Assessment Statements
D1 Origin of life on Earth

D.1.1 Describe four processes needed for the spontaneous origin of life on Earth.


• the non-living synthesis of simple organic molecules

• the assembly of these molecules into polymers

• the origin of self-replicating molecules that made inheritance possible

• the packaging of these molecules into membranes with an internal chemistry different from their surroundings.

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds.

The Miller-Urey experiment simulated the hypothetic conditions of early Earth and tested the occurance of chemical evolution. The experiment used water, methane, ammonia, and hydrogen gas. Electrical discharges and boiling and condensing water simulated lightning and rainfall.  The system yielded carbon in organic compounds, 15 amino acids, sugars, lipids, and some of the building blocks of nucleic acids.

D.1.3 State that comets may have delivered organic compounds to Earth.

Comets contain a variety of organic compounds. Heavy bombardment about 4,000 million years ago may have delivered both organic compounds and water to the early Earth.

D.1.4 Discuss possible locations where conditions would have allowed the synthesis of organic compounds.

Examples should include communities around deep-sea hydrothermal vents, volcanoes and extraterrestrial locations.

·         Deep sea vents: ammonia and methane are present, and were not present elsewhere in the early atmosphere. There are many organisms currently living around deep sea vents suggesting this is a possible explanation.

·         Volcanoes: volcanic eruptions involve the release of methane, ammonia, and hydrogen gases as well as water vapor. This, when combined with lightning, creates a real-life version of the Miller-Urey experiment.

·         Extraterrestrial locations: Comets contain a variety of organic compounds. Heavy bombardment may have delivered both organic compounds and water to the early Earth.

D.1.5 Outline two properties of RNA that would have allowed it to play a role in the origin of life.

Include the self-replicating and catalytic activities of RNA.

D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environmentdifferent from their surroundings.

Examples include coacervates and microspheres.

D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere.

Photosynthesizing prokaryotes, such as cyanobacteria, produced oxygen via photosynthesis.

D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes.

Both mitochondria and chloroplasts  have evolved from independent prokaryotic cells, which were taken into a larger cell by endocytosis. Instead of being digested, the cells were kept alive and continued to carry out aerobic respiration and photosynthesis because this increased energy was beneficial for the larger cell. The smaller inner cell also benefited (symbiotic relationship).

Evidence that supports endosymbiotic theory:

·         they grow and divide like cells

·         they have a naked loop of DNA like prokaryotes

·         they synthesize some of their own proteins

·         they have double membranes (because of endocytosis)

5.4 Evolution

5.4.1 Define evolution.
Evolution is the cumulative change in the heritable characteristics of a population.  We accept not only that species can evolve, but also that new species arise by evolution from pre- existing ones.  The whole of life can be seen as unified by its common origins. Variation within our species is the result of different selection pressures operating in different parts of the world, yet this variation is not so vast to justify a construct such as race having a biological or scientific basis.

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.
•    Fossil Record: A fossil is the ancient preserved remains of an organism. The fossil can be dated from the age of the rock formation. Sequences of fossil can show the gradual change of an organism over geological time. Continuous fossil records are rare with most containing large time gaps until subsequent discoveries are made.
•    Homologous structures: All of life is connected through evolutionary history and consequently those organisms more closely connected might reasonably be expected to share common or homologous structures. Group of organisms closely related share a common form or derived trait, which has been inherited from the common ancestor. Example: pentadactyl limb
•    Selective breeding: man has selectively breed animals and plants for thousands of years. If an animal posses a characteristic that is considered useful or valuable then this animal is selected for breading. The hope then is that this characteristic will be present in the next generation and at a higher frequency than before. In subsequent generations it may even then be possible to select from an even more advantageous characteristic.

D.5.6 Distinguish, with examples, between analogous and homologous characteristics.
Analogous/ convergent: serve the same biological function, but evolved independently. Example: wings on butterflies and bats. 

Homologous/ divergent: similar structures that evolved from a common ancestor but now serve a different function. Example: pentadactyl limb.

5.4.3 State that populations tend to produce more offspring than the environment can support.

5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

•    The struggle for survival is a consequence of overpopulation.
•    Individuals of the population are being selected “for” or “against”
•    Survivors form the new breeding population and produce offspring.
•    The frequency of advantageous alleles has increased.
•    This change in heritable characteristics= evolution.

