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level: 11.3 The light-independent reaction

Questions and Answers List

level questions: 11.3 The light-independent reaction

QuestionAnswer
What is the light-independent reaction (Calvin Cycle)- Doesn't use light energy directly - Stroma of the chloroplast - Relies on products of the light-dependent reaction - ATP + reduced NADP from light-dependent reaction supply energy + H to make simple sugars from CO2
Main steps of the Calvin Cycle- CO2 is combined with ribulose bisphosphate to form 2 molecules of glycerate 3-phospahte - ATP + reduced NADP reduces GP to triose phosphate - Ribulose bisphosphate is regenerated
CO2 + RuBP ----> GP- CO2 diffuses into the stroma of the chloroplast - Combined with ribulose bisphosphate (RuBP) (5C) - Catalysed by rubisco - Creates unstable 6C compound, quickly breaks down into 2 3C molecules of glycerate 3-phosphate (GP)
ATP + reduced NADP reduces GP to TP- Hydrolysis of ATP provides energy to turn GP into TP - NADPH2 donates H ions, recycled to NADP - Some TP is converted into useful organic compounds (like glucose) some continues in the Calvin Cycle to regenerate RuBP
Ribulose bisphosphate is regenerated- 5/6 molecules of TP produced regenerate RuBP - This uses the rest of the ATP produced by the L.D.R
TP and GP are converted into useful organic substances- Used to make carbohydrates, lipids + amino acids - 2 TP molecules together = hexose sugar - Joining hexose sugars in different ways = big carbs like starch - Lipids, glycerol made from TP, fatty acids made from GP - Some amino acids are made from GP
Site of the light-independent reaction- Stroma contains enzymes needed for reaction - Stromal fluid is membrane-bound in chloroplast - So manintains chemical environment with high con. of enzymes + substrate - Stroma fluid surrounds grana so products in the grana can readily diffuse into the stroma
Optimum conditions for photosynthesis- High light intensity of a certain wavelength - Temperature around 25 degrees - Carbon dioxide at 0.4% - Constant supply of water
High light intensity of a certain wavelength- Light provides energy for the L.D.R - Higher light intensity, more energy it provides - Only certain wavelengths of light are used for photosynthesis - Chlorophyll a, b + carotene only absorb the red + blue light in sunlight
Temperature around 25 degrees- Photo. involves enzymes like ATP synthase - If the temp. to low enzymes become inactive - But if the temp. is too high they may denature - At high temps. stomata close to avoid losing too much water - Causing photosyn. to slow down as less CO2 enters the leaf
Carbon dioxide at 0.4%- CO2 makes up 0.04% of the gases in the atmosphere - Increasing CO2 increases photo, any higher stomata will close
Constant supply of water- Too little and photosynthesis has to stop - Too much and the soil becomes waterlogged - Reducing the uptake of minerals such as magnesium, which is needed to make chlorophyll a
Limiting factors of photosynthesis- Light intensity - Temperature - CO2
Light intensity (on graph)- At the start of trend, rate of photo. limited by the light intensity - So as light intensity increases, so can the rate pf photosynthesis - But it reaches the saturation point, increasing light intensity after this point makes no difference - Graph plat. smt else has become limiting factor
Temperature (on graph showing 2 temperatures - 25 c + 15 c)- Both these graphs level off when light intensity is not longer the limiting factor - The graph at 25 c levels off at a higher point than the one at 15 c - Showing that temp. must have been a limiting factor at 15 c
CO2 (on graph with 2 lines showing different concentration of CO2)- Both graphs plat. when light intensity is no longer limiting factor - Graph at 0.4% CO2 plat. at a higher point than the one at 0.04% - So CO2 conc. must have been a limiting factor at 0.04% CO2
How do growers create optimum conditions in glasshouses- CO2 is added to the air - Light can get in through the glass, lamps provide light at night - Glasshouses trap heat energy from sunlight, warms the air, heaters + cooling systems to keep a constant optimum temp and air
