Biodiversity 12

• biodiversity


  a general term used to describe the variety of living organisms in a community/habitat. It includes species diversity and genetic diversity
• habitat


  place where an organism lives. Better to describe the habitat of a population of species
• community


  all the organisms (of different species) in a habitat
• species diversity


  measure of how many different species are present in an area and how many individuals of these species there are

  species richness is counting the number of different species in a habitat
• species diversity index


  it reflects

  • the number of different species present
  • the number of individuals in each species

  formula: D= N(N-1)/ sum of n(n-1)

  d= diversity index

  N= total number of organisms of all species

  n= total number of organisms of a particular species
• higher the value of D, the higher the diversity
• why is it more useful to calculate the diversity index rather than just record the number of species present?

  it measures the number of individuals in each species as well as the number of species and takes into account that some species may be present in very low or high numbers (under/over represented)
• what does a high value of d indicate about a habitat?

  the environment has favourable conditions e.g. tropical rainforest, temperate woodland.

  • many species present and populations are usually large
  • generally biotic factors such as competition and predation determine which species are present
  • ecosystems in these environments are usually stable
  • complex food webs so a change in population of one species is less likely to affect other populations.
• a low value of d indicates what?


  unfavourable/harsh environment (desert, Arctic, tundra, upper seashore)

  • few species present and often populations are small
  • generally abiotic factors determine which species are present
  • ecosystems in these environments are usually unstable
  • only a few species are adapted to survive in these conditions.
• why do we sample a community to calculate the species diversity index?

  it's impossible to identify and count all the individuals organisms in an area as this would be too time consuming and is likely to cause a lot of damage to the community. By sampling we aim to collect data which is representative of the community as a whole.
• 3 ways organisms may be distributed in an area

  random

  regular

  clumped
• which is the only unbiased method?

  random

  prevents researcher choosing areas where the plants are easy to get or are more obvious. Regular is also biased.
• Method for random sampling

  • a grid is laid out across the sample area using tape measures
  • a random numbers are generated (e.g. from a calculator or random number table) to provide coordinates on the grid. These are the sample points where a frame quadrat is placed
  • within each quadrat the community is sampled, in this case each organism in the quadrat is identified and the number of each species is counted
  • as any one sample point is unlikely to be representative of the area, a large number of randomly placed quadrats are used
• How many quadrats are needed to give a representative sample?

  at least 20

  or 10% of the area
• monoculture


  the growth of one crop species
• How does agriculture provide ideal conditions for crop photosynthesis and growth?

  • irrigation
  • fertilisers- NPK
  • crop species themselves are specially selected to grow well in the conditions provided
  • weeds are prevented from growing on the land as they compete for resources with the crops.
  • pests which eat the crops are also similarily removed
  • removing hedgerows and field boundaries allows maximum use of land for crops and removes sources of pests and disease
• how are weeds and pests removed?

  • pesiticides
  • herbicides
  • physically picked out as they start to grow
• why will so few species exist and therefore species diveristy be so low in the fields?

  only one type of crop can grow so there is little food variety so fewer species of herbivores. So fewer species of carnivores, less insects due to use of pesticides. Fewer plant species. Lower variety of habitats and niches
• conservation techniques


  • plant hedges rather than erect fences as field boundaries
  • maintain ponds and create new ones
  • leave wet corners of fields rather than drain them
  • plant native tree species on land with a low species diversity
  • reduced use of pesticides- use biological control where possible or gmo crops resistant to pests
  • use organic fertilisers ( manure)
  • leave the cutting of verges and field edges until after flowering and when seeds have dispersed
  • introduce conservation headlands- areas at edge of fields where pesticides are used restrictively so that wild flowers and insects can breed
• advantages of planting hedgerows to the farmer

  hedges may be habitats for predators or pests and also habitats for pollinating species so increases crop yields
• disadvantages of planting hedgerows

  take up a lot of space

  also habitats for pests so may lead to an increase in pest populations and reduce crop yields

  crops will face increased competition for resources e.g. minerals, light, water so reduces crop yields
• define genetic diversity

  the number of different alleles of genes in a population
• define a gene

  a section of DNA which codes for a protein
• define an allele

  different version of a gene
• members of the same species have the same genes but because they have different alleles, they are said to be genetically diverse
• the gene pool

  the set number of alleles within any one species, the bigger the gene pool, the greater the variation within the species. The greater the genetic diversity the better the survival chances of that species. Genetic diversity creates variation within a population. Which specific alleles will increase in proportion over time and which will decrease is dependant on if they cause differential changes in survival and reproduction, allows natural selection
• causes of genetic diversity

  • mutations- only way asexually reproducing organisms show variation
  • meiosis
  • random fusion of gametes
• What does a mutation cause?

  a change in the amount or sequence of bases in the DNA of an organism, can cause a change in the characteristics and can be passed onto the cells produced by division of mutant cell

  can lead to production of non-functional protein

  sequence of DNA bases altered

  changes sequences of amino acids

  h bonds, ionic and disulphide form in different places so different tertiary structure so loss or reduction in function of protein.
• Mutations can arise spontaneously during DNA replication and include base substitution or base deletion. However, as the code is degenerate not all base substitutions cause a change in amino acid sequence. Mutagenic agents increase rate of gene mutation.
• meiosis

  occurs in formation of gametes (special sex cells) e.g. ovum, sperm, ovule and pollen grain. Cells are genetically different from each other so meiosis is a major cause of intraspecific variation
• key features of meiosis

  1. the DNA replicates itself once but there are 2 nuclear divisions, not one as in mitosis, so 4 daughter cells are formed from each cell not 2
  2. the daughter cells have half the number of chromosomes found in a normal body cell. Called the haploid number
  3. when the male and female gametes join together at fertilisation, the diploid number is restored, therefore meiosis ensures that the chromosome number is kept constant from one generation to the next
• haploid number in humans

  23
• diploid number

  46- total number of chromosomes found in a body cell
• Meiosis I- homologous pairs separate and the cell becomes haploid

  Meiosis II- centromere breaks and chromatids separate

  parent cell= diploid, daughter cells= haploid
• meiosis diagram

  
• chromosome non-disjunction

  sometimes homologous chromosomes don't separate properly during meiosis and both chromosomes of a pair go into the same cell. As a consequence, after fertilisation zygotes can end up with an extra copy of particular chromosome. Down's syndrome is caused by having an extra chromosome 21
• independent segregation of homologous chromosomes


  one way meiosis provides opportunities for new combinations of alleles

  unlike mitosis, in the 1st division of meiosis the pairs of homologous chromosomes pair up at the start of the process. When the pairs of homologous chromosomes line up along the equator of the spindle, their orientation is completely random. Subsequent separation of these pairs results in different combos of maternal and paternal chromosomes in gametes formed
• if an organism has 'n' pairs of chromosomes, it has 2 to power of n combinations


  so a cell with 2 pairs of chromosomes has 2 to the power of 2 = 4 different combinations
• Crossing over


  Occurs before independent segregation
• Homologous pairs of chromosomes

  • Associate at the start of meiosis (prophase I)
  • Form a bivalent
  • One chromatid of each homologous chromosome becomes wrapped around each other at points called chiasmata