Photosynthesis Flashcards
What is the main photosynthetic pigment used in plants? What are some of the accessory pigments?
Chlorophyll a is the main one
Accessory include chlorophyll b (which broadens the spectrum of light for photosynthesis) and carotenoid
What is the purpose of the accessory pigments carotenoids?
Absorbs the excessive light that would damage the chlorophyll. They work by protecting against oxidative damage from excessive light energy.
oxidative stress
Oxidative stress occurs when an oxygen molecule splits into single atoms with unpaired electrons, which are called free radicals. These unpaired electrons (free radicals) can cause damage to tissues, cells, DNA, or proteins.
What is meant by excitation?
When pigments such as chlorophyll absorbs light, the pigment goes from ground state to excited state, which is unstable. When the excited electrons fall back to ground state, photons are given off.
What is a light harvesting complex? Why are they important?
Light-harvesting complexes (pigment molecules bound to proteins) gathers the light energy and transfers this energy of photons to reaction centres
What is the wavelength used for PSI [1] and PSII [2]?
Photosystem II (PS II) absorbs best at wavelength of 680 nm, this is why the reaction center is called P680
Photosystem I (PS I) absorbs best at wavelength of 700 nm
What is the purpose of PSII (what does it make)?
To take light and water, and by using a linear process of transporting electrons makes ATP.
What is the purpose of PSI?
The electron at the end of PSII doesn’t have enough energy, so PSI gives it a boost by adding more light photons (energy). At the end it will make NADPH which can go on to be used in the Calvin cycle.
How is the light cycle of photosynthesis similar to ETC?
Both generate ATP by chemiosmosis, but use different sources of energy
Mitochondria – protons pumped to intermembrane space and drive ATP synthesis as they diffuse back into mitochondrial matrix
Chloroplasts – protons pumped into thylakoid space and drive ATP synthesis as they diffuse back
The light part of photosynthesis can be described as linear or circular, what are the differences between these two processes (what are the outputs)?
Linear - primary pathway, involves both photosystems and produces ATP and NADPH using light energy
Circular – involves only PS1, makes ATP but not NADPH. No oxygen is released.
What is the primary function of the Calvin cycle?
Builds sugar from smaller molecules by using ATP and reducing power of electrons carried by NADPH
What are the three phases of the Calvin cycle? What happens at each phase
Carbon fixation (catalyzed by Rubisco) – CO2 is taken from the atmosphere and turned into something that can be used for organic processes
Reduction – sugars are made by reducing different carbon molecules and eventually making glucose
Regeneration – Need to make the starter enzyme again so the cycle can keep working
How many times must the cycle be completed to make one molecule of glucose?
six times
When would a plant use photorespiration?
In dry conditions plants have to close stomata to prevent desiccating, but this results in a build-up of oxygen. The cells need oxygen, but too much becomes toxic. When this occurs plants can undertake photorespiration.
