For plants to grow they need food, water, light and the right climate. They like to expose the maximal amount of leaf area to the sun to optimise the process of photosynthesis.
The Greek word of "Photosynthesis"('photo' meaning 'light' and 'synthesis' meaning 'putting together'), is a chemical process that converts carbon dioxide with the help of water and light energy into organic compounds (mostly sugars) and oxygen. The sugars are used for the immediate needs of the plants, the rest is stored in structures like tubers and bulbs, the oxygen is expelled into the air.
The formula used is:
6H2O + 6CO2 + light energy = C6H12O6 + 6O2
6 molecules of water + 6 molecules of Carbon Dioxide + light energy = 1 molecule of sugar + 6 molecules of oxygen
Photosynthesis is vital for life on earth, it maintains normal levels of oxygen in the atmosphere.
The process of Photosynthesis starts when light energy is absorbed by proteins held inside the Chloroplasts, situated principally in the Palisade layer of the Mesophyll area of the leaf, just underneath the Epidermis (the exterior coating of the leaf or stem of a plant).
Inside these Chloroplasts are Thykaloid membranes, these membranes contain Chlorophyll. Some of the light energy gathered by the Chlorophyll is stored, the rest of the light energy is used to remove the electrons from water. These electrons are then used in the reactions to turn carbon dioxide into organic compounds (especially sugars) and oxygen.
Another important part of the leaf is the vascular bundle. It is the transport system of the leaf and contains xylem and phleom vessels. Xylem (made up of dead cells), transports water and some minerals. Phloem (made up of live cells) carries a water based solution rich in sugar, to wherever the plant needs the sugar and storage areas such as tubers and bulbs.
Bibliography: Wikipedia; RHS -Pruning and Training