A2 Photosynthesis and Respiration Flashcards
What is the Equation for Photosynthesis?
6CO2 + 6H2O + Energy > C6H12O6 + 6O2
What is the Equation for Aerobic Respiration?
C6H12O6 + 6O2 > 6CO2 + 6H2O + Energy
What Properties of ATP make it a Good Energy Source?
- Releases small, manageable amount of energy, no energy wasted as heat
- Small, soluble molecule, easily transported
- Easily broken down, energy released quickly
- Quickly re-made
- Can make other molecules more reactive by transferring one of its phosphate groups
- ATP cant pass out cell, always has immediate supply of energy
Define phosphorylation and photophosphorylation
Adding phosphate to a molecule (using light)
Define Photolysis
The splitting of a molecule using light energy
Define photoionisation
When light energy ‘excites’ electrons in an atom or molecule, giving them more energy, causing them to be released. Atom becomes a positively-charged ion
Define decarboxylation and dehydrogenation
Decarboxylation - removal of CO2 from a molecule
Dehydrogenation - removal of H from a molecule
Describe redox reactions
Reduction:
- Gained electrons and may have gained hydrogen or lost oxygen
Oxidation:
- Lost electrons and may have lost hydrogen or gained oxygen
Oxidation of one molecule always involves reduction of another
Describe what a Co-enzymes is and their Involvement in Photosynthesis and Respiration
Molecule that aids the function of an enzyme by transferring a chemical group from one molecule to another
Photosynthesis:
- NADP - transfers hydrogen from one molecule to another, it can reduce or oxidise a molecule
Respiration:
- NAD/FAD - same as NADP
- Coenzyme A - transfers acetate between molecules
Describe the Structure of a Chloroplast
- Flattened organelles surrounded by double membrane
- Thylakoids stacked into grana
- Grana linked together by lamellae
- Photosynthetic pigments contained in thylakoid membranes, attached to proteins
- Protein and pigment called a photosystem
- Stroma contains enzymes, sugars and organic acids
- Carbohydrates stored as starch grains in stroma
What are the Products of the Light-Dependent Reaction?
- ATP made from ADP and inorganic phosphate
- Reduced NADP made from NADP
Describe the First Stage of the Light-Dependent Reaction (Photoionisation)
- Light energy absorbed by PSII
- Excited electrons in chlorophyll move up to higher energy level
- Electrons released from chlorophyll, move down ETC to PSI
Describe the Second Stage of the Light- Dependent Reaction (Photolysis)
- Electrons leaving PSII need replacing
- Light energy splits water into Protons (H+), electrons and oxygen
- H2O > 2H+ + 0.5O2
Describe the Third Stage of the Light-Dependent Reaction (Chemiosmosis)
- Electrons lose energy as they move down ETC
- Energy used to transport protons into thylakoid, higher conc. of protons than stroma
- Forms proton gradient across membrane
- Protons move down conc. gradient into stroma via ATP synthase, embedded in thylakoid membrane
- Energy from this combines ADP and inorganic phosphate to form ATP
Describe the Fourth Stage of the Light-Dependent Reaction (Reduced NADP)
- Light energy absorbed by PSI, excites electron to even higher energy level
- Electrons transferred to NADP, along with a proton from stroma
- Forms reduced NADP
Describe Cyclic Photophosphorylation
- Only uses PSI
- Electrons from chlorophyll not passed onto NADP, but passed back to PSI via electron carriers
- Electrons recycled through PSI
- No reduced NADP or oxygen produced, only produces small amount of ATP
Describe the First Stage of the Light-Independent Reaction (Glycerate 3-Phosphate)
- CO2 enters leaf through stomata, diffuses into stroma
- Combines with ribulose bisphosphate (RuBP), 5C compound
- Reaction catalysed by enzyme rubisco
- Produces unstable 6C carbon
- Breaks down into two 3C compounds, glycerate 3-phosphate (GP)
Describe the Second Stage of the Light-Independent Reaction (Triose Phosphate)
- Hydrolysis of ATP (from LDR) provides energy to turn 3C compound, GP, into different 3C compound, triose phosphate (TP)
- Reaction requires H+ ions from reduced NADP (from LDR), reduced NADP recycled to NADP
- Some TP converted to useful organic compounds (glucose) and some used to regenerate RuBP
Describe the Third Stage of the Light-Independent Reaction (Ribulose bisphosphate)
- 5 out of every 6 TP molecules used to regenerate RuBP, not make hexose sugar
- Regenerating RuBP uses rest of ATP from LDR
How are TP and GP Converted into Useful Organic Substances (Carbs, Lipids and Amino Acids)?
- Carbs - hexose sugars made from 2 TP molecules joined together, larger carbs, by joining hexose sugars
- Lipids - using glycerol, synthesised from TP, and fatty acids synthesised from GP
- Amino acids - some are made from GP
Explain Why the Calvin Cycle Turns 6 Times to Make 1 Hexose Sugar
- 3 turns produces 6 TP, 2 TP made for every CO2 molecule used
- 5 out of 6 TP molecules used to regenerate RuBP
- 3 turns, only 1 TP available for making a hexose sugar
- Hexose sugar has 6 carbons, 2 TP molecules needed
- Cycle must turn 6 times to produce 2 TP molecules used to make 1 hexose sugar
- 6 turns requires 18 ATP and 12 reduced NADP (from LDR)
What are the Optimum Conditions for Photosynthesis? (Name 3)
- High light intensity of certain wavelengths, only red and blue light absorbed from the sun
- Temperature around 25 degrees C, temp below 10C, enzymes inactive. Temp above 45C, enzymes denature
- Carbon dioxide at 0.4%, CO2 makes up 0.04% of atmosphere, increasing this, increases rate of photosynthesis
How could Growers Create Optimum Conditions in Greenhouses (Name 2)
- CO2 - CO2 added to air, burning small amount of propane in CO2 generator
- Light - lamps provide light during night
- Temperature - heaters and coolers can be used to keep constant optimum temperature. Air circulation systems can be used to keep temp. even throughout
Describe the First Stage of Glycolysis (Phosphorylation)
- Glucose phosphorylated using phosphate from ATP, creates 1 glucose phosphate and 1 ADP
- ATP used to add another phosphate, makes hexose bisphosphate
- Hexose bisphosphate split into 2 TP
