Extra's A Flashcards
Acinar cell
A cell from the pancreas. It produces
enzymes that are used in digestion.
Adaptive radiation
The way in which a common
ancestor may give rise to different species, each
occupying a different ecological niche. For
example, it is thought that all molluscs evolved
from a worm-like ancestor. There are now many
different species which are adapted to a wide
range of niches. Present-day molluscs include
slow-moving, land-dwelling herbivores such as slugs and snails, as well as rapid swimming
carnivores like squid.
Alga, Algal, Algae
A group of plant-like
organisms that include the one-celled organisms
that form phytoplankton as well as the
seaweeds. Although algae photosynthesise and
their cells are surrounded by a cell wall, they are
not plants. They belong to a group of organisms
called the Protoctista.
Aerobic, Aerobe
Aerobic means requiring the
presence of oxygen. Aerobic bacteria are
bacteria that can only live and multiply in the
presence of oxygen. Aerobic respiration is
respiration that requires the presence of
oxygen. Aerobes are organisms that respire
using oxygen.
Allergen
A substance that produces an allergic
reaction in a sensitive person. Many different
substances can act as allergens. One concern
over the widespread use of genetically modified
foods is that they may make allergens more
widespread.
Allergic reaction
In a person suffering from an
allergy, a reaction takes place involving a
particular substance, called an allergen, to
which the person is sensitive. As a result, large
amounts of histamine are produced. Some
allergens produce localised effects such as those
that occur with hay fever and asthma. Others are
more widespread and can be very serious.
Anaphylactic shock, for example, may occur in
response to nuts. It affects the lungs and the circulatory system, and may result in death
unless medical help can be given.
Amniotic fluid
A developing fetus is wrapped in
a membrane called the amnion. The space
between the amnion and the fetus is filled with a
fluid called amniotic fluid. This cushions and
supports the delicate tissues of the developing
fetus. Amniotic fluid contains some fetal cells.
These cells can be examined and their chromosomes observed, or the DNA that they
contain may be investigated.
Amphibian
A member of the class of animals
that includes frogs and toads. Amphibians have
moist skin that acts as an additional gas
exchange surface. They breed in water and
produce aquatic larvae called tadpoles, which
change into terrestrial adults.
Amylase
An enzyme that digests starch into
soluble sugars. This reaction involves the
addition of water molecules so it is an example
of hydrolysis. Amylases are important digestive
enzymes in animals but they are also found in
many microorganisms and plant tissues.
Amylose is a polysaccharide. Amylase is the
enzyme that breaks down amylose to maltose.
Anaemia
A condition in which there is a reduced
amount of haemoglobin, the oxygen-carrying
pigment found in red blood cells. People
suffering from anaemia tire easily and soon get
out of breath if they exert themselves. There are
several causes of anaemia. One of them involves
a shortage of iron in the diet.
Antenna, Antennae
A pair of long, jointed
structures found on the head of an animal such
as an insect, a woodlouse or a lobster. Antennae
have a sensory function and have sense organs
that are sensitive to touch or enable the animal to
detect the presence of particular substances.
Angiosperm
An angiosperm is another name for
a flowering plant. The angiosperms include a
variety of plants such as daffodils, oak trees and
grasses like wheat and rice. Most economically
important plants are angiosperms. Angiosperms
have reproductive organs, which are found in
flowers. Angiosperms produce seeds, which are
formed as a result of fertilisation. These seeds
are enclosed within fruits.
Anterior
The front or head end of an animal.
Antigen
A molecule of a substance that the body
regards as foreign or harmful. The presence of a
particular antigen produces the specific immune
response by white blood cells called lymphocytes. There are two types of
lymphocyte cells, B cells and T cells. B cells
produce antibodies in response to antigen. T
helper cells and T killer cells are activated by
the presence of antigens.
Antihypertensives
Drugs to reduce high blood
pressure (e.g. sympathetic nerve inhibitors).
