located in the inner membrane of chloroplasts—where
photosynthesis takes place. They appear as green gran-
ules under a microscope and contain the light-reactant
chemicals chlorophyll and carotenoid pigments. ATP is
generated during photosynthesis by chemiosmosis.
gravid Used in relation to pregnant insects and
meaning heavy with fully developed eggs or denoting
an advanced stage of pregnancy.
gravitropism The ability of an organism or specific
cells to respond, e.g., bend, to the gravitational pull; a
growth curvature induced by gravity.
See alsoGEOTROPISM.
Greek letters used
α:SeeHELIX(for ALPHA HELIX) and CYTOCHROME.
β:SeeBETA SHEET,BETA STRAND,BETA TURN, and
CYTOCHROME.
γ:SeeSORET BAND(for gamma band).
η:SeeHAPTOand ASYMMETRY PARAMETER.
κ:SeeDONOR ATOM SYMBOL(for kappa convention).
μ:SeeBRIDGING LIGAND(for mu symbol).
greenhouse effect The warming of an atmosphere
by its absorbing and reemitting infrared radiation while
allowing shortwave radiation to pass on through.
Certain gaseous components of the atmosphere,
called greenhouse gases, transmit the visible portion of
solar radiation but absorb specific spectral bands of
thermal radiation emitted by the Earth. The theory is
that terrain absorbs radiation, heats up, and emits
longer wavelength thermal radiation that is prevented
from escaping into space by the blanket of carbon
dioxide and other greenhouse gases in the atmosphere.
As a result, the climate warms. Because atmospheric
and oceanic circulations play a central role in the cli-
mate of the Earth, improving our knowledge about
their interaction is essential.
See alsoCARBON DIOXIDE.
gross primary productivity(GPP) The total energy
fixed by plants in a community through photosynthesis
(such as repackaging inorganic energy to organic ener-
gy) per unit area per unit time; total carbon assimila-
tion by plants; total mass or weight of organic matter
created by photosynthesis over a defined time line.ground meristem Meristem is embryonic tissue.
Ground meristem is one of the primary meristem tis-
sues that are differentiated from the apical meristem.
The primary meristem tissues include three different
tissues: protoderm, ground meristem, and procambi-
um. The protoderm differentiates into the epidermis;
the procambium differentiates into the vascular tissue;
and the ground meristem differentiates into three
regions: the cortex, which is several layers of
parenchyma cells under the epidermis of the stem and
root; pith ray, the parenchyma cells between the vascu-
lar bundles in the primary dicot stem; and pith, which
are parenchyma cells in the center of the primary dicot
stem. Parenchyma are isodiametric cells, i.e., approxi-
mately equal in length, width, and height, that are thin
walled and not extremely specialized. Ground meris-
tem gives rise to cells of the ground tissue system. The
ground tissue of a leaf, located between the upper and
lower epidermis and specialized for photosynthesis, is
called the mesophyll.ground tissue system The plant tissue system that
forms most of the photosynthetic tissue in leaves, com-
posed mostly of parenchyma cells and some collenchy-
ma (elongate and thick walled in strands) and
sclerenchyma (thick, rigid, secondary walls with lignin
to provide support) cells. It is found between the epi-
dermis and surrounding the vascular tissue system.
Acts also as supporting tissue and in water and food
storage.growth factor Acomplex family of organic chemi-
cals, especially polypeptides, that bind to cell surface
receptors and act to control new cell division, growth,
and maintenance by the bone marrow.
Synthetic growth factors are being used to stimu-
late normal white blood cell production following can-
cer treatments and bone marrow transplants.
Examples of growth factors are insulin (including
insulinlike growth factor (IGF), GF1, II, all of which152 gravid