ECOLOGY ESSAY QS

• Briefly explain the theory of evolution by natural selection.

  • parents produce more offspring than survive

  • there is competition among members of a species for survival

  • species show variation in phenotypes

  • certain variations will give a selective advantage/survival of the fittest

  • depending on environment

  • these variations will be passed on to the next generation

  • leading to change in allele frequency of population
• Outline four types of evidence which support the theory of evolution by natural selection.

  • fossils : fossilized horse ancestors show resemblance

  • homologous structures: pentadactyl limb

  ◦ ring species/other evidence from geographical distribution

  • recent observed evolution

  ◦ resistance to antibiotics/insecticides
• Outline one modern example of observed evolution by natural selection.

  example

  • beaks of Galapagos finches (example of adaptive radiation)

  • competition for food caused selective pressure

  • change in numbers/proportion of birds with different-sized beaks
• Explain the evidence from homologous anatomical structures that supports the theory of evolution.

  • homologous structures are similar structures in different species

  • derived from a similar embryonic origin

  • variations on the basic structure allow different functions

  • permitting the exploitation of different ways of life/adaptive radiation

  • the suggests divergence from a common ancestor

  • named example of a homologous structure (e.g. pentadactyl limb, flower, birds beaks)
• Outline how antibiotic resistance in bacteria can arise in response to environmental change

  • antibiotic resistance can be inherited or alleles for resistance can be passed from one cell to another by exchange of plasmids.

  • some varieties are more resistant than others;

  • bacteria reproduce very rapidly and have high mutation rate;

  • evolution can occur rapidly;

  • increased exposure to antibiotics is the environmental change that selects for resistant varieties;

  • resistant bacteria survive and pass on genes to next generation;

  • results in change in genetic makeup of population;
• Antibiotic resistance in bacteria is an example of evolution in response to environmental change. Using an example, explain how an environmental change can lead to evolution.

  • great tit;

  • bird that lays its eggs in spring;

  • global warming/climate change;

  • more caterpillars (on trees) in early spring;

  • laying eggs earlier in spring;

  • time of egg laying is (partly) genetically controlled;

  • eggs laid early hatch at start of period of greatest food abundance;

  • more young can be fed/young grow faster/fewer deaths;
• Discuss the definition of the term species.

  • a species is a group of organisms capable of making fertile offspring

  • share a common gene pool

  • showing similar morphology/characteristics

  • but dissimilar organisms sometimes interbreed

  • mule is a horse and donkey/ example of interspecific hybridisation

  • interspecific hybrids are sometimes fertile

  • sometimes organisms that are very similar will not interbreed

  • Example: Drosophila pseudoobscura and persimilis

  • reference to the problem of defining fossil species

  • reference to the problem of species that only reproduce asexually
• Outline allopatric and sympatric speciation. 4 marks

  • speciation is the formation of a new species by the splitting of an existing species;

  • allopatric speciation caused by geographical separation;

  • sympatric speciation occurring within the same habitat caused by feeding differences/behavioural differences/ reproducing patterns

  • both processes lead to isolation of sub-populations;

  • isolation favours certain genetic variations (within a species);

  • over time this leads to genetic barriers/speciation;
• Discuss the theory that evolution occurs by punctuated equilibrium.

  • long periods where there was no (apparent) change

  • short periods of rapid evolution

  • periods of mass extinctions leading to opportunities/caused by environmental disruption/rapid

  environmental change in short periods

  • supported by lack of fossils showing gradual changes

  • an example of such environmental disruption (meteors, earthquakes, volcanoes, etc.)

  • alternative theory is gradualism

  • punctuated equilibrium is based on fossil evidence rather than biochemical evidence
• Compare evolution by punctuated equilibrium with evolution by gradualism.

  • punctuated equilibrium involves faster mutation rates

  • punctuated equlibrium involves more powerful natural selection

  • punctuated equilibrium implies that the environment undergoes rapid changes followed by relative stasis

  • punctuated equibrium involves discontinuous evolution

  • gradualism implies continuous evolution

  • punctuated equilibrium involves faster evolution rates, while gradualism is a gradual change over time.
• Outline the international system used for naming species of living organisms.

  • binomial system

  • devised by Linnaeus

  • the first name is the genus name

  • the second name is the species name

  • genus name can be abbreviated

  • genus consists of a group of (closely related) species

  • upper case for first letter of genus name and the rest of the binomial is lower case

  • Sequoia sempervirens

  • local names can be confusing so helps international communication
• Name the levels and the specific taxa in the hierachy of classification using humans as an example.

  • (Kingdom) Animalia

  • (Phylum) Chordata

  • (Sub-phylum) Vertebrata

  • (Class) Mammalia

  • (Order) Primata

  • (Family) Hominidae

  • (Genus) Homo

  • (Species) sapiens
• Outline the structural differences which characterize bryophytes, filicinophytes,coniferophytes and angiospermophytes.

  bryophytes

  • small plants

  • no true stems or leaves

  • rhizoids only

  • dominant plant is haploid / is the gametophyte

  • spores produced in a capsule

  • non-vascular / lack of xylem and phloem

  filicinophytes

  • seedless

  • vascular tissues / xylem and phloem

  • roots

  • leaves and stems

  • spores produced in clusters / spores usually produced under leaves

  • prothallus / small gametophyte / gametophyte grows independently
• 3. Outline the structural differences

  coniferophyta

  • seeds not enclosed in ovary / pericarp / fruit

  • pollen and ovules

  • cones

  • often have narrow leaves / thick waxy cuticle

  • vascular tissue / xylem and phloem

  angiospermophytes

  • flowers / flowering plants

  • ovules / seed are enclosed

  • fruits

  • xylem vessels
• List the structural differences between bryophytes and angiospermophytes.