5.4.5 State that the members of a species show variation.

5.4.6 Explain how sexual reproduction promotes variation in a species.

•    Meiosis and independent assortment of chromosomes creates 2n   new combinations of chromosomes (n=haploid number)
•    Random fertilization increases the variation in the population
•    Variation is also increased by crossing-over in meiosis

5.4.7 Explain how natural selection leads to evolution.
Greater survival and reproductive success of individuals with favorable heritable variations can lead to change in the characteristics of a population.

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria. Other examples could include: the changes in size and shape of the beaks of Galapagos finches; pesticide resistance, industrial melanism or heavy-metal tolerance in plants.

Example 1: Staphylococcus aureus
This bacterium is associated with a variety of conditions including skin and lung infections. As an example of evolution it can be shown that the population of S. aureus has diverged into two forms, Methicillin-resistant (MRSA) and Methicillin-susceptible (MSSA).
How MRSA evolved:
•    Antibiotics kill susceptible forms of the bacteria. (The antibiotic is the selection pressure on the bacteria).
•    Random mutation produces a resistant gene at a low frequency.
•    Frequent use of the antibiotic puts MRSA at a selective advantage to survive and survives and reproduces.
•    The descendants will also carry the resistance gene
•    The resistance gene increases in frequency or there is a process of cumulative change in the heritable characteristics (resistance gene) in the population
•    The species has evolved into two forms.

Example 2: Industrial melanism
During  Industrialization in England, carbon residue covered many surfaces making moths unable to camflage with light colored leaves. The dark-colored (melanic) peppered moths gradually predominated the light-colored (non-melanic) form due to selective pecking of the latter by the birds. The dark-colored moths were able to blend in to tree bark and avoid being eaten.

D. 4 Hardy-Weinberg

D.4.1 Explain how the Hardy–Weinberg equation is derived.
If there are two alleles of a gene in a population, there are three possible genotypes- homozygous of each of the two alleles and heterozygous. The frequency of the two alleles in the population is represented by the letters p and q. The total frequency of the alleles in the population is 1.0. So:

p+q=1 → square both sides of the equation→ P2+2pq+q2=1

If there is random mating in the population, the chance of inheriting two copies of the first two alleles is p2 and the chance of inheriting two copies of the second allele is q2. The expected frequency of the heterozygous genotype is therefore 2pq. Again, the sum of these frequencies is 1.

D.4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy–Weinberg equation.

D.4.3 State the assumptions made when the Hardy–Weinberg equation is used.

•    Random mating
•    No natural selection
•    No mutation
•    Large population size
•    No immigration or emigration (i.e. constant population)

5.5 Classification

5.5.1 Outline the binomial system of nomenclature.
Each species is given a two-word name. The first word, which refers to the genus, is capitalized. The second word, which refers to the species, is written in lower case. Example: Homo sapiens

5.5.2 List seven levels in the hierarchy of taxa—kingdom, phylum, class, order, family, genus and species—using an example from two different kingdoms for each level.
Example: Human                     Example: Rose       
Kingdom: Animalia                  Kingdom: Plantae
Phylum: Chordata                    Division: Magnoliophyta
Class: Mammalia                     Class: Magnoliopsida
Order: Primates                       Order: Rosales
Family: Hominidae                  Family: Rosaceae
Genus: Homo                          Genus: Rosa
Species: sapiens                     Species: gallica

5.5.3 Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta.

Bryophyta: mosses, liverworts and hornworts
Filicinophyta: ferns
Coniferophyta: conifers and pines
Angiospermophyta: flowering plants and grasses

5.5.4 Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca and arthropoda.
Porifera: sponges
Cnidaria: jelly fish, sea anemones, corals
Platyhelminthes: flatworms
Annelida: round, segmented worms
Mollusca: snails, slugs, and octopus
Arthropoda: insects, crustaceans, spiders, scorpions, millipedes

5.5.5 Apply and design a key for a group of up to eight organisms.  A dichotomous key should be used.
Sample below:

Things that might be on the exam…

- PCR, Cloning, GMOs, Gel electrophoresis.

- Classification (plant and animal genera)

- Phylogeny, cladistics, etc.