Interpreting data on limiting factors (graph on effect of CO2 on plant growth in greenhouse - 2 lines, 1 without CO2, other with CO2)- In the greenhouse with added CO2 plant growth was faster + on average they were larger after 8 weeks than they were o the control greenhouse - This was because the plants use CO2 to produce glucose by photosynthesis - The more CO2 , the more glucose produced, meaning they can respire more + have ATP for DNA replication, cell division + proteins synthesis
Interpreting data on limiting factors (graph on effect o light intensity on plant growth, effect of 2 types of heater)- At the start of the graph, the greater the light intensity the greater the plant growth - At 200 ... of light the bottom graph flattens out, showing that CO2 conc. or temp, is a limiting factor - At 250 ... of light the top flattens out - The difference between the 2 graphs could be because the wood fires increases the temp. more than the electric heater - Or because increasing the conc. of CO2 in the air
Investigating the pigments in leaves using chromatography- Different species have different pigment proportions + mixtures - You an use chromatography (TLC) to identify pigments - Solvent moves upwards carrying the dissolved pigments - Some travel faster or further than others, which separates them out
Rf value meaning- Distance a substance has moved in relation to the solvent - Identify pigments by calculating Rf value + looking it up in a database - Each pigment has a specific Rf value
Key words used in chromatography- Mobile phase: where molecule can move - Stationary phase: where molecules cant move - Solvent front: the furthest point the solvent has reached
Using TLC to compare the pigments in different plants (1)- Grind up many leaves from shade-tolerant plant with some anhydrous sodium sulphate - Add few drops of propanone - Transfer liquid to test tube - Add some petroleum ether, shake tube - 2 distinct layers will form in liquid
Using TLC to compare the pigments in different plants (2)- Top layer is the pigment mixed in with petroleum ether - Transfer some liquid from top layer into other tube with some anhydrous sodium sulphate - Draw horizontal line pencil line near the bottom of the TLC plate - Build up a single concentrated spot of liquid on the line, point of origin
Using TLC to compare the pigments in different plants (3)- Once dry, put plate into small glass container w/solvent - Put lid on, leave plate to develop - As solvent spreads up plate, pigments move with it - Mark solvent front with pencil when solvent reaches near top - See several coloured spots between PoO + solvent front - Calculate Rf values, identify pigments, repeat with shade-intolerant plant
Investigation the activity of dehydrogenase in chloroplasts- In PSI, during L.D.R, NADP acts as an electron acceptor, reduced, catalysed by dehydrogenase enzyme - Dye acts exactly like NADP but colour changes when get reduced - Rate of the dehydrogenase activity measured by the rate at which DCPIP loses its blue colour
Colorimeter function- Measures how much light a solution absorbs when a light source is shone directly through it - A coloured solution absorbs more light than a colourless solution
What is a chilled isolation slution- A solution of sucrose, potassium chloride and phosphate buffer at pH 7)
Curvette meaning- A cuboid-shaped vessel used in colorimeters
Carrying out the investigation (1)- Cut leaves - Using a pestle + mortar, grind the leaf with some chilled isolation solution - Filter the liquid you make into a beaker through a funnel lined with muslin cloth - Transfer the liquid to centrifuge tubes + centrifuge them at high speed for 10 mins - Makes chloroplasts form pellet at bottom
Carrying out the investigation (2)- Get rid of supernatant, leaving the pellet - Re-suspend the pellet in fresh chilled isolation solution, this is your chloroplast extract, store in ice - Set up colorimeter with a red filter + zero it using cuvette containing the chloroplast extract + distilled water - Set up test tube rack at set distance from bench lamp
Carrying out the investigation (3)- Switch lamp on - Put test tube in rack, add set volume of chloroplast extract + set vol. of DCPIP, mix - Immediately take sample from the tube + put it to a clean curvette - Place curvette in colorimeter, record absorbance - Do this every 2 mins for next 10 mins - Repeat for each distance under investigation