B3: Life on Earth

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  • Group of organisms that can breed together and produce fertiel offspring are called species.
  • Individuals in a species are adapted to their living environment - their features work best with the environment that they live in.
  • All living things rely on their habitat and other species to survive.
  • Adaptations of living organisms enables them to live as long as possible.
  • The organisms that are alive long enough to reach reproduction age pass on their genes including the genes adaptation to the next generation - increases chance of survival.
  • Cactus - plant native to America that is adapted for living in conditions of high temperature and low rainfall
  • Spines prevent water loss, protect the cactus from herbivores and shades the stem to keep it cooler than the surrounding air.
  • Small surface area minimises water loss.
  • Roots are close to the soil surface to collect as much water as possible in the rare event of rain.
  • Green succulent stems do photosynthesis and store water during the drought season.
  • Cacti's adaptations for hot climates do not work in colder climates so they wouldn't survive, meaning that there is only cacti in hot climates.
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Food Chains and Food Webs

  • Food chains show direction of energy and material transfer betweem organisms.
  • Food webs show how all the food chains in a habitat are interrelated - all the organisms depend on other parts of the web (interdependance).
  • Chnages in environment alter numbers in food web.
  • If changes are too great for natural variation within a species to cope with, they will die out before they are able to reproduce, causing extinction.
  • Extinction also happens if a new species that is better at competing for resources is introduced.
  • If a species becomes extinct, this can affect other species, causing further extinctions.
  • Energy from the Sun enters the food chain when green plants (autotroph) do photosynthesis and store the energy in chemicals (such as cellulose) in its cells.
  • A herbivore heterotroph eats the autotroph and some of the energy stored in the plant is transferred to the herbivore and stored in its cells.
  • A carnivore heterotroph eats the herbivore heterotroph and some of the energy is transferred again.
  • A large proportion of the energy is lost to the environment as heat, excreted as waste products and trapped in indigestible material such as bones, cellulose and fur.
  • This means that at each tropic level (stage of the food chain) there is less energy so there is a limit to the number of levels in each food chain (usually four or five).
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Decay Organisms

  • Energy is transferred by decay organisms that break down organism after they die.
  • Decomposers (bacteria, fungi) break down dead material and use energy stored inside.
  • Detritivores (earthworms, woodlice) consume detritus (dead plants or animals and their waste) breaking it down into smaller particles that other decomposers and detritivores can use.
  • The percentage of energy efficiency can be calculated using the following formula:

Percentage of energy successfully transferred = amount used/amount potentially available X 100.

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  • Vital element for living things used in all organic molecules including sugars, proteins and amino acids - life on Earth is very much carbon-based.
  • Recycled through environment so it is available for life processed which can be seen in the carbon cycle:
  • (http://1.bp.blogspot.com/-lY0vUir0hHs/UJV6Xh3fe0I/AAAAAAAAAdE/2JdMO9_h0MQ/s1600/carbon+cycle.jpg)
  • Combustion: Fuel + Oxygen --> Carbon dioxide + Water + Energy released.
  • Respiration: Glucose + Oxygen --> Carbon dioxide + Water + Energy released.
  • Photosynthesis: Carbon dioxide + Water Light energy-> Glucose + Oxygen.
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  • Makes up 79% of the Earth's atmosphere.
  • Have a triple covalent bond between atoms of nitrogen which makes it impossible for most organisms to break the bond and use the nitrogen.
  • Nitrogen is 'fixed' into a form that plants and animals can use in two ways; lightning strikes and nitrogen fixing bacteria.
  • Has to be recycled to ensure that it is available for life processes which can be seen in the nitrogen cycle:


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Nitrogen 2

  • Nitrogen fixation is carried out by bacteria such as blue green algae ( Anabaena variabilis).
  • Denitrifiction is where denitrifying bacteria convert nitrates in dead plants and animals back into nitrogen gas which completes the cycle, releasing nitrogen back into the atmosphere.
  • Microorganisms convert ammonia to nitrites and then to nitrates via the process of denitrification.
  • Nitrogen is now in compounds in plant material passed through the food chain through the animals eating the plants.
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Measuring Environmental Changes

  • Changes in the environment are measured by using indicators (non-living or living).
  • Non-living Indicators - Nitrate levels can be measured using test kits with colour-changing chemicals which can be matched against a chart indicating how much nitrate is present.
  • Temperature can be measured using a thermometer or a data-logger (more accurate and reliable).
  • Carbon dioxide levels can be measured using data-loggers.
  • Biological Indicators - Changes in the environment affect living organisms so biologists can use changes in a pattern of where the organisms live to determine how environmental changes such as climate change and road-building projects are affecting the species.
  • In the ocean, phytoplankton are useful for detecting the effect of temperature change and changes in the food web.
  • Lichens grow very slowly and are susceptible to atmospheric pollutants and acid rain so a decline in their number indicates pollution.
  • River organisms (mayfly nymphs) can be used to indicate the quality of water because they can only live in clean river water with enough oxygen so if a river has mayfly nymphs, pollution levels are low.
  • River pollution typically caused mass growth of bacteria which use up all of the oxygen, causing the fish to die and pollution tolerant species such as bloodworm to grow instead.
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How Life Evolved

