1) The dark reaction (Calvin cycle) will not take place in the presence of light.
2) If the concentration of carbon dioxide increases, chances are photosynthesis will plateua if there is an insufficient amount of light.
The Calvin cycle reaction is independent of light.
Yes, there will be a plaateu
1) The statement is correct. The dark reaction or Calvin cycle is a series of chemical reactions that occur in the stroma of chloroplasts, where the energy produced during the light-dependent reactions is used to convert CO2 into glucose. However, the dark reaction does not require direct light energy and can occur in the absence of light. In fact, it is called the dark reaction because it can proceed in the dark as long as the necessary molecules and enzymes are present.
To understand why the dark reaction can occur in the absence of light, let's briefly go over the process involved. During the light-dependent reactions of photosynthesis, light energy is absorbed by chlorophyll molecules in thylakoid membranes, leading to the generation of high-energy electrons and the production of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These energy-rich molecules are then used in the dark reaction to convert CO2 into glucose.
The dark reaction proceeds in three steps:
1. Carbon Fixation: CO2 molecules react with a five-carbon compound called ribulose-1,5-bisphosphate (RuBP) to produce two molecules of a three-carbon compound called 3-phosphoglycerate (PGA).
2. Reduction: ATP and NADPH generated during the light-dependent reactions are used to convert PGA into another three-carbon compound called glyceraldehyde-3-phosphate (G3P).
3. Regeneration: Some G3P molecules are converted back into RuBP, allowing the cycle to continue, while others are used to produce glucose and other carbohydrates.
So, even though the dark reaction doesn't directly rely on light energy, it does depend on the products of the light-dependent reactions (ATP and NADPH) to drive the chemical reactions that convert CO2 into glucose.
2) The statement is partially correct. If the concentration of carbon dioxide (CO2) increases, photosynthesis rates may increase up to a certain point, but they will eventually plateau if there is an insufficient amount of light.
Photosynthesis is a complex process that requires several factors, including light intensity, temperature, and the availability of CO2 and water. These factors have specific optimal levels at which photosynthesis occurs at its maximum rate.
When there is an increase in atmospheric CO2 concentration, plants usually experience an initial increase in photosynthesis rates. This is because CO2 is an essential raw material for photosynthesis, and when the level of CO2 increases, the plants have more substrate to work with.
However, if the light intensity is insufficient, photosynthesis rates will eventually plateau regardless of the CO2 concentration. Light plays a crucial role in the light-dependent reactions of photosynthesis, where energy is captured to produce ATP and NADPH. Without enough light energy, the reactions cannot proceed at their maximum capacity, limiting the overall rate of photosynthesis.
In summary, an increase in CO2 concentration can initially enhance photosynthesis rates, but if there is a lack of sufficient light energy, the photosynthesis rates will eventually reach a maximum and plateau.