Question

Which process of Calvin cycle requires RuBP? (a) Carboxylation (b) Reduction (c) Regeneration (d) None of these

Short answer

The process of the Calvin cycle that requires Ribulose biphosphate (RuBP) is 'Carboxylation'.

Step-by-step solution

Understanding Calvin Cycle

Firstly, comprehend that the Calvin cycle consists of three stages: Carboxylation, Reduction, and Regeneration. Each stage involves different reactants and products. Each has its own specific role and requirements.

Identifying the role of RuBP in Calvin cycle

Now, identify the role of RuBP (Ribulose biphosphate) in the Calvin cycle. RuBP is a molecule that starts the process of fixing carbon dioxide from the atmosphere into organic molecules during the process of photosynthesis.

Associating RuBP with the correct stage

The molecule Ribulose biphosphate (RuBP) is actually a five carbon compound involved in the 'Carboxylation' stage of the Calvin cycle. In this stage, RuBP reacts with carbon dioxide to produce two 3-carbon molecules. So the correct answer here would be 'Carboxylation'.

Key concepts

Carboxylation

Carboxylation is a pivotal step in the Calvin cycle, a phase of photosynthesis. During carboxylation, the molecule ribulose biphosphate (RuBP) combines with carbon dioxide (CO2) from the atmosphere, catalyzed by the enzyme RuBP carboxylase/oxygenase, commonly known as Rubisco.

This reaction is vital because it is the first step in converting inorganic carbon into organic compounds within the plant. More specifically, it involves attaching CO2 to RuBP, resulting in the splitting into two molecules of 3-phosphoglycerate (3-PGA), each with three carbon atoms. This acts as the skeleton for synthesizing glucose and other carbohydrates that plants use for energy and growth.

In simpler terms, carboxylation is like the initial handshake between CO2 and the plant, starting a sequence of events that feed the plant and, ultimately, the ecosystems relying on it.

Photosynthesis Process

Photosynthesis is a remarkable process used by plants, algae, and certain bacteria to harness the energy from sunlight, converting it into chemical energy. This process occurs in two main stages: the light-dependent reactions and the Calvin cycle, the latter of which is often referred to as the light-independent reactions because it does not require light directly.

The light-dependent reactions take place in the thylakoid membranes of chloroplasts where sunlight is captured by chlorophyll and other pigments. Water molecules are split to release oxygen, and energy-rich molecules such as ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) are produced.

Following this, in the Calvin cycle, the ATP and NADPH are used to turn CO2 into glucose. It's essentially a biochemical assembly line where CO2 is progressively converted into more complex molecules. The cycle starts with carboxylation, as mentioned earlier, followed by the reduction stage where ATP and NADPH convert 3-PGA into glyceraldehyde-3-phosphate (a carbohydrate), then the regeneration phase that replenishes RuBP, allowing the cycle to continue.

Ribulose biphosphate (RuBP)

Ribulose biphosphate (RuBP) is a five-carbon sugar that plays a central role in the process of photosynthesis, specifically within the Calvin cycle. It serves as a critical component because it is responsible for the initial interaction with CO2 — a process fundamental for the synthesis of carbohydrates in plants.

RuBP is constantly regenerated through the Calvin cycle, which means it's not just a reactant but also a product of the cycle, making it intrinsically tied to the continuous process of photosynthesis. It's like a molecular baton that keeps the relay race going; as long as there is RuBP, the plant can keep fixing CO2 and producing glucose. Without RuBP, the whole cycle would stall, as no CO2 fixation could occur. As such, RuBP is not only a starting molecule but also the foundation that allows plants to create the sugars they need for life.