Quiz: The Electron Transport and the Z Scheme Quiz 1
In Lesson 8 we follow the electron itself, carrier by carrier, from the 680 nm excitation in Photosystem II to the final reduction of NADP+ at the end of Photosystem I. This quiz tests your grasp of that route: the reaction centre chlorophyll a, the cytochrome electron transport system, the downhill movement on a redox potential scale, the second excitation at 700 nm, and the reason the whole pathway is called the Z scheme.
What you should be able to do
- Identify the wavelength absorbed by the reaction centre of each photosystem.
- Explain why electrons are described as moving downhill on a redox potential scale.
- State what happens to electrons as they pass through the cytochrome chain.
- Describe the final acceptor and the product formed when NADP+ is reduced.
- Justify the name “Z scheme” from the shape traced on a redox potential scale.
Work carefully through each question — the sequence of carriers matters more than the individual names.
Q1. In Photosystem II, the reaction centre chlorophyll a absorbs red light of which wavelength?
The reaction centre chlorophyll a of PS II absorbs red light at 680 nm, which excites its electrons and starts the electron flow of the Z scheme.
Q2. After excitation in PS II, the electron is first surrendered to which entity?
The excited electron from the PS II reaction centre is picked up by an electron acceptor before entering the electron transport system.
Q3. The electron transport system lying between the two photosystems consists of which carriers?
The material states that the electron transport system between the photosystems consists of cytochromes.
Q4. As electrons pass along the cytochrome chain from PS II towards PS I, their movement is best described as:
The movement of electrons through the electron transport system is downhill in terms of an oxidation-reduction or redox potential scale.
Q5. What happens to the electrons as they pass through the electron transport chain?
The electrons are not used up as they pass through the chain; they are passed on to the pigments of photosystem PS I.
Q6. Electrons leaving the cytochrome chain are handed on to which pigments?
The electrons travelling down the chain are passed on to the pigments of photosystem PS I, where a second excitation awaits them.
Q7. Electrons in the reaction centre of PS I are excited by red light of which wavelength?
Electrons in the reaction centre of PS I are excited when they receive red light of wavelength 700 nm.
Q8. After excitation in PS I, the electrons are transferred to another acceptor molecule that has:
The electrons excited in PS I are transferred to another acceptor molecule that has a greater redox potential.
Q9. From the acceptor of PS I, the electrons finally move downhill to which molecule?
After the second excitation the electrons move downhill again, this time to a molecule of energy-rich NADP+.
Q10. The addition of electrons to NADP+ produces which product?
The addition of these electrons reduces NADP+ to NADPH + H+, the reducing currency that later drives carbon fixation.
Q11. The whole scheme of electron transfer described in the lesson begins at which photosystem?
The whole scheme of transfer of electrons starts from PS II, goes uphill to the acceptor, down the chain to PS I, and finally downhill to NADP+.
Q12. In the sequence of the Z scheme, the transfer of electrons from PS II to its acceptor is described as:
The scheme begins with an uphill transfer of electrons from PS II to the acceptor, which is why light energy is needed at this step.
Q13. Why is the entire pathway given the name “Z scheme”?
The pathway is called the Z scheme due to its characteristic shape, which is formed when all the carriers are placed in a sequence on a redox potential scale.
Q14. The characteristic Z shape appears when the carriers are:
This shape is formed when all the carriers are placed in a sequence on a redox potential scale.
Q15. Which statement correctly summarises the electron route of the Z scheme?
The route runs from PS II uphill to the acceptor, down the electron transport chain of cytochromes to PS I, then to another acceptor and finally downhill to NADP+, reducing it to NADPH + H+.