Autotrophic Bliss


‘Green’ energy!

    Photosynthesis is regarded as a defining feature of plants.  During photosynthesis, light reactions occur in the leaves.  Chlorophyll, contained in chloroplast, seizes energy from the sun.  About 400,000 chloroplasts are in each square millimeter of a leaf!

    For photosynthesis to take place, the leaf must be separated from external water.  To waterproof the leaf, each leaf is surrounded by an epidermis with a waxy cuticle surrounding the epidermis.  For more on this visit my page on adaptations

    Photosynthesis is carried out in all green parts of Tamarack, primarily the leaves.  During photosynthesis, light energy is taken up through the pigment chlorophyll, and a series of reactions proceed in the chloroplast to make chemical energy in the form of glucose.  The formula for photosynthesis is:

12H2O + 6CO2 + light energy ------> C6H12O6+ 6O2 + 6H2O

Carbon dioxide is obtained through small openings in the leaves called stomata.  In conifer trees, these holes are found on the part of the leaf that does not usually come in direct contact with sunlight.

    Photosynthesis occurs in two stages called the light reactions and the calvin cycle.  Refer to my diagram on the top of this page.  In the light reactions, electrons go through two photosystems, NADPH and ATP are ultimately produced.  Oxygen is a byproduct of the light reactions. These chemicals are used to fuel the Calvin Cycle. The Calvin Cycle takes place in the stomata on the leaves, proximal to carbon dioxide acquisition.  The Calvin Cycle ultimately converts carbon dioxide to CH2O, a building block of glucose.  NADP+ and ADP are recycled back to the light reaction photosystems. 

Transport in the Phloem

    Once the glucose is produced by the photosynthetic mesophyll cells, the nutrients move into the phloem.  For information on the Phloem, visit my page on Basic Plant Anatomy.  Once transmitted to the phloem, the nutrients are transported via a positive pressure gradient from glucose source to glucose sink.  A source of glucose would be photosynthetic cells, and glucose sinks refer to growing parts of the plant.  For example, a growing leaf may be a glucose sink, and a mature, photosynthetically active leaf is considered a glucose source.