Short & Long Question Answers with Solution: Respiration in Plants | Biology for Grade 12 PDF Download

Short Answer Type Questions

Q1: Explain the term “Energy Currency” of the cell?
Ans: ATP, or Adenosine triphosphate, serves as the cellular "currency" for energy. This organic compound consists of phosphate groups, adenine, and ribose sugar, and it plays a crucial role in fueling a wide range of biochemical processes within the body. This is why it is commonly referred to as the "Energy Currency of the Cell."

Q2: What is the end product of oxidative phosphorylation?
Ans: The outcome of oxidative phosphorylation includes the generation of ATP (Adenosine triphosphate) and water molecules as its final products.

Q3: Why are mitochondria called the powerhouse of the cell?
Ans: Mitochondria are often referred to as the cell's "energy factories" because they are essential for extracting energy from food molecules through a sequence of enzymatic reactions.

Q4: State why the respiratory pathway is referred to as an amphibolic pathway.
Ans: Fatty acids and proteins are broken down into acetyl CoA to enter the respiratory pathway. Conversely, when fats and proteins are synthesized, materials are taken from the respiratory pathway and utilized in anabolic processes. Anabolism refers to the creation of substances, while catabolism involves their breakdown. Because the respiratory pathway is responsible for both these processes, it is termed the "amphibolic pathway."

Q5: Anaerobic respiration is observed in entities living such as human and angiosperms in aerobic conditions. Why?
Ans: Under typical circumstances in the human body, aerobic respiration occurs. However, during strenuous activities like intense exercise, muscles demand a significant amount of energy (ATP), leading to increased energy consumption to produce the required ATP. This heightened demand can result in oxygen deficiency, prompting muscle cells to resort to anaerobic respiration, producing lactic acid as they strive to meet their energy requirements. In situations where oxygen is scarce, yeast cells undergo anaerobic respiration to generate ethyl alcohol and carbon dioxide.

Q6: The final product of glycolysis is pyruvic acid. Write the three metabolic fates of the pyruvic acid in anaerobic and aerobic conditions as seen in the diagram below.
Ans: Lactic acid is produced through the oxidation of pyruvic acid within skeletal muscles when oxygen is limited (anaerobic conditions). Ethanol is generated through the oxidation of pyruvic acid in yeast cells when oxygen is scarce (anaerobic conditions). Acetyl Co-A is formed by the oxidation of pyruvic acid within the mitochondria when ample oxygen is available (aerobic conditions).

Q7: Aerobic respiration has more efficiency. Justify.
Ans: In this metabolic process, one glucose molecule can potentially generate as many as 36 ATP molecules. In contrast, during anaerobic respiration or fermentation, each glucose molecule produces only 2 ATP molecules, which is notably lower than what is achieved through aerobic respiration. As a result, aerobic respiration is considered more efficient.

Q8: Why is a person fed with glucose or a fruit juice instead of a cheese sandwich that might give more energy, when a person is feeling dizzy?
Ans: Glucose provides rapid energy as it is quickly absorbed into the bloodstream. In contrast, a cheese sandwich takes time to be digested and absorbed. When individuals are unwell and require an immediate energy boost, they are typically provided with glucose or given fruit juice.

Long Answer Type Questions

Q1: Anaerobic respiration is observed in living entities such as humans and angiosperms in aerobic conditions. Why?
Ans: The process of obtaining ATP from glucose without the presence of oxygen is termed anaerobic respiration. In this process, electron acceptors substitute molecular oxygen to generate energy. Normally, aerobic respiration occurs in the human body. However, during strenuous activities like intense exercise and vigorous workouts, our muscles require an elevated level of energy. To meet this energy demand, ATP is generated, leading to a depletion of oxygen in muscle cells. To produce additional energy, muscle cells engage in anaerobic respiration, resulting in the production of lactic acid. In situations where oxygen is limited, yeast cells undergo anaerobic respiration, yielding ethyl alcohol and carbon dioxide as end products.

Q2: Explain the significance of Oxygen in aerobic respiration in the context of ETS.
Ans: Aerobic respiration occurs in the presence of oxygen, and oxygen's role is mainly concentrated in the final phase of this process. Oxygen is crucial as it facilitates the process by removing hydrogen from the system and acts as the ultimate hydrogen acceptor. Unlike photophosphorylation, where light energy is used to create a proton gradient necessary for phosphorylation, respiration relies on the energy from oxidation-reduction reactions, which is why it's called oxidative phosphorylation. When oxygen is absent, electrons cannot flow through the co-enzymes, preventing the proton pump from functioning, and consequently, ATP production is halted.

