5.2.1 Photosynthesis COMPLETE Flashcards
DEFINITION- Photosynthesis
The use of light energy to synthesise large organic molecules from smaller inorganic ones.
Autotrophs
Can synthesise their own organic nutrients using inorganic carbon source (self feeding)
Chemoautotrophs
Synthesise complex organic molecules using energy from exergonic chemical reactions
Photoautotrophs
Photosynthesising organisms, e.g. plants, some bacteria and phytoplankton
Heterotrophs
Eat and Digest
digest complex organic molecules into simple soluble ones.
Photosynthesis word equation
water + CO2 —> O2 + glucose
Glucose Symbol
C6H12O6
Light-Dependant Stage
Photolysis of water, produces ATP and NADP
Light-Independant Stage
Products from light reactions were used to reduce CO2 into sugars and organic molecules.
Importance of photosynthesis
- Oxygen required for aerobic respiration
- CO2 removed from the air
- Production of fossil fuels
- Controls greenhouse effect
Grana function
Chlorophyll are embedded, so provides a large SA for pigments
Inter-granal Lamella function
Where PS1 is found
Stroma function
Contains the enzymes for light independant reactions
Features of a Leaf for photosynthesis
- Large SA
- Transparent waxy cuticle
- Thin
- Lots of air space
- Stomata on the bottom to reduce water loss
Definition- Photosynthetic Pigments
A substance that absorbs certain wavelengths of light, photosynthetic ones capture light specifically for photosynthesis.
Chlorophyll Pigments
- Green pigments with a hydrocarbon tail that embeds itself into the thylakoid membrane
- The Porphyrin Head contains Mg and remains on the surface
- Chlorophyll a and Chlorophyll b exists
Carotenoid Pigments
- Includes both carotenes and xanthophylls
- Range of colours from red to orange to yellow
- They absorb the wavelengths not efficiently absorbed by chlorophyll
- Pass energy onto the chlorophyll
- May also help to protect the chlorophyll
Phycobilin Pigments
Red seaweeds contain additional pigments allowing blue/ green wavelengths to be absorbed
Chromatography
Thin layer chromatography can be used to operate leaf extracts to identify the pigments inside
Absorption and Action Spectrum
Rate of absorption and rate of action corresponds and when more light is absorbed photosynthesis increases.
Plants with more pigments can absorb more light
Photosystems
- Pigment molecules are arranged in clusters in the thylakoid membrane, these are photosynthetic units
- Chlorophyll a is the primary pigment and acts like the reaction centre for each photosystem
Two types of Photosystem
PS1- Contains chlorophyll a with an absorption peak at 700nm at its reaction centre
PS2- Contains chlorophyll a with an absorption peak at 680nm at its reaction centre
Photolysis
2H2O –> 4H+ + 4e- + O2
An enzyme in photosystem 2 splits water when activated by light.
The Hydrogen ions are used to reduce NaDP
Electrons replace those lost to PS1
Oxygen diffuses out and is used for respiration
Photophosphorylation
ADP + Pi –> ATP
Process of adding a phosphate to a molecule using light energy
When light hits chlorophyll a or energy is funnelled in, 2 electrons gain energy and become excited
Light dependant Stage Summary
Takes place in the thylakoid membrane Light is absorbed by photosystems Water is split to produce e- and H+ ATP and Reduced NADP produced Oxygen released as waste
Cyclic Photophosphorylation
Only involves PS1
Electrons get excited and move up
Electron carrier chains then move them down again to the same chlorophyll
Energy from electrons is used to make ATP
Non Cyclic Photophosphorylation
Electrons get excited in both PS1 and PS2
ATP generated as the electron carrier chains move the electrons down
However elections from PS2 replace those lost by PS1
Electrons lost by PS1 are used with H+ to produce reduced NaDP
Light independent Stage Summary
Takes place in the stroma of the chloroplast
Uses the ATP and reduced NaDP produced from the light stage
Sugar is being produced from the reduction of CO2
Reactions are called the Calvin cycle
Compounds involved in the Calvin cycle
- CO2 first combines with RIBULOSE BISPHOSPHATE
- The enzyme RUBISCO catalyses the reaction
- This forms an unstable intermediate that splits into two GLYCERATE 3 PHOSPHATE
- GP is then reduced in TRIOSE PHOSPHATE
- 5/6 of TP is used to regenerate RuBP
- 1/6 is converted into glucose
Uses of the products of the Calvin Cycle
- TP pairs can be used to form hexose sugars such as glucose or glycerol
- These can join to form saccharides such as sucrose
- GP can produce amino acids and fatty acids, nitrates and mineral ions will also be needed
- Fatty Acids + Glycerol can form lipids
Light intensity on Photosynthesis rate
Light provides energy for photosynthesis
So higher intensity means faster rate
Light is required for photolysis and photophosphorylation
Carbon Dioxide conc. on Photosynthesis rate
Its essential for the Calvin cycle so can be limiting
Concentration of CO2 will be lower in the chloroplast and stroma than the air
Temperature on Photosynthesis rate
Temp. mainly effects the light independent reactions
Increase temp increases the kinetics
All reactions in the Calvin cycle are enzyme controlled
Plants evolved lower optimum temps
If too high then enzymes denature
Or rubisco reacts with oxygen instead (competitive inhibition)
High temp also means more water loss
Photorespiration
Rubisco begins to catalyse the reaction of RuBP with O2 instead when temp is above 25 degrees
Water Stress on Photosynthesis rate
If roots can’t take up water fast enough to replace the loss from transpiration the stomata close so there’s less CO2 for the Calvin cycle
Plant roots produce Abscisic Acid which is translocated to the leaves
Limiting Factors of the Calvin cycle
Light intensity- ATP and NaDP produced which limits the conversion of GP to TP and the regeneration of RuBP, GP conc will increase if its limited
CO2- Less production of GP when limited so RuBP conc. will increase
Temp- All stages catalysed by enzymes so increased temp just increases rate
