The Sun is the Greatest form of Energy. Energy is the ability to do work. Work is the ability to change or move matter. Without the energy from the Sun, nothing as we know of on Earth would be able to exist. The Sun's Energy is stored in the chemical bonds that make up food. Some forms of life make their own food. These are the Autotrophs. Plants make their own food. Plants make food for their own energy needs and also store food as well. Some organisms can not make their own food. These are the Heterotrophs. Animals are heterotrophic. Heterotrophs must eat food. Some hetertrophs, like cows, eat autotrophic organisms (grass), and other heterotrophs, like lions, eat other heterotrophs, say a cow, to get their food. It does matter where the food comes from the energy all comes from the same place; the Sun.
Lesson #1 The Sun - Power house to the solar system
The Power house of the solar system and this planet is the Sun here is how the Energy generated on the Sun gets plants.
Lesson #2 The Generation of energy in the Sun starts with two protons.The Sun contains a large sum of protons from hydrogen that has turned to Plasma. Very often These free protons will react with each to form the basic Helium nucleus (atomic number 2).
For more information see the website http://www.astronomynotes.com/starsun/s2.htm
Energy is received by the leaf along with CO2
For more details see the website http://www.microscopy-uk.org.uk/mag/imgdec00/rnplant.jpg
This link is about chloroplasts: http://people.ku.edu/~jbrown/chloroplast.html
The following link is about mitochondria, the little powerhouse of cells: http://biology.about.com/library/weekly/aa040600a.htm