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230. After deamination of an amino acid, the remaining carbon skeleton most appropriately enters metabolism as:
ⓐ. a chlorophyll precursor outside respiration
ⓑ. an organic acid that joins the respiratory pathway
ⓒ. a fixed gas used directly in photosynthesis
ⓓ. a non-metabolic residue stored unchanged in vacuoles
Correct Answer: an organic acid that joins the respiratory pathway
Explanation: Deamination removes the amino group from an amino acid and leaves behind a carbon framework. This remaining carbon skeleton is metabolically useful and can enter respiration after conversion into an appropriate organic acid. Once it joins the respiratory pathway, it can contribute to further oxidation and energy release. This shows how proteins can act as respiratory substrates under suitable conditions. The step also illustrates the interconnection between protein metabolism and central respiration. Therefore the most appropriate fate of the deaminated carbon skeleton is entry as an organic acid into the respiratory pathway.
231. What is the respiratory quotient in plant respiration?
ⓐ. The ratio of ATP formed to glucose used during respiration
ⓑ. The ratio of carbon dioxide evolved to oxygen consumed during respiration
ⓒ. The ratio of oxygen evolved to carbon dioxide absorbed in leaves
ⓓ. The ratio of water formed to carbon dioxide released in cells
Correct Answer: The ratio of carbon dioxide evolved to oxygen consumed during respiration
Explanation: The respiratory quotient, usually written as RQ, is a numerical expression used in respiration studies. It is defined as the ratio of the volume or amount of carbon dioxide released to the volume or amount of oxygen taken in during respiration. This value helps in understanding the nature of the respiratory substrate being used by the plant. Different substrates produce different RQ values because they differ in chemical composition and oxygen requirement. The concept is therefore very useful in comparing carbohydrate, fat, protein, and organic acid respiration. Hence RQ is the ratio of carbon dioxide evolved to oxygen consumed.
232. Which formula correctly represents respiratory quotient?
ⓐ. $RQ = \frac{O_2\ \text{consumed}}{CO_2\ \text{evolved}}$
ⓑ. $RQ = \frac{\text{ATP formed}}{\text{glucose used}}$
ⓒ. $RQ = \frac{CO_2\ \text{evolved}}{O_2\ \text{consumed}}$
ⓓ. $RQ = \frac{CO_2\ \text{absorbed}}{O_2\ \text{released}}$
Correct Answer: $RQ = \frac{CO_2\ \text{evolved}}{O_2\ \text{consumed}}$
Explanation: The formula for respiratory quotient directly follows its definition. It compares the carbon dioxide produced during respiration with the oxygen consumed during the same process. This ratio is written as $RQ = \frac{CO_2\ \text{evolved}}{O_2\ \text{consumed}}$. The formula is important because it allows the respiratory behavior of different substrates to be compared quantitatively. If the numerator and denominator change in different proportions, the RQ value changes accordingly. Therefore the correct formula is $CO_2$ evolved divided by $O_2$ consumed.
233. What is the respiratory quotient when glucose is used as the respiratory substrate?
ⓐ. 1
ⓑ. 0.5
ⓒ. 2
ⓓ. 0.7
Correct Answer: 1
Explanation: When glucose is completely oxidized in aerobic respiration, the number of molecules of carbon dioxide produced is equal to the number of molecules of oxygen consumed. This leads to an RQ value of 1. Glucose is a carbohydrate, and carbohydrates typically show an RQ of 1 under complete aerobic conditions. The equality of carbon dioxide release and oxygen uptake makes this value especially easy to remember. It is often used as the standard reference while comparing other respiratory substrates. Hence the respiratory quotient for glucose is 1.
234. Why do fats generally have a respiratory quotient lower than 1?
ⓐ. Because fats release more carbon dioxide than oxygen they require
ⓑ. Because fats contain more oxygen within the molecule than carbohydrates
ⓒ. Because fats require relatively more oxygen for complete oxidation
ⓓ. Because fats do not produce carbon dioxide during respiration
Correct Answer: Because fats require relatively more oxygen for complete oxidation
Explanation: Fats are relatively poor in oxygen compared with carbohydrates, so they need more external oxygen for complete oxidation. Since the oxygen consumed becomes proportionally greater than the carbon dioxide released, the RQ value falls below 1. This is why fats generally show an RQ around 0.7. The lower value reflects the chemical nature of fat molecules rather than an absence of carbon dioxide formation. Their oxidation is therefore more oxygen-demanding than that of carbohydrates. Hence fats have an RQ lower than 1 because they require relatively more oxygen for complete oxidation.
