233
pitottube
ments are used to protect delicate tissues such as nerves from an excess of
light which would be fatal; they may function for the detection of light, for
absorption of heat rays, or as protective colors.~coloration in (marine) animals.
pigments, plants substances found in plants which absorb certain wavelengths of
visible light; the absorbed energy is used directly or indirectly for photosynthesis. Except for Cyanobacteria these pigments are located in chloroplasts
(~chromatophore). There are three groups of pigments: chlorophylls, carotenoids
and biliproteins. Chlorophyll-a is present in all plants, but each taxonomic
group of algae has its additional set of pigments and hence its special color
(red, green, brown, blue-green algae). The division of algae into classes is
largely based on pigments. In oceanography the concentration of the
chlorophylls is often used as a measure of phytoplankton abundance, while the
occurrence of specific pigments can be used as a tool to identify different
groups of algae. The degradation of algae is accompanied by partial degradation of their chlorophyll, and the degradation products, pheophytins, can
be used as an indicator of algal degradation.
pillow lava a general term for lavas that exhibit a sack-like, bulbous of structure
about a meter long; occurring mostly when lava flows underwater.
pinocytosis is the uptake of macromolecules into a cell by a drinking type of
action; compare phagocytosis.
Pisces (fish) this group of aquatic vertebrates (subphylum Vertebrata, phylum
Chordata) is now split up into more natural divisions, namely the four classes
Agnatha (lampreys and hagfish), Placodermi (extinct fish with heavy armour),
Chondrichthyes (catilaginous fish like sharks and rays) and Osteichthyes (the
"true" or bony fish). These classes thus have the same systematic level as the
other vertebrate classes, namely the Amphibia, Reptilia, Aves (birds) and
Mammalia (mammals). (Figure see p. 234)
piscivores (or ichtyophages), animals that feed mainly on fish. Many seabirds,
marine mammals, and most larger fish are piscivorous.
piston corer ~corer.
pitot tube a device for determining flow velocities by measuring a pressure
difference between a first orifice facing the flow and a second orifice, located downstream, parallel to the flow, utilizing Bernoulli's theorem. As the pitot
tube is a symmetric body, the first orifice, at its tip, is at a stagnation point
where the flow velocity is zero. As the second orifice (at its downstream side)
is at the same (separation) streamline the static pressure measured there
will be less than that at the first orifice, since, by Bernoulli's law, the total
pitottube
ments are used to protect delicate tissues such as nerves from an excess of
light which would be fatal; they may function for the detection of light, for
absorption of heat rays, or as protective colors.~coloration in (marine) animals.
pigments, plants substances found in plants which absorb certain wavelengths of
visible light; the absorbed energy is used directly or indirectly for photosynthesis. Except for Cyanobacteria these pigments are located in chloroplasts
(~chromatophore). There are three groups of pigments: chlorophylls, carotenoids
and biliproteins. Chlorophyll-a is present in all plants, but each taxonomic
group of algae has its additional set of pigments and hence its special color
(red, green, brown, blue-green algae). The division of algae into classes is
largely based on pigments. In oceanography the concentration of the
chlorophylls is often used as a measure of phytoplankton abundance, while the
occurrence of specific pigments can be used as a tool to identify different
groups of algae. The degradation of algae is accompanied by partial degradation of their chlorophyll, and the degradation products, pheophytins, can
be used as an indicator of algal degradation.
pillow lava a general term for lavas that exhibit a sack-like, bulbous of structure
about a meter long; occurring mostly when lava flows underwater.
pinocytosis is the uptake of macromolecules into a cell by a drinking type of
action; compare phagocytosis.
Pisces (fish) this group of aquatic vertebrates (subphylum Vertebrata, phylum
Chordata) is now split up into more natural divisions, namely the four classes
Agnatha (lampreys and hagfish), Placodermi (extinct fish with heavy armour),
Chondrichthyes (catilaginous fish like sharks and rays) and Osteichthyes (the
"true" or bony fish). These classes thus have the same systematic level as the
other vertebrate classes, namely the Amphibia, Reptilia, Aves (birds) and
Mammalia (mammals). (Figure see p. 234)
piscivores (or ichtyophages), animals that feed mainly on fish. Many seabirds,
marine mammals, and most larger fish are piscivorous.
piston corer ~corer.
pitot tube a device for determining flow velocities by measuring a pressure
difference between a first orifice facing the flow and a second orifice, located downstream, parallel to the flow, utilizing Bernoulli's theorem. As the pitot
tube is a symmetric body, the first orifice, at its tip, is at a stagnation point
where the flow velocity is zero. As the second orifice (at its downstream side)
is at the same (separation) streamline the static pressure measured there
will be less than that at the first orifice, since, by Bernoulli's law, the total