BYA5 SECTION 14.6Photosynthesis uses energy from sunlight to synthesise organic molecules from inorganic sources |
|
Metabolism → all chemical reactions in a cell → arranged into metabolic pathways
Intermediates in these pathways are called metabolites |
- Catabolic reactions (e.g. respiration) release energy
- Anabolic reactions (e.g. photosynthesis) use up energy
|
Leaf Structure |
- Phototropism → growth towards light
- Large leaf surface area → captures more light
- Thin leaves → few cell layer → more light captured by chlorophyll
- Leaf mosaic increases leaf exposure to light
|
Leaf Internal Structure |
- Cuctile → reduces H2O loss by evaporation
- Palisade mesophyll → chloroplast can move around cell for max light absorption
- Spongy mesophyll → allows diffusion of gases through leaves
- Phloem sieve tube → removes products of photosynthesis
|
Chloroplast |
- Thylakoid membrane: light-dependent → large surface area
- Associated with chlorophyll, accessory pigments, ETC, enzymes
- Grana: stacks of thylakoid membranes
- Enclose hydrogen reservoir used in chemiosmosis
- Lamella: tubular extensions forming a network between grana
- Stroma: RuBP carboxylase catalyses light independent reaction
- Starch granule → insoluble storage carbohydrate product of photosynthesis
|
Light Dependent Reaction
In Thylakoid Membrane / Granum |
 |
Chemiosmosis/Photophosphorylation produces ATP |
| //H+ from photolysis remain in thylakoid space |
- ETC releases energy
- Used to pump H+ from stroma into thylakoid space
- By active transport and electrochemical gradient
- H+ conc in thylakoid space > stroma
- H+ ions pass back from space between two mitochondrial membranes
- Through pores which are associated with the enzyme ATP synthetase
- Energy from the ETC will be used to produce ATP
- Diffuse down conc gradient across thylakoid membrane
- Produces ATP by photophosphorylation
|
Light Independent Reaction
In Stroma (Calvin Cycle) |
|
| Summary |
| The light dependent reaction takes place in the chloroplast and is important to produce ATP and NADPH + H+. Both molecules and carbon dioxide (CO2) are needed in the light independent reaction (Calvin Cycle) to produce a hexose sugar, such as glucose, from RuBP. Glucose is used to in the mitochondrion to produce the energy molecule ATP. NAD+ is also needed for respiration, but is not produced by photosynthesis. PARP (Poly-ADP-Ribose-Polymerase) and PARG (Poly-ADP-Ribose-Glycohydrolase) are important if the plant is exposed to excessive stress factors (such as extreme temperatures). Note: knowledge about PARP and PARG is not required for your exam. |
Picture 5-1 from Bayer research.
Genetic engineering improves crop yields,
Braving the drought [view article]
|
|
References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification; [PDF]
Fig5-1: BAYER RESEARCH (2006); Genetic engineering improves crop yields. Braving the drought; [INTERNET] (July 2006)
