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Classification, variation and inheritance

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o a) Species – groups of organisms that have many features in common
o b) Genus – contains several species with similar characteristics
o c) Family – comprising of several genera
o d) Order – comprising of several families
o e) Class – comprising of several orders
o f) Phylum – comprising of several classes
o g) The Five Kingdoms of life are
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2 Be able to describe the main characteristics of the five kingdoms
including:
o a) Animalia – animals are multicellular, do not have cell walls, do not
have chlorophyll, feed heterotrophically (heterotrophs can't make their
own food)
o b) Plantae – are multicellular, have cell walls, have chlorophyll, feed
autotroprically (autotrophs can make their own food)
o c) Fungi – multicellular, have cell walls, do not have chlorophyll, feed
saprophytically (saprophytes feed off dead organisms and decaying
material)
o d) Protoctista – unicellular (single celled), have a nucleus, protoctista
include algae
o e) Prokaryotes – unicellular (single celled), have no nucleus e
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bacteria
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o Viruses, which are smaller than bacteria, cannot reproduce
themselves, have protein coat containing a few genes, they invade
cells and make them reproduce the invading virus
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4 Be able to describe the main characteristics of the phylum Chordata as
animals with a supporting rod running the length of the body, an example of
this being the backbone in vertebrates
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5 Be able to explain how scientists place vertebrates into the five groups
based on:
o a) Oxygen absorption methods – lungs, gills and skin

b) Reproduction – internal or external fertilisation, oviparous (lay eggs)
or viviparous (give birth to live young)
o c) Thermoregulation – homeotherms ('warm blooded' - kept at a
constant temperature) and poikilotherms ('cold blooded' - body
temperature varies with external temperature)
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6 Be able to demonstrate an understanding of the problems associated with
assigning vertebrates to a specific group based on their anatomy and
reproduction methods and why many vertebrates are difficult to classify
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Not an easy one to
classify! but its closer to a mammal than any of the other four
vertebrate groups
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7 Be able to discuss why the definition of a species as organisms that
produce fertile offspring may have limitations:
o Some organisms do not always reproduce sexually and some hybrids
are fertile
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o Many closely related species can interbreed producing viable offspring
and technically classed as a different species
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8 HT only: Be able to explain why binomial classification is needed to
identify, study and conserve species, and can be used to target conservation
efforts
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ß The Latin name cannot be confused linguistically with 'local' or
country names
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ß From the database, species at threat can be identified and
preservation strategies put in place
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9 Be able to explain how accurate classification may be complicated by:
o a) variation within a species
o b) HT only: hybridisation in ducks produces viable new species
o c) HT only: ring species - a group of related populations that live near
each other, neighbouring populations may interbreed but those well
separated geographically may not
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o Does the organism do this or that? Structural features? etc
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working your way through an identification key
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11 Be able to explain how organisms are adapted to their environment and
how some organisms have characteristics that enable them to survive in
extreme environments, including deep-sea hydrothermal vents and polar
regions
o In studying these examples know and understand that organisms,
including microorganisms have features (adaptations) that enable them
to survive in the conditions in which they normally live and some cases
understand that some organisms have adapted to live in environments
that are very extreme
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ß Flamingos filter-feed on brine shrimp and blue-green algae and
their pink or reddish color comes from carotenoid proteins in
their diet of animal and plant plankton which can survive in the
very salty lakes the flamingos fly to for feeding
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The
bacteria cannot rely on photosynthesis so they make there own
food by using chemical energy derived from the minerals on and
around the vent
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ß There are creatures that happily live on the deep ocean beds
where the pressure from the water above is enormous
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Know and understand animals and plants may be
adapted for survival in the conditions where they
normally live, eg deserts, the Arctic
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This helps overheating,
particularly as they do not sweat much and
produce smaller volumes of concentrated urine,
both helping to reduce water loss
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Their bodies need to
compact with a minimum volume
- 'roundish' to minimise the surface area through
which heat is lost
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ß Thickness of insulating coat
ß Desert animals have thinner coats than animals in
colder climates, which aids heat loss
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The fur of animals
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like the arctic fox is an extremely good insulator
and can survive at temperatures as low as -50oC
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Bears, similarly, have thick fur coats
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ß Animals in arctic regions have
thick layers of insulating fat or
blubber AND these also act as
an important energy store fat/blubber has a very high
calorific value, useful in lean
times and scarcity of food
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Smaller white coated animals
are less likely to seen and
caught
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ß water-storage tissues
ß Plants like cacti have relatively thick fleshy stems
which contain groups of specialised cells that store
water
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ß extensive root systems
ß Cacti generally have one of two kinds of root
system
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(ii) Other cacti have many
shallow spread out roots that can rapidly absorb
water eg if it rains, which may be very infrequent in
desert regions
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12 Be able to demonstrate an understanding of Darwin’s theory of
evolution by natural selection including:
o a) variation – most populations of organisms contain individuals which
vary slightly from one to another, those with superior characteristics are
more likely to survive,
o b) over-production – most organisms produce more young than will
survive to adulthood ensuring some will survive,
o c) struggle for existence – because populations do not generally
increase rapidly in size there must therefore be considerable
competition for survival between the organisms,
o d) survival - those with advantageous characteristics are more likely to
survive this struggle,
o e) advantageous characteristics inherited – better adapted
organisms are more likely to reproduce successfully passing on the
advantageous characteristics to their offspring
o f) gradual change – over a period of time the proportion of individuals
with the advantageous characteristics in the population will increase
compared with the proportion of individuals with poorly adapted
characteristics, and the poorly adapted characteristics may eventually
be lost
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13 Be able to describe and understand that variation within a species can
be continuous or discontinuous
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o The causes of variation within a species are twofold - genetic and
environmental
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o Discontinuous variation occurs when a particular characteristic of the
species fits into a few particular and specific categories with no range
of variation
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14 Appreciate the variations within a species to illustrate continuous
variation and discontinuous variation
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ß The peak of the graph occurs at the mean value for a
given statistical population
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Examples of discontinuous variation in humans include eye colour,
blood grouping,
ß Any graph of the number of individuals versus the characteristic
will not show any systematic curve that you see with continuous
variation graphs
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15 Be able to interpret information on variation using normal distribution
curves
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ß (i) mutation - mutations that are inherited may change the
characteristics of the species
ß (ii) reproduction - the 'controlled randomness' of the possible
gene combinations of the offspring inherited from their parents
ensures that no offspring can be identical to either parent
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17 HT only: Demonstrate an understanding of how speciation occurs as a
result of geographic isolation
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o Speciation is the development of a new species and can happen when
populations of the same original species becomes so different
(genetically) that they can no longer interbreed to give fertile offspring
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o However, if each population can survive, by the process of natural
selection, two distinct species can evolve (or perhaps one population
remains the same, but the other has to adapt to a different
environment)
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18 Be able to explain how new evidence from DNA research and the
emergence of resistant organisms supports Darwin’s theory
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o DNA analysis shows a close relationship between species that have
relatively recently diverged from a common ancestor (a high
percentage of our DNA is the same as the DNA of apes!)
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o Today we can see evolution in action and the survival of the 'fittest
genes' eg
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The deadly bacteria MSRA is a strain of microorganism that has
survived and prospered by having genetic characteristics
making it resistant to most antibiotics
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ß Certain strains of rats have become resistant to the poison
warfarin
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19 Be able to explain the role of the scientific community in validating new
evidence, including the use of:
o a) scientific journals - enable new findings to be communicated to
other scientists working in the same areas of science, so ideas and
knowledge are widely spread AND other scientists can check whether
the research is valid eg do other scientists get the same results? do
other scientists draw the same conclusions? do other scientists agree
with, and find the theory valid?
o b) the peer review process - a sort of refereeing system, research
papers are read and checked by people competent to understand the
contents of research papers (their peers) - this ensures standards are
high in terms of 'good scientific practice'
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Its also a forum for
other scientists to hear about research which isn't necessarily exactly
their own specialist field, but broadens their own knowledge of related
fields of science
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20 Be able to describe the structure of the nucleus of the cell as containing
chromosomes, on which genes are located
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o Chromosomes carry the genes which control the development and
subsequent characteristics of an organism
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21 You must understand that genes exist in alternative forms called alleles
which give rise to differences in inherited characteristics
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o Alleles are essentially different versions of the same gene
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o Individual alleles can be 'dominant' or 'recessive' in character - see
section 1
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o In section 1
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o dominant - if two alleles for a characteristic are different
(heterozygous) then only one of the alleles can determine the nature of
the characteristic - know as the dominant allele (usually shown as a
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capital/upper case letter) eg a gene for height might be H, so HH or Hh
genotypes will give a tall organism
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o recessive - if an allele is not dominant, it is described as recessive
(small/lower case letter), and, in order for the recessive allele to be
expressed in the phenotype observed, you must have a double
recessive allele eg homozygous genotype hh will give rise to
phenotype short
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o Just an example, consider some of the results of Mendel’s work which
preceded the work by other scientists which links Mendel’s ‘inherited
factors’ with the chromosomes of the humble pea
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Punnett square genetic table for crossing tall
pea plants
Parent genotypes: Tt x Tt
Gametes: T and T
Genotypes of
children

