AQA Module 4 Revision Notes PDF

Module 4 (Diversity) Revision Notes What is Biodiversity?  variety in an ecosystem  variety of habitats and variety of species What is Species Diversity?  number of different species  number of individuals for each species What is Genetic Diversity?...

Module 4 (Diversity) Revision Notes What is Biodiversity?  variety in an ecosystem  variety of habitats and variety of species What is Species Diversity?  number of different species  number of individuals for each species What is Genetic Diversity?  variety of alleles in a species population  the larger number of individuals in a species, the larger the genetic diversity Benefit of high species diversity?  Stable ecosystem  each species is less likely to become extinct (due to high genetic diversity)  & if a species does become extinct it will not affect the food chain as there are other species available How to measure Species Diversity for an area?  Species Diversity Index  takes into account the number of different species and how many individuals there are for each species  the larger the species diversity index, the larger the species diversity How does deforestation lower species diversity?  (deforestation is the removal of trees for wood & space)  decreases plant species diversity  less variety of habitats  less variety of food sources  decreases animal species diversity How does agriculture/farming lower species diversity?  deforestation to make space for farm  only grow a few plants & keep a few animal species  selectively breed plants & animals  use pesticides to kill other species What is Classification? placing organisms into groups What is Hierarchical Classification?  large groups divided into smaller groups with no overlap  domain, kingdom, phylum, class, order, family, genus, species What is Binomial Naming System?  using Genus name and Species name to name organism  Genus name first in capital, Species name second in lower case  e.g. tiger = Felix tigris What is a Species? a group of individuals with similar characteristics that can interbreed to produce fertile offspring Why are the offspring from 2 different species mating infertile?  offspring will have a odd number of chromosomes  therefore, cannot perform meiosis, cannot produce gametes  example: horse + donkey = mule, mule is infertile, horse has 64 chromosomes/donkey has 62 chromosomes, horse gamete has 32 chromosomes/donkey gamete has 31 chromosomes, therefore, mule has 63 chromosomes What is Phylogenetic Classification? based on evolutionary relationships – how closely related different species are and how recent a common ancestor they have 3 ways of comparing relationship between different species? DNA Hybridisation: comparing DNA base sequence - take DNA from 2 species to be compared - radioactively label one of the DNA - heat both sets so double strand separates - cool so single strands join together - look for Hybrid DNA (one strand from species A, one strand from species B) - identify Hybrid DNA by 50% radioactivity - heat Hybrid DNA to measure similarity results = higher temperature required more hydrogen bonds present more complementary base pairing more similar the base sequence  more similar the species more closely related more recent a common ancestor AA Sequence: comparing AA sequence for the same protein (e.g. haemoglobin in mammals) results = more similar the AA sequence more similar the DNA base sequence more similar the species more closely related more recent a common ancestor (comparing DNA sequence better then comparing AA sequence: DNA sequence provides information on INTRONS and triplet code is DEGENERATE) Protein Shape: comparing shape of the same protein (e.g. albumin) using immunological technique - comparing species A and species B - take albumin from species A - place in a blood of rabbit - rabbit will make antibodies against albumin of species A - takes these antibodies and place in blood from species B - if the albumin in species B has a similar shape to species A, the antibodies will bind to form antigen-antibody complexes, this will then form a precipitate results = more precipitate more complexes more similar shape more similar the species more closely related more common recent ancestor What is Variation? difference in characteristics between organisms Types of Variation? intraspecific = differences between organisms of the same species interspecific = differences between organisms of different species Causes of Intraspecific Variation? Genetic Factors = same genes but different alleles (allele are different type/forms of genes) Environmental Factors Causes of Interspecific Variation? Genetic Factors = different genes and different alleles  Environmental Factors Types of Characteristics? Discontinuous and Continuous Properties of Discontinuous Characteristics? characteristics fall into certain groups with no overlap (e.g. blood group) – determined by genetics only (a single gene) Properties of Continuous Characteristics? characteristics show a range (e.g. height) – determined by genetics (a few genes, polygenes) and environment What is Genetic Diversity? genetic variation, the variety of alleles within a population of a species Benefit of high genetic diversity? species able to adapt with changes in the environment e.g. if a new disease arises, some individuals will have characteristics to survive, and will reproduce passing on their alleles, so the species does not become extinct What can lower genetic diversity? small population size (e.g. founder effect – where the numbers start low, or genetic bottleneck – where the numbers decrease) What is natural selection and adaptation?  variation in population of species (genetic diversity/genetic variation/variety in gene pool)  new alleles arise by random mutation  environment applies a selection pressure on the population  those with favourable characteristics/favourable alleles/selection advantage/better adapted survive, the others die [natural selection]  the ones that survive will reproduce, passing on their favourable alleles  if this happens for many generations, then that characteristic will become most common – the allele will become more frequent [adaptation] What are the 2 types of selection? stabilising and directional What is stabilising selection?  