235. The respiratory quotient of fats is usually closest to:
ⓐ. 1.0
ⓑ. 1.5
ⓒ. 0.7
ⓓ. 2.0
Correct Answer: 0.7
Explanation: Fats generally have an RQ lower than 1 because their molecules contain less oxygen and require more oxygen from outside for complete oxidation. The commonly accepted approximate value for fat respiration is about 0.7. This value is important in distinguishing fat metabolism from carbohydrate metabolism, which usually gives an RQ of 1. The lower RQ is therefore a useful indicator that fats are acting as the respiratory substrate. It is one of the standard values taught in plant respiration. Thus the respiratory quotient of fats is usually about 0.7.
236. Which of the following substrates typically shows an RQ greater than 1?
ⓐ. Fats
ⓑ. Proteins
ⓒ. Glucose
ⓓ. Organic acids
Correct Answer: Organic acids
Explanation: Organic acids generally show an RQ greater than 1 because they already contain a comparatively high proportion of oxygen within their molecules. As a result, less oxygen needs to be taken from outside during respiration in relation to the carbon dioxide released. This raises the value of the ratio above 1. Such a value contrasts with fats and proteins, which usually give RQ values less than 1. Therefore an RQ greater than 1 is commonly associated with organic acids as respiratory substrates. This makes them distinct from carbohydrates and fats in RQ comparisons.
237. The respiratory quotient of proteins is generally:
ⓐ. around 0.9
ⓑ. exactly 2.0
ⓒ. exactly 1.0
ⓓ. nearly infinite
Correct Answer: around 0.9
Explanation: Proteins usually show an RQ lower than 1, but it is not as low as that of fats. Their commonly accepted approximate RQ value is around 0.9. This happens because the chemical composition of proteins differs from that of carbohydrates and fats, especially after deamination and further oxidation of their carbon skeletons. The value therefore reflects the nature of proteins as respiratory substrates. It is useful in comparing their respiratory behavior with that of other organic compounds. Hence the respiratory quotient of proteins is generally about 0.9.
238. In alcoholic fermentation, the respiratory quotient (RQ) is considered:
ⓐ. zero
ⓑ. one
ⓒ. half
ⓓ. infinite
Correct Answer: infinite
Explanation: Respiratory quotient is calculated as:
$RQ = \frac{CO_2\ \text{evolved}}{O_2\ \text{consumed}}$
In alcoholic fermentation, carbon dioxide is evolved but oxygen is not consumed. Therefore, the denominator becomes zero, so the RQ is considered infinite.
239. If the amount of carbon dioxide evolved is equal to the amount of oxygen consumed, the respiratory quotient will be:
ⓐ. less than 1
ⓑ. more than 1
ⓒ. equal to 1
ⓓ. equal to 0
Correct Answer: equal to 1
Explanation: Respiratory quotient is calculated by dividing carbon dioxide evolved by oxygen consumed. When both values are equal, the ratio becomes 1. This situation is typical of carbohydrate respiration under complete aerobic conditions, especially when glucose is used as the substrate. The equality means that neither gas dominates in the ratio. It therefore produces the standard RQ value associated with carbohydrates. Hence if carbon dioxide evolved equals oxygen consumed, the respiratory quotient is 1.
240. Why is the respiratory quotient useful in plant physiology?
ⓐ. It helps identify the probable type of respiratory substrate being used
ⓑ. It shows the exact number of chloroplasts present in a tissue
ⓒ. It measures the total water content of a respiring organ
ⓓ. It determines the rate of transpiration through stomata
Correct Answer: It helps identify the probable type of respiratory substrate being used
Explanation: The respiratory quotient is useful because different respiratory substrates tend to show different characteristic values. Carbohydrates usually give an RQ of 1, fats around 0.7, proteins about 0.9, and organic acids above 1. By comparing the observed RQ with these values, one can infer the likely nature of the substrate being respired. This makes RQ an important physiological indicator rather than just a mathematical ratio. It helps in interpreting metabolic conditions inside plant tissues. Therefore its usefulness lies in indicating the probable respiratory substrate.
