30 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”“addresses” of their destinations inside and outside (for secretion) the
cell. The ER is also the place where lipids and complex carbohydrates
are synthesized. The Golgi apparatus is a modified endoplasmic reticu-
lum, appearing like a stack of membranes, where proteins are packaged
for secretion. (See Fig. 3.1.)
Chloroplasts are large organelles found in photosynthetic plants.
The chlorophyll inside the chloroplasts absorbs solar energy in the form
of light and uses it to convert carbon dioxide and water to carbohydrate
and oxygen. Photosynthesis is a reductive process for carbon, the opposite
of oxidative process in mitochondrial respiration. The general equation
is also the reverse of sugar oxidation: 6H 2 O + 6CO 2 → C 6 H 12 O 6 + 6O 2.
The sugars produced by photosynthesis are usually stored in the form of
Fig. 3.8. Diagram of metabolic network in the human cell, consisting of more than
500 enzyme-catalyzed chemical reactions. The dots represent metabolites, while the
lines, steps of chemical transformation, either for energy production or biosynthesis.
[See Note 68; permission Oxford Univ. Press.]