Photosynthesis

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Autotroph - an organism that uses light or chemical energy and inorganic molecules to synthesise complex organic molecules. 
Heterotroph - organisms that ingest and digest complex organic molecules releasing the chemical potential energy stored in them.

Light energy is used during photosynthesis to produce complex organic molecules.

Photoautotrophs and heterotrophs can release the chemical potential energy in complex organic molecules which were made during photosnthesis by respiring them. They use oxygen, which was first released into the atmosphere as a product of photosythesis, for aerobic respiration.

In plants, photosynthesis is a two-stage process taking place in chloroplasts.

The inner membrane contains transport proteins which control the entry and exit of substances between the sytoplasm and the stroma. 
The grana provide a surgace area for photosynthetic pigments, electron carriers, and ATP synthase, all involved in the light-dependent reaction.
The photosynthetic pigments are arranged into photosystesm to allow for maximum absorption of light energy.
Proteins embedded in the grana hold the photosystems in place.
The stroma contains enzymes needed to catalyse the reactions in the light-independent stage. The stroma surrounds the grana, so the products of the light-dependent reaction, needed in the light-independent reaction, can readily pass into the stroma.
Chloroplasts can make some of the proteins they need for photosynthesis using the genetic instructions on their chloroplast DNA, and the chloroplast ribosomes to assemble the proteins.

Photosynthetic pigment - moelcules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption. Other wavelengths are reflected.
They are substances that absorb certain wavelengths of light and reflect others. They appear to u the colour of the wavelength they reflect. There are many different pigments that act together, to capture as much light energy as possible. They are in thylakoid membranes, arranged in funnel shaped structures called photosystems, held in place by proteins.
Chlorophyll in a leaf reflects, and so does not absorb, green light so in green light there is little photosynthesis as there is no light dependent reaction, no photolysis. In an experimental situation using pond weed this would mean that no carbon dioxide is fixed and because some carbon dioxide is produced during respiration there would be an increase in carbon dioxide, increasing the acidity and therefore decreasing the pH.

The light-dependent stage takes place in thylakoid memrbanes and the light-independent stage takes place in the stroma.

When a proton hits a chlorophyll a molecule the energy of the photon is transferred to two electrons and they become excited. These electrons are captured by electron acceptors and passed down a series of electron carriers embedded in the thylakoid membranes. Energy is released as the electrons pass down the chain of electron carriers. This energy is used to pump protons (hydrogen ions) across the thylakoid membrane into the thylakoid space where they accumulate. A proton gradient is formed across the thylakoid membrane and the protons flow down their gradient, through proteins associated with ATP synthase enzymes. This flow of…

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