Light Reactions
Give the abbreviated names for photosystems 1 and 2.
P700 and P680, respectively
What is the source of carbon in the Calvin cycle?
carbon dioxide absorbed by plants through the stomata.
What is the tradeoff associated with terrestrial plants in arid climates?
The need for water conservation to prevent dehydration and stomata opening to intake CO2 for the Calvin cycle.
The two primary electron flows?
cyclic electron flow and linear electron flow
Light can be described as what type of energy?
electromagnetic energy
What is a light-harvesting complex?
pigment molecules bound to proteins that transfer photon energy to the reaction center complex.
What is the end product of the Calvin cycle?
G3P a 3 carbon sugar. which can later be reacted to form glucose and other sugars.
The wasteful process that occurs when CO2 is not available _________
photorespiration where rubisco binds with O2 instead of CO2.
Which electron flow pathway is most efficient and why?
Linear electron flow because it uses both photosystems and produces ATP and NADPH
Visible light is described as what specific wavelengths? Why does this matter to photosynthesis and vision?
(380mm to 740mm) light in this range produces the colors seen by human eyes and drives photosynthesis.
Describe the movement of the photon through a photosystem.
First the light harvesting complex captures the photon and transfer it to the chlorophyll a molecules in the reaction-center complex which excites an electron which binds to the primary electron acceptor and is carried to the cytochrome complex or NADP reductase depending on photosystem 2 or 1.
How many times must the Calvin cycle run to synthesize one net G3P?
3 times to fix three molecules of CO2
How do C4 plants help to minimize energy losses?
they incorporate CO2 into a 4 carbon compound in the Calvin cycle. Also PEP carboxylase has higher affinity for CO2 and can fix CO2 when concentrations are low.
Which photosystem is utilized in cyclic electron flow?
photosystem 1 P700
Explain the concept of the electromagnetic spectrum.
It is the entire range of electromagnetic energy or radiation
The energy from the light reactions is then used to create ______ in what process?
to create ATP by photophosphorylation.
How does carbon fixation occur and what is the necessary CO2 acceptor and enzyme?
It occurs as CO2 binds to a 5 carbon sugar RuBP. This is catalyzed by rubisco and then the resulting 6 carbon intermediate is split into two 3-molecule phosphoglycertes.
What does CAM stand for, how does it differ from C3 and C4?
Crassulacean acid metabolism. These plants open their stomata at night and incorporate CO2 into organic acids stored in vacuoles.
If the goal was maximum photosynthetic efficiency, which electron flow would you choose and why?
Linear electron flow because it produces more energy products ATP and NADPH which can be utilized later in the Calvin Cycle.
List and describe the three pigments within a chloroplast.
chlorophyll a, key light-capturing pigment
chlorophyll b, accessory pigment
carotenoids, yellow or orange color due to absorption of violet/blue green light to increase photosynthesis
Why does ATP need to be produced in the light reactions? What reaction does it power? and NADPH?
To power the Calvin cycle which is anabolic reaction synthesizing G3P. The NADPH provides reducing power from transporting electrons and the ATP gives the energy to drive the Calving cycle and carbon fixation.
What are the energy requirements for the Calvin cycle to run completely and form a G3P.
nine molecules of ATP and six molecules of NADPH from the light reactions. The six G3P from three CO2 molecules being fixed only result in one net G3P as 5 G3P are needed to regenerate RuBP.
When stomata close during the day for CAM plants where is CO2 sourced?
the organic molecules stored during the night release CO2 for use in the Calvin cycle.
For linear electron flow, draw on the board the general order of photosystem use and where ATP and NADPH are produced.
Photosystem 2 (P680) is used first and generates ATP with the cytochrome complex, then photosystem 1 (P700) is excited to pass electrons through a protein to NADP reductase to make NADPH
Where in the chloroplast is the chlorophyll a located?What are the most and least effective light color for photosynthesis?
They are on the thylakoid membrane within the photosystem and embedded in the reaction-center complex. Most efficient: violet-blue, red light
least efficient: green light