extra s Flashcards
Sphincter
A ring of muscle which runs round the
wall of a tubular organ. When it contracts, it
makes the lumen of the organ narrower. There
are sphincter muscles where some arterioles
join the capillaries they supply. The opening
and closing of the sphincter muscles regulates
the flow of blood to the part of the body
concerned. Other sphincter muscles are found in
the gut and urinary system.
Stigma
Female part of a flower, where pollen
lands during pollination. Stigmas have
adaptations which allow them to trap pollen.
When one of the pollen grains germinates, it
produces a pollen tube. The pollen tube grows
down through the tissue of the style to the
ovary.
Squamous epithelium
Epithelial cells form the
outer surface of many animals, and line cavities
inside organs. Squamous epithelial cells are very
thin and flattened; they line the walls of the
alveoli in the lungs.
Stereoscopic vision
Stereoscopic vision allows
depth to be perceived. Among mammals,
stereoscopic vision is particularly well
developed in species which live in trees, and in
predators, where the ability to judge distance
accurately is important to the animal’s way of
life. It depends on the slight differences in
sensory information coming from the two eyes.
Cells in the visual cortex are able to compare the
input from one eye with that from the other.
Style
The part of the flower between the stigma
and the ovary. During pollination, a pollen
grain lands on the stigma. It germinates and
produces a pollen tube which grows down
through the tissue of the style to the ovary
Surface area to volume ratio
Calculated by
dividing the total surface area of a cell or
organism by its volume.
Suspensor
A column of cells found in a
developing seed. The suspensor attaches the
embryo to the wall of the embryo sac.
Sustainability
The principle that the use of
resources (or the environment in general) should
only be permitted if it can be done without
damaging or reducing those resources in the
long term
Sugar
A general name used to describe
carbohydrates that have small molecules.
Sugars cannot be further broken down
(hydrolysed) by water, and they are soluble in
water. Sugars are either monosaccharides
consisting of single sugar units or disaccharides
where two sugar units are combined. Glucose,
fructose and sucrose are sugars.
Super-coiling, Super-coiled
When DNA is
supercoiled, enzymes twist it around protein
molecules. The genes on super-coiled sections
of DNA are inaccessible and cannot be
transcribed. Super-coiling of the
X chromosome explains why some female cats
have a tortoiseshell appearance.
System
A group of organs in the body that has a
specific function. For example, the heart, the
arteries and the veins are organs. They work
together, forming part of the circulatory system.
The function of the circulatory system is to
transport substances round the body. Other
systems include the digestive system and
excretory system
Systemic
Referring to an entire system or body.
For example, mammals have a double
circulation. Blood is pumped to the lungs from
the right ventricle of the heart. It returns to the
heart where it is pumped again, this time by the
left ventricle. It now goes to all the other organs
of the body. The loop of the circulatory system
that supplies the majority of the body organs is
described as the systemic circulation.
Territory
An area that an animal defends against
other animals, usually those of the same species.
Thoracic duct
The thoracic duct in the neck
drains most of the lymph from the lymphatic
system back into the bloodstream.
Thrombosis
A condition in which a blood vessel
is blocked by a blood clot. If blockage is
permanent, cells may be damaged since they will
not be supplied with oxygen. In arteries
supplying the heart, thrombosis may result in a
heart attack or myocardial infarction. In
arteries supplying the brain, it results in a
stroke.
