Photosynthesis

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Autotrophs:- Self Feeders. They sustain themselves without eating anything derived from other living beings.

Photoautotrophs:- These organisms use light energy to drive the synthesis of organic molecules from CO2 and (in most cases) H2O

Land- Plants

In aquatic environments

unicellular and multicellular algae e.g. Kelp

non-algal unicellular protists e.g. Euglena

Some prokaryotes e.g. Cyanobacteria and Purple Sulphur Bacteria

Below the waxy cuticle of the epidermis are mesophyll cells. These cells contain 30-40 small organelles known as chloroplasts.

In endosymbiotic theory chloroplasts are considered to be photosynthetic prokaryotes.

Chloroplasts have a double membrane surrounding a dense fluid called the stroma.

A 3rd membrane system called the thylakoids are suspended in the stroma. These membranous sacs are arranged in stacks called grana (sng granum).

Chlorophyll the green pigment responsible for giving plants their characteristic green colour. Chlorophyll traps light from the sun and uses it to synthesise organic molecules from CO2 and H2O.

6CO2+6H20 ---------> C6H12O6 +6O2

The prevailing hypothesis was that the carbon dioxide was split to form O2.

In the 1930's C.B. Van Niel challenged this after investigating photosynthesis in bacteria that make their carbohydrate from CO2 but do not release O2.

CO2 + 2H2S--------> [CH2O] + H2O + 2S

In the sulphur releasing bacteria the CO2 is not split to form oxygen. The hydrogen sulphide is split to form sulphur and the hydrogen atoms used to make sugar.

Therefore for plants:-

CO2 + H2O ----------> [CH2O] + H2O + O2 (hydrolysis reaction taking place produces the O2)

The photosynthetic agents

Anatomy of the Chloroplast

Tracking atoms through photosynthesis