Photosynthesis Flashcards
Where does the light dependent reaction occur?
Thylakoid Membrane in the chloroplast
Where does the light independent reaction occur?
In the stroma of the chloroplast
What does the light dependent reaction produce?
ATP & NADPH
What is the advantage of different pigments having their peaks at different wavelengths of light?
- allows greater range of wavelengths to be absorbed
- photosynthesis can take place over a greater range of wavelengths
How does photoionisation occur during the LDR?
- light energy is absorbed by the chlorophyll in photo system 2
- this excites an electron to move up to a higher energy level and leave the chlorophyll and enter the thylakoid membrane
- electron passes along a series of carrier proteins through a series of redox reactions along the ETC until it reaches photo system 1
Describe how the movement of the electron through the ETC generates an electrochemical gradient (chemiosmosis).
- energy is released during the series of redox reactions that move the electron through the ETC
- this energy is used to pump H+ across the thylakoid membrane by active transport through the carrier proteins
- this generates an electrochemical gradient as there is a higher concentration of H+ inside the thylakoid than the stroma
- H+ diffuse back across the membrane through protein channels formed by ATP Synthase (chemiosmosis)
How is ATP produced as H+ moves through ATP Synthase?
- movement of H+ causes a shape change of ATP Synthase which catalyses the synthesis of ATP (photophosphorylation)
ADP + Pi —> ATP
What is photolysis?
Light energy splits water molecules into:
O , 2H+ , 2electrons
Describe how NADPH is produced during the LDR.
- chlorophyll in PS1 absorbs light energy which excites an electron to a higher energy level and is released
- electrons are transferred to NADP to reduce it to NADPH
Describe the process of the Calvin Cycle.
- carbon dioxide diffuses into the stroma and reacts with RuBP, catalysed by Rubisco, to produce an unstable 6 carbon molecule that splits into 2 molecules of Glycerate Phosphate
- Glycerate Phosphate is reduced into 2 molecules of Triose Phosphate and requires ATP & NADPH from the LDR. ATP is hydrolysed into ADP + Pi to release the energy needed to convert GP to TP, and NADPH is oxidised and GP gains hydrogen to become reduced.
- Most TP is used to regenerate RuBP which requires Pi from ATP hydrolysis
- Some TP is used to make organic molecules such as glucose
- Glucose molecules can be joined together in condensation reactions to produce starch which can be stored in the stroma
How does light intensity affect the rate of photosynthesis?
- Initially as light intensity increases, the rate of photosynthesis increases
- Light intensity becomes a limiting factor so rate of photosynthesis decreases
- Something other than light intensity becomes a limiting factor so the rate f photosynthesis stabilises
How does the concentration of carbon dioxide affect the rate of photosynthesis?
- Initially as the concentration of carbon dioxide increases, the rate of photosynthesis increases
- Carbon dioxide concentration becomes a limiting factor so rate of photosynthesis decreases
- Something other than the concentration of carbon dioxide becomes a limiting factor so the rate of photosynthesis stabilises
How does temperature affect the rate of photosynthesis?
- Initially as temperature increases, molecules have more kinetic energy so the rate of photosynthesis increases.
- At the optimum temperature, the rate of reaction is at its highest
- As temperature surpasses the optimum, the enzymes begin to denature so the rate of photosynthesis decreases to zero.
What methods can be used by farmers to maximise the rate of photosynthesis for maximum yields?
- Growing plants under artificial lighting maximises light intensity
- Heating a greenhouse increases temperature to its optimum
- Burning fuels (e.g. Parafin burners) releases more carbon dioxide so maximise the concentration
RP7 - How is chromatography used to investigate the different pigments found in leaves from different plants?
- Draw a straight line in pencil around 1cm above the bottom of the filter paper
- Cut a section of leaf and grind it together with acetone to realise the pigments
- Use a capillary tube to extract some of the pigment and blot it onto the centre of the pencil line drawn
- Place the filter paper into solvent but don’t submerge the pencil line and leave the paper in a dark cupboard until the solvent has run up the paper to near the top
- Remove the paper from the solvent and make down the solvent front using a pencil line .
- Determine the distance traveled by each pigment and also the length of the sole vent front.
- Calculate the Rf value for each pigment by diving distance solute travelled by distance solvent travelled.
- Compare calculated Rf values to a database to identify the names of the pigments present in the leaves
9.Repeat with leaves from different plants and compare Rf values
