PHOTOSYNTHESIS

Photosynthesis converts light energy to chemical energy of food. 

Autotrophs: "self feeders" they are the ultimate source of organic compounds making them producers.

Heterotrophs: live on compounds made by other organisms- making them consumers. (decomposers like fungi are considered heterotrophs).

Chloroplasts: the specific sites of photosynthesis in plant cells they include the stroma (dense fluid filled area), thylakoids (network of membrane sacs) and chlorophyll (the light absorbing pigment that drives photosynthesis and makes plants green)

Stomata: tiny pores in which CO2 enters and O2 and water vapor leaves 

Equation for photosynthesis: 6H2O+6CO2 leads to 6O2+C6H12O6

There are two stages of photosynthesis: 

    1. The light reactions: occurs in the thylakoid membranes where solar energy is converted to chemical energy. 

   2. Calvin cycle: Occurs in the stroma, where CO2 is incorporated into organic molecules in carbon fixation (does not require light)

The light reactions convert solar energy to the chemical energy of ATP and NADPH

-light behaves as though it is made of particles called photons- each having a fixed quantity of energy

-pigments:  substances that absorb light. Different pigments absorb light at different wave lengths 

Absorption spectrums and action spectrums: show a pigments light absorption vs wavelength and its effectiveness respectively\

photosystems:  certain groups of pigment molecules in the thylakoid membrane 

- they consist of: 

   1. light harvesting complex: made up of many chlorophyll and carotenoid molecules

    2. reaction center: made of 2 chlorophyll a molecules which donate electrons to the primary electron acceptor  

Alternative modernisms of carbon fixation have evolved in hot, arid climates

- C3 plants struggle in hot climates because they have to keep their stomata closed to conserve water, causing no CO2 uptake 

photorespiration: is the oxidation of ROBP resulting in a loss of energy and carbon for the plant

Alternatives mechanisms of carbon fixation have evolved in hot arid climates 

-C4 plants have two strategies to combat photorespiration: 

   1. structural strategy: the two stages of photosynthesis are split among two different cells 

   2. Biochemical strategy: C4 plants have an extra enzyme : PEP carboxylase which acts as a pump that keeps CO2 concentrations high in the cells that go through the calvin cycle 

CAM photosynthesis: is another adaptation to hot dry climates 

-CAM plants keep their stomata closed during the day and they open up during the night 

-CAM plants also separate the two stages of photosynthesis temporally