Photosynthesis Flashcards
Photosynthesis
• endergonic
Adaptations of the leaf
- large SA
- minimal overlapping between leaves
- thin
- transparent cuticle and epidermis
- long, narrow pallisade mesophyll cells containing many chloroplasts
- many stomata
- sur spaces in mesophyll layer
- xylem
- phloem
Photosynthetic pigments
- found in thylakoid membrane
- clustered into antennae complexes
- chlorophylls À and B (red and blue-violet)
- carotenoids
Describe carotenoids
- antioxidants
- carotene and xanthophyll
- absorb in blue-violet region
Describe absorption spectra
Indicate how much light a particular pigment absorbs at each wavelength
Describe action spectra
• show rate of photosynthesis at each wavelength
Describe the light-dependent rection
- occurs in thylakoid membrane
- photophosphorylation
- photolysis
- photoactivation
- photoionisation
- electron transport system
- proton pumping
- proton flow
Describe photophosphorylation
Light absorbed by chlorophyll a yo provide energy to convert ADP + Pi -> ATP
Describe photolysis
- light energy trapped by chlorophyll a is used to split water molecules, releasing electrons, protons and oxygen
- 2H2O -> 4H+ + 4e- + O2
Describe photoactivation and photoionisation
• light energy raises energy level of electrons in chlorophyll a
• ground state -> excited state
• electron pair leaves chlorophyll, oxidising it
(replaced by photolysis)
Describe the electron transport system and proton pumping
- reduce electron carriers (cytochromes)
- subsequent carriers have higher affinity to electrons
- electrons release energy as they pass down, which, combined with the energy and protons from photolysis, is used to pump protons from stroma-thylakoid
Describe proton flow
- protons accumulate in thylakoid space
- flow back, down a concentration gradient, through ATP synthase channel protein
- protons taken up by NADP
Describe the ATP synthase channel protein
- changes shape as protons pass through
* catalyses ATP formation
Adaptations of chloroplasts for LDR
- large SA provided by thylakoid membranes, where pigments, electron carriers and enzymes are attached
- proteins in grana hold pigments in a specific way
- granal membranes have ATP synthase channels
- granal membranes are selectively permeable; establishes proton gradient
- contain DNA and ribosomes
Light independent reaction
• occurs in stroma
1) CO2 + RuBP -(RUBISCO)-> 2GP
2) GP + NADPH -(ATP)-> TP + NADP
