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PLASTIDS - CHLOROPLASTS
| Plastids
are the site of photosynthesis in eukaryotic cells. Only some euglenids
have plastids. Those which do are either obligate autotrophs or they are
facultative autotrophs (that is they can feed heterotrophically in the dark).
Some lineages seem capable of loosing their plastids and becoming colourless.
This may be linked to the method by which plastids first evolved. incorporatePlastids
(a generic term for chloroplasts) in euglenids come in a variety of shapes.
They have a bright green colour because of the presence of chlorophyll B
in the photosynethic armoury.
Plastids
may or may not have a proteinaceous pyrenoid (dark body) and may or may
not have associated starch (paramylon) in grey. Electron-micrograph of a
plastid in Euglena gracilis.Plastids are membrane bound organelles,
and contain flattened membranous sacs called thylakoids. These are clustered
into groups or lamellae. The photosynethic pigments are mostly located in
these membranes. The high level of folding allows the plastids to contain
high concentrations of photosynthetic pigments and increases the effectiveness
of the organisms. More detail example |
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