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Light (Dependant) Reactions of Photosynthesis Animation

Photosynthesis takes the human/animal waste product carbon-dioxide (CO2) and in the presence of light and water creates the things we need for cellular respiration, oxygen and glucose.See the following links:
Cellular Respiration -
http://...
Calvin Cycle -
http://...
Light and Pigments -
http://...

The initial stage of the photosynthetic system is the light-dependent reactions, which convert light -solar energy- into chemical (potential) energy. The light dependent reactions specifically produce oxygen gas and convert ADP into ATP and NADP+ into NADPH.

Organisms form the kingdom Plantae usually use noncyclic(do not reCYCLE same electrons) photophosphorylation, a two-stage process involving two different chlorophyll photosystems.

First, light strikes a plant, specifically a cell. This cell has an organelle(s) called a chloroplast that gives photosynthetic cells their characteristic green color. Chloroplasts have structures called stroma. Stroma are full of hollow disks (similar to a whoopie cushion) called thylakoids arranged in stacks call grana. There are membrane proteins implanted into the surface of the thylakoid called photosystem II and photosystem I that have a pigment called chlorophyll located on the top of these proteins.***Photo System I comes second, but was discovered first and Photo System II was found second and named for that reason even though it comes first.***

Light particles, called photons, strike the electrons located in the chlorophyll of photo system II, Now in an excited state, they travel along the thylakoid membrane to photo system I where they are re-excited by photons again moving them to the acceptor molecule NADP+. The flow of electrons through the membrane proteins creates a concentration gradient, also known as proton motive force, which drives ATP synthesis through chemiosmosis (see http://...

The electrons originally lost in Photo System II must be replaced. A water molecule is broken down into 2H+ + 1/2 O2 + 2e- by a process called photolysis (or light-splitting). The two electrons from the water molecule replenish electrons lost in photosystem II's chlorophyll. Meanwhilethe 2H+ and 1/2O2 are left out for further use.


The photosystem II complex replaced its lost electrons from an external source, however, the two other electrons are not returned to photosystem II as they are in the analogous cyclic pathway(prokaryotes like cyanobacteria). The highly excited electrons are transferred to the acceptor molecule, but this time are passed on to an enzyme called Ferredoxin- NADP reductase(NADP+ reductase), for short FNR, which uses them to catalyze the following reaction (as shown):

NADP+ + 2H+ + 2e- → NADPH + H+

This consumes the H+ ions produced by the splitting of water, leading to a net production of 1/2O2, ATP, and NADPH+H+ with the consumption of the light(photons) and water.

Next are the dark reactions(not light dependant)... The Calvin Cycle -
http://...







Channel: Tech
Uploaded: September 21, 2008 at 3:08 am
Author: DaggerBiology

Length: 00:01:32
Rating: 4.96
Views: 18464

Tags: Dependant grana Photosynthesis plants energy atp thylakoid Light Reactions chlorophyll stroma

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