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Edexcel Categories Archives: Topic 5: On the Wild Side

INVESTIGATING POPULATIONS

INVESTIGATING POPULATIONS

Looking at the abundance and distribution of a species in an area

Abundance = number of individuals of one species in a particular area.

Distribution = a particular species within the area being investigated

  • Random sampling: Choose an area to sample – random to avoid bias. Use appropriate technique to sample the population and repeat to give a reliable estimate of the whole area.
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VALIDATING SCIENCE

VALIDATING SCIENCE

In order to test theories, data needs to be collected to prove or disprove it. Scientists within the scientific community accept evolution as there is evidence to make it reliable and valid.

Scientists validate data in 3 ways:

  • Scientific journals – scientists publish articles describing their work – share ideas, theories, experiments, evidence and conclusions. Allows others to replicate experiments with the same method. If results are replicated repeatedly, the scientific community can be relatively confident in the reliability
  • Peer review – other specialised scientists anonymously assess and review the work in attempt to validate published research
  • Conferences – meeting scientists attend to discuss each others work, share ideas
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SPECIATION

SPECIATION

Speciation is the formation of a new species.

Species = A group of organisms with similar morphology, physiology and behaviour which can interbreed and are reproductively isolated from other species.

For a new species to arise, a group of individuals has to be reproductively isolated from the rest of the population. There are many factors, in addition to geographical isolation, why two species may not be able to breed and produce fertile offspring:

  • Ecological isolation: Species occupy different habitats
  • Temporal isolation: Species reproduce at different times
  • Behavioural isolation
  • Physical isolation: Physical factors preventing them from mating
  • Hybrid inviability: Hybrids produced but don’t live long enough to reproduce
  • Hybrid sterilisation: Hybrid survives long enough to breed but is infertile
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EVOLUTION

EVOLUTION

Evolution is a change in allele frequency in a population of organisms over time.

Natural selection

Many organisms are unable to move to new habitats and will only survive if they can adapt to new conditions – there is a struggle for existence. Organisms experience selection pressures due to climate change. Individuals within a population vary because they have different alleles. The more adapted to the environment, the more likely they will survive and reproduce, passing on their genes (survival of the fittest). So a greater proportion of the proportion will have the beneficial allele, increasing the allele frequency.

Gene mutations

The gene pool is the complete range of alleles present in a population. New alleles are generated through mutations of the gene during DNA replication. How often an allele occurs in a population is the allele frequency. The frequency of an allele changes over time.

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ENZYME ACTIVITY

ENZYME ACTIVITY

Temperature has a direct effect on enzyme activity – at low temperatures enzyme activity is low because substrate and enzyme don’t collide often. This increases with temperature until optimum temperature is reached. Any higher than the optimum temperature, enzymes become denatured and enzyme activity lowers.

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MAINTAINING THE BALANCE

MAINTAINING THE BALANCE

  • Biofuels – fuels directly from biomass which are burnt to release energy, producing carbon dioxide. Because the amount of carbon dioxide released when burnt is the same removed by photosynthesis, plants are carbon neutral so have no net increase. Plants can be grown all the time so are a renewable energy source. Examples are wood, straw and vegetable oil. They can reduce the use of limited fossil fuels, reducing carbon emissions. However they cause the destruction of forests, causing the loss of habitats and reducing biodiversity.
  • Reforestation – the planting of new trees in existing forests that have been depleted – more carbon dioxide is removed from the atmosphere by photosynthesis – carbon store as carbon dioxide is converted into carbon compounds and stored as plant tissues in trees – more carbon is kept out of the air.

 

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CARBON CYCLE

CARBON CYCLE

The circulation of carbon

Carbon dioxide levels have been rising, suggesting the cycle isn’t in balance due to mainly combustion of fossil fuels and deforestation.

Coal is a fossil fuel formed from trees fallen into anaerobic conditions millions of years ago so bacteria and fungi could not decompose them. The carbon becomes locked in wood rather than being released into the air and becomes a carbon sink and its accumulation involves the net removal of carbon dioxide. When fossil fuels are burned the carbon is released back into the air.

  • Carbon is absorbed by plants during photosynthesis becoming carbon compounds in their tissues
  • Carbon is passed on to animals when they eat plants and to decomposers when they decompose dead organic matter
  • Carbon is returned to the atmosphere as living organisms carry out respiration producing carbon dioxide
  • Carbon in fossil fuels is released as carbon dioxide when burnt (combustion)
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GLOBAL WARMING

GLOBAL WARMING

The sun radiates energy and is absorbed by the earth which re-emits infra-red radiation. Gases that stop infrared radiation escaping from the earth are greenhouse gases. This keeps the earth warm enough for life and is called the greenhouse effect.

  • Methane is produced through anaerobic decay of organic matter, domestic waste in landfills, belching of animals and combustion of fossil fuels. As temperature increases, methane will be released from natural stores
  • A rise of carbon dioxide levels in the atmosphere and global warming are linked, there is evidence supporting the theory. Carbon dioxide is increasing due to burning of fossil fuels, changes in the Earth’s orbit, solar radiation, volcanic eruptions and deforestation. Measured using ice core samples, bubbles trapped in ice contain carbon dioxide so levels can be measured.
  • Aerosols are very small particles in the atmosphere

Other factors of climate change are:

  • Degree of reflection from ice and snow
  • Extent of cloud cover
  • Changes in sun’s radiation

Extrapolation = extending a line on a graph – we assume there is enough data to establish the trend accurately and present trends continue. Extrapolation is often the basis for predictions.

Computer models can get it wrong because:

  • Limited data or (computer) knowledge
  • Failure to include all factors affecting the climate
  • Changing trends in factors

 

Impacts of global warming:

Changes to species distribution

Climate change may cause a shift in plant distribution. Some may benefit and dominate while others may be lost from the community. As the average temperature rises, species migrate closer to the equator. Species may colonise new areas, out-competing existing species, making them extinct. Other factors affect species distribution such as change in rainfall pattern, soil moisture, winds and rising sea levels.

Changes to development

In many reptiles, temperature affects the sex – global warming could cause a change in sex ratios of these species.

Changes to life cycles

The rate of metabolic reactions will change. Insects may get through their life cycles quicker and be ready to feed on plants that are not yet mature. Plants may flower earlier or later.

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CLIMATE CHANGE

CLIMATE CHANGE

Climate change is supported by evidence from temperature records, pollen grains in peat bogs and tree rings.

 

Temperature records

Some go back 2 or 3 centuries – long-term data can be recorded with thermometers.

 

Pollen analysis

Pollen grains are well preserved in the acidic and anaerobic conditions of peat bogs. It is useful for reconstructing past environments because they are resistant to decay, easy to identify as each plant species produces distinct pollen and each has best conditions to survive in. Peat forms in layers and carbon dating allows the age of each to be established.

 

Dendrochronology

Tree rings are used because every year new xylem vessels are formed by division of cells underneath the bark. The diameter depends on the season (wide in spring, narrow in summer). The rings can be clearly seen when the tree is cut, with a ring for each year of the growth.

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