyanobacteria.

What hypothesis was tested by researchers investigating Philodendron plants in Section 6.10?

That heat produced by the plant helped attract insect pollinators.

What three steps did researchers take to test their hypothesis regarding Philodendron heat production?

1) Tested temperature differences in flower regions; 2) Measured $\text{CO}_2$ from active/resting beetles at different temps; 3) Calculated energy saved by beetles lingering at warm flowers.

In the beetle experiment comparing 20°C and 30°C holding environments, which group was predicted to fly farther at 20°C?

The beetles held at 30°C.

What are two reasons why beetles kept at 30°C fly farther than those kept at 20°C?

1) They used less energy initially so they have more energy for flight; 2) Flight muscles use energy more efficiently when warm.

What Latin word root is present in 'respiration', and what does it mean?

It contains the root spiro, which means 'to breathe'.

Why was cellular respiration named after whole-body breathing?

Cells use $\text{O}_2$ and expel $\text{CO}_2$ in cellular respiration, just as lungs absorb $\text{O}_2$ and get rid of $\text{CO}_2$ in breathing.

Which process was understood long before cellular respiration was discovered?

Whole-body respiration.

What intermediate molecule connects glycolysis to the Krebs cycle?

Acetyl CoA (formed from pyruvate during the transition step).

What would happen to the Krebs cycle if glycolysis stopped working?

The Krebs cycle would stop due to the absence of acetyl CoA.

What would happen to the electron transport chain if the Krebs cycle stopped working?

Its main source of electron carriers (NADH and $\text{FADH}_2$) would be lost, stopping most ATP synthesis.

What essential electron acceptor molecules are regenerated when NADH and $\text{FADH}_2$ donate electrons to the ETC?

$\text{NAD}^+$ and $\text{FAD}$.

Why do glycolysis and the Krebs cycle stop if the electron transport chain is shut down?

Because $\text{NAD}^+$ and $\text{FAD}$ are not regenerated.

Why is a mitochondrion's double membrane more efficient for establishing a proton gradient than a single membrane?

The intermembrane space is small and confined, requiring fewer $\text{H}^+$ ions to create an effective gradient.

What would happen to the proton gradient if a mitochondrion had only one membrane?

$\text{H}^+$ ions would be pumped into the huge cytosol, making it extremely difficult to establish a usable gradient.

Why is buying 'pyruvate plus' energy supplements unnecessary?

Cells naturally produce their own pyruvate by breaking down glucose via glycolysis.

What is a cheaper alternative to 'pyruvate plus' supplements that accomplishes the same outcome?

Glucose (or another simple sugar).

What happens to the electron transport chain when a person cannot breathe oxygen?

It becomes 'clogged' with electrons, preventing NADH and $\text{FADH}_2$ from unloading electrons.

Why are fat reserves depleted when a person starves for an extended period?

The body breaks down stored fats into glycerol and fatty acids to feed into energy pathways.

Why is muscle tone lost during extended starvation?

Proteins in muscle tissue are broken down into amino acids and used for energy.

Where do glycolysis and the Krebs cycle occur in a bacterial cell?

In the bacterial cytosol.

Where is the electron transport chain embedded in a bacterial cell?

In the bacterial cell membrane.

How does endosymbiosis account for the location of the electron transport chain in mitochondria?

The engulfed bacterium's cell membrane evolved into the mitochondrial inner membrane.

How does endosymbiosis account for the location of the Krebs cycle in mitochondria?

The engulfed bacterium's cytoplasm evolved into the mitochondrial matrix.

When might human muscle cells shift from aerobic respiration to fermentation?

When oxygen supply is insufficient during strenuous exercise.

In what habitats do organisms rely solely on fermentation?

In habitats with plenty of sugar but little to no oxygen.

Why do diverse species like humans and yeasts use identical energy extraction pathways?

The pathways evolved early in a common ancestor shared by humans, yeasts, and other species.

How many ATP molecules are required to synthesize one glucose molecule in photosynthesis?

18 ATP molecules (plus 12 NADPH molecules).

How does the ATP requirement of producing glucose in photosynthesis compare to the ATP yield of aerobic respiration?

Photosynthesis requires 18 ATP to make one glucose, while aerobic respiration yields about 30 ATP per glucose.

How does the ATP yield of fermentation compare to the ATP required for photosynthesis?

Fermentation yields only 2 ATP per glucose, far less than the 18 ATP required in photosynthesis.

What is the source of carbonation in beer that is bottled uncarbonated with yeast?

Yeast carries out fermentation inside the bottle, producing alcohol and $\text{CO}_2$ gas.

How many total NADH molecules are produced during the transition step per glucose?

2 NADH molecules.

How many total NADH molecules are produced during the Krebs cycle per glucose?

6 NADH molecules.

How many total $\text{FADH}_2$ molecules are produced during the Krebs cycle per glucose?

2 $\text{FADH}_2$ molecules.

How many total ATP molecules are produced by substrate-level phosphorylation in the Krebs cycle per glucose?

2 ATP molecules.

How many total NADH molecules are supplied to the electron transport chain from one glucose molecule?

10 NADH molecules (2 from glycolysis, 2 from transition step, 6 from Krebs cycle).

How many total $\text{FADH}_2$ molecules are supplied to the electron transport chain from one glucose molecule?

2 $\text{FADH}_2$ molecules (both from Krebs cycle).

How many ATP molecules are generated per single NADH in the electron transport chain?

3 ATP molecules.

How many ATP molecules are generated per single $\text{FADH}_2$ in the electron transport chain?

2 ATP molecules.

What is the total theoretical gross ATP output from all three stages before subtracting transport costs?

38 ATP molecules (2 from glycolysis + 2 from Krebs + 34 from ETC).

What is the net yield of ATP in glycolysis?

2 ATP molecules.

What is the formula of glucose?

$$\text{C}_6\text{H}_{12}\text{O}_6$$

What reactants are required for aerobic respiration?

Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) and Oxygen ($\text{O}_2$).

What products are created by aerobic respiration?

Carbon dioxide ($\text{CO}_2$), Water ($\text{H}_2\text{O}$), and ATP.

What molecule accepts electrons at the end of the electron transport chain in aerobic respiration?

Oxygen ($\text{O}_2$).