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B3 -INTERDEPENDENCE. Classification. Use of similarities and differences between living things on earth in order to group them separately . Species. A group of organisms that can breed together to produce fertile offspring. Adaptations.

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Use of similarities and differences between living things on earth in order to group them separately


A group of organisms that can breed together to produce fertile offspring

  • Features that help an organism survive in the environment it lives in
  • These increase survival chances of an organism and therefore increase the chance of it successfully reproducing.
  • Change in environment – organisms not so adapted and therefore affects survival rate.
  • If poorly adapted to environment - less likely to survive and reproduce than those who are. Also possible for them to become extinct.


food web
Food web
  • A number of food chains joined together and shows how the importance of each organism for the survival of the rest – interdependence of living things.
  • Fossil records show many species have become extinct since the beginning of life on earth.
  • Still occurring mainly due to human activity
  • Northern elephant seals as a result of direct activity of humans.
extinction factors
Extinction Factors
  • Sudden environmental changes
  • Diseases
  • Predators (when one food source disappears, predator must find new one to survive)
  • New competitors
indirect activity of humans
Indirect activity of humans
  • Caused dodo extinction
  • Lived in uninhabited islands with no natural predators then colonised by the Dutch who hunted them for food as they were easy to catch due to them being flightless and large.
  • Also brought new competitors to the island (dogs, cats) which ate their eggs.
the sun
The Sun
  • Most organisms dependant on energy from the sun
  • Plants use photosynthesis as a process of harnessing light energy to convert carbon dioxide into glucose .
energy transfer
Energy Transfer
  • Animals don’t make their own food so energy transferred between organisms and used for a number of life processes.
  • 10% passed on – rest passes out of food chain through;

- heat energy

- life processes like movement

- uneaten parts passed to decomposers

  • Less energy transferred at each level therefore number of organisms decrease

Producers to primary consumers efficiency:

4,500kJ + 500kJ = 5,000kJ

500kJ ÷ 5,000kJ) X 100 = 10%

carbon cycle
Carbon cycle
  • All cells contain carbon as they all contain fats, carbohydrates and proteins.
  • Passed from atmosphere as carbon dioxide to living things then to different organisms then returns to atmosphere.
  • Photosynthesis by green plants and carbon becomes part of their complex molecules
  • Animals eat plants and carbon as part of their proteins and fats and when they die microorganisms feed on waste material and carbon becomes part of them
  • Carbon dioxide returns to atmosphere – respiration (plants, micro organisms and animals)
  • http://www.youtube.com/watch?v=a6n54IlhDM8
  • Living things decay as digested by microorganisms
  • Happens faster in warm, moist conditions and plenty of oxygen – otherwise slow
nitrogen cycle
Nitrogen cycle
  • Need nitrogen to make proteins and not get directly from air as gas unreactive.
  • Plants take it up as compounds (nitrates and ammonium salts) from soil.
nitrogen fixation
Nitrogen fixation
  • Making nitrogen compounds from air.
  • Happens in;

1. Energy in lightening splits nitrogen molecules into separate atoms which react with oxygen to form Nitrogen Oxides. These then washed to ground by rain to form nitrates in soil.

2. Nitrogen fixing bacteria (in soil and some plants) fix the gas into compounds.

3. Haber process by industry to produce ammonia (which is then used to make compounds used as fertilisers) from N & H.

nitrogen compounds
Nitrogen compounds
  • In living things –returned to soil through excretion and egestion by animals and decay of dead plants and animals
  • Denitrifying bacteria in soil break down the compounds and release gas into air.
  • Know Earth is 4500 million years old and evidence living things existed 3500 million years ago
  • Earth was hotter and atmosphere consisted of mostly carbon dioxide
  • Main theory: living things developed from molecules that could replicate and originate from either conditions of earth at that time or from somewhere else (another planet)
  • Over millions of years molecules joined together with other molecules and became more complex and dependant on each other
  • Evolution by natural selection lead to life on earth today
darwin s theory
Darwin’s theory
  • All different species evolved from simple life forms which first developed 3 billion years ago
  • Evolution happens by natural selection ;

- individuals show wide range of variation due to differences in genes

- those with characteristics most suited to environment will survive and reproduce and genes passed on

  • Those poorly adapted less likely therefore genes not passed on and species gradually evolve.
  • Although variation caused by genes and environment, only genetic can be passed on.
selective breeding
Selective breeding
  • Only occurs when humans intervene – different to natural selection
  • Choose desired characteristics then breed them together and form offspring – repeated over many generations
  • Used by farmers to increase cattle milk yield and larger chicken eggs..etc
  • Changes that occur in genes at random and sometimes severe so cells die or divide uncontrollably and become cancerous but changes very rarely useful
  • Caused by e.g. background radiation and chemicals
  • In normal body cells – die and in sex cells (sperm and ova) possibility genes passed on.
  • When passed on – natural selection ensure selection if useful or disappear from gene pool if not
  • Combined effect of mutations, environmental changes and natural selection sometimes produces great changes causing new species but rare as only happens when mutated no longer breed with original.
developing explanations
Developing explanations
  • Lamarck another scientist developed alternative theory involving;

- law of use and disuse

- law of inheritance of acquired characteristics

  • Characteristics used more by organism becomes bigger and stronger and those not useful disappear and only improved features passed to offspring.
  • Doesn’t account for all organisms as “simple ones disappear”
  • Fossil records – show how much organisms changed over time.
  • Problem: contains gaps and not all organisms fossilise well. Also many destroyed by Earth movements or not yet discovered.
  • E.g. moths during industrial revolution – most pale birch trees then black with soot so black camouflaged. Resistant bacteria.
  • Scientists use DNA to see how closely two species related and eventually how evolved. Found DNA supports evolution theory.
  • Organisms classified into different groups according to characteristics, similarities and differences including physical features and DNA.
  • Into large group like kingdom with little in common or small group with more like species.
  • Having a wide range of different species
  • Maintaining important for sustainability of the environment e.g. cutting down trees
  • Monoculture (continuous production of one type of crop often genetically identical) disadvantages:

- chemical pesticides used in large amounts to prevent pests harming it. Harms environment therefore not sustainable.

- whole crop wiped out in case of natural disaster

improving sustainability
Improving sustainability
  • Recycle packaging
  • Using biodegradable packaging – decomposes quickly in landfill sites. However, oxygen presence required for decomposition to produce carbon dioxide only but this not the case in landfills causing production of methane greenhouse gas