Photosynthesis — Set 2
Biology · प्रकाश संश्लेषण · Questions 11–20 of 50
Plants that open their stomata at night to conserve water are known as?
Correct Answer: D. CAM plants
CAM plants fix carbon dioxide at night and store it as organic acids. This adaptation allows them to survive in extremely arid environments like deserts. Cacti and pineapples are well-known examples of plants using this pathway.
Which of the following is considered the 'Energy Currency' produced during light reactions?
Correct Answer: C. ATP
ATP carries the energy captured from sunlight to power the chemical synthesis of sugars. It is formed during the process of photophosphorylation in the thylakoid. This molecule is essential for all cellular work within the plant.
The rate of photosynthesis is generally highest at which temperature range?
Correct Answer: B. 25-35°C
Photosynthesis involves enzymes that function optimally within a moderate temperature range. Extremes in temperature can denature these enzymes and stop the process entirely. The specific ideal temperature can vary based on the plant's natural habitat.
Which organisms were the first to evolve oxygenic photosynthesis?
Correct Answer: A. Cyanobacteria
Cyanobacteria, often called blue-green algae, pioneered the release of oxygen into Earth's atmosphere. This evolutionary step paved the way for the development of aerobic life forms. They are ancient prokaryotes that contain chlorophyll similar to plants.
What happens to the rate of photosynthesis if light intensity is increased indefinitely?
Correct Answer: A. It reaches a saturation point
The rate of photosynthesis increases with light intensity up to a certain limit. Beyond this saturation point, other factors like CO2 concentration or temperature become limiting. Very high light intensity can also cause damage to the photosynthetic apparatus.
Which of the following is an accessory pigment that protects plants from excessive light?
Correct Answer: A. Carotenoids
Carotenoids absorb excess light energy that could damage the chlorophyll molecules. They give fruits and vegetables their vibrant orange, yellow, and red colors. They also expand the spectrum of light that can be used for photosynthesis.
The process by which ATP is synthesized in the presence of light is called?
Correct Answer: C. Photophosphorylation
Photophosphorylation occurs during the light reactions as electrons move through a transport chain. This creates a proton gradient that drives the production of ATP. It can be either cyclic or non-cyclic depending on the electron path.
In C4 plants, the initial fixation of carbon dioxide occurs in which cells?
Correct Answer: C. Mesophyll cells
Mesophyll cells in C4 plants capture CO2 using the enzyme PEP carboxylase. This adaptation helps the plant minimize photorespiration in hot and dry climates. Sugarcane and maize are classic examples of highly efficient C4 plants.
Which substance acts as the final electron acceptor in the non-cyclic light reactions?
Correct Answer: D. NADP+
NADP+ picks up high-energy electrons to become NADPH at the end of the electron transport chain. NADPH then carries these electrons to the Calvin cycle for sugar production. This molecule provides the reducing power needed for carbon fixation.
The conversion of inorganic carbon into organic compounds by living organisms is called?
Correct Answer: A. Carbon fixation
Carbon fixation is the process of incorporating CO2 into stable organic molecules like sugar. This is the fundamental way energy from the sun enters the global ecosystem. Photosynthesis is the most widespread form of carbon fixation on Earth.