AQA A Level Biology复习笔记4.4.5 Environmental Adaption

• Environmental factors that affect the chance of survival of an organism are selection pressures
  • For example, there could be high competition for food between lions if there is not plentiful prey available; this environmental factor ‘selects’ for faster, more powerful lions that are better hunters

   

• These selection pressures can have different effects on the allele frequencies of a population through natural selection
• Certain alleles within a species population can produce features that make an organism better suited to its environment - adaptations
• When new alleles of genes result from mutation there is the potential for relatively rapid change in a species if their environment changes
• For example, a favourable allele in the lion population could result in a higher proportion of fast-twitch muscle fibres in their legs, which is advantageous for sprinting after prey
• Natural selection will select for favourable alleles that produce adaptations
  • The lions with the advantageous alleles are more likely to catch prey and survive
  • These lions will produce more offspring
  • The allele frequency will increase in the population
  • The resulting adaptation will become more common in the population
  • The species will be better suited to their environment

   

• Natural selection will select against unfavourable alleles
  • The slower lions that have the unfavourable allele are less likely to catch prey and survive
  • These lions will produce less offspring
  • The allele frequency will decrease in the population
  • The species will be better suited to their environment

   

• This means that over time natural selection will cause favourable allele frequencies to increase and unfavourable allele frequencies to decrease, making the species better adapted to their environment

Types of Adaptations

• Adaptations enable organisms to survive in the conditions in which they normally live
• An adaptation can be anatomical, physiological and behavioural
• Anatomical adaptations
  • Structural/physical feature
  • Example: The white fur of a polar bear provides camouflage in the snow so it has less chance of being detected by prey

   

• Physiological adaptations
  • Biological processes within the organism
  • Example: Mosquitos produce chemicals that stop the animal’s blood clotting when they bite, so that they can feed more easily

   

• Behavioural adaptations
  • The way an organism behaves
  • Example: Cold-blooded reptiles bask in the sun to absorb heat

   

• Adaptation and selection contribute to the large diversity of living organisms and are major factors in the process of evolution
• Evolution is the change in adaptive features of a population over time as a result of natural selection
• If an environment is static and does not change, then selection pressures will not change and evolution will not occur
• If the environment changes or a chance mutation produces a new allele, selection pressures may favour individuals with different characteristics or with the new allele
• Natural selection results in a process of adaptation, which means that, over generations, those features that are better adapted to the environment become more common
• This means whole populations of organisms become better suited to their environment
• If two populations of one species are isolated from each other and become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species
• The formation of new species (speciation) from pre-existing species over time, is a result of accumulated genetic differences
• Evolution drives speciation and so is responsible for the large number of species that exist on earth