Test: Photosynthesis - UPSC MCQ

Therefore, Photosynthesis is an Oxidation-Reduction reaction which takes place in two steps; light reaction and dark reaction. With the help of Question and Answers we have tried to cover the whole process and also we come to know how light energy is converted into chemical energy.
It can be explained via equation also:
6Co₂ + 12 H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O

The metal present in chlorophyll 'a' and 'b' is C. Magnesium. Chlorophyll is a pigment found in chloroplasts of plants and is essential for photosynthesis. It consists of a complex ring structure known as a porphyrin ring, with a central magnesium atom. The magnesium ion plays a crucial role in capturing light energy and converting it into chemical energy during the process of photosynthesis.

In bacteria, the color of light responsible for photosynthesis is primarily red light. Bacterial photosynthesis is carried out by pigments called bacteriochlorophylls, which absorb light energy to drive the photosynthetic process. These bacteriochlorophylls are adapted to absorb light in the red region of the electromagnetic spectrum, allowing bacteria to perform photosynthesis under low-light conditions, such as in deep water or soil.

Photosynthesis is an anabolic process. Anabolic processes involve the synthesis or building of complex molecules from simpler ones, typically requiring an input of energy. In the case of photosynthesis, plants and some other organisms use energy from sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂). This process involves the synthesis of glucose, a complex organic molecule, from simpler inorganic molecules.

On the other hand, catabolic processes involve the breakdown of complex molecules into simpler ones, typically releasing energy. Exothermic (option C) refers to processes that release heat energy. While photosynthesis is a metabolic process (option D) as it involves chemical reactions in living organisms, the specific category that describes it is anabolic (option B).

The rate of photosynthesis does not depend on the duration of light. It is primarily influenced by factors such as the quality of light (option A), intensity of light (option B), and temperature (option D).

Quality of light refers to the specific wavelengths of light that are available for photosynthesis. Different pigments, such as chlorophyll, absorb light at different wavelengths, and the efficiency of photosynthesis can vary depending on the quality of light.

Intensity of light refers to the amount or brightness of light. The rate of photosynthesis generally increases with higher light intensity, up to a certain saturation point. Beyond that point, further increases in light intensity may not significantly enhance the rate of photosynthesis.

Temperature plays a crucial role in photosynthesis as it affects enzyme activity and the overall metabolic processes involved. Photosynthesis rates tend to increase with higher temperatures within a certain range, but excessively high or low temperatures can negatively impact the process.

However, the duration of light, within reasonable limits, does not significantly affect the rate of photosynthesis. As long as the necessary factors like light quality, intensity, and temperature are favorable, the rate of photosynthesis will primarily depend on those factors rather than the duration of light exposure.

The thylakoid is the structural unit of photosynthesis. It is a flattened membrane-bound compartment found within the chloroplasts of plant cells and some algae. Thylakoids are arranged in stacks called grana (option B), and they contain pigments such as chlorophyll (option D). The thylakoid membranes contain the photosystems and other components necessary for capturing light energy and carrying out the light-dependent reactions of photosynthesis.

The stroma (option C) is the gel-like fluid surrounding the thylakoids within the chloroplasts. It is where the light-independent reactions, also known as the Calvin cycle, take place. While the stroma is an important part of the chloroplast, it is not the specific structural unit of photosynthesis.

Therefore, option A, the thylakoid, is the correct answer as the structural unit of photosynthesis.

Quantasomes, also known as photosynthetic units or light-harvesting complexes, are found in the thylakoid membrane of chloroplasts. Thylakoid membranes are the internal membrane systems within chloroplasts where photosynthesis takes place.

Quantasomes are specialized protein-pigment complexes that are responsible for capturing light energy during the light-dependent reactions of photosynthesis. They consist of various pigments, such as chlorophyll and carotenoids, along with associated proteins. These pigments absorb light energy and transfer it to the reaction centers in the thylakoid membrane, where further processes of photosynthesis occur.

Therefore, option B, the thylakoid membrane of chloroplasts, is the correct location where quantasomes are found.

Chlorophyll is the pigment responsible for the absorption of light in plants. It is a group of green pigments found in the chloroplasts of plant cells. Chlorophyll absorbs light energy from the sun and plays a critical role in photosynthesis, where it captures light energy and converts it into chemical energy that can be used by the plant to produce glucose and oxygen.

The other options mentioned are not pigments but different plant structures or tissues. Stoma refers to the small openings on the surface of leaves that allow for gas exchange. Xylem and phloem are vascular tissues responsible for the transport of water, nutrients, and sugars throughout the plant.

For photosynthesis in green plants to occur, all of the mentioned factors are required. Green plants require:

A. Chlorophyll: Chlorophyll is the primary pigment responsible for capturing light energy and initiating the process of photosynthesis.

B. Light: Light energy is necessary for the photosynthetic process to take place. It provides the energy needed to convert carbon dioxide and water into glucose and oxygen.

C. Carbon dioxide and water: Green plants require carbon dioxide (CO2) and water (H2O) as the raw materials for photosynthesis. These molecules are used to produce glucose and oxygen through the process of photosynthesis.

Therefore, all three factors - chlorophyll, light, and carbon dioxide/water - are essential for photosynthesis in green plants to occur, making option D the correct answer.

The dark reaction, also known as the Calvin cycle or the light-independent reaction, is called "dark" because it does not directly require light energy to occur. Unlike the light-dependent reactions of photosynthesis, which require light energy to generate ATP and NADPH, the dark reaction can occur in the absence of light. It takes place in the stroma of the chloroplasts and utilizes the ATP and NADPH produced during the light-dependent reactions to convert carbon dioxide (CO2) into glucose and other organic compounds. Hence, it is called the dark reaction because it can occur in the dark or in the absence of light.