Category Archives: Unit 4 Biology

Welcome Back – Term 3!

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Year 12 students will be counting down the next 14 weeks until their VCE Biology exam on the morning of Friday 30th October. We will start this term with a review of the structure of DNA, using the GTAC resources, “Exploring the structure of DNA“.

On Wednesday 22nd July we will be heading to the University of Melbourne Genetics Department to complete three practical activities that will contribute to your school-based assessment:

  1. An investigation using a DNA tool and a manipulation technique
  2. An investigation of inheritance in Drosophila melanogaster including a review of meiosis in gamete formation
  3. Meiosis in Drosophila

On Friday 4th September you will have the opportunity to travel to Brauer College and participate in GTAC outreach program, “From Hominoids to Hominins”.

On Tuesday 13th October you will be able to attend a “Get into Genes” program as revision prior to your exam.

Semester 2 Biology – Adaptations (Y11) and Heredity (Y12)

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This semester we will be starting Unit 2 (Organisms in their Environment) Area of Study 1: Adaptations of Organisms and Unit 4 (Continuity and Change) Area of Study 1: Heredity. We have created Quizlet Sets for each of these topics:

 

VCE Biology 2015

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  Welcome to VCE Biology for 2015! Biology is the study of all living organisms and life itself. So, what do all living organisms have in common?

  1. Living organisms are composed of cells and the products of cells
  2. Living organisms (usually) require oxygen and nutrients (inputs)
  3. Living organisms produce wastes (outputs)
  4. Living organisms respond to stimuli
  5. Living organisms reproduce

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Unit 1: Area of Study 1: Cells in Action (Year 11)

In our first week of Year 11 Biology we will be looking at size and scale, using light microscopes and viewing plant and animal cells. Check out these websites:

Unit 3: Area of Study 1: Molecules of Life  (Year 12)

In our first week of Year 12 Biology we the chemical nature of cells. All living matter is made up primarily of carbon, hydrogen, oxygen, phosphoros, sulfur and nitrogen (CHOPSN). These elements are combined into compounds, with the four classes of biological macromolecules being carbohydrates, lipids, proteins and nucleic acids. Which are which in the diagram below?

biomacromolecules

Human intervention in evolution

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Humans have had an influence on evolutionary processes for much longer than you may have thought – we have tamed wolves and wild cats to become the many breeds of domestic dogs and cats that share our homes today and we have selected cattle, sheep, goats and pigs over many generations for food characteristics. Our main food crops such as rice, corn, wheat, as well as many fruit and vegetables, are very different to their wild ancestors.

Artificial selection, or selective breeding, is the process by which humans breed other animals and plants for particular traits; for example, increased size, fast muscle growth or sweeter taste. This can be a deliberate process, like when farmers choose to breed animals or plants with particular characteristics or it can be accidental. In Asia and Africa, over many centuries, bull elephants with particularly large tusks have been targeted as trophies and for their valuable ivory. As a consequence, individuals with large tusks produce fewer offspring and become less frequent in the population. (Read more about elephant evolution here and here).

In more recent times, due to greater understanding of genetic inheritance and modern gene technology, we have been able to identify specific genes that code for particular characteristics and create new breeds of organisms with beneficial traits – drought tolerance, increased productivity or improved storage life, for example.

Play the videos from ABC Splash “Genetic Engineering of Crops”

Some sites that may be useful for your research project:

Geological time, Fossils and Radiometric dating

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Geological Time Periods

Fossils

Radiometric Dating

Patterns of Evolution

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Speciation: Due to natural variation between individuals, selection pressure, “survival of the fittest” and favourable traits being passed on to offspring over many generations, new species are formed. Biologists refer to allopatric (geographical), sympatric (same location and habitat), and parapatric (habitat differences) speciation.

Divergent Evolution: Over time, due to selection pressures, sub-species or species become less and less alike, as they become better adapted to their niche. Adaptive radiation (below) is a specific type of divergent evolution. The human foot and the foot of a chimpanzee is an example – they are quite different (divergent), although they evolved from a common ancestor, due to the differing habitats of the upright walking man, compared to the knuckle-walking chimpanzee.

Adaptive Radiation: The process by which organisms change over generations to fill different niches, especially when changes in the environment make new resources available. Charles Darwin famously documented the different beak shapes of finches on the Galapagos Islands, which he postulated had arisen form a common ancestor. Above, you can see the variations of honeycreepers from the Hawaiian islands.

Convergent Evolution: In this form of change over time, different species begin to look more alike, despite having no recent common ancestor. Analogous structures develop, that have the same form and function, but were not present in the most recent common ancestor. Examples include flying insects, birds and bats, who have all developed wings as a solution to escaping from predators or finding more food and mates. Hedgehogs and echidnas are a good example of convergent evolution.

Parallel Evolution: Parallel evolution is similar to convergent evolution, in that different organisms display similar characterisitics, but tend to be more closely related. So, gliding frogs for example, evolved in parallel from multiple types of tree frog. Some examples that are closer to home include the Tasmanian tiger and the European wolf; the flying squirrel and gliding possums and marsupial and placental moles/mice.

