Photosynthesis

1. During photosynthesis, O₂ of the atmosphere is fixed with the help of

During photosynthesis, O₂ of the atmosphere is fixed with the help of H₂O and sunlight to synthesize carbohydrate and O₂ is evolved by the splitting of

Subscribe on YouTube
CO₂
H₂O
NO₃⁻
PO₄³⁻
This question was previously asked in
UPSC CISF-AC-EXE – 2020
Download PDFAttempt Online
During photosynthesis, $O_2$ is evolved by the splitting of H₂O.
– Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment.
– The overall equation for photosynthesis is $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.
– The process occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
– The light-dependent reactions take place in the thylakoid membranes of chloroplasts. In this stage, light energy is absorbed by chlorophyll, leading to the splitting of water molecules ($H_2O$). This process is called photolysis.
– Photolysis of water ($2H_2O \rightarrow 4e^- + 4H^+ + O_2$) releases electrons (used in the electron transport chain to produce ATP and NADPH), protons ($H^+$), and oxygen gas ($O_2$) as a byproduct. This oxygen is released into the atmosphere.
– The light-independent reactions (Calvin cycle) take place in the stroma of chloroplasts and use the ATP and NADPH produced during the light reactions to fix carbon dioxide ($CO_2$) from the atmosphere and synthesize carbohydrates.
– The question contains a slight inaccuracy by stating “$O_2$ of the atmosphere is fixed with the help of $H_2O$ and sunlight…”. It should be “$CO_2$ of the atmosphere is fixed…”. However, the second part of the sentence correctly asks what $O_2$ is evolved from.
– Based on the mechanism of photosynthesis, the oxygen gas evolved comes directly from the splitting of water molecules during the light-dependent stage.
The origin of oxygen produced during photosynthesis was a significant scientific question. Experiments using isotopic tracers ($^{18}O$) demonstrated that the oxygen evolved comes from water and not from carbon dioxide.

Join Our Telegram Channel

2. Which one of the following is the process involved in photosynthesis?

Which one of the following is the process involved in photosynthesis?

Join Our Telegram Channel
Potential energy is released to form free energy
Free energy is converted into potential energy and stored
Food is oxidized to release carbon dioxide and water
Oxygen is taken, and carbon dioxide and water vapour are given out
This question was previously asked in
UPSC IAS – 2014
Download PDFAttempt Online
Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.
A) Potential energy is released to form free energy: This describes processes like respiration (breakdown of glucose to release energy) or combustion, where stored chemical energy (potential) is converted into usable energy (free).
B) Free energy is converted into potential energy and stored: In photosynthesis, light energy from the sun (a form of free energy) is absorbed and converted into chemical energy stored in the bonds of glucose molecules (a form of potential energy). This is the fundamental energy conversion process in photosynthesis.
C) Food is oxidized to release carbon dioxide and water: This describes respiration, where organic food molecules are broken down in the presence of oxygen to release energy, carbon dioxide, and water.
D) Oxygen is taken, and carbon dioxide and water vapour are given out: Plants take in carbon dioxide and water for photosynthesis and release oxygen as a byproduct. Taking in oxygen and giving out carbon dioxide and water is the process of respiration (which plants also do).
– Photosynthesis uses light energy (free energy) to synthesize organic compounds (food).
– Chemical energy is stored in the bonds of these organic compounds (potential energy).
– The process converts light energy into chemical energy.
The overall equation for photosynthesis is: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$. This shows that carbon dioxide and water, using light energy, are converted into glucose (sugar) and oxygen.

Subscribe on YouTube

3. Which one of the following is not a function of chlorophyll?

Which one of the following is not a function of chlorophyll?

Subscribe on YouTube
Splitting of water
Absorption of photon
Oxidation of carbohydrate
Conversion of light energy into chemical energy
This question was previously asked in
UPSC CAPF – 2021
Download PDFAttempt Online
Chlorophyll is the primary pigment involved in photosynthesis in plants, algae, and cyanobacteria. It is located in chloroplasts and absorbs light energy necessary for the process.
Chlorophyll’s main functions in photosynthesis include the absorption of light energy (photons), initiation of the light-dependent reactions which include the splitting of water molecules (photolysis) to produce oxygen, protons, and electrons, and facilitating the conversion of light energy into chemical energy in the form of ATP and NADPH. The oxidation (breakdown) of carbohydrates, such as glucose, to release energy (ATP) is the process of cellular respiration, which occurs in mitochondria (or cytoplasm/cell membrane in some organisms) and is distinct from the function of chlorophyll and photosynthesis.
Photosynthesis involves two main stages: the light-dependent reactions, where light energy is captured and converted into chemical energy (ATP and NADPH) and water is split; and the light-independent reactions (Calvin cycle), where the chemical energy is used to fix carbon dioxide and synthesize carbohydrates. Chlorophyll is directly involved in the light-dependent reactions.

