factors limiting the rate of photosynthesis 4.1.2

• the limiting factors of photosynthesis are carbon dioxide percentage, light intensity, temperature and chlorophyll levels
• a limiting factor is a variable that is in short supply and therefore it prevents the rate of a process from being as fast as it could be, if a variable is a limiting factor, increasing this variable will make the rate faster, if a variable is not a limiting factor increasing this variable will have no effect on the rate
• on a graph, if the variable is a limiting factor, increasing this factor will cause the line to increase, but if it is not a limiting factor, increasing it has no effect and the line will level off
• as the distance of the light from the plant increases, the light intensity decreases
• inverse square law means its not linear so the light intensity increases or decreases in inverse proportion to the square of the distance
• light intensity - 1 / distance^2
• the graph of distance v light intensity never touches the x axis
• A) no light means no photosynthesis can occur
• B) increasing the light intensity means more energy can be absorbed by chlorophyll, so the rate of photosynthesis also increases, light intensity is a limiting factor
• C) increasing the light intensity further has no effect on the rate of photosynthesis, so light intensity is not a limiting factor. temperature or CO2 concentration is likely to be the main limiting factor at this stage
• light intensity would be a limiting factor in the winter seasons or at nightime
• when there is no light, the rate of O2 production begins to decrease, as no photosynthesis can occur, but the plant is respiring so oxygen is used up
• the light compensation point is the light intensity that means the rate of photosynthesis and the rate of respiration are equal
• the rate of photosynthesis is far greater than the rate of respiration for most of the day
• photosynthesis needs enzymes, at higher temperatures, molecules have more kinetic energy, so there are more collisions, and more enzyme substrate complexes form
• optimum temperature means it is the temperature that works best for the reaction
• the rate of photosynthesis decreases at temperatures higher than the optimum temperature as the enzymes become denatured and the active site changes shape so fewer enzyme -substrate complexes form
• temperature would be a limiting factor on cold days eg winter or early morning or late evening
• plant diseases could reduce the rate of photosynthesis because the leaves lack chlorophyll so not as much light is absorbed, leading to less photosynthesis
• variegated leaves have less chlorophyll so less photosynthesis