photosynthesis

Question 1

what is a metabolic pathway?

Answer 1

a series of enzyme-controlled reactions

Question 2

chemical equation for photosynthesis

Answer 2

6CO2 + 6H2O → C6H12O6 + 6O2

Question 3

which molecules are formed in the LDR and are used in the LIR.

Answer 3

ATP and NADPH

Question 4

what does reduced NADP provide

Answer 4

reducing power within the light independent reaction as it donates this
hydrogen/electron, becoming oxidised to NADP.

Question 5

where does the LDR take place

Answer 5

thylakoid membranes

Question 6

describe the LDR

Answer 6

1. Light energy is absorbed by the chlorophyll- photoionisation of chlorophyll. Electrons are
   excited to a higher energy level, leaving and oxidising the chlorophyll.
2. The electrons reduce a protein carrier, and pass down an electron transport chain in the thylakoid membrane in a series of redox reactions, losing energy as they pass down
   the chain.
3. This energy is used to pump H+
   ions (protons)
   across the thylakoid membrane, building up to high concentrations
   in the thylakoid space, creating a proton
   gradient.
4. They pass back through the thylakoid
   membrane into the stroma, down an
   electrochemical gradient through ATP synthase- chemiosmosis.
5. As protons pass through ATP synthase, energy is released to synthesise ATP, from ADP and Pi.
6. At the end of the electron transport chain, the electrons combine with a proton to form hydrogen, which is used to reduce NADP forming reduced NADP.
7. Photolysis also occurs, where light splits a water molecule into protons, electrons and oxygen (a waste product used in aerobic respiration). Protons combine with electrons at end of ETC to form hydrogen to reduce NADP, and electrons replace those lost by chlorophyll.

Question 7

where does the LIR occur

Answer 7

chloroplasts stroma

Question 8

describe the LIR

Answer 8

1. CO2 reacts with RuBP to form two 3-carbon GP, catalysed by the enzyme rubisco.
2. The hydrogen from NADPH and energy from the hydrolysis of ATP (both from the light dependent
   reaction) are used to reduce GP to triose phosphate
3. Some of the triose phosphate (1/6) is converted into useful organic substances (e.g. glucose, amino
   acids and triglycerides.)
4. Rest of the triose phosphate (5/6) is used to regenerate RuBP via phosphorylation by ATP.

Question 9

limiting factors of photosynthesis

Answer 9

Temperature (increases enzyme kinetic energy, so more enzyme substrate complexes)
* CO2 concentration (more CO2 reacts with more RUBP to form more GP)
* Light intensity (more NADPH and ATP made in LDR, so more GP is reduced to
triose phosphate in the LIR)
The highest rate of photosynthesis occurs when all factors are at the optimum level.

Question 10

describe this graph in terms of limiting factors

Answer 10

The graph initially shows the rate of photosynthesis is directly proportional to light intensity, the limiting factor.
* As light intensity increases to a certain level, the curve starts to level off and light is no longer limiting. Other factors such as temperature and CO2 concentration now may be limiting the rate of photosynthesis. If the concentration of CO2 or temperature are increased the rate of photosynthesis will increase again.
* Once all 3 factors have been increased, rate of photosynthesis will eventually level off. At this point something else is limiting the rate of photosynthesis such as amount of chlorophyll or concentration of
Rubisco enzyme

Question 11

how can growers increase plant growth for crops + name how the limiting factors are controlled

Answer 11

commercial glasshouses.
1. Artificial light may be used to increase light intensity to the optimum levels. Blinds may be used to shade plants if light intensity is very high as this could damage the chlorophyll.
2. CO2 concentration can be increased by burning fossil fuels or add CO2 into the glasshouse
3. Heaters can be used to raise the temperature to optimum level