Join Our Telegram Channel

4. Which one of the following statements is correct?

Which one of the following statements is correct?

Subscribe on YouTube
In photosynthesis by green plants, carbon dioxide is used for making carbohydrate.
During photosynthesis, plants use oxygen for making carbohydrate.
The carbohydrate generated by plants comes from soil.
The carbohydrate generated by plants comes from urea.
This question was previously asked in
UPSC CAPF – 2018
Download PDFAttempt Online
Photosynthesis is the process by which green plants convert light energy into chemical energy in the form of organic compounds (carbohydrates). The inputs for photosynthesis are carbon dioxide (CO₂) and water (H₂O), and the outputs are glucose (a carbohydrate, C₆H₁₂O₆) and oxygen (O₂). The overall chemical equation is approximately 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂. This equation shows that carbon dioxide is directly incorporated into the carbohydrate molecule. Plants absorb CO₂ from the atmosphere through their stomata.
Let’s evaluate the other options:
B) Oxygen is produced as a byproduct during photosynthesis, not used to make carbohydrate.
C) While water and minerals essential for plant growth come from the soil, the carbon atoms that form the backbone of the carbohydrate molecule come from atmospheric carbon dioxide.
D) Urea is a nitrogenous compound used as a fertilizer to provide nitrogen for plant growth. Nitrogen is essential for synthesizing proteins and nucleic acids, but the carbon backbone of carbohydrates comes from CO₂.
Therefore, the correct statement is that carbon dioxide is used for making carbohydrate in photosynthesis.
In photosynthesis, plants use carbon dioxide and water, with the help of light energy and chlorophyll, to synthesize carbohydrates and release oxygen. Carbon dioxide is the source of carbon atoms in the carbohydrate.
Photosynthesis occurs in two main stages: the light-dependent reactions (where light energy is converted into chemical energy in the form of ATP and NADPH, and water is split) and the light-independent reactions (Calvin cycle), where the chemical energy is used to fix carbon dioxide and synthesize glucose.

Join Our Telegram Channel

5. Consider the following statements describing the functions of plants :

Consider the following statements describing the functions of plants :

Subscribe on YouTube
  • 1. Photosynthesis is a process to convert light energy from the Sun into chemical energy i.e., Carbohydrates are synthesized from carbon dioxide and water using sun light
  • 2. Fermentation or Zymology is a metabolic process that converts carbohydrate to alcohols and carbon dioxide

Which of the statements given above is/are correct ?

1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC CAPF – 2014
Download PDFAttempt Online
Both statement 1 and statement 2 are correct descriptions of biological processes that are functions of plants.
Statement 1 is correct. Photosynthesis is the primary metabolic process in most plants (and other photoautotrophs) where light energy is converted into chemical energy in the form of glucose and other carbohydrates using carbon dioxide and water.
Statement 2 is correct. Fermentation is a metabolic process that can occur in plants, particularly under anaerobic or low-oxygen conditions (e.g., in flooded roots or germinating seeds). Alcoholic fermentation, as described, converts carbohydrates into ethanol and carbon dioxide. While not as central a function as photosynthesis, it is a metabolic pathway found in plants. Zymology is the study of fermentation. The description of the process is accurate.
Photosynthesis is essential for the survival of autotrophic plants, forming the base of most food webs. Fermentation in plants can serve various purposes, such as generating ATP under anaerobic conditions, regenerating NAD+ for glycolysis, or producing secondary metabolites. While alcoholic fermentation producing ethanol and CO2 is common (e.g., in yeast), some plants also perform this process. Other types of fermentation exist (e.g., lactic acid fermentation), but the statement specifically describes alcoholic fermentation. Both statements accurately describe processes that are functions of plants.

Join Our Telegram Channel

6. Statement I: When a piece of brick lying on grass for a number of days

Statement I: When a piece of brick lying on grass for a number of days is removed, the covered part of the grass appears pale.
Statement II: Synthesis of chlorophyll, which gives green pigment, occurs in presence of sunlight.

Subscribe on YouTube
Both the statements are individually true and Statement II is the correct explanation of Statement I
Both the statements are individually true but Statement II is not the correct explanation of Statement I
Statement I is true but Statement II is false
Statement I is false but Statement II is true
This question was previously asked in
UPSC CAPF – 2013
Download PDFAttempt Online
Both statements are individually true, and Statement II is the correct explanation of Statement I.
– Statement I describes an observed phenomenon: grass covered by an opaque object (like a brick) becomes pale. This is a common observation.
– Statement II provides a scientific fact: Chlorophyll, the pigment responsible for the green color in plants, requires sunlight for its synthesis. This process is part of photosynthesis.
– The paleness of the grass (loss of green color) occurs because the brick blocks sunlight, preventing the grass from synthesizing chlorophyll. Without chlorophyll, the green pigment is absent or significantly reduced. Therefore, Statement II directly explains why Statement I occurs.
– This phenomenon is an example of etiolation, a process where plants grow in the absence of light, resulting in pale, elongated stems and small leaves due to lack of chlorophyll development.

