Splitting of Water and Cyclic and Non-cyclic Photo-phosphorylation Quiz

Quiz: Splitting of Water and Cyclic and Non-cyclic Photo-phosphorylation

This quiz accompanies Lesson 9 of the photosynthesis course and tests the two ideas that keep the light reaction running: the splitting of water that replenishes electrons lost by photosystem II, and the two routes of photo-phosphorylation — cyclic and non-cyclic.

Why PS II must have its electrons replaced, and how water does it.
The water-splitting equation and the fate of protons, oxygen and electrons.
Where the water splitting complex sits in the thylakoid membrane.
Which products arise from non-cyclic versus cyclic electron flow.
Why grana lamellae and stroma lamellae differ in their protein complement.

Work through the fifteen questions carefully — each explanation is written to reinforce the exact terminology of the lesson.

Q1. The electrons that are moved away from photosystem II during the light reaction must be replaced. According to the lesson, this replacement is achieved by:

Electrons made available through the splitting of water

Electrons donated by NADPH + H+

Electrons released by the reduction of NADP+

Electrons returned from photosystem I

The lesson states directly that the electrons moved from photosystem II must be replaced, and that this is achieved by electrons available due to the splitting of water.

Q2. The splitting of water in the light reaction is associated with which photosystem?

Photosystem I

Photosystem II

Both photosystems equally

Neither photosystem

The lesson emphasises that the splitting of water is associated with PS II, and that the water splitting complex is physically located on the inner side of the thylakoid membrane.

Q3. In the notation of the lesson, water is split into which three products?

##\ce{2H+}##, ##\ce{[O]}## and electrons

##\ce{2H+}##, ##\ce{O2}## and protons

##\ce{OH-}##, ##\ce{[O]}## and electrons

##\ce{2H+}##, ##\ce{[O]}## and ##\ce{NADPH + H+}##

The source states that water is split into ##\ce{2H+}##, ##\ce{[O]}## and electrons, and that this creates oxygen, one of the net products of photosynthesis.

Q4. Which balanced equation correctly represents the splitting of water as given in the lesson?

##\ce{2H2O -> 4H+ + 4e- + O2}##

##\ce{H2O -> 2H+ + 2e- + O2}##

##\ce{2H2O -> 2H+ + 2e- + O2}##

##\ce{4H2O -> 4H+ + 4e- + 2O2}##

The lesson writes the reaction as two molecules of water yielding four protons, four electrons and one molecule of oxygen, i.e. ##\ce{2H2O -> 4H+ + 4e- + O2}##.

Q5. The oxygen released during the light reaction of photosynthesis originates from:

Carbon dioxide

The water molecule being split at the photosystem II reaction centre

Glucose

NADP+

The lesson stresses that the gas evolved by a green leaf originates not from carbon dioxide but from the water molecule being dismantled at the photosystem II reaction centre.

Q6. The electrons needed to replace those removed from photosystem I are provided by:

Photosystem II

The splitting of water at photosystem I

NADP reductase

The stroma lamellae

The lesson states explicitly that the electrons needed to replace those removed from photosystem I are provided by photosystem II.

Q7. The water splitting complex is physically located:

On the outer side of the thylakoid membrane

On the inner side of the membrane of the thylakoid

In the stroma

In the intermembrane space of the mitochondrion

The lesson emphasises that the water splitting complex is associated with PS II, which itself is physically located on the inner side of the membrane of the thylakoid.

Q8. Since water splitting occurs on the inner side of the thylakoid membrane, the protons and ##\ce{O2}## formed are most likely to be released:

Into the stroma, on the outer side of the membrane

Into the lumen of the thylakoid

Into the cytoplasm

Into the intermembrane space

The lesson notes that water splitting takes place on the inner side of the membrane, so the protons produced accumulate within the lumen of the thylakoids.

Q9. According to the lesson, living organisms extract energy from oxidisable substances and store it in the form of bond energy. Which substance is described as carrying this energy in its chemical bonds?

##\ce{NADP+}##

ATP

##\ce{O2}##

##\ce{CO2}##

The lesson states that special substances like ATP carry energy in their chemical bonds, after organisms extract energy from oxidisable substances.

Q10. The process through which ATP is synthesised by cells in mitochondria and chloroplasts is named:

Photo-phosphorylation

Phosphorylation

Oxidation

Reduction

The lesson defines phosphorylation as the synthesis of ATP by cells in mitochondria and chloroplasts; photo-phosphorylation is the special case requiring light.

Q11. Photo-phosphorylation is best defined as:

The synthesis of ATP from ADP and inorganic phosphate in the presence of light

The reduction of ##\ce{NADP+}## to ##\ce{NADPH + H+}##

The splitting of water into protons, oxygen and electrons

The cycling of electrons within photosystem I

The lesson defines photo-phosphorylation as the synthesis of ATP from ADP and inorganic phosphate in the presence of light.

Q12. Non-cyclic photo-phosphorylation occurs when:

Only PS I is functional

The two photosystems work in series, first PS II and then PS I

Only light beyond 680 nm is available

Water splitting is blocked

The lesson states that when the two photosystems work in a series, first PS II and then PS I, a process called non-cyclic photo-phosphorylation occurs.

Q13. Which products are synthesised by non-cyclic electron flow?

ATP only

##\ce{NADPH + H+}## only

Both ATP and ##\ce{NADPH + H+}##

Neither ATP nor ##\ce{NADPH + H+}##

The lesson states that both ATP and ##\ce{NADPH + H+}## are synthesised by non-cyclic electron flow, where the two photosystems are connected through an electron transport chain.

Q14. When only PS I is functional, the electron is circulated within the photosystem. The result of this cyclic flow is:

Synthesis of ATP but not of ##\ce{NADPH + H+}##

Synthesis of ##\ce{NADPH + H+}## but not of ATP

Synthesis of both ATP and ##\ce{NADPH + H+}##

Splitting of water and release of oxygen

The lesson states that the cyclic flow results only in the synthesis of ATP, but not of ##\ce{NADPH + H+}##, because the excited electron does not pass on to ##\ce{NADP+}## but is cycled back to the PS I complex.

Q15. Which statement about the lamellae of the chloroplast is correct according to the lesson?

Grana lamellae have both PS I and PS II, while stroma lamellae lack PS II and NADP reductase enzyme

Stroma lamellae have both PS I and PS II, while grana lamellae lack PS II

Both grana and stroma lamellae lack NADP reductase enzyme

Grana lamellae contain only PS I

The lesson states that the membrane or lamellae of the grana have both PS I and PS II, whereas the stroma lamellae membranes lack PS II as well as NADP reductase enzyme; a possible location for cyclic flow is the stroma lamellae.