1.1.1 sampling bias- when unrepresentative
choices are made either deilberately or
unknowingly by investigators.
1.1.2 chance-even if sampling bias is
avoided, the individuals chosen may
not be representative.
1.1.3 random sampling is the best way to
prevent sampling bias and a method of
doing this is to measure out the area
studying and divide into a grid of numbered
lines. use a random number generator and
use the number given as a coordinate and
then tae samples from each coordinate
1.1.4 using a lagre sample size prevents the results
from becoming invalid as it reduces the
likeliness that chance will affect the results.
1.2 causes of variation
1.2.1 genetic differences such as
mutations in genes which
may or may not be passed
on through each generation.
1.2.2 meiosis-forms gametes
which mix up genetic
material before its passed to
offspring to produce
1.2.3 fusion of gametes- in
characteristics from both
parents so causes
2 DNA and meiosis
2.1 4 bases... Guanine, adenine, thymine and
cytosine, each paired together by hydrogen
2.2 nucleotides are made
up of a deoxyribose
sugar, a phosphate
group and an organic
2.3 DNA shaped in a double helix
with deoxyribose and phosphate
providing a backbone around the
pairs of bases.
2.4 DNA is the material responsible for
passing genetic information from cell to
cell and generation through generation.
2.5 the triplet code- when trying
to find how DNA bases code
for amino acid, scientists
found that there must be a
minimum of 3 bases that
code for each amino acid.
they found this as only 20
amino acids occur in
proteins and there are 4
bases so 20/4=3
2.6 homologous chromosomes- a pair of
chromosomes, one maternal and one
paternal that have the same gene loci
therefore produce the same features.
2.7 allele- a form of a gene
2.8 meiosis- 1st division- the homologous
chromosomes pair up and their
chromatids wrap around each other.
one chromosome from each pair goes
into one of the two daughter cells
2.9 meiosis 2nd division- the chromatids move
apart, four cells are formed and in humans,
each one of these cells contains 23
2.10 meiosis produces variation
due to independent
recombination by crossing
2.11 in crossing over, the chromatids of each pair
become twisted around one another causing
tensions which causes part of the chromatid to
break off. the broken bits then rejoin with the
chromatids of it homologous partner.
3 genetic diversity
3.1 selective breeding- known as
artificial selection which involves
choosing which individuals
characteristics are wanted and
using them to parent the next
3.2 the founder effect- this
occurs when just a few
individuals colonise a new
region. these few people will
carry only a few alleles from
the population so these
alleles will then be passed
on through generations
showing no genetic diversity
3.3 genetic bottlenecks- populations
sometimes suffer from a dramatic
drop in population numbers . this
could be due to a chance event e.g
a volcano/earthquake. the few
survivors will possess a small variety
of alleles which will be passed on
through generations so will have a
low genetic diversity.
4 variety of life
4.1 haemoglobin-a grop of
chemically similar molecules
which consist of four
polypeptide chains. they
each have a quaternary
structure in which all four
polypeptides are linked
together to form a spherical
molecule. each Hb has a
haem group which can
combine with a single
4.2 each haemoglobin can carry
four oxygen molecules
4.3 the role of Hb is to transport oxygen and
to do this it must readily associate with
oxygen at the surface where gas
exchange takes places and also readily
dissociate from oxygen at tissues that
4.4 haemoglobins with a high affinity for
oxygen take up oxygen easily but
release it less readily. Hb's with a low
affinity for oxygen struggle to take up
oxygen but release it more readily.
4.5 in an area of little oxygen, a
haemoglobin with a high affinity for
oxygen is required but an organism
with a high metabolic rate needs to
release oxygen readily into its tissues
so needs HB with a low affinity for
5 the cell cycle
5.1 nuclear division- the process by
which the nucleus divides (mitosis/meiosis)
5.2 cell division- follows nuclear
division and is the process in which
the whole cell divides.
5.3 mitosis produces two
daughter nuclei that have
the same number of
chromosomes as the
parent cell and each
5.4 stages of
5.5 interphase- when DNA replicates,
the chromosomes are invisible and
the cell is synthesising proteins.
5.6 prophase- chromosome
become visible and the
5.7 metaphase- chromosomes line up in
the middle of the cell and spindle
5.8 anaphase- spindle fibres
attach to chromatids and
pull chromatids apart
towards the poles.
5.9 telophase- nuclear envelope
reforms and spindle fibres
disintegrate. two daughter
nuclei are formed.
5.10 cell cycle has 3 stages... interphase,
nuclear division and cell division.
6 cellular organisation
6.1 epithelial cells- found in animals
and consist of a sheet of cells
that line the surface of organs
and often have a protective
function.they can also be found
where diffusion takes place e.g
the alveoli of the lungs.
6.2 xylem- occurs in plants and is used
to transport water and mineral ions
throughout the plant and also gives
6.3 an organ is a combination
of tissues that are
coordinated to perform a
variety of functions. e.g the
digestive system which is an
7 exchange and transport
7.1 things which need to be
interchanged between an organism
and its environment... respiratory
gases, nutrients, excretory products
7.2 exchange surfaces to allow
effective transfer of materials...a
large surface area to volume ratio,
very thin so that the diffusion
distance is short, partially
permeable to allow selected
materials to cross without
obstruction, movement of the
internal medium e.g blood to
maintain a diffusion gradient.a
7.3 gas exchange in insects... to reduce water loss
they have waterproof coverings on their body
surfaces and a small surface area to volume ratio
to minimise the area over which water is lost.
