Photosynthesis (A-level only) Flashcards – AQA A-Level Biology - (7402)

What is photoionisation of chlorophyll?

The release of electrons from chlorophyll when it absorbs light energy.

How do electrons released from chlorophyll contribute to ATP production?

They pass along electron carriers, transferring energy that contributes to ATP production.

What roles do electrons and protons play in the formation of reduced NADP?

Electrons provide reducing power, while protons contribute to NADP reduction.

What are the three products of light-driven photolysis of water?

Electrons, protons and oxygen; the oxygen is released.

What happens to the electrons produced by photolysis of water?

They replace electrons lost from chlorophyll.

How does electron transfer create a proton gradient across the thylakoid membrane?

Energy transferred from electrons drives the accumulation of protons inside the thylakoid.

How does the proton gradient drive ATP synthesis in chloroplasts?

Protons flow down the gradient through ATP synthase, supplying energy to form ATP from ADP and inorganic phosphate.

What is chemiosmosis in chloroplasts?

The coupling of electron transfer, a proton gradient and ATP synthesis.

What inputs do the light-independent reactions use to produce triose phosphate?

Carbon dioxide, ATP and reduced NADP.

What happens to carbon dioxide when it enters the Calvin cycle?

It combines with ribulose bisphosphate (RuBP), producing two molecules of glycerate 3-phosphate (GP).

Which enzyme catalyses the combination of carbon dioxide with RuBP?

Rubisco.

What is required to reduce GP to triose phosphate?

Reduced NADP and energy from ATP hydrolysis.

What role does triose phosphate play in allowing the Calvin cycle to continue?

Some triose phosphate is used to regenerate RuBP.

What substances can be formed from triose phosphate produced by the Calvin cycle?

Simple sugars and other useful organic substances.

Where do the ATP and reduced NADP used in the Calvin cycle come from?

The light-dependent reactions.

How does the electron acceptor DCPIP change colour when reduced?

It changes from blue when oxidised to colourless when reduced.

How can DCPIP and a colorimeter be used to estimate the rate of electron transfer in a chloroplast extract?

Measure absorbance at regular intervals and calculate its decrease per unit time.

How can the effect of light intensity on chloroplast dehydrogenase activity be investigated?

Vary light intensity while controlling other relevant conditions, including the amounts of chloroplast extract and DCPIP.

Why repeat measurements in an investigation of chloroplast dehydrogenase activity?

To help assess the reliability of the results.

Why use appropriate controls in an investigation of chloroplast dehydrogenase activity?

To help assess whether the observed change is associated with activity in the chloroplast extract.