Temperature significantly affects the rate of photosynthesis, mainly through its influence on the enzymes that catalyse the various biochemical reactions. Within a certain range, an increase in temperature accelerates the enzymatic activities, thereby speeding up the rate of photosynthesis. This is because higher temperatures increase the kinetic energy of molecules, leading to more frequent and effective collisions between enzymes and substrates. However, there is an optimum temperature range (usually between 15-25°C for most plants), beyond which the rate of photosynthesis begins to decline. Extremely high temperatures can lead to the denaturation of enzymes, impairing the photosynthetic process, while low temperatures can reduce enzyme activity, slowing down the reactions. Therefore, temperature is a key factor in determining the efficiency of photosynthesis, and variations outside the optimal range can have significant impacts on plant growth and productivity.

The Calvin Cycle is referred to as the light-independent reactions because it does not directly require light to proceed. This part of photosynthesis occurs in the stroma of chloroplasts and involves the fixation of carbon dioxide into organic molecules, ultimately producing glucose. The Calvin Cycle uses ATP and NADPH produced during the light-dependent reactions, but the actual processes of carbon fixation, reduction, and regeneration of the starting molecule (ribulose-1,5-bisphosphate or RuBP) do not require light. This naming distinguishes it from the light-dependent reactions, which cannot occur without light as they involve the absorption of photons by chlorophyll and other pigments. However, it's important to note that although the Calvin Cycle itself is light-independent, it is still indirectly dependent on light because the ATP and NADPH required are products of the light-dependent reactions.

Magnesium plays a vital role in photosynthesis, primarily as a central component of the chlorophyll molecule. In chlorophyll, magnesium is located at the centre of the porphyrin ring and is essential for the absorption of light energy. This central position enables magnesium to directly influence the ability of chlorophyll to capture light photons, which is a critical step in the light-dependent reactions of photosynthesis. Additionally, magnesium is involved in the activation of several enzymes required in the process of photosynthesis, including those in the Calvin Cycle. It also helps in the stabilisation of ribosome structures, facilitating protein synthesis. A deficiency in magnesium can lead to chlorosis (yellowing of leaves), which is indicative of impaired chlorophyll production and, consequently, reduced photosynthetic efficiency. Thus, adequate magnesium availability is crucial for optimal plant growth and photosynthetic activity.

Water plays a fundamental role in photosynthesis, serving as the source of the electrons and protons needed for the biochemical reactions. During the light-dependent reactions in the thylakoid membranes, water molecules are split in a process known as photolysis. This splitting of water provides the necessary electrons to replace those lost by chlorophyll during the absorption of light. Additionally, the protons (H⁺ ions) released during this process contribute to the formation of a proton gradient across the thylakoid membrane, which is essential for the synthesis of ATP through chemiosmosis. Furthermore, the splitting of water also releases oxygen as a by-product, which is crucial for sustaining aerobic life on Earth. Without the availability of water, the entire process of photosynthesis would be halted, underscoring its vital role in this process.

Different wavelengths of light affect photosynthesis in varying degrees due to the absorption spectrum of chlorophyll. Chlorophyll primarily absorbs light in the blue and red regions of the spectrum and less in the green, which is why plants appear green. Blue light, with a wavelength range of about 450-495 nm, is absorbed efficiently and maximises the rate of photosynthesis. It is crucial for early stages of plant growth. Red light, at wavelengths of 620-750 nm, also contributes significantly to photosynthesis, especially in flowering and fruiting stages. However, green light (495-570 nm) is least effective as it is largely reflected or transmitted through the leaf, not absorbed. This differential absorption of light wavelengths is integral to the efficiency of photosynthesis, influencing plant growth and development. Adjusting light conditions, such as in greenhouses, can optimise photosynthesis and thus enhance plant growth and crop yield.