  • bryophytes have a thallus

  • bryophytes have rhizoids

  • bryophytes contain archegonia and antheridia

  • angiospermophytes have a (complex) vascular system /xylem / phloem

  • angiospermophytes have a cuticle / bark on their surface

  • angiospermophytes have lignified tissues

  • angiospermophytes have flowers

  • angiospermophytes grow pollen tubes / produce pollen

  • angiospermophytes have (enclosed) seeds / fruits

  • angiospermophytes have roots / stems / leaves
• 5. Outline the value of classifying organisms.

  • classification arranges organisms into groups

  • classification allows identification of species / organisms

  • classification allows prediction of related taxa / based on common characteristics

  • classification reveals evolutionary links / shared derived characteristics / inherited from common

  ancestors

  • classification allows effective communication: same terminology

  • classification avoids problem of convergence / ignores analogies

  • classification emphasizes homologous structures / traits derived from common ancestry
• The DNA/genetic code is universal, with the same four bases adenine, cytosine, guanine and thymine.
• The DNA always pairs A T and G C.
• The structure of the double helix of complementary strands is the same for DNA.
• The same 20 amino acids are used in proteins of all organisms.
• The same enzymes are used in the processes of protein synthesis in all organisms.
• Humans have the same biochemistry as all organisms, indicating a common evolutionary history.
• Mitochondrial DNA is used to determine maternal lines, and the y chromosome is used to determine paternal lines.
• The endosymbiotic theory, mitochondria, and chloroplast structures indicate common lines of evolution.
• Explain how variations in specific molecules can indicate phylogeny

  • differences between molecules can be used to deduce phylogeny

  • phylogeny is the evolutionary history of a (taxonomic) group

  • mutation rates in DNA occur with predictable rates

  • compare nucleotide sequences (of DNA) between taxa

  • compare amino acid sequences (of proteins) between taxa

  • differences can be used as a molecular clock

  • to develop phylogeny

  • to determine time since common ancestry

  • variation can be due to mutations;

  • mutations are chance events
• Discuss how biochemical variations used as an evolutionary clock.

  • differences in nucleotide base sequences / DNA / amino acid sequences / proteins

  • accumulate gradually over time

  • differences accumulate at (roughly) predictable rates

  • therefore the number of differences can be used as a clock

  • to measure time since two divergent groups shared common ancestor

  • example; amino acid sequences in globin genes

  • however variations are partly due to mutations

  • which are unpredictable chance events

  • so there must be caution in interpreting data
• Distinguish, with examples, between analogous and homologous characterisitcs

  analogous characteristics:

  • analogous characteristics are structures with a common function

  • but a different evolutionary origin

  • example: dolphin fins and shark fins

  homologous characteristics:

  • homologous characteristics are structures that have a common evolutionary origin

  • even if they have different functions

  • example: dolphin forelimbs and human arms
• Discuss the relationship between cladograms and the classification of living organisms.

  • cladograms (often) confirm existing classifications

  • since both are based on phylogeny

  • cladograms are (sometimes) different than traditional classifications

  • because nodes can be placed at any point / arbitrary

  • cladograms (sometimes) radically alter existing classifications

  • example: birds grouped with dinosaurs

  • strength of cladistics is that the comparisons are objective / rely on molecular homologies

  • weakness of cladistics is that molecular differences are based on probabilities
• Compare the ways in which autotrophic, heterotrophic and saprotrophic organisms obtain energy.

  • autotrophs use an external / non-organic energy source

  (reject statements suggestion that energy is made)

  • (some) autotrophs use light / (some) autotrophs use photosynthesis

  • (some) autotrophs use inorganic chemical reactions / (some) autotrophs use chemosynthesis

  • heterotrophs obtain energy from other organisms

  • heterotrophs (usually) ingest food / consume food

  • saprotrophs obtain energy from non-living matter / dead organisms

  • saprotrophs digest organic matter extracellularly
• The source of energy in a food chain is from sunlight, which is captured by plants/autotrophs/producers/first trophic level.
• Plants use part of the energy they capture for their own energy requirements and lose the rest through cell respiration.
• Consumers use energy for their own requirements from organisms in the previous trophic level.
• Energy travels between trophic levels from the producer to the first consumer, from the first consumer to the second consumer, and from the second consumer to the third consumer.
• Not all material is assimilated or consumed in a food chain.
• Only a small amount of energy, approximately 10–20%, is passed between trophic levels.
• Most of the energy of a trophic level, approximately 80–90%, is lost and not transferred.
• The loss of energy from organisms in a food chain occurs in the form of heat.
• Energy is not recycled in an ecosystem but nutrients are.
• Ecologists sometimes display data from an ecosystem using a diagram called a pyramid of energy.
• Pyramids of energy show the flow of energy from one trophic level to the next in a community.