- Origin of Life

- Evolution

- Human evolution

- Hardy-Weinberg

- Nerves, hormones, homeostasis

6.5 Nerves, hormones, and homeostatis

6.5.1 State that the nervous system consists of the central nervous system

(CNS) and peripheral nerves, and is composed of cells called neurons that

can carry rapid electrical impulses.

6.5.2 Draw and label a diagram of the structure of a motor neuron.

Include dendrites, cell body with nucleus, axon, myelin sheath, nodes of Ranvier and motor end plates.

6.5.3 State that nerve impulses are conducted from receptors to the CNS

by sensory neurons, within the CNS by relay neurons, and from the CNS to

effectors by motor neurons.

6.5.4 Define resting potential and action potential (depolarization and repolarization).

  • Resting potential is the negative charge registered when the nerve is at rest and not conducting a nerve impulse.
  • Action potential is the positive electrochemical charge generated at the nerve impulse. Normally this is seen as the ‘marker’ of the nerve impulse position.
  • Depolarisation is a change from the negative resting potential to the positive action potential.
  • Re-polarisation is the change in the electrical potential from the positive action potential back to the negative resting potential

6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron. Include the movement of Na + and K+ ions to create a resting potential and an action potential.

In resting neurons, there exists an imbalance of ions inside and outside of the cell membranes. The important ions are K+ (potassium) and Na+ (sodium). K+ is more concentrated inside the cell and therefore tends to diffuse out of the cell. It is this diffusion that causes the charge potential across the plasma membrane (in resting neurons it is about -70 mV). Na+ is more concentrated outside of the cell and thus tends to diffuse into the cell, but at a very slow rate due to the low permeability of the plasma membrane to Na+. Sodium-potassium pumps imbedded in the plasma membrane work against both ions’ diffusion gradients in order to preserve the gradients and the membrane potential.

6.5.6 Explain the principles of synaptic transmission.

Include the release, diffusion and binding of the neurotransmitter, initiation of an action potential in the post- synaptic membrane, and subsequent removal of the neurotransmitter.

  • The junction between two neurons is called a synapse.
  • An action potential cannot cross the synaptic cleft between neurons, and instead the nerve impulse is carried by chemicals called neurotransmitters.
  • These chemicals are made by the cell that is sending the impulse (the pre-synaptic neuron) and stored in synaptic vesicles at the end of the axon.
  • The cell that is receiving the nerve impulse (the post-synaptic neuron) has chemical-gated ion channels in its membrane, called neuroreceptors.
  • These have specific binding sites for the neurotransmitters

1)    Nerve impulse reaches the end of the pre-synaptic neuron.

2)    Ca2+ diffuses through calcium channels.

3)    Vesicles of neurotransmitters move to cell membrane and release contents.

4)    Neurotransmitters diffuse across the synapse and bind to neuroreceptors.

5)    Na+ enters the post-synaptic neuron causing depolarization.

6)    Nerve impulse sets off along the post-synaptic neuron.

6.5.7 State that the endocrine system consists of glands that release

hormones that are transported in the blood.

6.5.8 State that homeostasis involves maintaining the internal environment

between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

6.5.9 Explain that homeostasis involves monitoring levels of variables and

correcting changes in levels by negative feedback mechanisms.

·       This model represents the main features of a negative feedback model.

·       Specialised receptors detect changes within the internal conditions.

·       This information is relayed to a central coordinator that determines the level of response.

·       The coordinator in turn relays such a decision to the effector that is specialised to produce the response behaviour.

·       Notice that this response will modify the internal environment and that these new conditions will in turn become the new stimuli.

·       The cycle will continue until conditions are reduced back to within narrow acceptable limits (fixed regulation point).

·       Notice that system works responding to conditions which are lower than and higher than the fixed regulation point.

·       Very efficient systems allow very little in the way of undershoot and overshoot.

6.5.10 Explain the control of body temperature, including the transfer

of heat in blood, and the roles of the hypothalamus, sweat glands, skin

arterioles and shivering.

When Cold

When Hot

  • Lower than regulation temperature blood reaches the hypothalamus.
  • The hypothalamus signals the vasoconstriction (narrowing) of arterioles
  • Muscle effectors are produces the rapid contraction relaxation of muscles known as shivering which produces more body heat.
  • Sweat is secreted onto the surface of skin when body temperature is high.
  • Sweat is largely composed of water which has a high specific heat capacity (absorbs a heat easily).
  • Body heat is transferred from skin and blood to the sweat.
  • The sweat evaporates transferring heat away and in doing so cools the body

6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and the pancreatic islets.

