Photosynthesis — Set 3

Correct Answer: B. Atmospheric CO2

Atmospheric carbon dioxide is the sole source of carbon for building the glucose skeleton. It enters the plant through leaf pores and is fixed during the Calvin cycle. This makes plants essential 'carbon sinks' that help regulate global climate.

Correct Answer: B. Maximize light absorption

The stacking of thylakoids into grana increases the surface area for light-harvesting pigments. This organization ensures that solar energy is captured with maximum efficiency. These grana are connected by stroma lamellae within the chloroplast.

Correct Answer: B. Melvin Calvin

Melvin Calvin used radioactive carbon-14 to trace the steps of the dark reactions. His work led to the description of the Calvin cycle, for which he received a Nobel Prize. This cycle explains how plants convert CO2 into energy-rich sugar.

Correct Answer: D. A wasteful process

Photorespiration occurs when rubisco binds with oxygen instead of carbon dioxide. This process consumes energy and releases CO2 without producing any sugar. It is considered a wasteful process that reduces the efficiency of photosynthesis.

Correct Answer: C. Chemical

Photosynthesis transforms solar radiation into the chemical energy stored in molecular bonds. This energy is stored first in ATP/NADPH and then in stable sugars. This chemical energy sustains nearly all life forms on our planet.

Correct Answer: A. Stomata

Stomata are microscopic pores on the leaf surface controlled by guard cells. They regulate the entry of carbon dioxide and the exit of oxygen and water vapor. Their opening and closing are vital for balancing gas exchange and water loss.

Correct Answer: A. Summer

Summer provides the longest duration of sunlight and warmer temperatures conducive to the process. Deciduous plants have full leaf canopies during this time to maximize energy production. In winter, many of these plants lose their leaves and become dormant.

Correct Answer: A. Trigger electron transport

The reaction center contains special chlorophyll a molecules that lose an electron when excited. This electron is passed to a primary acceptor, initiating the light reaction pathway. It is the site where light energy is actually converted to electrical energy.

Correct Answer: B. Oxygen

Oxygen is a product of photosynthesis, not a requirement for the reaction to occur. The primary needs are light energy, water, carbon dioxide, and functional pigments. Without any of these essential inputs, the process cannot proceed.

Correct Answer: B. Efficiency in high temperatures

C4 plants are adapted to high light and high temperature conditions with minimal photorespiration. They use a spatial separation of CO2 fixation and the Calvin cycle to remain productive. This makes them highly competitive in tropical and subtropical regions.