Join Our Telegram Channel

7. Plants capable of performing photosynthesis belong to which one among

Plants capable of performing photosynthesis belong to which one among the following types of organisms?

Subscribe on YouTube
Heterotrophs
Saprotrophs
Autotrophs
Chemoheterotrophs
This question was previously asked in
UPSC CAPF – 2013
Download PDFAttempt Online
C) Autotrophs
Organisms are classified based on how they obtain energy and carbon.
– Autotrophs are organisms that can produce their own food using light, water, carbon dioxide, or other chemicals. Plants capable of photosynthesis use light energy (photoautotrophs) to synthesize organic compounds from inorganic sources like CO2 and water.
– Heterotrophs obtain carbon by consuming other organisms (plants or animals).
– Saprotrophs are heterotrophs that feed on dead organic matter.
– Chemoheterotrophs obtain both energy and carbon from consuming organic compounds.
Plants that perform photosynthesis are the primary producers in most ecosystems and are classified as autotrophs.
Photosynthesis is a vital process for life on Earth, converting light energy into chemical energy stored in organic molecules. This process releases oxygen as a byproduct, which is essential for the respiration of many organisms, including animals. Algae and some bacteria also perform photosynthesis.

Join Our Telegram Channel

8. Which one of the following is NOT a requirement for photosynthesis ?

Which one of the following is NOT a requirement for photosynthesis ?

Join Our Telegram Channel
Chlorophyll
CO₂
Water
O₂
This question was previously asked in
UPSC NDA-2 – 2023
Download PDFAttempt Online
D) O₂ is NOT a requirement for photosynthesis.
– Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose.
– The main reactants required for photosynthesis are carbon dioxide (CO₂), water (H₂O), and light energy. Chlorophyll is the pigment that captures light energy.
– The general equation for photosynthesis is: 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ (glucose) + 6O₂.
– Chlorophyll is essential as it absorbs light energy necessary to drive the process.
– Carbon dioxide is the source of carbon for synthesizing glucose.
– Water provides hydrogen atoms and electrons, and is also a source of oxygen which is released as a byproduct.
– Oxygen (O₂) is a product of photosynthesis, not a requirement for the process itself. Plants release oxygen into the atmosphere during photosynthesis.

Subscribe on YouTube

9. Which one of the following statements about the process of photosynthe

Which one of the following statements about the process of photosynthesis is correct ?

Join Our Telegram Channel
Chemical energy is converted into light energy.
Carbon dioxide is oxidised to form carbohydrate.
Water molecule splits into hydrogen and oxygen.
Light energy is directly used to split water.
This question was previously asked in
UPSC NDA-2 – 2021
Download PDFAttempt Online
During the light-dependent reactions of photosynthesis, water molecules are split (photolysis) using light energy absorbed by chlorophyll. This process yields oxygen, electrons, and protons (hydrogen ions). Oxygen is released as a byproduct.
Photosynthesis involves two main stages: light-dependent reactions and light-independent reactions (Calvin cycle). The splitting of water occurs in the light-dependent reactions and is crucial for providing electrons and protons for subsequent steps and releasing oxygen.
The overall equation for photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. Carbon dioxide is reduced to carbohydrate, not oxidized. Light energy is converted into chemical energy stored in glucose and other organic molecules.

Subscribe on YouTube

10. The oxygen evolved during photosynthesis comes from splitting of

The oxygen evolved during photosynthesis comes from splitting of

Subscribe on YouTube
water
carbon dioxide
oxygen
light
This question was previously asked in
UPSC NDA-2 – 2018
Download PDFAttempt Online
During photosynthesis, the oxygen gas evolved as a byproduct comes from the splitting of water molecules (photolysis).
– The overall equation for photosynthesis is 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂.
– Experiments using isotopic tracing (specifically, using water labeled with the heavy oxygen isotope ¹⁸O) demonstrated that the ¹⁸O appeared in the evolved oxygen gas, while using carbon dioxide labeled with ¹⁸O resulted in the ¹⁸O appearing in the glucose product, not the oxygen gas.
Water splitting occurs during the light-dependent reactions of photosynthesis, providing electrons for the electron transport chain, protons for the proton gradient used in ATP synthesis, and oxygen as a waste product. The oxygen atoms in glucose are derived from carbon dioxide.

Join Our Telegram Channel
Page 1Page 2Page 3Page 4Page 5