241. A respiring plant tissue gives out 12 mL of carbon dioxide while consuming 12 mL of oxygen. What is its respiratory quotient?
ⓐ. 0.5
ⓑ. 2.0
ⓒ. 1.0
ⓓ. 0.7
Correct Answer: 1.0
Explanation: Respiratory quotient is calculated by dividing the amount of carbon dioxide evolved by the amount of oxygen consumed. In this case, both values are equal, so the ratio becomes 12 divided by 12, which is 1. A value of 1 is typical of carbohydrate respiration under complete aerobic conditions. The question tests direct application of the RQ formula rather than simple recall. Equal carbon dioxide output and oxygen uptake always produce this value. Therefore the respiratory quotient here is 1.0.
242. A seed tissue is found to have an RQ of about 0.7 during active respiration. Which respiratory substrate is most likely being used predominantly?
ⓐ. Organic acids
ⓑ. Proteins
ⓒ. Carbohydrates
ⓓ. Fats
Correct Answer: Fats
Explanation: An RQ of about 0.7 is characteristically associated with fats. Fats require relatively more oxygen for complete oxidation because they contain less oxygen within their own molecules than carbohydrates. As a result, the oxygen consumed is proportionally greater than the carbon dioxide evolved, bringing the RQ below 1. This value is therefore a useful clue in identifying the substrate being respired. In practical biology, oil-rich seeds often show such values. Hence an RQ near 0.7 suggests that fats are being used predominantly.
243. A respiring tissue shows an RQ greater than 1. Which conclusion is most appropriate?
ⓐ. It is most likely using organic acids as the substrate
ⓑ. It must be using fats because they require more oxygen
ⓒ. It must be carrying out only protein respiration
ⓓ. It cannot be undergoing respiration at all
Correct Answer: It is most likely using organic acids as the substrate
Explanation: An RQ greater than 1 means that more carbon dioxide is being evolved relative to the oxygen consumed. This pattern is typical of organic acids because they already contain a relatively high proportion of oxygen in their molecules. Due to this internal oxygen content, less external oxygen is needed for complete oxidation. That makes the ratio rise above 1. This is different from fats and proteins, which usually have RQ values below 1. Therefore the most appropriate conclusion is that organic acids are likely being used.
244. Assertion (A): The RQ of alcoholic fermentation is considered infinite.Reason (R): In alcoholic fermentation, oxygen consumption is zero while carbon dioxide is evolved.
ⓐ. Both A and R are true, and R is the correct explanation of A.
ⓑ. Both A and R are true, but R is not the correct explanation of A.
ⓒ. A is true, but R is false.
ⓓ. A is false, but R is true.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: In alcoholic fermentation, oxygen is not used, so the denominator in the RQ formula becomes zero. Since carbon dioxide is evolved, the ratio becomes infinite. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.
245. A student says, “An RQ lower than 1 means that no carbon dioxide is produced during respiration.” Which correction is most accurate?
ⓐ. An RQ lower than 1 means carbon dioxide is absent from all respiratory pathways
ⓑ. An RQ lower than 1 means oxygen consumption is proportionally greater than carbon dioxide evolution
ⓒ. An RQ lower than 1 means only anaerobic respiration is occurring
ⓓ. An RQ lower than 1 means carbon dioxide is converted back into glucose immediately
Correct Answer: An RQ lower than 1 means oxygen consumption is proportionally greater than carbon dioxide evolution
Explanation: A value below 1 does not mean that carbon dioxide is not produced. It simply means that the amount of oxygen consumed is greater than the amount of carbon dioxide released. This situation is commonly seen when fats or proteins are used as respiratory substrates. The carbon dioxide output still exists, but it is proportionally smaller in the ratio. The misunderstanding comes from confusing a reduced ratio with complete absence of one component. Therefore the correct correction is that oxygen consumption is proportionally greater than carbon dioxide evolution.