Q3: Explain Glycolysis. State where it occurs and its end products. Both aerobic and anaerobic respiration determine the fate of these products.
Ans: The process in which glucose, a six-carbon compound, divides into two pyruvic acid molecules, each containing three carbons, is known as the EMP pathway of glycolysis. This glycolytic process takes place in the cell's cytoplasm. Glucose is anaerobically broken down into pyruvic acid, and pyruvic acid can be derived from sucrose found in plants, which is a product of photosynthesis. Sucrose is converted into fructose and glucose by an enzyme called invertase, and these resulting products then enter the glycolytic pathway. Glycolysis involves a sequence of 10 reactions, each regulated by different enzymes, leading to the production of pyruvate from glucose. Pyruvic acid is the primary output of glycolysis, and its metabolic fate depends on the cell's specific needs.
Cells have three ways to handle pyruvic acid generated during glycolysis: lactic acid fermentation, aerobic respiration, and alcoholic fermentation. In anaerobic conditions, such as in unicellular eukaryotes and prokaryotes, fermentation occurs, and pyruvic acid is processed accordingly. In contrast, pyruvic acid enters the Krebs cycle in organisms performing aerobic respiration, a process that results in the complete oxidation of glucose, producing end products like carbon dioxide and water, requiring an oxygen supply. During aerobic respiration, the molecule also enters the Krebs cycle and the electron transport chain, resulting in the production of 38 ATP molecules.
In anaerobic respiration, the molecule undergoes breakdown to form either lactic acid or alcohol, with only 2 ATP molecules generated during this process.

Q4: What are some of the assumptions we make in the respiratory balance sheet? Are these valid enough to be applied to living systems? State comparisons between aerobic respiration and fermentation corresponding to respiration.
Ans: Assumptions:

• The assumed sequence involves the TCA cycle, glycolysis, and the electron transport system (ETS) occurring in the cytoplasm, mitochondrial matrix, and inner mitochondrial membrane, respectively.
• NADH, produced in glycolysis, enters the electron transport chain (ETC) for phosphorylation.
• None of the intermediates in this pathway are used to create other compounds.
• Glucose serves as the primary respiratory substrate.

However, these assumptions do not accurately reflect biological reality because:

• In living systems, these pathways take place simultaneously rather than sequentially.
• ATP is utilized by cells only as needed.
• Enzyme activity is regulated by various mechanisms to control the rate of reactions.

Comparison between Fermentation and Aerobic Respiration:

• Fermentation involves the incomplete breakdown of glucose, whereas aerobic respiration is a complete breakdown of glucose.
• The oxidation of NADH to NAD+ is a slow process in fermentation, whereas it is a rapid reaction in aerobic respiration.
• Fermentation generates 2 ATP molecules, while aerobic respiration produces 38 ATP molecules.

Q5: Discuss “The respiratory pathway is an amphibolic pathway.”
Ans: Respiration is commonly regarded as a catabolic process, where various substances are broken down to extract energy. Different organic compounds like fats, carbohydrates, and proteins release energy as they undergo breakdown within the respiratory pathway. Carbohydrates are first converted into glucose before entering this pathway, while fats are transformed into fatty acids and glycerol, with fatty acids further converted into acetyl CoA for respiration. Similarly, proteins are broken down into amino acids. Interestingly, during the synthesis of fatty acids, acetyl-CoA is removed from the respiratory pathway. This process, which primarily acts as a catabolic pathway for respiratory substrates, also functions as an anabolic pathway for the production of various metabolic products and secondary metabolites. Consequently, the respiratory pathway serves as both a catabolic and anabolic pathway, earning it the term "amphibolic pathway" where catabolism and anabolism coexist.

