BIOLOGY 2 pt 2

BIOLOGY 2 pt 2

1. NATURAL SELECTION

   • CHARLES DARWIN'S THEORY OF NATURAL SELECTION
     • He knew that organisms in a species show wide variation & that organisms have to compete for limited resources in an ecosystem
       • He concluded that the organisms that are the best adapted would be more successful competitors and would be more likely to survive - SURVIVAL OF THE FITTEST
         • The successful organisms that survive are more likely to reproduce and pass on the adaptations to their offspring
           • The organisms that are less well adapted would be less likely to survive and reproduce, so they are less likely to pass on their characteristics to the next generation
             • Over time, successful adaptations become more common in the population and the species evolves
     • The theory wasn't perfect - there was no explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring
       • DNA wasn't discovered until 50 years after his theory was published
       • We now know that adaptations are controlled by genes & new adaptations arise because of mutations.
         • Successful adaptations are passed on to future generations in the genes that parents contribute to their offspring
     • DARWIN'S THEORY WAS CONTROVERSIAL:
       • It went against common religious beliefs about how life on Earth developed - it was the first plausible explanation for our own existence without the need for a Creator - he was ridiculed by religious leaders
       • He couldn't explain why new, useful characteristics appeared or how they were inherited
       • There wasn't enough evidence to convince many scientists, because not many other studies had been done into how organisms change over time
       • It is now widely accepted because: it has been debated&tested and there is no conclusive evidence to disprove it. The theory offers a plausible explanations for so many observations of plants and animals
   • LAMARCK'S CONFLICTING THEORY OF EVOLUTION
     • He argued that if a characteristic was used a lot by an animal then it would become more developed. He thought that these ACQUIRED CHARACTERISTICS could be passed on to the animal's offspring
       • EG if a rabbit did a lot of running and developed big leg muscles, Lamarck thought that the animal's offspring would also have big leg muscles
         • The theory was rejected because people eventually concluded that acquired characteristics don't have a genetic basis - so they're unable to be passed on
   • SPECIATION: THE DEVELOPMENT OF A NEW SPECIES
     • Over a long period of time, organisms may change so much because of natural selection that a completely new one is formed
     • Happens when populations of the same species change enough to become reproductively isolated - they can't interbreed to produce fertile offspring
       • Reproductive isolation can be caused by geographic isolation
         • A physical barrier divides a population of species (eg the river changes its course) & the 2 populations are unable to mix
           • Different mutations create new features in the 2 groups & natural selection works on the new features so that, if they are of benefit, they spread through each of the populations
             • Since conditions on each side of the barrier will be slightly different, the features that are beneficial will be different for each population
               • Eventually, individuals from the two populations will have such different features that they won't be able to breed together to produce fertile offspring. They'll have become reproductively isolated and the 2 groups will be separate species

