Essential Cell Biology 5th edition

The Eukaryotic Cell
19
chloroplasts
chlorophyllcontaining
membranes
Figure 1–20 Chloroplasts in plant cells
capture the energy of sunlight. (A) A
single cell isolated from a leaf of a flowering
plant, seen in the light microscope, showing
many green chloroplasts. (B) A drawing
of one of the chloroplasts, showing the
inner and outer membranes, as well as the
highly folded system of internal membranes
containing the green chlorophyll molecules
that absorb light energy. (A, courtesy of
Preeti Dahiya.)
inner
membrane
outer
membrane
(A)
10 µm
(B)
Chloroplasts carry out photosynthesis—trapping the energy of sunlight
in their chlorophyll molecules and using this energy to drive the
manufacture of energy-rich sugar molecules. In the process, they release
oxygen as a molecular by-product. Plant cells can then extract this stored
chemical energy when they need it, in the same way that animal cells do:
by oxidizing these sugars and their breakdown products, mainly in the
mitochondria. Chloroplasts thus ECB5 enable e1.19-1.20 plants to get their energy directly
from sunlight. They also allow plants to produce the food molecules—
and the oxygen—that mitochondria use to generate chemical energy
in the form of ATP. How these organelles work together is discussed in
Chapter 14.
Like mitochondria, chloroplasts contain their own DNA, reproduce by
dividing in two, and are thought to have evolved from bacteria—in this
case, from photosynthetic bacteria that were engulfed by an early aerobic
eukaryotic cell (Figure 1–21).
Internal Membranes Create Intracellular Compartments
with Different Functions
Nuclei, mitochondria, and chloroplasts are not the only membraneenclosed
organelles inside eukaryotic cells. The cytoplasm contains a
nucleus
early aerobic
eukaryotic cell
mitochondrion
internal
membranes
photosynthetic
eukaryotic cell
photosynthetic
bacterium
loss of membrane derived
from the plasma membrane
of the engulfing early
eukaryotic cell
chloroplasts
Figure 1–21 Chloroplasts almost certainly
evolved from engulfed photosynthetic
bacteria. The bacteria are thought to have
been taken up by early eukaryotic cells that
already contained mitochondria.