Photosynthesis Flashcards
Define heterotrophs
Organisms that must consume and digest complex organic molecules
Define autotroph
Organisms that can synthesise complex organic molecules from inorganic molecules and an energy source
What are the different parts of the chloroplast
Granum consisting of thylakoids, envelope, stroma, intergranal lamella
Describe a photosystem
A funnel-shaped light-harvesting cluster of photosynthetic pigments, held in place in the thylakoid membrane of a chloroplast. The primary pigment reaction centre is a molecule of chlorophyll a. The accessory pigments consist of molecules of chlorophyll b and carotenoids
What are the 2 forms of chlorophyll a
P-680 and P-700
What kinds of light do carotenoids absorb?
Blue light, they reflect yellow and orange light
Describe cyclic photophosphorylation
Using only photosystem 1 the excited electrons pass to an electron carrier and then back to the chlorophyll molecule. There is no photolysis of water or production of reduced NADP but small amounts of ATP are produced
Describe non-cyclic photophosphorylation
Light strikes photosystem 2 exciting a pair of electrons. The electrons pass along the electron carriers and the energy released is used to synthesise ATP. Light has struck photosystem 1 and a pair of electrons has been lost. These electrons along with protons, produced by the photolysis of water at photosystem 2, join NADP to form reduced NADP. Protons from the photolysis water take part in chemiosmosis to make ATP and are then captured by NADP to be used in the light dependant stage
Describe the role of water in the light dependant stage
It is a source of hydrogen ions for chemiosmosis and the production of reduced NADP for the light independent stage. It is also a source of electrons to replace those lost by the oxidised chlorophyll
Describe the Calvin cycle
Co2 diffuses into the leaf across various cells/membranes and combines with RuBP, which is catalysed by rubisco. This forms 2 molecules of GP. GP is reduced and phosphorylated to TP. ATP and reduced NADP are used in this process. 5 of every 6 molecules of TP are recycled by phosphorylation using ATP, to 3 molecules of RuBP
How are the products of the Calvin cycle used?
Some GP can be used to make amino and fatty acids. Pairs of TP molecules form 6 carbon sugars. Glucose may be isomer used to form fructose which in turn can be used to make sucrose. Hexose sugars can be polymerised into other carbohydrates. TP can also be converted to glycerol.
What are the limiting factors of photosynthesis?
Water available, light intensity, co2 concentration, temperature.
