Putting It Together: The Summary of Photosynthesis in Higher Plants
This closing quiz consolidates the whole architecture of photosynthesis in higher plants — from the leaf and its stomata to the regeneration of RuBP in the stroma. You will trace how light captured at the thylakoid membrane is finally spent on building sugar, and how each stage depends on the one before it.
What this quiz covers
- The leaf as the organ of photosynthesis, stomatal entry of ##\ce{CO2}##, and the carbohydrate products glucose and starch
- Mesophyll chloroplasts, with the light reaction on the membranes and the carbon-fixing pathway in the stroma
- Antenna pigments funnelling energy to reaction centre chlorophylls P700 (PS I) and P680 (PS II)
- Electron flow through PS II and PS I, the thylakoid proton gradient, and ATP synthesis via the ##F_0## part of ATPase
- Water splitting at PS II releasing ##\ce{O2}##, protons and electrons
- RuBisCO adding ##\ce{CO2}## to RuBP to give two molecules of PGA, sugar formation and RuBP regeneration
- Photorespiration in C3 plants and the C4 pathway of some tropical plants
Read each question as part of one continuous account: the two stages, their locations, their inputs and outputs, and the logic that binds them.
Q1. Green plants make their own food by photosynthesis. Which raw material is taken in by leaves through stomata and used for making carbohydrates?
According to the summary, carbon dioxide from the atmosphere is taken in by leaves through stomata and used for making carbohydrates, principally glucose and starch.
Q2. The carbohydrates produced in photosynthesis are principally which two substances?
The summary states that the carbohydrates made are principally glucose and starch.
Q3. In which parts of a plant does photosynthesis take place?
Photosynthesis takes place only in the green parts of the plants, mainly the leaves; a non-green tissue cannot sustain the process however well supplied with water and minerals.
Q4. Within the leaf, which cells contain a large number of chloroplasts responsible for ##\ce{CO2}## fixation?
Within the leaves, the mesophyll cells have a large number of chloroplasts that are responsible for ##\ce{CO2}## fixation.
Q5. Within the chloroplast, where does the light reaction take place?
Within the chloroplasts, the membranes are sites for the light reaction, while the chemosynthetic pathway occurs in the stroma.
Q6. In the light reaction, light energy absorbed by the pigments in the antenna is funnelled to which molecules?
Light energy absorbed by the pigments present in the antenna is funnelled to special chlorophyll a molecules called reaction centre chlorophylls.
Q7. Which reaction centre chlorophyll is present in PS I, and at what wavelength does it absorb?
PS I has a 700 nm absorbing chlorophyll a ##\ce{P700}## molecule at its reaction centre, while PS II has a ##\ce{P680}## reaction centre that absorbs red light at 680 nm.
Q8. After light absorption, electrons are excited and transferred through the photosystems. What is the final acceptor named in the summary?
After absorbing light, electrons are excited and transferred through PS II and PS I and finally to NAD forming NADH.
Q9. During the light reaction, a proton gradient is created across which membrane?
During the light reaction a proton gradient is created across the membrane of the thylakoid.
Q10. The breakdown of the proton gradient as protons move through the ##\ce{F0}## part of ATPase releases enough energy for which process?
The breakdown of the proton gradient due to movement through the ##\ce{F0}## part of the ATPase enzyme releases enough energy for synthesis of ATP.
Q11. Splitting of water molecules is associated with PS II. Which products are released by this splitting?
Splitting of water molecules is associated with PS II resulting in the release of ##\ce{O2}##, protons and transfer of electrons to PS II.
Q12. In the carbon fixation cycle, RuBisCO adds ##\ce{CO2}## to a 5-carbon compound. What is this compound, and what is formed from it?
##\ce{CO2}## is added by the enzyme RuBisCO to a 5-carbon compound ##\ce{RuBP}## that is converted to 2 molecules of 3-carbon PGA.
Q13. Which two products of the light reaction are utilised during the Calvin cycle?
During the Calvin cycle, ATP and NADPH synthesised in the light reaction are utilised.
Q14. RuBisCO also catalyses a wasteful oxygenation reaction in C3 plants. What is this reaction called?
RuBisCO also catalyses a wasteful oxygenation reaction in C3 plants: photorespiration.
Q15. In the C4 pathway shown by some tropical plants, where is the 4-carbon first product formed, and where is the Calvin pathway carried out?
In C4 plants the first product of ##\ce{CO2}## fixation, which takes place in the mesophyll, is a 4-carbon compound; in the bundle sheath cells the Calvin pathway is carried out for the synthesis of carbohydrates.