Factors Affecting Photosynthesis - 1 | Agriculture Optional Notes for UPSC PDF Download

External Factors Affecting Photosynthesis

Various external factors can impact the process of photosynthesis. These factors include:

• Light Intensity: Light intensity is a crucial factor affecting photosynthesis. It positively influences the rate of photosynthesis up to a certain point. However, excessively high light intensities can lead to a plateau or even a decrease in the photosynthesis rate due to potential damage to chlorophyll molecules. Additionally, the quality of light matters, with photosystems I and II being most efficient at absorbing energy at specific wavelengths (700 nm and 680 nm).
• Carbon Dioxide Concentration: Carbon dioxide concentration is another critical determinant. Increased levels of carbon dioxide lead to higher rates of carbon incorporation into carbohydrates during the light-independent reaction, ultimately boosting photosynthesis. However, this increase in rate eventually plateaus when the maximum rate of carbon fixation is reached.
• Oxygen: Oxygen, a by-product of photosynthesis, can also influence the process. In C₃ plants, oxygen is essential for photorespiration, which generates CO₂ needed for photosynthesis. However, excessive oxygen levels can inhibit photosynthesis as it can disrupt the intermediates formed during the process.
• Temperature: Temperature has a significant impact on photosynthesis, particularly on the light-independent reactions, which are temperature-dependent. As temperatures approach the optimum range for the enzymes involved, the photosynthesis rate increases. Beyond this optimal temperature, enzymes start to denature, causing a decline in the rate and eventual cessation of photosynthesis.
• Water: Water is a crucial reactant in photosynthesis. It plays a role in the light-dependent reactions by producing oxygen, protons, and electrons, which are essential for generating energy carriers like ATP and NADPH. Moreover, water aids in the absorption and transport of vital nutrients from the soil to the leaves. However, water scarcity can result in the closure of stomata, tiny leaf openings responsible for gas exchange, to prevent water loss. This closure restricts the intake of carbon dioxide, a key photosynthesis reactant, leading to a reduced photosynthesis rate. Consequently, the availability of water significantly affects both photosynthesis and overall plant health.

Internal Factors Affecting Photosynthesis

Photosynthesis is subject to not only external influences but also various internal factors that regulate the process. These internal factors include protoplasmic components, chlorophyll levels, end product accumulation, and leaf structure, each of which plays a distinct role in governing the rate of photosynthesis.
Here, we'll delve into these internal factors affecting photosynthesis in detail:

• Protoplasmic Factors: Protoplasmic factors encompass the constituents within the cell's protoplasm that impact photosynthesis. Among these factors are enzymes crucial for the chemical reactions involved in photosynthesis. These enzymes, situated in the chloroplasts, are indispensable for both the light-dependent and light-independent phases of photosynthesis. Their effectiveness can significantly influence the photosynthesis rate. For example, Rubisco, an enzyme catalyzing carbon dioxide fixation in the Calvin cycle, is pivotal for photosynthesis. Changes in protoplasm, such as shifts in pH or temperature, can affect the activity of Rubisco, potentially altering the photosynthesis rate.
• Chlorophyll Content: Chlorophyll, the green pigment found in plants, is another vital internal factor in photosynthesis. It is responsible for capturing light energy, which is then transformed into chemical energy during photosynthesis. The quantity of chlorophyll within a plant directly impacts the photosynthesis rate. Higher chlorophyll levels result in increased light energy absorption, thus raising the rate of photosynthesis. Conversely, plants with lower chlorophyll content absorb less light energy, leading to a slower photosynthesis rate. Factors such as nutrient availability, plant age, and disease can influence chlorophyll levels.
• Accumulation of End Products: The buildup of photosynthesis end products, including glucose and oxygen, can also affect the photosynthesis rate because these products can inhibit the enzymes involved in photosynthesis. For example, a high concentration of glucose within chloroplasts can impede the activity of phosphofructokinase, a crucial enzyme in the Calvin cycle. This inhibition results in a deceleration of the Calvin cycle, reducing the rate of carbon dioxide fixation and, consequently, the overall photosynthesis rate.
• Structure of Leaves: The structural attributes of leaves, including factors like stomatal size, position, behavior, and the presence of intercellular spaces, can impact the photosynthesis rate. Leaf structure determines the extent to which carbon dioxide can enter the leaf and reach the chloroplasts. Leaves with higher stomatal density permit increased carbon dioxide entry, potentially enhancing photosynthesis. Similarly, leaves with more intercellular spaces facilitate carbon dioxide diffusion to the chloroplasts. Nevertheless, these structural features must strike a balance to prevent excessive water loss via transpiration.