Photosynthesis
- Created by: Labake
- Created on: 14-10-14 10:37
View mindmap
- Photosynthesis
- The light dependent stage
- Takes place on the thylakoid membrane
- Light photon hits a chlorophyll molecule in PSII in the primary pigment reaction centre and excites electrons
- Electrons are accepted by an electron acceptor and passed along electron transport chain
- Energy used to pump protons into thylakoid space, conc. gradient made and protons diffuse back down to stroma through ATPsynthase making ATP
- Flow of protons called Chemiosmosis
- Kinetic energy from proton flow converted to chemical energy in ATP to be used in LI stage
- Light photons hit PSI and electrons excited and accepted by electron acceptor
- 2H+ (from photolysis) and 2e- (from PSI) react with NADP and make redNADP (used in LI stage)
- Energy used to pump protons into thylakoid space, conc. gradient made and protons diffuse back down to stroma through ATPsynthase making ATP
- Water splits by Photolysis, producing Oxygen, 2H+ and 2e-
- 2e- reduce the oxidises PSII
- 2H+ (from photolysis) and 2e- (from PSI) react with NADP and make redNADP (used in LI stage)
- 2e- reduce the oxidises PSII
- Electrons are accepted by an electron acceptor and passed along electron transport chain
- Cyclic Photo phosphorylation- excited PSI electron accepted by 2 electron acceptors then back to PSI
- How the structure of chloroplasts enables them to carry out their functions
- INNER MEMBRANE- Less permeable, has transport proteins for entry into stroma, folded into lamellae
- Lamellae is stacked up, each stack called granum, between each grana is intergranal lamellae
- GRANA- stacks called thylakoids, sites for light absorption and ATP synthesis in LD stage
- THYLAKOID MEMBRANE- have photosynthetic pigments arranged into photosystems for maximum absorption of a range of light wavelengths
- PHOTO SYNTHETIC PIGMENTS- absorb certain wavelengths of light and reflect others
- Chlorophyll A (450nm) is always the primary pigment
- Chlorophyll B (500-640nm) and Carotenoid (and Xanthophyll) are accessory pigments
- Photosystem II = P680/ nm + Photosystem I = P700/nm
- PHOTO SYNTHETIC PIGMENTS- absorb certain wavelengths of light and reflect others
- THYLAKOID MEMBRANE- have photosynthetic pigments arranged into photosystems for maximum absorption of a range of light wavelengths
- GRANA- stacks called thylakoids, sites for light absorption and ATP synthesis in LD stage
- Lamellae is stacked up, each stack called granum, between each grana is intergranal lamellae
- OUTER MEMBRANE- Permeable to many small ions
- STROMA- Fluid filled matrix for LI stage , contains RUBISCO and ATPase
- DNA and RIBOSOMES- for coding and synthesising proteins needed for photosynthesis
- INNER MEMBRANE- Less permeable, has transport proteins for entry into stroma, folded into lamellae
- Limiting factors and the Calvin cycle
- Light Intensity
- Measure of how much energy is associated with the light
- L= 1/d^2 -- as the light spreads so if distance is doubled, light intensity is quartered
- Increase of it affects the rate of the LD stage
- More light energy to excite more electrons
- More electrons in Photo phosphorylation so more ATP and redNADP
- More ATP and redNADP means more H and energy for LI stage (GP to TP) and more ATP for TP to RuBP
- Decrease of it stops LD stage and then LI stage as it need LD products
- No GP to TP - GP accumulates and levels of TP fall
- Less RuBP, so less carbon fixation and more GP formation
- Temperature
- At first, increase of temperature increases kinetic energy, faster enzyme activity so rate of LI stage increased
- CO2 concentration
- Leads to an increase in Carbon dioxide fixation (if light not a limiting factor)
- More GP and more TP and more RuBP so more products of GP and RuBP
- BUT more stomata open for gas exchange- increased transpiration and plant wilts due to transpiration exceeding soil water uptake- lower rate of photo synthesis
- CO2 conc decreases below 0.01% means RuBP accumulates and levels of TP and GP drop
- Leads to an increase in Carbon dioxide fixation (if light not a limiting factor)
- Light Intensity
- The light independent stage
- CO2 from air diffuse into the leaf through open stomata into stroma in chloroplast
- CO2 (1C) combines with RuBP (5C) using enzyme RUBISCO
- Occurs in stroma of chloroplasts
- 3 cycles for 1 glucose
- CO2 from air diffuse into the leaf through open stomata into stroma in chloroplast
- Limiting factors
- Factors present in the environment which may affect the rate of photosynthesis
- Factors present in the least favourable level is the one that limits the process
- When light intensity gets higher that the optimum, its no longer the limiting factor as it doesn't alter the rate, CO2 must be
- Increasing CO2 conc. increases the rate until temp. becomes a limiting factor
- Zero light intensity means no photosynthesis- its the limiting factor as when it increases the rate does too
- Light intensity causes stomata to open so CO2 can enter
- Light photon are trapped by chlorophyll A to excite electrons
- Light photons split water molecules (photolysis) to make protons
- Increasing the temp. increases the rate of photosynthesis till another factor limits the process
- When temp. gets to 25 degrees, RUBISCO starts to catalyse O2 and RuBP making Phosphoglycolate that needs to be actively transported ->mitochondria-> redNADP-> ->GP (photorespiration)-> back to chloroplast
- Called photorespiration as it occurs in both the chloroplast and the mitochondria
- When temp. gets to 25 degrees, RUBISCO starts to catalyse O2 and RuBP making Phosphoglycolate that needs to be actively transported ->mitochondria-> redNADP-> ->GP (photorespiration)-> back to chloroplast
- The importance of photosynthesis
- Autotrophs are organisms that synthesise complex organic molecules from inorganic molecules and energy
- Chemoautotrophs use energy from exergonic chemical reactions
- Photoautotrophs use light energy for photosynthesis, using CO2 and H2O as inorganic molecules e.g.plants, some bacteria + some prokaryotes
- Make carbs, proteins, nucleic acids and vitamins
- Chemoautotrophs use energy from exergonic chemical reactions
- Can both release chemical potential energy in complex organic molecules (that are made in photosyn.) in respiration
- Heterotrophs are organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them
- Synthesise lipids, proteins and nucleic acids
- Heterotrophs are organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them
- Make carbs, proteins, nucleic acids and vitamins
- Heterotrophs are organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them
- Synthesise lipids, proteins and nucleic acids
- Autotrophs are organisms that synthesise complex organic molecules from inorganic molecules and energy
- The light dependent stage
Comments
No comments have yet been made