Unit 1 - Lifestyle, Transport, Genes and Health
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Topic 5: On the Wild Side
This topic builds an appreciation that photosynthesis is the primary process that
underpins the majority of ecosystems, and provides students with an understanding
of how ecosystems work. The topic continues by looking at whether climate change
will lead to extinction of species or evolution by natural selection, and looks at the
evidence for climate change and its effects on plants and animals. By the end of the
topic students should appreciate how scientific understanding can make us aware of
our responsibilities as stewards of the environment.
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 investigating food webs in a
habitat, and investigation of the effect of changing carbon dioxide levels on
temperature.
Opportunities for developing mathematical skills within this topic include
recognising and using expressions in decimal and standard form, making estimates
of the results of calculations, using ratios, fractions and percentages , using a
scatter diagram to identify a correlation between two variables, plotting two
variables from experimental data, drawing and using the slope of a tangent to a
curve as a measurement of rate of change, calculating rate of change from a graph
showing a linear relationship, determining the slope and intercepts of a linear
graph, solve algebraic equations, change the subject of an equation, understand
the principles of sampling as applied to scientific data, and using a statistical test.
(Please see Appendix 6: Mathematical skills and exemplifications for further
information.)
Students should:
5.1 Understand the terms ecosystem, community, population and habitat.
5.2 Understand that the numbers and distribution of organisms in a habitat are
controlled by biotic and abiotic factors.
5.3 Understand how the concept of niche accounts for distribution and abundance
of organisms in a habitat.
CORE PRACTICAL 10:
Carry out a study on the ecology of a habitat, such as using quadrats and
transects to determine distribution and abundance of organisms, and
measuring abiotic factors appropriate to the habitat.
5.4 Understand the stages of succession from colonisation to a climax community.
5.5 Understand the overall reaction of photosynthesis as requiring energy from
light to split apart the strong bonds in water molecules, storing the hydrogen in
a fuel (glucose) by combining it with carbon dioxide and releasing oxygen into
the atmosphere.
5.6 Understand how phosphorylation of ADP requires energy and that hydrolysis of
ATP provides an immediate supply of energy for biological processes.
5.7 Understand the light-dependent reactions of photosynthesis including how light
energy is trapped by exciting electrons in chlorophyll and the role of these
electrons in generating ATP, reducing NADP in photophosphorylation and
producing oxygen through photolysis of water.
5.2 - Distribution and Abundance of Organisms in a Habitat is Controlled by Abiotic or Biotic Factors
• The distribution and abundance (population) of organisms in a habitat is controlled by both
o biotic (living) factors like:
▪ Competition - for food, light, water, space
• Can be interspecific – between species
• Can be intraspecific – within species
▪ Grazing, Predation, Disease, Parasitism
▪ Mutualism – where both partners benefit
o abiotic (non-living factors) like
▪ Solar energy input – light, latitude, season
▪ Climate – Temperature, rainfall, wind exposure
▪ Topography – altitude (slopes)
▪ Oxygen concentration
▪ Edaphic – geology has effect on plant distribution
▪ Pollution – of air water or land
▪ Catastrophes – volcanos, earthquakes, floods
• Biotic factors are density dependent – effects related to size of the populations for area available
o Larger density = larger competition for food, space, water
• Anthropogenic factors – arises from human activity (is either biotic or abiotic)
o For e.g. Deforestation, grazing, fertilizers affect ecosystems to make them unnatural
5.3 - Species Distribution and Abundance of an Organism due to their Niche
• Ecological niche - role a species has in its environment and how it meets its needs for food and shelter, how
it survives, and how it reproduces. So abiotic and biotic interaction with the environment also matter.
• If different species share the same ecological niche
1. They will compete
2. The better adapted species will outcompete the other and exclude it from the habitat
3. Two species can share the same habitat but each species MUST occupy a Different Niche
• Primary productivity - Rate at which energy is turned to organic matter in an ecosystem
o Producers are autotrophs s organisms make own organic compounds
o Some producers are chemosynthetic autotrophs
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