  • Life on Earth began 3500 million years ago.
  • All life on Earth evolved from simple living things so all organisms share common ancestor.
  • Charles Darwin thought about how organisms are related and drew a tree of life to illustrate his thinking.
  • Evidence of organisms sharing a common ancestor comes from the fossil record + genomics.
  • Fossils indicate the history of species and can show evolutionary changes in organisms over millions of years.
  • Fossils are formed from hard parts of animals that did not decay easily or did not decay because the conditions needed to decay were absent.
  • Similarities and differences in  DNA can lead to relationships being worked out between all life on Earth.
  • Analysing DNA of living and fossilised specimens show similarities and differences.
  • More shared genes organisms have, the more closely related they are.
  • Mapping similarities and differences enables family relationships between organisms to be measured.
  • All organisms have DNA - organisms in a species differ from one another due to the environment and genetic differences in the DNA, only genetic mutations can be passed on to offspring.
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Gene Mutation

  • Genetic variation is caused when mutations take place in the gene.
  • Mutations cause dfferent proteins to be produced and this changes the gene's function.
  • Sometimes a mutation causes a gene to be copied twice which means more variation occurs.
  • If mutations occur in the gamete, the mutated gene can be passed on to the offspring.
  • Most of the time, mutations have no significant affect but they sometimes cause new characteristics.
  • Genetic variation between individuals in a species means that those with characteristics that improve chance of survival are more likely to live to adulthood.
  • When these individuals reproduce, the pass on the beneficial characteristics to offspring.
  • Individuals that have characteristics poorly-fitting to their environment are less likely to survive long enough to reproduce.
  • The population of individuals with beneficial characteristics increases and the individuals with non-beneficial characteristics decreases because of this.
  • The selective agent is the organism's environment.
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Selective Breeding and Natural Selection.

  • Selective breeding is where animals and plants with certain traits are purposely mated together to produce offspring with desirable characteristics.
  • Creates new varieties of organisms and increases the yield of animals and plants.
  • With selective breeding, humans choose desirable traits but with natural selection, the environment chooses the desirable traits.
  • Peppered moths are an example of natural selection.
  • Dalmations are an example of selective breeding.
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  • Combined effects of mutations, natural selection, environmental changes and isolation can all lead to the formation of new species.
  • Jean-Baptiste Lamarck proposed that the environment changed an organism and the organisms passed on the characteristic to their offspring (evolution through inheritance of acquired characteristics)
  • Charles Darwin collected data and made the connection between varieties, competition, the survival of the fittest and the passing on of desirable features to the next generation.
  • This fitted with available evidence at the time and it fits with our modern understanding of genetics today but, there was not any evidence or scientific mechanism for Lamarck's ideas.
  • The scientific community accepted Darwin's ideas over Lamarck's after repeating his experiments and peer reviewing his work.
  • Today it is accepted that all life on Earth arose through the process of evolution through natural selection.
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Biodiversity and Classification

  • Biodiversity refers to the variety of life on Earth and can be measured by the number of different species present in an area, the range of different types of organism and the genetic variation within a species.
  • The greater these are, the greater the biodiversity.
  • Enables ecosystems and the species within them to survive natural disasters.
  • It is important for humans because we rely on crops to feed a growing population.
  • Plants are also the source of compounds that are effective against disease and genetic disorders which could potentially be used in medicines.
  • If ecosystems are destroyed and biodiversity is reduced, some drugs and food may be lost for future generations.
  • All life on Earth can be divided into groups based on similarities and differences in their physical features and in their DNA.
  • Groups start off large with high numbers of organisms with a few features in common and reduce in size as they are sub-divided into much smaller groups containin organisms with similar features.
  • Classifying both living and fossil organisms can help make sense of the enormous biodiversity on Earth and to show the evolutionary relationships between organisms.
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  • Throughout history of the Earth, species of animals and plants have become extinct.
  • The rate of extinctions on Earth has been increasing due to human activity which can be direct or indirect.
  • Direct causes - Excessive hunting of animals, removal of habitats to extract resources or for building.
  • Indirect causes - Introducing predators to new locations, activities causing global- human activity indirectly change environmental conditions, trying to eradicate a pest - this can have a knock-on effect on other members of a food web.
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  • About meeting the needs of people today without damaging the Earth for future generations.
  • In the past, farmers grew a variety of different crops and separated the different parts of the farm with hedgerows but, in the 20th century it changed and giant fields made from earlier fields joined together were planted with monocultures (a single variety of crop).
  • Intensive farming maximises amount of food available for population but, it reduces biodiversity.
  • Intensive farming is not sustainable because it does not maintain biodiversity.
  • To ensure all people have food, scientists need to work out new ways of optimising intensive farming while maximising sustainability.
  • Most products in industrialised world rely on oil and products made from it so to improve sustainability, alternatives need to be found.
  • Manufacturers need to consider what materials are used, how much energy is needed in the process for packaging material and the amount of pollution produced as a result.
  • Crude oil takes millions of years to form and plastic made from it will not biodegrade so using oil is unsustainable as it cannot be remade.
  • Sustainable alternatives would be packaging made from paper or cellulose-based plastics as the plants can be replanted.
  • When packaging gets to landfill sites, there'll be slow decomposition as there is a lack of oxygen
  • Manufacturing and transporting packaging also use up energy and produce pollution.
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