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Questions and Answers
What is the primary respiratory substrate used in cellular respiration?
What is the primary respiratory substrate used in cellular respiration?
- Organic acids
- Fats
- Carbohydrates (correct)
- Proteins
All the energy from respiratory substrates is released at once during cellular respiration.
All the energy from respiratory substrates is released at once during cellular respiration.
False (B)
What acts as the energy currency of the cell?
What acts as the energy currency of the cell?
ATP
The sequence of use of respiratory substrates is carbohydrates, _____, and proteins.
The sequence of use of respiratory substrates is carbohydrates, _____, and proteins.
Match the following respiratory substrates with their calorific values:
Match the following respiratory substrates with their calorific values:
Which of the following statements accurately describes cellular respiration?
Which of the following statements accurately describes cellular respiration?
Plants have specialized organs for gas exchange.
Plants have specialized organs for gas exchange.
What are the alternatives to carbohydrates that can be used as respiratory substrates?
What are the alternatives to carbohydrates that can be used as respiratory substrates?
What type of respiration occurs when carbohydrates or fats are oxidized inside the cell?
What type of respiration occurs when carbohydrates or fats are oxidized inside the cell?
Plants require large volumes of gases for respiration during photosynthesis.
Plants require large volumes of gases for respiration during photosynthesis.
What is the primary end product of aerobic respiration?
What is the primary end product of aerobic respiration?
Plants utilize __________ respiration when no oxygen is present.
Plants utilize __________ respiration when no oxygen is present.
Match the type of respiration with its key characteristic:
Match the type of respiration with its key characteristic:
How many molecules of ATP are gained from anaerobic respiration for each molecule of glucose?
How many molecules of ATP are gained from anaerobic respiration for each molecule of glucose?
During aerobic respiration, oxygen acts as the final hydrogen acceptor.
During aerobic respiration, oxygen acts as the final hydrogen acceptor.
Name an example of a substance that can act as a hydrogen acceptor during alcoholic fermentation.
Name an example of a substance that can act as a hydrogen acceptor during alcoholic fermentation.
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Study Notes
Cellular Respiration
- Oxidation of C–C single bonds in complex compounds releases energy and synthesizes ATP.
- Energy is released gradually through a series of enzyme-controlled reactions to prevent excessive heat generation.
- ATP serves as the energy currency of the cell, breaking down when energy is needed.
- Respiratory substrates primarily include carbohydrates (mainly glucose), fats, proteins, and organic acids.
- Gross calorific values:
- Carbohydrates: 4.1 kcal/g
- Proteins: 5.65 kcal/g
- Fats: 9.45 kcal/g
- Physiological values:
- Carbohydrates: 4.0 kcal/g
- Proteins: 4.0 kcal/g
- Fats: 9.0 kcal/g
- Sequence of use for respiratory substrates: carbohydrates → fats → proteins.
- Organic acids, such as malic acid, can also serve as respiratory substrates under specific conditions.
Features of Cellular Respiration
- Cellular respiration is an amphibolic process, producing carbon skeletons used for synthesizing other molecules.
- It is an exergonic process, as it releases significant energy from breaking C–C bonds.
Respiration in Plants
- Plants lack specialized organs for gas exchange, relying on stomata and lenticels.
- Each plant part manages its gas exchange, resulting in minimal gas transport needs.
- Gas exchange demands in plants are low compared to animals.
- While photosynthesis occurs, O2 is released, alleviating O2 availability issues for cells.
- Gas diffusion distances are short within the plant, facilitating access to air by most cells.
- Parenchyma cells create air spaces that further enhance gas exchange.
Types of Respiration
Based on Respiratory Substrates
- Floating Respiration: Involves oxidation of carbohydrates or fats, utilizing these substrates stored within the cell.
- Protoplasmic Respiration: Involves oxidation of proteins, occurring in starved cells as proteins are constituents of protoplasm.
Based on Presence of Oxygen
-
Aerobic Respiration:
- Complete oxidation of glucose yielding CO2 and H2O.
- Intermolecular respiration with a yield of 36 or 38 ATP molecules per glucose.
- NADH is oxidized vigorously to NAD+; O2 serves as the final hydrogen acceptor.
- Reaction: C6H12O6 + 6O2 → 6CO2 + 12H2O + 686 kcal.
-
Anaerobic Respiration/Fermentation:
- Partial breakdown of glucose producing lactic acid or ethanol and CO2.
- Intramolecular respiration with a yield of only 2 ATP molecules per glucose.
- NADH oxidation occurs slowly; hydrogen acceptors include acetaldehyde (alcoholic fermentation) or pyruvate (lactic acid fermentation).
- Reaction: C6H12O6 → 2CH3CH2OH + 2CO2 + less than 7% of energy of glucose.
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