  • Low glucose concentration is detected by the pancreas.
  • Alpha cells in the pancreatic islets secret glucagon.
  • Glucagon flows through the blood to receptors on liver cells.
  • Liver responds by adding glucose to blood stream.
  • High blood glucose levels stimulate the beta pancreatic cells
  • Beta pancreatic cells secrete insulin.
  • Insulin flows through the blood to the receptors on liver cells.
  • Insulin stimulates the liver to remove blood glucose and store this as glycogen (insoluble)

6.5.12 Distinguish between type I and type II diabetes.

Type I Diabetes

Type 2 Diabetes

  • Auto-immune disease in which the beta-cells pancreatic are destroyed.
  • Unable to produce insulin.
  • Responds well to regular injection of insulin probably manufactured as the genetically engineered humulin.
  • Reduced sensitivity of the liver cells to insulin.
  • Reduced number of receptors on the liver cell membrane.

In both types of diabetes there is:

·       a build of glucose in the blood stream and it will then subsequently appear in urine.(test with a Clinistic )

·       High concentrations of blood glucose (hyperglycaemia) results in the movement of water from cells by osmosis.

·       This extra fluid in the blood results in larger quantities of urine production.

·       A lack of glucose in cells means that fats then proteins have to be metabolised in respiration.

·       Particularly the breakdown of protein for energy creates organ damage.




D2 Species and Speciation

D.2.1 Define allele frequency and gene pool.

Allele frequency: proportion or percent of a specific variation of a gene in a population.

Gene pool:  all of the genetic information present in the reproducing members of a population.

D.2.2 State that evolution involves a change in allele frequency in a population’s gene pool over a number of generations.

D.2.3 Discuss the definition of the term species.

Biological species concept: to be part of the same species the organisms must be able to actually or potentially interbreed in nature. A species is the largest gene pool possible in nature. Cannot be applied to bacteria and other organisms that reproduce asexually. What about geographical boundaries? What about hybrids?

Recognition species concept: members of the same species can recognize each other as potential mates. How can one measure recognition with plants, fungi, bacteria?

Phenetic species concept: members of a species are phenotypically similar

Phylogenetic: a species is the smallest set to share an ancestor.

D.2.4 Describe three examples of barriers between gene pools.

Examples include geographical isolation, hybrid infertility, temporal isolation and behavioural isolation.

D.2.5 Explain how polyploidy can contribute to speciation.

Polyploidy: cells contain 3 or more sets of chromosomes (3n, 4n, etc.)

Plants (that are both male and female and therefore can fertilize themselves) and other asexual organisms do this and reproduce offspring that are different from existing species.

D.2.6 Compare allopatric and sympatric speciation.
Speciation: the formation of a new species by splitting of an existing species.
Sympatric: in the same geographical area.
Allopatric: in different geographical areas.

D.2.7 Outline the process of adaptive radiation.

Adaptive radiation: similar but distinct species evolve relatively rapidly from a single species or from a small number of species. Variation in a species results in some members of the population being more suited to a different niche. Example: Galapagos finches

D.2.8 Compare convergent and divergent evolution.

Convergent evolution: species become more similar over time (analogous traits)

Divergent evolution: species become less and less similar over time (homologous traits)

D.2.9 Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.
Gradualism is the slow change from one form to another. Punctuated equilibrium implies long periods without appreciable change and short periods of rapid evolution.

D.2.10 Describe one example of transient polymorphism.

Transient polymorphism: one form is gradually being replaced by another. As the name implies, it represents a temporary situation.

Example: Industrial melanism- During  Industrialization in England, dark-colored (melanic) peppered moths gradually predominated the light-colored (non-melanic) form due to selective pecking of the latter by the birds. 

D.2.11 Describe sickle-cell anemia as an example of balanced polymorphism.
Sickle-cell anemia is an example of balanced polymorphism where heterozygotes (sickle-cell trait) have an advantage in malarial regions because they are fitter than either homozygote.

D3 Human Evolution

D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K. Knowledge of the degree of accuracy and the choice of isotope to use is expected.

