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A level Biology Edexcel A - Topic 4
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Notes for Edexcel Biology Topic 4. Detailed and Concise Notes that will get you an A*. They are well laid out and easy to learn
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Topic 4: Biodiversity and Natural ResourcesThe topic focuses on biodiversity and the wealth of natural resources used by
humans. Why there are so many different species is considered first, with the
concept of niche and adaptation explored. The topic looks at how all this diversity
has come about through adaptation and natural selection and how this leads to
evolution. The concerns for disappearing biodiversity and loss of potential natural
resources are used to highlight the need for biologists to identify, name and classify
species. The topic has sections on both traditional and novel uses of plants and
plant fibres and the use of chemical extracts from animals and plants. The
relationship of plant anatomy to function and the structure and role of cellulose and
starch is studied. The topic ends with the issue of sustainability and the role of zoos
and seed banks in conservation of endangered species.
Students should be encouraged to carry out a range of practical experiments
related to this topic in order to develop their practical skills. In addition to the core
practicals detailed below possible experiments include investigation of the
biodiversity of different habitats, investigation of taxonomic hierarchy using
biological specimens, and examination of animal cells under the microscope and
using electron micrographs.
Opportunities for developing mathematical skills within this topic include using
ratios, fractions and percentages, calculating areas of circumferences and areas of
circles and volumes of cylinders, substituting numerical values into algebric
equations using appropriate units for physical quantities, solving algebraic
equations and understanding the principle of sampling as applied to scientific data.
(Please see Appendix 6: Mathematical skills and exemplifications for further
information.)
Students should:
4.1 Know that over time the variety of life has become extensive but is now being
threatened by human activity.
4.2 i) Understand the terms biodiversity and endemism.
ii) Know how biodiversity can be measured within a habitat using species
richness and within a species using genetic diversity by calculating the
heterozygosity index (H):
number of heterozygotes
H=
number of individuals in the population
iii) Understand how biodiversity can be compared in different habitats using a
formula to calculate an index of diversity (D):
N ( N −1)
D=
Σn ( n −1)
4.3 Understand the concept of niche and be able to discuss examples of adaptation
of organisms to their environment (behavioural, physiological and anatomical).
4.4 Understand how natural selection can lead to adaptation and evolution.
14 Pearson Edexcel Level 3 Advanced GCE in Biology A (Salters-Nuffield)
Specification – Issue 3 – July 2016 © Pearson Education Limited 2016
,Students should:
4.5 i) Understand how the Hardy-Weinberg equation can be used to see whether a
change in allele frequency is occurring in a population over time.
ii) Understand that reproductive isolation can lead to accumulation of different
genetic information in populations, potentially leading to the formation of new
species.
4.6 i) Understand that classification is a means of organising the variety of life
based on relationships between organisms using differences and similarities in
phenotypes and in genotypes, and is built around the species concept.
ii) Understand the process and importance of critical evaluation of new data by
the scientific community, which leads to new taxonomic groupings, including
the three domains of life based on molecular phylogeny, which are Bacteria,
Archaea, Eukaryota.
4.7 Know the ultrastructure of plant cells (cell walls, chloroplasts, amyloplasts,
vacuole, tonoplast, plasmodesmata, pits and middle lamella) and be able to
compare it with animal cells.
4.8 Be able to recognise the organelles in 4.7 from electron microscope (EM)
images.
4.9 Understand the structure and function of the polysaccharides starch and
cellulose, including the role of hydrogen bonds between β-glucose molecules in
the formation of cellulose microfibrils.
4.10 Understand how the arrangement of cellulose microfibrils and secondary
thickening in plant cell walls contributes to the physical properties of xylem
vessels and sclerenchyma fibres in plant fibres that can be exploited by
humans.
CORE PRACTICAL 6:
Identify sclerenchyma fibres, phloem sieve tubes and xylem vessels and their
location within stems through a light microscope.
4.11 Know the similarities and differences between the structures, position in the
stem and function of sclerenchyma fibres (support), xylem vessels (support
and transport of water and mineral ions) and phloem (translocation of organic
solutes).
4.12 Understand the importance of water and inorganic ions (nitrate, calcium ions
and magnesium ions) to plants.
CORE PRACTICAL 7:
Investigate plant mineral deficiencies.
CORE PRACTICAL 8:
Determine the tensile strength of plant fibres.
4.13 Understand the development of drug testing from historic to contemporary
protocols, including William Withering’s digitalis soup, double blind trials,
placebo, three-phased testing.
4.14 Understand the conditions required for bacterial growth.
Pearson Edexcel Level 3 Advanced GCE in Biology A (Salters-Nuffield) 15
Specification – Issue 3 – July 2016 © Pearson Education Limited 2016
, Topic Four Biology
Species – group of organisms with similar morphology, physiology and behaviour and can breed fertile offspring and are
reproductively isolated from other species
Habitat – where a organism lives
Population – a group of interbreeding individuals of the same species found in an area
Community – various populations in an area
Niche – the way an organism exploits its environment
Biodiversity – the variety of life
Evolution – change in genetic/heritable characteristics over successive generations
Natural selection – when genetic traits increase an organisms chance of survival and reproduction
Extinction – loss of a species, death of last individual
Inextricably linked – loss of one will lead to extinction of others
The concept of Niche
• a niche is a description of the organism and role in its environment
o where an organism lives and what it does there
• all the species sharing a habitat have different ecological niche
• if two species live in same habitat with the same roles the 2 species will compete against each other
o the better adapted organisms will out compete the other
Orchid Niches
• orchids exploit the behaviour of insects as part of their highly specialised pollinating mechanism
o male bees visit orchids to feed and collect aroma chemical, important in attracting a female mate
• pyramidal orchids produce scent that attracts day-flying moths, a parcel of pollen in the shape of collar attaches itself
with quick-drying glue around the moth’s tongue
• some orchids are so specialised they can only be pollinated by one species of insect (mirror orchid) but if that species
becomes extinct then the plant can’t reproduce
Woodpecker Niches
• all woodpeckers have powerful breaks for probing into wood and theres three species of woodpecker in Britain:
o lesser spotted – prefers finer branches at the top of frees
o greater spotted – feed on broader branches
o green woodpecker – feed on the ground
• each specie co exists in the same habitat as they have different niches
• they eat woodlice, beetle larvae, ants using a long tongue
Organisms can be Adapted to Their Niche in Three Ways
• adaptations are features that increase an organisms chance of survival and reproduction
• They can be:
o Behavioural adaptations - ways an organism acts that increase its chance of survival and reproduction
▪ Plants reacting to sunlight
o Physiological adaptations-processes inside organisms body that increase its chance of survival & reproduction
▪ Cabbage family has adaptation allowing it to tolerate high salt concentrations
▪ Some bacteria have heat stable enzymes so can tolerate 350 degrees
o Anatomical adaptations-structural features of an organisms body that increase chance of survival
▪ Bodies of bubble bees adapted to collect nectar and pollen
▪ They have a long tongue to suck nectar from flowers
• Co adaptation – when the plant and the pollinator become more dependent on each other so evolve in tandem
o E.g. the brazil but and the orchid bee or stinging ants living in whistling thorn
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