Photosynthesis+and+Cellular+Respiration+-+The+Big+Picture

=Photosynthesis and Cellular Respiration=

The Big Picture
Photosynthesis and Cellular Respiration, though very different, have many similarities. To get an idea of how the two of them work together, we are going to take a look at a plant, one of the organisms with the ability to carry out both.

A plant is an organism known as an **autotroph**, an organism that can make its own food. It gathers energy from the sun to make food. This food is then broken down to produce the energy necessary for growth to occur. To get an inside idea of how this amazing process works, we will begin at the primary source: the sun.

The sun is the source of the vast majority of light that shines on planet Earth. It is with this light that we begin. The sun radiates light of every wavelength down onto the Earth. This light appears white to our eyes because all the different colors are mixing. However, when light hits a particular object, that object absorbs some of the light, and the light reflected back is what we see. For example, a red ball reflects only red light.

Photosynthesis is a harvesting of this light. It consists of two steps:
 * 1) Light Reaction
 * 2) Calvin Benson Cycle

The Light Reaction
Within all plant cells are chloroplasts. These organelles have the ability to move to other plant cells if a new source of light is discovered. A chloroplast looks like a green ellipsoid with smaller green dots inside of it. These smaller green dots are known as **thylakoids** and are arranged in stacks called **grana**. The rest of the chloroplast is filled with a thick fluid called **stroma**. Like all eukariotic membranes, each thylakoid is made of a phospholipid bilayer. Enclosed **within is another fluid called lumen.**

The light reaction occurs in the membrane of the thylakoid. It is started off when a packet of light energy, called a **photon**, hits a special molecule called **chlorophyll**. Chlorophyll reflects mainly green light, hence the green color of plants. It is a **pigment**, or a molecule that absorbs light, and it takes in mainly red-orange light. Chlorophyll is contained in two special structures called **photosystems** that reside within the thylakoid membrane. Each photosystem consists of chlorophyll and several other pigments called **carotenoids** (which reflect yellow-orange light and are responsible for carrots and leaves in autumn) arranged like an antennae. A photon collides with a chlorophyll molecule placed in the center of Photosystem II (the first photosystem used in photosynthesis, but the second one discovered) and causes two of its electrons to leap off. This electron is immediately dragged in by the pull of a nearby molecule, called the **primary electron acceptor**. The acceptor molecule is only the first in a long chain of reactions where one molecule gains an electron (becomes **reduced**) while the one before it loses an electron (becomes **oxidized**). This combination of reduction and oxidation is known as a **redox reaction** and the chain of reactions is called an **electron transport chain**. Meanwhile, H2O is split in two to replace the lost electrons of Photosystem II.

Along the electron transport chain, energy is released every time a reaction occurs. This energy is used to actively transport H+ ions into the lumen, creating a gradient. The ions then diffuse through a series of enzymes called ATP synthase, providing energy to change ADP and an inorganic phosphate group into the energy-rich ATP. This sub-process is known as **chemiosmosis**.

As the electrons near the end of the chain, light hits another photosystem called Photosystem I, producing two more electrons. The lost electrons of this photosystem are replaced by the ones that have traveled by the chain. Photosystem I's electrons, on the other hand, are used combine NADP+ and H20's lost H+ ions into NADPH, an electron carrier.

RESULT:
 * Oxygen gas is released as a byproduct
 * ATP and NADPH carry electrons to the Calvin Benson Cycle

GENERAL EQUATION
 * H2O + NADP+ + ADP + P + light ---> NADPH + ATP + ½O2 + H+**





The Calvin Benson Cycle
The Calvin Benson Cycle was discovered by Melvin Calvin and Andrew Benson in 1950. It is also known as the dark reaction or the light independent reaction. During this cycle, carbon dioxide is transformed into glucose, the food for the cell. It takes place in the stroma of the chloroplast.

First, 6 carbon dioxide molecules from the air around the plant are absorbed through pores called **stomata**. These molecules are then combined with 6 molecules of an organic 5-carbon compound called RuBP to make 6 more molecules an unstable 6-carbon compound. This rapidly breaks down into 12 molecules of 3-PGA, a 3-carbon compound. With the help of the NADPH and ATP from the light reaction, all of the 3-PGA is configured into G3P. Two of these G3P molecules jump off the cycle, combining to form the six carbon sugar known as glucose. The rest get another dose of ATP and become RuBP. Thus the cycle can continue.

During the reaction, H2O is accidentally released. The glucose formed leaves to float around in the cytoplasm, which is where we will go next.

RESULT:
 * Water is lost from the plant
 * Glucose is formed for later use in cellular respiration

GENERAL EQUATION
 * 6 CO2 + 6 RuBP + 12 NADPH + 18 ATP -> 12 NADP+ + 18 ADP + 18 P + C6H12O6**





//more coming very soon//