5.7 photosynthesis

Question 1

Light-dependent reaction (non-cyclic phosphorylation)

Answer 1

when PSII absorbs light, electrons in chlorophyll gain energy (get excited). these excited electrons leave chlorophyll and move the electron transport chain. Since chlorophyll lost those electrons, water is split and its electrons go to chlorophyll (photolysis). The electron transport chain transports electrons, as it does the energy in electrons used to pump H+ ions across the thylakoid membrane into the thylakoid. this creates a high concentration of H+ Ions in the thylakoid.
chemiosmosis
ATP synthase allows them to passively diffuse from high to low concentration creating an electrochemical gradient. this flow of hydrogen ions through ATP synthase causes the ATP synthase to spin and produce ATP.

When electrons reach the end of this first electron transport chain, they go to PSI where light excites them once again, they travel to a shorter electron transport chain where they are accepted by NADP TO MAKE REDUCED NADP.
NADP + H+ + 2e —> Reduced NADP

Question 2

light-independent reaction (STROMA)

Answer 2

The 5-carbon molecule ribulose biphosphate (RuBP) reacts with carbon dioxide this reaction is catalyzed by ribulose bisphosphate carboxylase (RUBisCO) from this reaction we make two molecules of glycerate 3-phosphate (2 X GP). Each molecule of glycerate 3-phosphate is reduced triose phosphate (TP) this reaction uses reduced NADP and ATP from the light-dependent reactions. the reduced NADP provides the hydrogen needed for reduction and the ATP provides energy. the final stage is called regeneration

Question 3

Limiting factors

Answer 3

when light intensity is very low, the rate of photosynthesis is also low. that’s because the light intensity will be too low for the light-dependent reactions to function at their maximum rate. Levels of ATP and reduced NADP will also be low so the light-independent reactions will also be running slowly. As we increase the light intensity, the rate of photosynthesis increases. that’s because the light- dependent reactions have increased in rate. Producing more ATP and reduced NADP. And because of this, the light-independent reactions are also happening at a faster rate.

At very high light intensities, the light-dependent reactions are running at a very fast rate. this means the levels of ATP and reduced NADP are very high. so in this case, the light-independent reactions could run at a very fast rate. However, the light-independent reactions also require CO2.

temperature - if the temp is too low rubisco will not be functioning at a fast rate. so this will limit the rate of light-independent reactions and the overall rate of photosynthesis.

if the light intensity is low then the overall rate of photosynthesis is less affected by temperature. at low light intensities, the overall rate of photosynthesis is limited by the rate of light-dependent reactions. these are less dependent on enzymes and so are less affected by temperature.

at low light intensities, the light-dependent reactions are slow and the concentration of ATP and reduced NADP fall less GP can now be converted to GALP. concentration of GP increase and the concentration GALP decrease as RuBP is made from GALP, the concentration of RuBP also falls

at low co2 concentration less co2 will react with RuBP to form GP which means there will be less GP and so less GALP HOWVER the concentration of RuBP will increase as less RuBP is reacting with carbon dioxide