Variation and Selection

• Describe the development of antibiotic resistant bacteria. When antibiotics are used, certain strains of bacteria die, however, antibiotic resistant strains do not. With prolonged or inconsistent use of antibiotics, the population of antibiotic resistant bacteria e.g. MRSA increases exponentially to an extent such that the antibiotic is rendered ineffective.
• State two purposes of selective breeding, with specific examples.

  Selective breeding is used to produce animals and plants with higher economic value.

  For example, it can be used to produce crops that are disease resistant, or to produce domesticated dogs that are docile.
• Describe selective breeding. (3 references)

  In selective breeding, organisms withe desirable features and from the same species are selected by a human. Then, they are cross-bred to produce a new generation.

  The offspring from the new generation that exhibit the same desirable traits are cross-bred together, and the process is repeated until the desirable features are exhibited consistently.
• Describe the disadvantages of artificial selection.

  Artificial selection produces offspring with less gentic variation than their parents, thereby increasing their susceptibility to disease and reducing their ability to adapt to changes in the environment. Useful genes may be lost permanently during artificial selection.
• Describe the differences between natural and artificial selection.

  Firstly, natural selection results in adaptations that increase the ability of an organisms to survive and reproduce, whereas artificial selection results in adaptations that are desirable from a human perspective.

  
  

  Secondly, natural selection occurs naturally, but artificial selection involves human intervention and selective breeding.

  
  

  Finally, Artificial selection creates genetic changes more rapidly than natural selection.
• Describe natural selection.


  In natural selection, genetic variation occurs and many offspring are produced.

  The offspring then compete for resources e.g. food, mates.

  Amongst the offspring, the ones which are more adapted to their environment have a higher survival rate and reproduce more as a result.

  Over time, the population of better adapted, fitter individuals outnumbers that of the less adapted and there is a change in the population.
• Define evolution.

  Evolution is the change in adaptations of organisms over time as a result of natural selection.
• Describe adaptation.


  Adaptation is a process, resulting from natural selection, whereby organisms become more suited for their environment.
• Explain the adaptive features of xerophytes to their environment.

  Xerophytes are adapted to live in dry regions with minimal water.

  
  

  Their leaves are reduced to spines or are small, so as to minimise water loss through transpiration.

  During the day, the stomata of xerophytes remain closed to prevent excessive water loss.

  The waxy cuticle also prevents excessive water loss.

  Extensive roots maximise water absorption.
• Explain the adaptive features of hydrophytes to their environment. (4)

  Hydrophytes are adapted to live in or around water.

  
  

  They have short roots as their stems and leaves are able to absorb water.

  Their stomata are mostly on the upperside of their leaves, thereby increasing the efficiency of gas exchange.

  The water provides their broad leaves with buoyancy, which causes the leaves to absorb sunlight more efficiently as they float closer to its surface.
• Describe an adaptive feature.

  An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment
• State four sources of genetic variation in populations.

  Random mating

  Random fertilisation

  Mutations

  Meiosis
• State two factors that increase the rate of mutation.

  Ionising radiation e.g. Ultraviolet radiation

  Chemicals e.g. tar from tobacco
• State the cause of discontinuous variation.

  Discontinuous variation is caused solely by genes.
• State the results of discontinuous variation, and give examples of discontinuous variation.


  Discontinuous variation results in a distinict, limited range of phenotypes, with no intermediates. Examples include blood type, ability to roll the tongue, and sex.
• State the results of continuous variation, and give examples of continuous variation.

  Continuous variation results in a range of phenotypes between two extremes. Examples include body length and body mass.
• Describe variation.

  Variation is the visible differences between individuals of the same species.
• Define a gene mutation.

  A permanent change in the sequence of bases of DNA.
• Define mutation.

  A mutation is a spontaneous genetic change resulting in the formation of new alleles.
• Natural selection involves three key components: variation, inheritance, and environmental change.
• Variations are differences between individuals within a population that can be passed on to their offspring through reproduction.
• Environmental changes refer to factors such as climate, food availability, predators, and competition that affect an organism's ability to survive and reproduce.
• The process of natural selection occurs when some members of a population have traits that allow them to better adapt to changing conditions than others.
• The process of natural selection occurs when some members of a population have characteristics that make them better adapted to their environment than others.