Cambridge International A Level Biology Revision Guide

Cambridge International AS and A Level Biology
522
phagocytosis see endocytosis
phenotype the characteristics of an organism, often
resulting from an interaction between its genotype and its
environment
phloem tissue containing sieve tubes and other types of cell,
responsible for the translocation of assimilates such as
sucrose through a plant
phospholipid a substance whose molecules are made up of a
glycerol molecule, two fatty acids and a phosphate group; a
bilayer of phospholipids forms the basic structure of all cell
membranes
phosphorylation the transfer of a phosphate group to an
organic compound
photoautotroph autotroph that uses light energy in
photosynthesis
photolysis the splitting of water using light energy:
H 2
O → 2H + + 2e − + O 2
photophosphorylation the synthesis of ATP from ADP and
P i
using light energy in photosynthesis (compare oxidative
phosphorylation)
photorespiration a wasteful reaction in which RuBP
combines with oxygen rather than carbon dioxide; it is
favoured by high temperatures and high light intensities
photosystem a cluster of light-harvesting accessory pigments
surrounding a primary pigment or
reaction centre
pinocytosis see endocytosis
plant growth regulator (plant hormone) any chemical
produced in plants that influences their growth and
development, e.g. auxins, gibberellins, cytokinins and
abscisic acid
Plantae one of the four kingdoms of the domain Eukarya;
eukaryotic organisms which are multicellular, have cell
walls that contain cellulose and can photosynthesise
plasmid a small, circular piece of DNA in a bacterium (not
its main ‘chromosome’); plasmids often contain genes that
confer resistance to antibiotics
plasmodesma (plural: plasmodesmata) a pore-like structure
found in plant cell walls; plasmodesmata of neighbouring
plant cells line up to form tube-like pores through the cell
walls, allowing the controlled passage of materials from one
cell to the other; the pores contain ER and are lined with
the cell surface membrane
podocyte one of the cells that makes up the lining of
Bowman’s capsule surrounding the glomerular capillaries
polymer a giant molecule made from many similar repeating
subunits joined together in a chain; the subunits are much
smaller and simpler molecules known as monomers;
polymers may also be referred to as macromolecules;
examples of biological polymers are polysaccharides,
proteins and nucleic acids; see monomer
polynucleotide a chain of nucleotides
polypeptide a long chain of amino acids formed by
condensation reactions between the individual amino
acids; proteins are made of one or more polypeptide chains;
see peptide bond
polyploidy possessing more than two complete sets of
chromosomes
polyribosome the group of ribosomes working on the same
mRNA molecule
polysaccharide a polymer whose subunits are
monosaccharides joined together by glycosidic bonds
population all of the organisms of the same species present
in the same place and at the same time that can interbreed
with one another
positive feedback a process in which a change in some
parameter brings about processes that move its level even
further in the direction of the initial change
postsynaptic neurone the neurone on the opposite side
of a synapse to the neurone in which the action
potential arrives
potometer a piece of apparatus used to measure the rate of
uptake of water by a plant
presynaptic neurone a neurone ending at a synapse from
which neurotransmitter is secreted when an action
potential arrives
primary pigment see reaction centre
primary structure the sequence of amino acids in a
polypeptide or protein
probe a length of DNA that has a complementary base
sequence to another piece of DNA that you are trying
to detect
progesterone a steroid hormone secreted by the corpus
luteum in the ovary after ovulation; used in contraceptive
pills
prokaryote see prokaryotic cell
prokaryotic cell a cell that does not contain a nucleus or any
other membrane-bound organelles; bacteria and archeans
are prokaryotes
promoter a length of DNA that controls the expression of a
gene
prosthetic group a non-protein component that is attached
to a protein to form a complex molecule; it aids the protein
in its function; an example is the iron-containing haem
group, which is attached to α-globin and β-globin to form
haemoglobin
Protoctista one of the five kingdoms; eukaryotic organisms
which are single-celled, or made up of groups of similar
cells
protoctist a member of the Protoctista kingdom
protoplast the living contents of a plant cell, including the cell
surface membrane, but excluding the cell wall
Purkyne tissue an area of tissue in the septum of the heart
that conducts the wave of excitation from the atria to the
base of the ventricles
quadrat a square frame which is used to mark out an area for
sampling of organisms
quaternary structure the three-dimensional arrangement of
two or more polypeptides, or of a polypeptide
and a non-protein component such as haem, in a
protein molecule