Extras :N Flashcards
Nucleotide base, Base
The nucleic acids DNA
and RNA are polymers. They are built up of a
large number of nucleotides. Each nucleotide
contains a five-carbon or pentose sugar,
phosphate and a nucleotide base. Four different
nucleotide bases are found in the nucleotides
which make up a DNA molecule. These are
adenine, thymine, cytosine and guanine. In
RNA, thymine is replaced by another base,
uracil. It is the sequence of nucleotide bases in
nucleic acids which forms the basis of the
genetic code.
Nucleic acid
Nucleic acids are polymers made up
of a number of nucleotides joined to each other
by condensation. There are two sorts of nucleic
acid: DNA and RNA.
Oligosaccharide
A carbohydrate that is made
up of three to ten sugar units or monosaccharides joined by condensation.
Oligosaccharides are combined with protein in
glycoproteins on cell membranes
Omnivore
An organism that feeds on both plants
and animals. Omnivores feed at more than one
trophic level in a food web. In woodland food
webs, field mice are omnivores. They eat both
producers and consumers
Organelle
A structure with a specific function
found inside a cell. Some organelles, such as
mitochondria and chloroplasts, are surrounded
by membranes. They are called membranebound
organelles. Other organelles such as
ribosomes are not surrounded by membranes.
Organism
A living thing. Organisms are divided
into five kingdoms: animals, plants, fungi,
prokaryotes such as bacteria, and protoctists.
Operant conditioning
A form of learning in
which the consequences of an animal’s
behaviour affect whether that behaviour will
happen again. Training of dogs involves operant
conditioning. If the animal is given a reward,
when it carries out a particular pattern of
behaviour, it is likely to repeat this behaviour.
The reward acts as a reinforcement.
Osmotic pressure
The pressure due to movement
of water from a solution with a low
concentration of solute molecules to a solution
with a higher concentration of solute molecules.
The osmotic pressure exerted by blood plays an
important part in the formation of tissue fluid
and its return to capillaries.
Optic nerve
The nerve which conveys impulses
from the retina to the brain.
Ovary, Ovaries
The structure in which female
gametes are produced. In a plant, the ovary is
the part of the flower which contains the ovules.
After fertilisation it develops into a fruit. In an
animal, the ovaries produce the ova or female
gametes.
Ovulation
The process in which an egg cell or
ovum is released from an ovary. In women,
ovulation takes place approximately once every
28 days. An ovum and some of the follicle cells
that surround it are released from the ovary and
enter the Fallopian tube.
Ovule
Part of the ovary of a flowering plant. The
ovule contains a number of nuclei. One of these
is the egg nucleus, sometimes called the egg cell.
This fuses with a male gamete to form a zygote.
The embryo sac also contains two polar nuclei.
These fuse with a second male gamete to form a
nucleus with three sets of chromosomes. This
eventually develops into the endosperm, which
provides food for the developing embryo. The
ovule is also called the embryo sac.
Oxygen availability
The amount of oxygen,
dissolved in water or otherwise, available for
organisms (e.g. fish, invertebrates, bacteria).
Partially permeable
Cell membranes are
partially permeable. This means that they allow
some molecules to pass through but not others.
Partially permeable membranes let water
molecules pass into or out of cells by osmosis.
Paternal chromosome
The chromosomes an
organism inherits from its father. In humans, the
diploid number of chromosomes is 46. This
means the body cells have two copies of each of
23 chromosomes. During sexual reproduction,
sex cells fuse to become a zygote. One set of the
chromosomes in the zygote comes from the
father: these are the paternal chromosomes. The
other set comes from the mother: these are the
maternal chromosomes.