when the environment favours those with the most common characteristic – those on the extreme dies out  the common characteristic increases in proportion  the range (standard deviation) will reduce What is directional selection?  when the environment favours those individuals with characteristics on one of the extremes  over time this will become the most common characteristic   normal distribution will shift to that extreme What is a Gene?  a section of DNA that codes for a protein  made out of intron and exon  intron = non-coding DNA (function e.g. turns gene on or off)  exon = coding DNA (codes for protein) How does a Gene/Exon code for a Protein?  made out of a sequence of bases  each 3 bases code for 1 amino acid (called triplet code)  therefore,  sequence of bases  determines sequence of triplet codes  which determine the sequence of AAs  = polypeptide chain/primary structure (folds to secondary, then to tertiary/quaternary) Properties of triplet code?  degenerate = each AA has more than one triplet code  non-overlapping = each base is read only once  stop codes = occur at end of sequence – do not code for an AA How does a mutation lead to a non-functional enzyme?  change in base sequence  change in sequence of triplet codes  change in sequence of AAs  change in primary structure  change in hydrogen/ionic/disulfide bonds  change in tertiary structure (3D shape)  change in active site shape  substrate no longer complementary  can no longer form enzyme-substrate complex How is a protein assembled? by transcription and translation transcription = production of a single stranded complementary copy of a gene (called mRNA)  translation = use sequence of codons on mRNA to assemble protein (tRNA brings in AAs) DNA vs RNA?   deoxyribose sugar vs ribose sugar  thymine vs uracil  double stranded vs single stranded  one type vs two types (mRNA and tRNA) What is mRNA?  messenger RNA  single stranded complementary copy of a gene  carries the code for assembling protein (on DNA called triplet code, on mRNA called codon) What is tRNA?  transfer RNA  single stranded RNA folded over into a 'clover leaf' shape (held by hydrogen bonds between the bases)  has an AA attachment site on the top  has 3 specific bases on the bottom (anticodon)  anticodon binds to complementary codons on mRNA What is Transciption?  occurs in nucleolus of nucleus  producing a single stranded complementary copy of a gene (called mRNA)  DNA is double stranded, 1 strand called coding strand & 1 strand called template strand, the template strand will be used to build mRNA  process,  DNA Helicase breaks the hydrogen bonds between complementary bases in the gene  the double strand of the gene unwinds  leaves 2 separate strands (1 coding strand and 1 template strand)  complementary RNA nucleotides bind to exposed bases on the template strand  RNA Polymerase joins the sugar-phosphate backbone of the RNA strand  leaves pre-mRNA (contains introns and exons)  the copies of the introns are removed by splicing  leaves mRNA What is Translation?  takes place on ribosomes of Rough Endoplasmic Reticulum  uses the sequence of codons on the mRNA to assemble the protein (tRNA brings in AAs)  process,  mRNA leaves nucleus via nuclear pore  mRNA attaches to a ribosome  complementary tRNA carrying specific AAs bind to the codons on mRNA via their anticodon  the AAs on the tRNA are joined by peptide bonds What does Meiosis produce? 4 genetically different cells, haploid (half the amount of chromosome/DNA) Benefits of Meiosis? produces gametes which will be used in sexual reproduction in animals & plants (2 gametes fuse to form a zygote, zygote develops into organisms) Stages of Meiosis? Interphase/Meiosis I/Meiosis II/Cytokinesis Interphase? G1: protein synthesis S: DNA replication (doubles set of DNA) G2: organelle synthesis Meiosis I? Prophase I: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form, crossing over occurs Metaphase I: homologous pair of chromosomes line up in middle of cell and attach to spindle fibre via centromere Anaphase I: spindle fibres pull, homologous pair of chromosomes separate to opposite sides by independent assortment Telophase I: chromosomes uncoil, nucleus reforms (left with 2 nuclei) Meiosis II? Prophase II: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form Metaphase II: chromosomes line up in middle of cell and attach to spindle fibre via centromere Anaphase II: spindle fibres pull, centromere splits, sister chromatids move to opposite sides by independent assortment Telophase II: chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei) Cytokinesis? separating cell into 4 (each receives a nucleus and organelles/cytoplasm) How does Meiosis produce Variation? Crossing Over and Independent Assortment What is crossing over? occurs in Prophase I of Meiosis I homologous pairs of chromosomes wrap around each other and swap equivalent sections of chromatids – produces new combination of alleles What is independent assortment? - in Anaphase I of Meiosis I – the homologous pairs of chromosomes separate - in Anaphase II of Meiosis II – the chromatids separate - independent assortment produces a mix of alleles from paternal and maternal chromosomes in gamete What happens to DNA mass in meiosis? quarters What happens to Chromosome number in meiosis? halves (haploid) What is Mutation?  Change in DNA  2 types: Chromosome Mutation and Gene Mutation What causes mutation? random or due to mutagens (e.g. chemicals, radiation) What is a Chromosome Mutation?  In plants, inherit more than one diploid set of chromosomes – called polyploidy  In animals, homologous pair of chromosome do not separate in meiosis, so either inherit one extra or one less chromosome – called non-disjunction What is a Gene Mutation?  a change in the base sequence of DNA  2 types = substitution and insertion/deletion  substitution = replace one base for another, changes one triplet code can be silent (new triplet code codes for same AA), mis-sense (codes for a different AA, so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain not produced)  insertion = adding a base, deletion = removing a base both insertion/deletion causes frameshift, all the triplet codes after the mutation changes, so normal polypeptide chain/protein not produced