2. POPULATION AND POLLUTION

   • Human population is increasing very quickly
     • This happens when birth rate > death rate
     • Puts pressure on environment - more resources are being used up & more pollution being produced
     • Higher standard of living in MEDCs demands more resources
       • MEDCs have a smaller proportion of population but cause a large proportion of pollution
   • Increasing amounts of pollution are causing:
     • GLOBAL WARMING
       • Burning of fossil fuels releases lots of CO2 - a greenhouse gas. Greenhouse gases trap heat in the atmosphere which causes global temperature to rise = global warming
       • Scientists have predicted that, if global temperature continues to go up, sea level will rise, weather systems will become less predictable and agricultural output will fall
       • Lots of people, companies & countries are measuring the amount of greenhouse gases they're giving off, so they can reduce their emissions.- carbon footprint = the amount of greenhouse gases given off in a certain period of time
     • ACID RAIN
       • When fossil fuels and waste materials are burned they release SULFUR DIOXIDE
         • Sulfur dioxide reacts with water in the atmosphere to form sulfuric acid which falls as acid rain
           • Acid rain causes lakes to become more acidic, which has a severe effect on the lake's ecosystem.
             • Many organisms are sensitive to changes in pH and can't survive in more acidic conditions - many plants & animals die
             • Acid rain damages limestone; ruining buildings and stone statues
             • Acid rain damages soils and can kill trees
     • OZONE DEPLETION
       • CFCs used to be used in aerosols, fridges, air-con units, polystyrene foam
         • They break down ozone in the upper atmosphere, this allows more harmful UV rays to reach Earth's surface
         • Being exposed to more UV rays will increase the risk of skin cancer. Australia has a high rate of skin cancer because it is under an ozone hole
         • The increase in UV rays could kill plankton in the sea - this could have a massive effect on the sea ecosystem because plankton are at the bottom of the food chain. Scientists predict that fish levels will drop
   • INDICATOR SPECIES
     • LICHENS
       • Used to monitor air quality - they're damaged by pollution. The cleaner the air, the greater the diversity of lichens that survive
     • MAYFLY LARVAE
       • Used to measure water quality - they can't survive in polluted water. The cleaner the water, the more mayfly larvae that survive
     • WATER MICE, RAT-TAILED MAGGOTS, SLUDGEWORMS
       • Indicate polluted water. Rat-tailed maggots and sludgeworms indicate a very high level of pollution
   • Measuring pollution
     • Using indicator species
       • Survey: To see if a species was present of absent. This is a quick way of telling whether an area is polluted or not - but not HOW polluted
       • Counting the number of times an indicator species occurs in an area gives a numerical value, allowing measurements from different areas to be compared so you can see how polluted it is
       • Advantages
         • Quick, cheap, easy - no expensive equipment or highly trained workers needed
       • Disadvantages
         • Factors other than pollution (eg temp) can influence the survival of indicator species - not always reliable
     • Non-living methods
       • Sensitive instruments can measure the concentrations of chemical pollutants eg CO2 or SO2 in samples of air or water
       • Satellite data can be used: satellites can show where the ozone is thin or absent, which is linked to CFC level
       • Advantages
         • Reliable, numerical data that is easy to compare & exact pollutants can be identified
       • Disadvantages
         • More expensive equipment & trained workers

3. SUSTAINABILITY

   • ENDANGERED SPECIES
     • Species become extinct if certain factors fall below critical level:
       • Number of habitats:
         • it's hard for organisms to find resources like food and shelter if there aren't enough suitable habitats to support them
       • Number of individuals
         • if there are only a few individual members of a species left, it'll be hard to find mates * there won't be much genetic variation in the population
       • Genetic variation
         • the number of different alleles in a population. If genetic variation is low, then a species is less likely to be able to adapt to changes in the environment or survive the appearance of a new disease
     • EVALUATING CONSERVATION PROGRAMMES
       • Genetic variation
         • the species should have enough variation to survive the appearance of new diseases and cope with environmental changes
       • Viability of populations
         • Populations should be able to reproduce so must contain males and females of reproductive age. They should be large enough to prevent related individuals breeding together
       • Available habitats
         • There should be plenty of suitable habitats to live in - v. important if organisms are specialists
       • Interaction between species
         • important that species interact like they would in a natural habitat, eg: predator hunting prey
     • BENEFITS OF CONSERVATION PROGRAMMES
       • help humans&wildlife
       • Protecting human food supply
         • Over-fishing has reduced fish stocks, conservation ensures that future generations have fish
       • Minimal damage to food chains
         • if one species becomes extinct it will affect all the organisms around it in the food chain - whole food chain is affected
       • Providing future medicines
         • many new medicines come from plants. Undiscovered plant species may contain new medicinal chemicals. If they became extinct (rainforest destruction) we could miss out on medicines
       • Cultural aspects
         • individual species may be important in a nation's or area's heritage, eg the Bald Eagle in the USA is being conserved as it is regarded as a national symbol