More about patterns of evolution:

Population genetics

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Population genetics is the study of distributions and changes in allele frequency in a population, as the population is subject to the four main evolutionary processes:

  • Natural selection
  • Genetic Drift
  • Mutation
  • Gene flow (by migration or distribution of pollen and seeds)

Variation between individuals and species and polymorphism: In any normal population there is some variation between individuals – a box of apples may have individual apples that are slightly different sizes and shapes with slightly different colour variations, even when they come from the same tree. So, not all variation is caused by genetic differences. It may be environmental differences that result in the variation – for example, the amount of light, temperature or soil nutrients in the case of plants or the nutrition and experiences provided to animals. Some characteristics , such as height or wing length might show continuous variation, while other characteristics can be clearly separated into different categories (discontinuous variation). An example of discontinuous variation in humans might be the ability to roll one’s tongue – you can either do this or you can’t – there is no blending, or in-between characteristic. Polymorphism occurs when two or more clearly defined phenotypes are present in the population. A classic example is the light and dark coloured morphs of the peppered moth. The ABO blood grouping is an example in human populations.

Inherited variationsFrom our Unit 3, Area of Study 2 work, we understand that the DNA molecule, present in every cell of living organisms, codes for proteins that determine the phenotype of an organism. DNA is passed from one generation to the next through reproduction, which can occur asexually or sexually (with the production of gametes (meiosis) and fusion of sperm and egg). So, families of individuals tend to look more alike than non-related individuals due to these inherited characteristics. This was seen in our work with pedigree trees, showing how genetic diseases can be passed on through several generations.

Mutations – sources of variation: The source of these variations is genetic mutations – check pages 371-372 and 477-478 in your textbook “Nature of Biology”. Genetic mutations may be spontaneous or may be induced by exposure to mutagenic agents (X-rays and Gamma rays and some chemicals, such as benzene and mustard gas).

Gene pool, gene flow, genetic drift (by chance): The gene pool is the set of all genetic information in a population, while gene flow describes how genes leave and arrive in a population by death and emigration or births and immigration. Genetic drift is the change of gene frequencies due to random sampling.

Polygenes, polygenetic traits: Polygenes are non-allelic genes that together influence a phenotypic trait – often the precise loci of these genes is unknown to biologists. Examples of polygenetic traits in humans are height, weight and skin colour.

Mitochodrial DNA: Mitochondrial DNA is a single, circular strand of DNA found in the mitochondria of eukaryotic cells. In most species, mitochondrial DNA is inherited solely form the mother. In humans, mitochondrial DNA was the first significant part of the human genome to be sequenced.

Founder and bottleneck effects:The founder effect is the lost of genetic variation that occurs when a new population is established by a small group of individuals from a larger population. The people of Easter Island and Pitcairn Island show limited genetic variability (small gene pools) due to this effect. A similar effect is the bottleneck effect, when large numbers of a population are removed, leaving a small gene pool.  As a species, cheetahs have famously low levels of genetic variation. In fact, cheetahs are so closely related to each other that transplanted skin grafts do not evoke an immune response. This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age. However, the situation has worsened in modern times. Habitat encroachment and poaching have further reduce cheetah numbers, consequently snuffing out even more genetic variation and leaving cheetahs even more vulnerable to extinction.

 

 

DNA evidence for evolution

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Last week we had another opportunity to connect with the Gene Technology Access Centre to learn about how biologists use genetic information to discover more about evolutionary relationships. Tony discussed some of the features of the ‘old world’ monkeys and the hominids – including opposable thumbs and the presence or absence of a tail. We then used a computer program, the Biology Work Bench, to compare the similarities and differences of DNA sequences between the different species. The fewer differences in DNA base pairs, the greater the similarities between species and therefor it is assumed that they are more closely related, with a more recent common ancestor.

Evolutionary biologists have been investigating the existence of a ‘molecular clock‘ for the past 40 years – the theory is that some evolutionary changes (mutations) occur at a regular rate, which gives us a powerful tool to estimate how long since different species diverged from a common ancestor. Using molecular clocks to estimate divergence dates depends on other methods of dating. In order to calculate the rate at which a stretch of DNA changes, biologists must use dates estimated from other relative (stratigraphy) and absolute dating techniques (radiometrics). There are many different methods that scientists can use to estimate the age of fossils. Read more at the Smithsonian National Museum of Natural History.

Evidence for Evolution

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Image Source – Haeckel’s drawings

What evidence supports the theory of evolution? – some good questions here!

This interactive animation, “Evolution in Action” outlines the evidence for evolution and gives an opportunity for students to particpate in a simulated natural selection experiment.

Origins of Life

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1. Download the student worksheet from Ages 16-19: Highlighting Important Stages in Evolution

2. Watch the “Tree of Life” video, narrated by David Attenborough

3. Click on “Interactive” to view the “Tree of Life” Interactive timeline

4. Answer the questions on the student worksheet.

Other Resources: