Photosynthesis Flashcards
Light depend vs Independent reactions
The light-dependent reactions capture energy from sunlight and convert it into chemical energy stored in ATP, while the light-independent reactions use that stored energy to convert carbon dioxide into glucose, requiring no direct sunlight to function.
Energy of Different Wavelengths
Short wavelengths have high energy (violent and blue - X-rays, U-V radiation) while long wavelength have low energy (Red - infrared radiation, radio waves)
Function of Chlorophyll
Chlorophyll is the photosynthetic pigment that dominates in most plant species.
Chlorophyll absorbs all wavelengths of visible light, except green, which it reflects.
When sunlight hits a leaf, the red and blue wavelengths of light are absorbed (light throughout the entire day) by chiorophyll and used for photosynthesis.
Different pigments in plants
When piments absorb light, their electrons become excited. Different pigments require different a unis of energy to cre electrons which is why they absorb different wavelengths of light. This energy can be used to create chemical bonds (being
converted to chemical energy).
Chlorophyll a → only pigment that can transfer the energy of light to the carbon-fixation reactions of photosynthesis.
Chlorophyll b → acts as accessory pigment, absorbing photons that chlorophyll a absorbs poorly or not at all.
Carotenoids → absorb blue and green colours (reflecting orange)
What’s the Rf value
(Rf value =
distance component travels / distance solvent travels)
These values can be compared to known values to identify the pigment.
What can limit the rate of photosynthesis
temperature, light intensity and carbon dioxide concentrations.
These factors are referred to as “limiting factors” since they can limit the rate of photosynthesis if they are below their optimal level.
If these one factor is brought closer to its optimum then the rate of photosynthesis increases.
What is photolysis?
In photosynthesis, “photolysis” refers to the process where light energy is used to split water molecules into hydrogen ions and oxygen gas, essentially breaking down water using light, which occurs during the light-dependent reactions within the chloroplasts of plants; it’s a crucial step as it provides the electrons needed to carry out the photosynthetic process and releases oxygen as a byproduct.
How does light intensity affect the rate of photosynthesis?
Light energy absorbed by chlorophyll is converted to ATP and H*
At very low light levels (a) the plant will be respiring only not photosynthesizing.
As the light intensity increases then the rate of photosynthesis increases.
At high light intensities the rate becomes constant, even with further increases in light intensity there are no increases in the rate.
The plant is unable to harvest the light at these high intensities and indeed the chlorophyll system can be damaged by very intense light levels
Effect of CO2 concentration on Photosynthesis
Similar to temperature
(a) Oz is used up as the plant is not photosynthesizing but only respiring.
(b) As the concentration of the carbon dioxide (substrate) increases the rate of reaction increases.
(c) The atmospheric levels of carbon dioxide and the associate rate of photosynthesis.
(d) Maximum rate of photosynthesis (see section e).
(e) This is a range of values for different plants reaching their saturation level with carbon dioxide. Once the saturation level has been reached there is no further increase in the rate of photosynthesis.
Effect of Temperature on Rate of Photosynthesis
Temperature as we have already met is a change in the average kinetic energy
Max-
The graph the left should look familiar as this is the same one covered in the section on the effect of temperature on the rate of an enzyme catalysed reaction.
(a) Increasing rate of photosynthesis as the kinetic energy of reactants increases.
(b) Maximum rate of reaction of photosynthesis at the ‘optimal’ temperature.
(c) Decrease in rate of photosynthesis as the enzymes become unstable and denature.
