Nature's Manufacturer of the "Food of the Gods!"
| The cacao tree, like all green plants, is a phototroph. This means that it produces its own food through photosynthesis. This process occurs in two steps called the light dependent and light independent reactions. The light dependent reactions occur first when energy from the sun is collected via the leaves and used to make adenosine triphosphate (ATP). ATP, along with other molecules made during the light dependent reactions, is then used as an energy source to produce carbohydrates that the tree can use for food. This process makes up the light independent reactions. The general equation used to represent photosynthesis is as follows: |
CO2 + H2O + light energy ---› carbohydrates + H2O + O2
For more information about photosynthesis visit http://bioweb.wku.edu/courses/Biol120/images/Photosynthesis.asp
So how does the tree transport the nutrients it makes in the leaves to the rest of the tree? These nutrients are sent through tubes called phloem, which are located towards the outer edge of the tree, underneath the bark. The phloem is made up of cells called sieve tube members, companion cells and parenchyma cells. Nutrients (sugars, etc.) travel through the sieve tube members, which do not contain a nucleus. The function of companion cells is to take over metabolism for the sieve tube members, while parenchyma cells are used for storage and support. (Check out these other cool organisms that gain nutrition by photosynthesis: English Daisy and Dandelion.
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The nutrients from photosynthesis travel from a high solute concentration (leaves) to a low solute concentration (rest of tree). In order to keep the system moving nutrients must be continually added to already high concentrations of solute. This requires active transport by companion cells to move stored sugars from parenchyma cells to the sieve tube members. *It should be noted that nutrients do not always move from leaves to roots in phloem. In spring, when leaves have not begun to photosynthesize, sugars that have been stored in roots travel up the tree to nourish the leaves. (Check out the Adaptations and Interactions Page to learn about organisms that use the cacao as their food source.)
Water and carbon dioxide are also necessary for the tree's survival, specifically to photosynthesize. Carbon dioxide enters leaves through tiny openings called stomata. Water is absorbed by the roots and is pulled up to the tree via tubes called xylem. When water evaporates from leaves, water from the xylem flows in by diffusion. Water is then drawn up the xylem since the cohesion of the molecules and the adhesion to the sides of the tube prevent the column of water from being broken. That's a long ways considering some trees grow hundreds of feet tall!
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