factors limiting photosynthesis Flashcards
what are some of the environmental factors that would limit the rate of photosynthesis?
carbon dioxide concentration, light intensity, temperature, water availability
what happens if one of these factors falls below a certain level?
it will start to limit the rate of photosynthesis
what is a limiting factor and how is it found?
although temperature, carbon dioxide and light intensity may all effect rates of photosynthesis, only the one that is in the shortest supply will limit the rate at any particular point in time. this is the limiting factor.
how do you increase the rate of photosynthesis?
by increasing the factor that is the limiting factor
how does light intensity affect rate of photosynthesis - use diagram for help?
(A) when light is the limiting factor, the rate of photosynthesis is directly proportional to light intensity.
(B) as light intensity is increased, the volume of oxygen produced and carbon dioxide absorbed due to photosynthesis will increase to a point at which it is exactly balanced by the oxygen absorbed and the carbon dioxide produced by cellular respiration. at this point there will be no net exchange of gases into or out of the plant. this is known as the light compensation point.
(C) further increases in light intensity will cause a proportional increase in the rate of photosynthesis and increasing volumes of oxygen will be given off and carbon dioxide taken up.
(D) a point will be reached at which further increases in light intensity will have no effect on photosynthesis.
(E) at this point, some other factor, such as carbon dioxide concentration or temperature, is limiting the reaction.
what does high light intensity lead to in relation to temperature?
when light intensity is high, increasing temperature will have a significant effect on the rate of photosynthesis. providing that other factors are not limiting, the rate of photosynthesis increases in direct proportion to the temperature. between 10 degrees and 35 degrees, a ten degree rise in temperature will double the rate of photosynthesis.
what volume of air does carbon dioxide usually make up? how does this compare to the optimum value for photosynthesis? what does this mean?
carbon dioxide usually makes up only 0.04% of the volume of air. this is lower than the optimum value of 0.1% for photosynthesis. this means carbon dioxide concentration is often the limiting factor, particularly in tropical areas where temperature and light intensity are high.
how does carbon dioxide concentration effect rate of photosynthesis?
carbon dioxide concentration affects enzyme activity, especially the enzyme that catalyses the combination of ribulose biphosphate with carbon dioxide in the light independent reaction.
how does knowledge of limiting factors effect those growing crops in glasshouses?
knowledge of limiting factors can enable growers to increase the yield of crops grown in glasshouses. the costs of maintaining optimum temperature, light intensity and carbon dioxide concentration needs to be outweighed by the greater income from the crop.
what are the benefits of producing crops in glasshouses in the uk?
- to achieve higher yields
- allow crops to be grown out of season and so provides a better economic return
- plants can be grown in regions where they would not naturally grow
why does faster rate of photosynthesis benefit growers?
the faster the rate of photosynthesis, the more carbohydrates the plants can make. the more carbohydrates made, the more energy and materials are available for growth and fruit formation.
how do you increase each of the three limiting factors?
light intensity
- artificial lighting
- special wavelengths can be used (ie those absorbed by chlorophyll)
carbon dioxide concentration
- pump carbon dioxide into the glasshouse
- use paraffin heaters
- ventilation ?
temperature
- glass stops heat from escaping
- optimal temperature can be achieved using heating (and cooling) mechanisms and thermostat/thermometers
- ventilation ?
what can happen at ideal temperatures for photosynthesis and how will growers resolve this?
at ideal temperatures for photosynthesis, water loss by transpiration is likely to be high. excessive water loss can lead to plants closing their stomata using guard cells to limit the loss. this means that carbon dioxide would not be able to enter the leaves and rates of photosynthesis would be dramatically reduced. growers need to ensure plants have plenty of water and many glasshouses have automatic watering systems with sprinklers and humidifiers.
how will a humidifier ensure plants have plenty of water?
- increases amount of water vapour in the air (inside glasshouse)
- decreases water potential gradient (between leaves and air)
- less water vapour diffuses out of spongy mesophyll (air spaces) of leaves
- less transpiration
what can these factors be controlled using?
all of these factors can be controlled using computers. sensors are used to monitor the level of each factor.
what is a negative to controlling the environment and why can it be worth it?
there are costs involved in controlling the environment and these are only worthwhile if the increased yield produces enough profit to exceed these costs. a grower will try to achieve an optimum yield by balancing out these factors.
