Question

During photosynthesis, when PGA is changed into phosphoglyceraldehyde, which of the following reaction occurs? (a) Oxidation (b) Reduction (c) Electrolysis (d) Hydrolysis

Short answer

The reaction of changing PGA into phosphoglyceraldehyde during photosynthesis can be classified as reduction.

Step-by-step solution

Understanding the process of photosynthesis

Photosynthesis involves converting carbon dioxide and water into glucose and oxygen, using sunlight for energy. During this process, PGA undergoes some changes to produce phosphoglyceraldehyde.

Classification of different reactions

Oxidation involves losing electrons, reduction involves gaining electrons, electrolysis refers to breaking down of compounds due to electric current, and hydrolysis refers to breakdown of a compound due to reaction with water. Let’s determine which type suits the PGA to phosphoglyceraldehyde conversion.

Identifying the conversion process

PGA is changed into phosphoglyceraldehyde by gaining a hydrogen atom. An addition of hydrogen atoms typically corresponds to gaining of electrons, hence this is a reduction process.

Key concepts

Photosynthetic Pigments

One of the primary steps of photosynthesis in plants involves the absorption of light, which is made possible through the use of photosynthetic pigments. These pigments are crucial as they capture solar energy and convert it into chemical energy. The most known pigment is chlorophyll, which gives plants their green color. But there are other pigments too, such as carotenoids and phycobilins, that absorb light in different spectrums and pass that energy onto chlorophyll.

These pigments are located in the chloroplasts of plant cells, more specifically, within the thylakoid membranes. Each pigment has a specific role. For instance, while chlorophylls absorb mainly blue and red light, carotenoids can capture blue-green light, broadening the range of light that can be used in photosynthesis. This diversity allows plants to maximize the use of available light for energy.

Light-Dependent Reactions

The light-dependent reactions are the first phase of photosynthesis where the energy from sunlight is captured by the photosynthetic pigments. This set of reactions takes place in the thylakoid membranes of the chloroplasts. During these reactions, water molecules (H₂O) are split into oxygen, protons, and electrons in a process known as photolysis. The electrons are excited to a higher energy state and transported through a series of proteins, collectively called the electron transport chain.

As the electrons move through the chain, their energy is used to pump hydrogen ions into the thylakoid lumen, creating a proton gradient. This gradient drives the synthesis of ATP (adenosine triphosphate) from ADP (adenosine diphosphate) and inorganic phosphate, through a process called chemiosmosis. Additionally, the electrons reduce NADP⁺ to NADPH. The ATP and NADPH produced are then used in the Calvin cycle, the next stage of photosynthesis, to fix carbon into sugar.

Calvin Cycle

The Calvin cycle, also known as the light-independent reactions or the dark reactions, is the second stage of photosynthesis. Unlike the light-dependent reactions, this cycle doesn't require light directly, but it does depend on the ATP and NADPH generated in the first phase. The Calvin cycle occurs in the stroma of chloroplasts, where carbon dioxide (CO₂) is converted into glucose through a series of enzyme-assisted steps.

In this process, the enzyme ribulose bisphosphate carboxylase/oxygenase, commonly known as rubisco, attaches CO₂ to a five-carbon sugar named ribulose bisphosphate (RuBP). This leads to the formation of two three-carbon molecules of PGA (3-phosphoglycerate). With the use of ATP and NADPH, PGA is then reduced to G3P (glyceraldehyde-3-phosphate), a reaction involving the addition of electrons, thus classifying it as a reduction. G3P can eventually be turned into glucose and various other sugars, which are used by the plant for energy and growth.