3.2.2 Photosynthesis Flashcards
(19 cards)
photosynthesis
- chemical reaction involving light energy being transformed into chemical energy (held in bonds within glucose)
- occurs in chloroplasts of all plants, some protists and some bacteria
autotrophs
make their own organic molecules from inorganic carbon
chloroplast structure
- double membrane
- grana: stacks of thylakoid membrane containing chlorophyll
- stroma: liquid filled space between grana containing other chemicals necessary for photosynthesis
pigments
- chlorophyll A is directly involved in photosynthesis (absorbs red and blue and reflects green)
- other accessory pigments absorb different wavelengths of light
light dependent
grana
- chlorophyll absorbs light energy
- electrons in chlorophyll become excited transforming light into chemical energy
- H2O split and release e- and H+ which are added to NADP+ converting it to NADPH
- phosphorus added to ADP to make ATP
- oxygen is released
light independent
stroma
- rubisco catalyses fixing of C from inorganic CO2 (1C) with RuBP (5C) to form unstable(6C) which splits to from PGA (3C)
- 12 ATP and 12 NADPH used to from PGAL (3C)
- PGAL with CO2 and H+ and e- from NADHP form glucose using energy from ATP which combines them
- 6 ATP converts PGAL (3C) into RuBP (5C)
photosynthesis overall equation
6CO2 + 12H2O -> (sunlight) C6H12O6 + 6 O2 + 6H2O
light dependent equation
12H2O + (12NADP+ + H+ + e-) + (18ADP +Pi) -> 6O2 + (12NADPH) + (18ATP)
light independent equation
6CO2 + (12NADPH) + (18ATP) -> C6H12O6 + 6H2O +( 12NADP+) + (18 ADP +Pi)
rubisco
catalyses fixing of C from inorganic CO2 into an organic molecule initiating Calvin Cycle
photorespiration
- wasteful process where rubisco uses O2 as substrate instead of CO2 thus making less glucose
- occuring when temps are higher and O2 levels are high enough to outcomete CO2 for active site of rubisco
photorespiration outcome
- less efficient glucose production
- less 3PGA made
- ATP used to make CO2 rather than glucose to wastes energy
- may produce some amino acids
C4 pathway
- PEP carboxylase (higher affinity for CO2) fixes PEP (3C) into oxaloacetate (4C)
- oxaloacetate converted to malic acid (4C)
- malic acid travels to different location (bundle sheath cells) and release CO2 into Calvin Cycle where low O2 and high CO2 concentration ensures rubisco works
CAM pathway
- at night stomata open to allow CO2 and PEP carboxylase CO2 to PEP making oxaloacetate (4C)
- oxaloacetate converted to malic acid and stored in a vacuole of same cell
- at day (different time) stomata close and malate travels to chloroplast to release CO2 into calvin cycle where rubisco works due to high levels of CO2
light as a factor
- as light intensity increases, rate of photosynthesis increases until saturation point due to other limiting factors
- light wavelength also impacts rate with red being peak and green being lowest
temperature and pH
- same as enzyme activity
- C3 cooler temps, C4 and CAM warmer temps
- warmer temps make Rubisco’s affinity for CO2 lower and higher for O2 so Rubisco binds to O2 more and undergoes photorespiration decreasing rate of photosynthesis
CO2 availability
- as CO2 (substrate) concentration increases, rate of photosynthesis increases until saturation point
- if CO2 conc. low plants may undertake wasteful photorespiration as O2 is more likely to bind to Rubisco, decreasing photosynthesis rate (C4 and CAM have adaptations)
water availability
- low water (from increased temp) means stomata close to prevent water loss but prevents entry of CO2 and O2 making phtoorespiration more likely to occur due to O2 more abundant than CO2, decreasing rate of photosynthesis
chlorophyll as a factor
- increasing chlorophyll means increased rate until they become saturated with light and unable to absorb light at a faster rate