246. Which comparison between carbohydrate respiration and fat respiration is correct in terms of RQ?
ⓐ. Carbohydrates usually give RQ below 1, while fats usually give RQ equal to 1
ⓑ. Carbohydrates usually give RQ above 1, while fats usually give RQ below 1
ⓒ. Carbohydrates usually give RQ equal to 1, while fats usually give RQ below 1
ⓓ. Carbohydrates usually give infinite RQ, while fats usually give RQ above 1
Correct Answer: Carbohydrates usually give RQ equal to 1, while fats usually give RQ below 1
Explanation: Carbohydrates such as glucose generally show an RQ of 1 because the carbon dioxide released equals the oxygen consumed during complete aerobic oxidation. Fats, however, contain less oxygen within their molecules and therefore require more external oxygen for complete oxidation. This extra oxygen requirement lowers their RQ below 1, typically around 0.7. The comparison is a standard one in plant physiology and helps identify the likely substrate under respiration. Thus carbohydrate respiration and fat respiration can be distinguished clearly by their RQ values. Therefore carbohydrates usually give 1, while fats usually give a value below 1.
247. A plant organ consumes 20 units of oxygen and releases 10 units of carbon dioxide. Which statement is correct?
ⓐ. Its RQ is 2, so organic acids are certainly being used
ⓑ. Its RQ is 1, so carbohydrate is certainly the substrate
ⓒ. Its RQ is 0.5, showing oxygen consumption exceeds carbon dioxide evolution
ⓓ. Its RQ is infinite, showing anaerobic respiration
Correct Answer: Its RQ is 0.5, showing oxygen consumption exceeds carbon dioxide evolution
Explanation: Respiratory quotient is calculated as carbon dioxide evolved divided by oxygen consumed. Here the value is 10 divided by 20, which gives 0.5. This shows that the tissue is consuming proportionally more oxygen than the amount of carbon dioxide it is releasing. Such a value is below 1 and therefore does not match the usual pattern of carbohydrate respiration. The question mainly tests numerical application of the RQ formula and interpretation of a low value. Hence the correct statement is that the RQ is 0.5 and oxygen consumption exceeds carbon dioxide evolution.
248. Which observation would best support the inference that an oil-rich seed is using stored reserves during germination?
ⓐ. The seed shows an RQ close to 1.0 throughout respiration
ⓑ. The seed shows an RQ below 1, near the value typical of fats
ⓒ. The seed shows an RQ greater than 1, typical of organic acids
ⓓ. The seed shows an infinite RQ, indicating no oxygen use at all
Correct Answer: The seed shows an RQ below 1, near the value typical of fats
Explanation: Oil-rich seeds store much of their reserve food as fats. When these fats are used in respiration, the RQ generally remains below 1 because fats require relatively more oxygen for their oxidation. A value near the typical fat RQ therefore supports the inference that stored oils are being utilized during germination. This is a practical application of respiratory quotient in plant physiology. The observation links reserve food composition with the measured gas exchange pattern. Therefore an RQ below 1, near the value typical of fats, best supports that conclusion.
249. What is meant by the rate of respiration in plants?
ⓐ. The speed at which chlorophyll is formed in green tissues
ⓑ. The speed at which respiratory substrates are broken down and energy is released
ⓒ. The speed at which water moves upward through xylem vessels
ⓓ. The speed at which carbon dioxide enters leaves for photosynthesis
Correct Answer: The speed at which respiratory substrates are broken down and energy is released
Explanation: The rate of respiration refers to how fast respiratory reactions proceed in living cells. It is usually understood in terms of the speed of substrate breakdown, oxygen use, carbon dioxide release, and energy liberation. Since respiration is an enzyme-controlled metabolic process, its rate can vary depending on internal and external conditions. A higher rate means respiratory reactions are proceeding more rapidly. This concept is important in plant physiology because the energy needs of tissues differ under different conditions. Therefore the rate of respiration is the speed at which substrates are oxidized and energy is released.