Molecular Biology - 2.9 Photosynthesis Flashcards
NOTES !!!
A lot of the information for this topic (SL) and the bridging HL points can all be found on IRL notes (mainly Lucy’s)
Photosynthesis is dependent on a number of favourable conditions, including:
Understanding: “Temp, light intensity and CO2 concentration are possible limiting factors on the rate of photosynthesis”
Temperature
Light intensity
Carbon dioxide concentration
Temperature’s effect on photosynthesis:
- Photosynthesis is controlled by enzymes, which are sensitive to temperature fluctuations
- As temperature increases reaction rate will increase, as reactants have greater kinetic energy and more collisions result
- Above a certain temperature the rate of photosynthesis will decrease as essential enzymes begin to denature
Light intensity’s effect on photosynthesis
- As light intensity increases reaction rate will increase, as more chlorophyll are being photo-activated !!!!!
- At low light there is a shortage of NADPH and ATP from the light-dependent reactions
- At low light the products of light-dependent reactions are also low and this slows the Calvin Cycle
- Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP)
- At a certain light intensity photosynthetic rate will plateau, as all available chlorophyll are saturated with light
- Different wavelengths of light will have different effects on the rate of photosynthesis (e.g. green light is reflected)
Carbon dioxide concentration’s effect on photosynthesis
- Carbon dioxide is involved in the fixation of carbon atoms to form organic molecules
- As carbon dioxide concentration increases reaction rate will increase, as more organic molecules are being produced
- At a certain concentration of CO2 photosynthetic rate will plateau, as the enzymes responsible for carbon fixation are saturated
- At low/medium concentrations it is the combining of CO2 to my glycerate 3 phosphate that controls the rathe of photosynthesis
- At high concentrations other factors will limit the rate - increased CO2 will increase photosynthesis but only up to a point
Measuring the rate of photosynthesis (3 ways)
- CO2 uptake
- O2 production
- Biomass (indirect)
CO2 uptake - Measuring the rate of photosynthesis (3 ways)
- Carbon dioxide uptake can be measured by placing leaf tissue in an enclosed space with water
- Water free of dissolved carbon dioxide can initially be produced by boiling and cooling water
- Carbon dioxide interacts with the water molecules, producing bicarbonate and hydrogen ions, which changes the pH (↑ acidity)
- Increased uptake of CO2 by the plant will lower the concentration in solution and increase the alkalinity (measure with probe)
- Alternatively, carbon dioxide levels may be monitored via a data logger
Oxygen production - Measuring the rate of photosynthesis (3 ways)
- Oxygen production can be measured by submerging a plant in an enclosed water-filled space attached to a sealed gas syringe
- Any oxygen gas produced will BUBBLE out of solution and can be measured by a change in meniscus level on the syringe
- Alternatively, oxygen production could be measured by the time taken for submerged leaf discs to surface
- Oxygen levels can also be measured with a data logger if the appropriate probe is available
Measuring Biomass (Indirect) - Measuring the rate of photosynthesis (3 ways)
- Glucose production can be indirectly measured by a change in the plant’s biomass (weight)
This requires the plant tissue to be completely dehydrated prior to weighing to ensure the change in biomass represents organic matter and not water content - An alternative method for measuring glucose production is to determine the change in starch levels (glucose is stored as starch) Starch can be identified via iodine staining (turns starch solution purple) and quantitated using a colorimeter
Capturing light energy - the Absorption and Action spectrum
Understanding: “ Visible light has a range of wavelengths with violet being the shortest and red the longest. Chlorophyll absorbs red/blue light most effectively and reflects green light more than other colours”
Photosynthetic pigments
Chlorophyll a and Chlorophyll b
- other pigments = carotenoids (carotene and xanthophylls) - pick up different wavelengths of light (green and blue) and reflect orange and red
Absorption spectrum - must be able to draw on diagram!
shows the % of wavelength absorbed by the common chlorophyll pigments (Chlorophyll a and b)
- it shoes the greatest absorption in for violet/blue and red areas of the light spectrum and the least in the yellow-green range
Action spectrum - must be able to draw on diagram!
shows the % USE of different wavelengths of light by chlorophyll
- it shows violet/blue/red light are used most efficiently and the least efficient is in the yellow/green range
