Organelles that capture and release energy.

Before we get to the organelles, we have to look at two molecules that create the energy produced in those organelles that follow.The first molecule is ATP (Adenosine Triphosphate). ATP has the following structure:

ATP is used to produce energy in the cell – think of a flashlight powered by a fully charged Lithium Ion battery. The energy is produced by breaking the bond between the 2nd and 3rd phosphate group. This converts ATP to ADP (Adenosine Diphosphate). ADP is then ready to be “recharged” by adding another phosphate group on to it.We will see in a bit more detail in Photosynthesis.

Chloroplasts – Chloroplasts are found in plants and some animals (ex. Euglena)and can thought of a solar power stations.Chloroplasts convert sunlight into chemical energy (stored in the bonds of sugars) through the process called Photosynthesis.

Photosynthesis-the little engine that could

Photosynthesis takes place in Chloroplasts. Chloroplasts are specialized organelles that contain pigment containing stacked membranes called Thylakoids. The green pigment, contained within the thylakoid membranes, is called Chlorophyll.

The overall reaction of photosynthesis is:6CO2 + 6H2O + light = C6H12O6 + 6O2

A simplified diagram of a chloroplast

NADPH NADP+

You will notice, on the previous diagram, the 2 molecules NADPH and NADP+ . These molecules, along with the ATP ADP cycle, are used to drive the Calvin Cycle. (The Calvin Cycle is also called the “Dark reaction” of photosynthesis because it is light independent. We discuss this shortly).

NADPH NADP+ continued

NADP+ (nicotinamide adenine dinucleotide phosphate)is an electron carrying protein that is used to transfer high-energy electrons from the “Light reaction” of photosynthesis to the “Dark reaction”.The NADP+ molecule reacts with an H2O molecule and strips off the 2 hydrogen ions, leaving an Oxygen ion behind. This Oxygen ion combines with another

Oxygen ion to form O2. Oxygen gas is released by the plant.The NADPH molecule, acting as an energy storage unit powers the Calvin Cycle (along with ATP/ADP) by having the electrons stripped off, returning to NADP+ and being reused.We will now look at the Calvin Cycle.

The Calvin Cycle (aka the “Dark reaction”

The ATP and the NADPH produced by the “Light reaction” contain an abundance of energy but neither of these molecules are stable for more than a few minutes. This is where the Calvin cycle comes in (the Calvin cycle was named after American scientist Melvin Calvin, the discoverer of this process).Plants use the energy contained in ATP and NADPH to build stable, high-energy carbohydrate molecules that can store energy for long periods of time.

The end resultsThe two sets of photosynthetic reactions work together – the light-dependent reactions trap the energy from sunlight in chemical form, and the light-independent reactions use that chemical energy to produce stable high-energy sugars from carbon dioxide and water. In the process, heterotrophs like us, get plenty of food and an atmosphere rich in oxygen.

Factoring affecting Photosynthesis

The most important factors that affect the rate of photosynthesis are:

a) Temperatureb) Intensity of Lightc) Availability of water

Temperature: The enzymes that make Photosynthesis possible have a preferred range of temperatures from 0°C to 35°C. Temperatures higher than that will slow the process down. At low temperatures, the process will cease entirely.Light Intensity: As you would expect, the intensity (brightness) of the light will have an impact. Bright light will speed up the process but photosynthesis does have a “top end limit”. The pigments in chlorophyll have preferred parts of the spectrum – Violet/Blue and Orange/Red (400-525nm and 650-700nm)

Availability of Water: Because water is one of the raw materials of photosynthesis, a lack or shortage of water will slow down or stop photosynthesis. Water loss can also damage plant tissues (shown by wilting or dying).Plants living in arid or hot environments have adapted by having leaves with waxy coatings to reduce water loss.