Page 16 - Demo 1

vacuoles contain not only water, sugars, and salts but also pigments and toxic
materials. These toxic substances help ward off herbivorous animals. Few
animals have vacuoles. Fat cells or adipocytes have very large lipid-containing
vacuoles that take up almost two-thirds of the volume of the cell.

The energy-related organelles – the chloroplasts, which only occur in
algae and plants and the mitochondria, which occur in the cells of all but a
very few eukaryotes – are responsible for generang majority of the energy
necessary for fueling cellular processes.
A chloroplast is an
organelle that uses solar
energy to
manufacture
carbohydrates from carbon
dioxide gas and
water through
the process
of photosynthesis.
Chloroplasts are larger than
mitochondria and have a
more complex internal structure. They are bounded by a
double
Figure 3. Structure of a Chloroplast
membrane, an outer Source: https://sites.google.com/site/cellproject31113/_/
membrane and an inner rsrc/1350592529323/home/chloroplast/Chloroplasts.jpg
membrane.

Inside the chloroplasts, another series of membranes are fused to form
stacks of closed vesicles called thylakoids, where light dependent reacons of
photosynthesis occur. The thylakoids are stacked on top of one another to
form a column called a granum (plural, grana). The large inner space
containing a mixture of concentrated enzymes is called the stroma.
Chloroplasts have a circular DNA molecule, where many of the genes coding
for the proteins required for photosynthesis are found. Plant cells can have
one to several hundred chloroplasts, depending on the species.

The mitochondrion is smaller than a chloroplast, and is usually visible only
under an electron microscope. Like chloroplasts, mitochondria are bounded
by a double membrane. The inner membrane is bent into numerous folds
called cristae (singular, crista) that project into the matrix.

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