7.4 insects use tracheae to diffuse
respiratory gases by an internal network of
small tubes called tracheoles.this allows
air to be brought directly to respiring
7.5 how gases move in and out of insects...
along a diffusion gradient- oxygen is used up
and so the concentration towards the end of
the tracheoles falls creating a diffusion
gradient that causes gaseous oxygen to
diffuse from the atmosphere to the cells.
7.6 gases enter and leave tracheae
through tiny pores called
spiracles. these spiracles can be
opened and closed by a valve.
this means that when spiracles
are open, water can evaporate
from the insect but most of the
time spiracles are closed to
prevent water loss.
7.7 plant leaves and gas exchange- most occurs
in the leaves which have adaptations for rapid
diffusion... a thin flat shape produces a large
surface area, many small pores (stomata) and
numerous interconnnecting air spaces that
occur throughout mesophyll.
7.8 stomata- minute pores on the underside of leaves
which are surrounded by guard cells which can
open and close to control the rate of gaseous
exchange which is important to prevent water loss
8.1 a species is similiar to one another
but different to members form other
8.2 a species is capeable of breeding to produce
living fertile offspring and therefore when
reproducing sexually, any of the genes of
individuals can be combined with any other so
belong to the same gene pool.
8.3 the bionomial system is used to name
species and the first (generic) name says
which genus the organism belongs and
the second (specific) name says which
species the species belongs to.
8.4 both names are printed in italics
or if handwritten are underlined to
indicate the scientific names
8.5 classification- the grouping together of organisms
8.6 taxonomy is the practice of biological classification.
8.7 artificial classification divides
organisms due to differences such
as colour, size or number of legs
8.8 natural classification is
based upon evolutionary
organisms and their
9 relationships between organisms
9.1 DNA determines the the proteins of an organism and proteins determine the
features of an organism. by comparing DNA and proteins of different species helps
scientists to determine evolutionary relationships between them.
9.2 DNA hybridisation depends upon particular properties of
of DNA double helix. when DNA is heated it splits into 2
complementary single strands.
9.3 when cooled the complementary strand
bases on each strand recombine, using this
property, DNA hybridisation can be used to
compare the DNA of two species.
9.4 hybridisation... DNA from two species is extracted and cut
into short pieces. the DNA from one species is then
labelled by fluorescent raker and mixed with the other
species. the mixtures of both species DNA is heated to
separate strands and then cooled to allow strands to reform
with complementary bases.
9.5 hybrid strands once cooled can then be
seperated out and the temperature be
increased in stages.the higher the
temperature, the more hydrogen bonds are
formed so the more hydrogen bnds formed,
the stronger the hybrid strand will be
showing that the species are closely related
if a high temperature is reached.
9.6 courtship behaviour is the behaviours shown when two
members of the same species want to breed. it helps to
achieve finding a mate as it allows animals to recognise
members of their own species, to identify a mate that is
capable of breeding and it allows them to form a pair bond.
10 adaptation and selection
10.1 mutations- are changes in DNA that result in different characteristics.
10.2 conjugation- occurs when one bacterial cell transfers DNA to another.
10.3 one cell produces a thin projection that meets
another cell and forms a conjugation tube between
the cells. the donor cell then replicates one of its
smaller plasmids. the plasmid is then broken to make
it linear before it passes through the tube into the
recipient cell. contact between cells is brief so only a
portion of the donors DNA is transferred. the recipient
cell acquires new characteristics from the donor cell.
10.4 antibiotics- are substances produced by living organisms
that can destroy or inhibit the growth of microorganisms.
10.5 antibiotics work by preventing bacteria from making normal cell walls.they inhibit
the synthesis and assembly of peptide cross linkages between bacterial cell walls.
this weakens the walls making them unable to withstand pressure so are unable to
prevent water from entering and so osmotic lysis occurs killing the bacterium.
11.1 species diversity-the number of different
species and the number of individuals of
each species within any one community
11.2 genetic diversity- the variety of
genes possessed by the individuals
that make up any one species
11.3 ecosystem diversity- refers to the
range of different habitats within a
11.4 agriculture- can cause species diversity to drop
due to farers selecting crops for specific
characteristics so only a few features are grown
whereas a large range of species needs to be
available to be economic.
11.5 deforestation- many different species
are adapted to living in forest/ woodland
environments and since deforestation is
the clearing of forests for
grazing/housing/reservioirs, many of
these habitats are being destroyed
causing a drop in the biodiversity
12 starch, glycogen and cellulose
12.1.1 a polysaccharide that is
found in many parts of a
plant in the form of small
12.1.2 it is an important component of
food and is a major energy source
in most diets.
12.1.3 made up of chains of
linked by glycosidic
bonds that are fromed
12.1.4 the unbranched
chain is tightly
12.2.1 similar structure to starch but
has shorter chains, is highly branched and is found
12.2.2 it is stored as granules in the
muscles and liver and due to
the shorter chains it is more
readily hydrolysed to alpha
12.3.1 differs from starch and glycogen as it is
made up of monomers of beta glucose. to
form glycosidic links, this means that
each beta glucose molecule has to rotate
180 degrees to its neighbour.
12.3.2 unlike starch, cellulose has straight
unbranched chains that run parallel to one
another allowing hydrogen bonds to form
cross linkages between adjacent chains.
12.3.3 due to a large number of
hydrogen bonds, cellulose is
fairly strong making it a valuable
structural material. due to this
cellulose is a major component
in plant cell walls and provides
the plant with rigidity.
12.3.4 the cellulose cell wall also prevents the
cell from bursting as water enters by
osmosis. this occurs by it exerting an
inward pressure to stop any further influx