Fossils and rocks can be dated using radioisotopes (radioactive isotopes of chemical elements). When an atom of a radioisotope decays, it changes to another isotope and gives off radiation. The rate of decay (half-life) is different for different radioisotopes. C-14 and K-40 are the two radioisotopes most commonly used. In radiocarbon dating the percentage of surviving C-14 atoms is measured. The half-life is 5730 years so it can be used to date samples between 1000 and 50,000-60,000 years old. In K-40 dating the proportions of K-40 atoms to Ar-40 atoms is measured. The half-life of K-40 is 1.26 billion years so it is useful for dating samples over 100,000- 1 million years old.

D.3.2 Define half-life.

The time it takes for the radioactivity to fall to half of its original level

D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope.
D.3.4 Describe the major anatomical features that define humans as primates.

Vision: binocular, stereoscopic vision provides over-lapping fields of vision and good depth perception. Color vision.

Face shape and snout: snout is shorter, so sense of smell is less good.

Teeth shape/Dental arrangement: generalized dental plan so primates can have an omnivorous diet.

Brain size and specialization: brain is large and complex than other mammals.

Collarbone: has been retained allowing a flexible shoulder joint.

Posture: erectness in upper body, associated with walking, sitting, leaping, standing.

Hands and feet: Nails are found on some digits. Climbing is achieved by grasping (not using claws) and is aided by tactile pads at the end of digits. Hands and feet are flexible and have a lot of prehensility (grasping ability).

Reproduction: longer gestation period than other mammals allows for efficient fetal nourishment. Single births are the norm.

Social organization: infant dependency is prolonged with large parental investment in each offspring.

D.3.5 Outline the trends illustrated by the fossils of Ardipithecus ramidus, Australopithecus including A. afarensis and A. africanus, and Homo including H. habilis, H. erectus, H. neanderthalensis and H. sapiens. Knowledge of approximate dates and distribution of the named species is expected.

Trend: migration out of Africa

Trend: increased adaption to bipedalism

Trend: decreasing relative size of face, jaw, teeth, esp. canines; increasing relative size of brain case, forehead

Trend: increase in brain size

Ardipithecus ramidus: 5.8 to 4.4 million years

Distribution: Eastern Africa

Australopithecus afarensis: 3.9 to 2.5 million years

Distribution: Eastern Africa

Australopithecus africanus: 3 to 2.3 million years

Distribution: southern Africa

Homo habilis: 2 to 1.6 million years

Distribution: Eastern and possibly southern Africa

Homo erectus: 1.8 to .3 million years

Distribution: Africa, Asia, Indonesia, and Europe

Homo neanderthalensis: 150,000- 30,000 years

Distribution: Europe and western Asia

Homo sapiens: 160,000 to 60,000 years

Distribution: Africa and western Asia

D.3.6 State that, at various stages in hominid evolution, several species may have coexisted.

Example: H. neanderthanlensis and H. sapiens

D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution.

To become a fossil an organism needs to have hard parts, die and be buried in an anaerobic environment very quickly, and then be preserved through geological time, without being destroyed by tectonism or metamorphism, or removed by erosion. These are pretty rare circumstances, so fossils are very rare. It is hard to find complete fossils of hominid ancestors or find all the ‘missing links.’ It is unclear how the various hominid species are related. There are few fossils of savanna- or forest-dwelling hominids.

D.3.8 Discuss the correlation between the change in diet and increase in brain size during hominid evolution.

Large brains require more energy, more calories. Change in diet from mostly vegetarian to more omnivorous diets corresponds to the increase in brain size. Eating meat increases supply of protein, fat and energy, making larger brain growth possible. Hunting and killing prey on savannas is more difficult than gathering plant foods, so natural selection might have favored larger brains with greater intelligence

D.3.9 Distinguish between genetic and cultural evolution.

The larger brains (genetic evolution) allowed later Hominids to learn. Language, tool-making skills, hunting techniques, methods of agriculture, religion, art, and many other forms of behavior are passed from one generation to the next by teaching and learning. These learned behaviors (as opposed to innate behaviors which are the result of genetic evolution) are the culture. New methods, inventions, or customs can be passed on (cultural evolution).  Genetic evolution is vertical and chronological, whereas cultural evolution can be horizontal and can move backwards as well as forwards.

D.3.10 Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans.

Cultural evolution has allowed much more rapid change than genetic evolution in the recent evolution of humans.