Page 176 - The Miracle in the Cell

THE MIRACLE IN THE CELL
Photosynthesis takes place in two phases called the light phase
(light-dependent reactions) and the dark phase (light-independent reac-
tions). Light-dependent reactions take place in the so-called thylakoids,
small disc-like regions found in the chloroplasts (See Figure 10.3c). Here,
the pigment molecules lose an electron as they absorb energy from the
sun. As a result of the movement of the electrons, an energy packet is
produced as either ATP or NAPDH. In the light-independent reactions,
however, carbon dioxide-with the help of the ATP and NAPDH pro-

a) Cross section of a sunflower leaf, showing the
chloroplasts within the cells
b) Cross section of a chloroplast
c) Two grana. This region, which is made of thy-
lakoid disks, is where light-dependent reactions
take place.
d) Where photosynthetic reactions occur. Electrons
activated by solar energy are transferred to the
electron-transport system within the membrane.
The electron is used to split water molecules into
hydrogen and oxygen. Oxygen is released, while
hydrogen ions are kept inside. The balance of oxy-
gen in the world is maintained as a result of this
complex process that most of us are never even
aware of. Electrons that have gone through the
electron-transport system facilitate the production
of ATP and NADPH. The next stage, the light-inde-

Figure 10.3
a b

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