Limiting Factors In Photosynthesis Flashcards
What is a limiting factor and which 3 can limit photosynthesis?
-light, temperature and carbon dioxide
-if any one of these factors are too low or too high it will slow down the rate of photosynthesis. Even if the other factors are at the perfect level, it won’t make any difference to the speed of photosynthesis if one remains at the wrong level.
Explain how light intensity and wavelength can be limiting factors of photosynthesis
-light is needed to provide the energy for the light dependent reaction, the higher the intensity of light the more energy it provides (so affects both stages of photosynthesis)
-only certain wavelengths of light are used for photosynthesis- the pigments chlorophyll a, chlorophyll b and carotene only absorb red and blue light in sunlight
Interpret this graph referring to points A and B on light being a limiting factor of photosynthesis
-between points A and B the rate of photosynthesis is limited by the light intensity, so as light intensity increases so can the rate of photosynthesis
-point B is the saturation point, whereby increasing light intensity no longer makes any difference to the rate of photosynthesis as something else has become the limiting factor
Explain how temperature can be a limiting factor for photosynthesis
-photosynthesis involves enzymes (e.g ATP synthase and RuBisCo). If the temperature falls below 10 degrees the enzymes become inactive, but if temperature is more than 45 degrees they start to denature
-also at high temperatures: the stomata close to avoid losing too much water, causing photosynthesis to slow down because less co2 is enters the leaf. Thylakoid membranes may be damaged, reducing the rate of the light dependent stage reactions as less sites available. Membranes around chloroplasts could be damaged causing enzymes to be released into the cell. Chlorophyll may also be damaged reducing the amount of pigment that can absorb light energy
Explain how carbon dioxide concentration can be a limiting factor for photosynthesis
-carbon dioxide makes up 0.04% of the gases in the atmosphere
-increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close
-carbon dioxide is needed in the light independent stage, joining with RUBISCO enzyme to produce 2 x GP
Explain this graph
-the graph levels off so no longer light intensity limiting rate of phs
-by increasing the carbon dioxide concentration from 0.04% to 0.4% rate of photosynthesis increases again
What other factors may potentially limit the rate of photosynthesis
-availability of pigment molecules
-number of chloroplast
-mineral ion availability
Why does water availability rarely become a limiting factor?
-this is because when water is in short supply plants close their stomata in order to reduce transpiration rate
-if the stomata close carbon dioxide can’t enter the leaf so phs stops anyway, before the water availability inside the leaf can become a limiting factor
