PHOTOSYNTHESIS 1

The power for life,that we call energy, flows into the food chain through our friends the busy plants. The plants do something with that energy that seems miraculous. They turn it into food. This is very nice of the plants because animals can't eat sunshine. They can only eat plants or each other.

The Leaf -
It's amazing what's inside a leaf.The whole leaf looks green to us,but most of the cells and cell material are colourless or clear. The green color comes from the chlorphyll molecules in the chloroplasts.

Leaf Section-
Cut out a little section of the leaf.There are many different types of cells, specialized to do different things - all for the good of the tree, of course.On the top and bottom are the cuticle layer and the epidermal cells.In the middle, between the epidermis cells on the top and bottom, are the mesophyll cells where the chloroplasts live. On the bottom only, in most plants, are the stomatas which let carbon dioxide in and oxygen out.

Mesophyll Cells -
The chloroplasts, where photosynthesis occurs, are in the mesophyll cells.There are two kinds of mesophyll cells in our typical leaf. a)The palisade parenchyma region-this is where most photosynthesis is done.
b)The spongy parenchyma region. Here the cells aren't so close. There are roomy air spaces between them.

Chloroplast -
Each chloroplast is a little carbohydrate factory, powered by solar energy, & for which the only raw materials are carbon dioxide, water, and a few minerals.Out of this little factory comes food for plants and practically every other living thing on earth - including us.

Granum-
The little round flat pillow or pancake shaped things are called thylakoids. A stack of them is called a granum. Two or more stacks are called grana.There can be from 2 to around 100 thylakoids in one granum. The little tube like strands connecting thylakoids from granum to granum are called stroma lamellae.

Thylakoid
The chlorphylls and other pigments that start the process are here, on the outer layer of the thylakoids. Photons from sunlight hit the pigments, electrons are "knocked" loose, and off they go to energize the complicated process of photosynthesis.Sometimes the thylakoid is also called the photosynthetic membrane.The membrane and the space inside it,is where the light or light-dependent reaction takes place. The so-called dark, or light independent reactions, take place in the stroma.This power for life,that we call energy, flows into the food chain through our friends the busy plants.

Mechanism of photosynthesis
Photosynthesis occur in two phases.Photochemical(light reaction) & Biochemical(dark reaction).
1)Light reaction- also called Hill reaction because it was discovered by R Hill.In light reaction photolysis of water take place in grana.
a)Photolysis of water -water molecule is split into hydrogen & oxygen.It also indicates that oxygen which is released is derived from water & not from carbon dioxide.
b)Formation of ATP -
i)Photophosphorylation takes place which means formation of ATP from ADP & inorganic phosphate.
ii)NADP get reduced.

2)Dark reaction- The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn't directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Actually, notice that the first product of photosynthesis is a three-carbon compound called glyceraldehyde 3-phosphate. Almost immediately, two of these join to form a glucose molecule.
The overall chemical reaction involved in photosynthesis is:
6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2.