Question

The majority of the G3P produced during the reduction and carbohydrate production phase is used in making a. glucose. b. ATP. c. RuBP to continue the cycle. d. rubisco. e. all of the above.

Short answer

The majority of G3P produced during the reduction and carbohydrate production phase is used to make RuBP to continue the cycle.

Step-by-step solution

Understanding the Calvin Cycle

The Calvin cycle, also known as the dark phase of photosynthesis, is where G3P is made and used. It involves three stages: carbon fixation, reduction and regeneration of RuBP.

Understanding the Use of G3P in the Calvin Cycle

In the Calvin cycle, one molecule of G3P leaves the cycle while the other five molecules are used to regenerate RuBP. Therefore, the majority of the G3P produced is used in the regeneration of RuBP to keep the cycle going.

Determining the Answer

Considering the information that the majority of the G3P is used to regenerate RuBP in the Calvin Cycle, the answer is therefore (c) RuBP to continue the cycle.

Key concepts

G3P

G3P, short for Glyceraldehyde 3-phosphate, is a crucial 3-carbon molecule in photosynthesis. It's central to what's known as the Calvin Cycle. The curiosity lies in its double nature; G3P is both a product and a reactant within the cycle.

During the cycle, carbon dioxide is fixed into a more stable organic form. A series of enzymatic reactions transform it until G3P is created. This molecule may not sound as famous as glucose, its six-carbon sugar cousin, but it's actually the main building block for it. For every three turns of the Calvin Cycle, five G3P molecules are recycled to regenerate RuBP (ribulose bisphosphate), which is necessary for the cycle to keep spinning. The sixth G3P molecule exits the cycle, eventually leading up to the synthesis of glucose and other carbohydrates crucial for the plant's energy economy.

Understanding G3P's role in photosynthesis emphasizes the beauty of cellular processes where each molecule has a specific, indispensable function.

RuBP Regeneration

RuBP regeneration might sound like a complex process, but it’s the backbone that allows plants to continuously undergo photosynthesis. RuBP, or Ribulose-1,5-bisphosphate, goes on quite the journey within the Calvin Cycle. It starts off eager to bond with CO2, effectively fixing inorganic carbon into an organic form. Once CO2 is fixed, RuBP is transformed through a sequence of reactions until G3P is produced.

Recycling – The Plant Way

Even though some G3P molecules leave the cycle to become sugars, most of G3P stays within the cycle to regenerate RuBP. This regeneration is essential because without RuBP, the cycle cannot start again, and no more carbon fixation can occur. Plants have mastered the art of recycling; they convert the majority of the G3P back into RuBP, readying it to catch more CO2 and continue the cycle. Thus, the answer to our exercise question is (c) RuBP, because it is the primary 'product' created from the G3P during the cycle.

Photosynthesis Stages

Photosynthesis can be thought of as nature’s solar panel, capturing the sun’s energy and storing it in chemical bonds. It has two main stages: the light-dependent reactions and the Calvin Cycle, or the light-independent reactions.

Harvesting Light

In the light-dependent stage, which occurs in the thylakoid membranes of chloroplasts, the energy from sunlight is trapped and used to produce ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). Water molecules are split, releasing oxygen as a byproduct.

The Carbon Factory

The second stage, the Calvin Cycle, occurs in the stroma, the fluid-filled area of the chloroplast outside the thylakoids. Here, the energy and reducing power from ATP and NADPH are used to convert CO2 into G3P. This G3P can eventually turn into glucose or be recycled to regenerate RuBP, perpetuating the cycle. Both stages are critical — the light stage provides the energy, and the Calvin Cycle closes the loop by fixing carbon into a stable form.