| 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 |