Q6: Explain Glycolysis. State where it occurs and its end products. In both aerobic and anaerobic respiration, determine the fate of these products.
Ans: This metabolic process occurs within the cell's cytoplasm and is a universal feature among all living organisms. During this process, glucose undergoes partial oxidation, resulting in the formation of two pyruvic acid molecules. These pyruvic acid molecules can be derived from sucrose found in plants, which is a product of photosynthesis. An enzyme called invertase converts sucrose into fructose and glucose, both of which enter the glycolytic pathway. These sugars are then phosphorylated to produce glucose-6-phosphate, which undergoes isomerization to form fructose-6-phosphate.
Glycolysis involves a sequence of ten reactions, each regulated by different enzymes, ultimately leading to the production of pyruvate from glucose. Pyruvic acid is the primary output of glycolysis, and its fate within the cell is determined by its specific metabolic needs. Cells have three methods for managing pyruvic acid produced during glycolysis: lactic acid fermentation, aerobic respiration, and alcoholic fermentation.
In anaerobic conditions, such as those found in unicellular eukaryotes and prokaryotes, fermentation is the prevailing process. In contrast, entities that engage in aerobic respiration, like oxygen-dependent organisms, utilize the Krebs cycle for the complete oxidation of glucose into carbon dioxide and water, a process that requires the presence of oxygen.

Q7: What is oxidative phosphorylation?
Ans: Oxidative phosphorylation is a metabolic route that produces ATP by adding a phosphate group to ADP through the electron transport system. This phosphorylation process takes place within the inner mitochondrial membrane of the cell. ATP synthase becomes active as hydrogen protons move through this mitochondrial membrane. The energy necessary for phosphorylation comes from the oxidation-reduction reactions that occur in respiration. ATP is generated following the transfer of electrons from NADH or FADH₂ to O₂, facilitated by a sequence of electron carriers. As a result, this process is termed oxidative phosphorylation.

Q8: The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration. Explain?
Ans: Aerobic respiration involves the complete oxidation of a glucose molecule, while anaerobic respiration leads to incomplete glucose oxidation. Consequently, aerobic respiration results in higher energy production compared to anaerobic respiration. Both processes yield ATP, but the quantity of ATP generated in aerobic respiration surpasses that of anaerobic respiration.
In aerobic respiration, a single glucose molecule produces a total of 36 ATP molecules, whereas in anaerobic respiration, one glucose molecule yields only two ATP molecules. Therefore, aerobic respiration provides a greater energy yield.

Q9: Explain fermentation.
Ans: Cellular respiration that occurs in the absence of oxygen is referred to as aerobic respiration. Fermentation, on the other hand, is an anaerobic pathway commonly found in many prokaryotes and unicellular eukaryotes. During fermentation, glucose undergoes partial oxidation, leading to the production of acids and alcohol. In plants, glucose is incompletely oxidized during the fermentation process, which unfolds through a series of reactions under anaerobic conditions.
In organisms like yeast, glucose is initially converted to pyruvic acid through partial oxidation. Subsequently, pyruvic acid is further transformed into ethanol and carbon dioxide (CO₂). This particular anaerobic process is known as alcoholic or ethanol fermentation and is catalyzed by two enzymes, pyruvic acid decarboxylase and alcohol dehydrogenase.
In some animal muscle cells and bacteria, pyruvic acid is reduced to lactic acid under anaerobic conditions, with NADH₂ serving as the reducing agent that oxidizes to NAD⁺ during the process. This is termed lactic acid fermentation. The end products of these anaerobic pathways, such as lactic acid, are considered harmful and are often referred to as hazardous processes. For instance, if the concentration of alcohol produced by yeast cells exceeds 13%, it can be lethal to the cells. Additionally, both alcohol and lactic acid fermentation yield significantly less energy compared to aerobic respiration.
Fermentation processes are widely utilized in the food, beverage, and pharmaceutical industries. They play a role in the production of various products, including yogurt, vinegar, bread, and alcoholic beverages.

Q10: Oxygen is critical for aerobic respiration. Explain its role concerning ETS.
Ans: NADH₂ and FADh₂ serve as carriers of energy within the electron transport system and are crucial for ATP production. These electrons undergo a series of steps and ultimately combine with oxygen molecules, with oxygen acting as the final hydrogen acceptor to produce water molecules. In the final phase of aerobic respiration, oxygen becomes indispensable for this process.
Oxidative phosphorylation involves a sequence of events where electrons are transported across an electron gradient, akin to the flow of water through a faucet. Just as the flow of water is obstructed until the tap is opened, the transfer of electrons in this system relies on the presence of oxygen. Oxygen functions as a hydrogen acceptor, initially capturing the first electron, allowing for the subsequent flow of electrons through the electron transport system (ETS). Therefore, oxygen plays a crucial role in establishing a gradient that facilitates the passive transfer of electrons.