Equation
Write the balanced overall chemical equation for photosynthesis using the correct formulas for carbon dioxide, water, glucose, and oxygen.
6CO2+6H2O+light→C6H12O6+6O2
State the location (in the chloroplast) where the light reactions occur.
Thylakoid membranes (specifically the thylakoid membrane within the chloroplast).
Give the three main stages of the Calvin Cycle (use the common stage names).
Carbon fixation, reduction, regeneration.
Name three main limiting factors that affect the rate of photosynthesis.
Temperature, Light Intensity, Carbon Dioxide concentration
Define "stomata." What role do they play in photosynthesis?
Stomata: pores on leaf surfaces that allow gas exchange (CO2 in, O2 out) and transpiration.
Identify which part(s) of the overall equation correspond to the Light Reactions and which to the Calvin Cycle. Briefly explain why.
Light Reactions produce O2O2 and energy carriers (ATP, NADPH) from H2OH2O and light; Calvin Cycle uses CO2CO2, ATP, and NADPH to produce glucose.
Name the two photosystems involved in the light reactions and give the order in which they operate.
Photosystem II (PSII) then Photosystem I (PSI
What enzyme catalyzes the first major step of carbon fixation, and what molecule does it act on?
Rubisco acts on RuBP
Describe in words the typical shape of a graph of rate of photosynthesis versus light intensity and explain why it plateaus.
Curve rises steeply at low light, then levels off (saturation) when another factor (e.g., enzymes, CO2) limits rate.
Define "chlorophyll" and explain its role in capturing light energy.
Chlorophyll: pigment in thylakoid membranes that absorbs light (primarily blue/red) and initiates electron excitation.
Show how energy from photons is captured and stored in the form of chemical energy during the light reactions. Name the two main energy carriers produced.
Light excites electrons in chlorophyll; energy is transferred through photosystems and ETC to produce ATP (via chemiosmosis) and NADPH
Describe the role of the electron transport chain between photosystem II and photosystem I. Include how proton gradients are formed.
ETC transfers electrons from PSII to PSI, pumping protons into the thylakoid lumen to create a proton gradient used by ATP synthase to make ATP.
For one turn of the Calvin Cycle, how many molecules of ATP and NADPH are consumed (approximate typical classroom values)?
Per CO2 fixed typical classroom values ~ 3 ATPand 2 NADPH (so per glucose: 18 ATP and 12 NADPH). Review specific curriculum numbers.
Explain how low CO2 concentration can cause NADPH to accumulate and slow the Calvin Cycle.
If CO2 is low, the Calvin Cycle slows; NADPH is not oxidized back to NADP+ as fast, so NADPH accumulates, limiting further light-driven reduction steps.
What is an electron carrier? Give two examples used in photosynthesis.
Electron carrier: molecule that transports electrons (e.g., NADP+/NADPH, plastoquinone).
Using the Calvin Cycle, write the simplified stoichiometric relationship showing how many molecules of CO2CO2 are fixed to make one molecule of glucose (you may state the number of turns needed).
Using the Calvin Cycle, write the simplified stoichiometric relationship showing how many molecules of CO2 are fixed to make one molecule of glucose (you may state the number of turns needed).
Explain photolysis (water-splitting): give the reactants and products and state why it is necessary.
Photolysis: 2H2O → 4H+ + 4e−+ O2 ; it provides electrons to replace those lost by PSII and produces O2O2.
Explain what is meant by "regeneration" in the Calvin Cycle and why it is important for continued carbon fixation.
Regeneration reforms RuBP so the cycle can accept new CO2CO2 molecules; without it carbon fixation stops.
Describe what photorespiration is and explain how it reduces photosynthetic efficiency. Mention the enzyme involved.
Photorespiration occurs when Rubisco fixes O2O2 instead of CO2CO2, producing a 2‑carbon product and wasting energy/carbon; reduces net photosynthetic gain.
Define "photorespiration" and contrast it with carbon fixation during the Calvin Cycle.
Balance the following partial reaction: NADP+ + H+ + 2 e- → NADPH.
NADP+ + H+ + 2e− → NADPH. Electrons come from water via photosystem II and the electron transport chain; light provides energy to drive electron excitation.
Compare cyclic and noncyclic electron flow. State one reason a plant would use cyclic electron flow instead of noncyclic.
Cyclic flow recycles electrons from PSI to the ETC to produce ATP without making NADPH or O2; used when ATP demand is high relative to NADPH.
A student claims the Calvin Cycle can run in the dark because it is called the "dark reaction." Evaluate this claim and explain the conditions required for the Calvin Cycle to proceed.
The Calvin Cycle is light-independent in the sense it does not require photons directly, but it depends on ATP and NADPH made by light reactions; without those (or sufficient energy carriers) it cannot proceed at normal rates.
Predict how increasing temperature affects photosynthesis rate for plants adapted to low vs. high temperature, and explain the biochemical causes of the decline at extremes.
Increasing temperature speeds enzyme reactions up to an optimum, then high temps denature enzymes (e.g., Rubisco), causing rate to fall; low-temp-adapted plants have lower optimums.
Define "limiting factor" in the context of photosynthesis and give an example where temperature becomes the limiting factor even though light and CO2 are abundant.
A limiting factor is the resource in shortest supply that limits the rate; example: at high light and high CO2, low temperature can limit enzyme activity and slow photosynthesis.