Production of Oxygen
As shown in Figure 7,pigments involved in plant photosynthesis are
located in the chloroplasts of leaf cells. Clusters of pigments are
embedded in the membranes of disk-shaped structures called
(THIE luh koydz).When light strikes a thylakoid in a
chloroplast, energy is transferred to electrons in chlorophyll. This
energy transfer causes the electrons to jump to a higher energy level.
Electrons with extra energy are said to be “excited.” This is how
plants first capture energy from sunlight.
Excited electrons jump from chlorophyll molecules to other
nearby molecules in the thylakoid membrane, where the electrons
are used to power the second stage of photosynthesis. The excited
electrons that leave chlorophyll molecules must be replaced by
other electrons. Plants get these replacement electrons from water
molecules, H 2 O. Water molecules are split by an enzyme inside the
thylakoid. When water molecules are split, chlorophyll molecules
take the electrons from the hydrogen atoms, H, leaving hydrogen
ions, H+. The remaining oxygen atoms, O, from the disassembled
water molecules combine to form oxygen gas, O 2.
thylakoids
SECTION 2 Photosynthesis 99
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Topic:Light Absorption
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Thylakoid
space
Thylakoid
Thylakoid
membrane
Inner
membrane
Cluster of
pigments
Water-splitting
enzyme
Thylakoid
space
Outside of
thylakoid
Outer
membrane Chloroplast
Plant cell
Leaf
e–
4H+
2H 2 O O
2
Thylakoid
membrane
Pigment molecules are embedded in thylakoid membranes, as are other
molecules that participate in photosynthesis.
Figure 7 Chloroplast