TT

Tt

t

Tt

tt

The first resulting offspring (F1) were all tall pea plants, and these were
then crossed with each other, to give the second set of offspring (F2)
shown above
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Instead of being round and flexible, the
sickle red blood cells become shaped like a crescent (hence the
name 'sickle')
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These painful effects can last from a few
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t

T

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T

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minutes to several months
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Symptoms of sickle cell anaemia include
tiredness, painful joints and muscles and breathlessness,
especially after exercise ie any extra physical exertion
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Cystic fibrosis causes thick, sticky mucus to
build up in the lungs, digestive tract, and other areas of the body
and is one of the most common chronic lung diseases in
children and young adults
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The thick mucus
builds up in the breathing passages of the lungs (causing lung
infections) and in the pancreas, the organ that helps to break
down and absorb food (causing digestion problems)
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26 HT only: Be able to evaluate the outcomes of pedigree analysis when
screening for genetic disorders:
o a) sickle cell disease
o For sickle cell anaemia to occur in a child, both parents must carry the
recessive allele for sickle cell disease, but neither is affected by it
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Punnett square genetic table for sickle cell
anaemia
Genotypes of parents: Aa x Aa
normal but both carriers
Gametes: F,f plus F,f
Genotypes of
children

A

a

A

AA

Aa

a

Aa

aa

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b) cystic fibrosis
The parents may be carriers of the cystic fibrosis disorder without
actually having the disorder themselves
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Punnett square genetic table for cystic fibrosis
Genotypes of parents: Ff x Ff
normal but both carriers
Gametes: F,f plus F,f
Genotypes of
F
children

f

F

FF

Ff

f

Ff

ff

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Cystic fibrosis is caused by a recessive allele f (so it needs genotype
ff, a double recessive allele)
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