MODULE 1 – CELLS AS THE BASIS OF LIFE

CELL STRUCTURE CELLULAR STRUCTURES – PROKARYOTIC & EUKARYOTIC CELLS

INQUIRY QUESTION- what distinguishes one cell from another? Cells are the basis for all life. They and their products make up all organisms and are the means by which organisms survive, grow, repair and reproduce. The obvious diversity of life on earth can be partly attributed to the diversity of cells and their differing structures and functions. Cells are:

o The basic structural and functional units of life that make up all organisms o The product of pre-existing cells dividing o Separated from their environment by a cellular membrane o Diverse, despite having some common structures Cells vary in size, shape, composition, function and mobility. Unicellular organisms carry out all the processes needed to support life. Cells that are part of a multicellular (many-celled, complex) organism may carry out specialised role and rely on other cells working together to provide some of their needs and remove their wants. Cells are classified as either prokaryotic or eukaryotic cells. Prokaryotic cells are smaller, simpler and considered primitive.

PROKARYOTIC CELLS Prokaryotic organisms include a range of types of bacteria, some which live in extreme environments such as highly salty, hot, acidic, alkaline or without oxygen and may be called ‘extremophiles’. They are mainly unicellular. EUKARYOTIC CELLS Eukaryotic organisms include all plants, animals, fungi (multicellular organisms) as well as protists (unicellular or colonial organisms). They develop specialised structures and functions to enable coordinated activities needed in a colonial or multicellular organism. Eukaryotic cells reproduce by mitosis.

A RANGE OF TECHNOLGIES USED TO DETERMINE A CELLS STRUCTURE & FUNCTION Cytology, microbiology and biochemistry are the branches of biology that have contributed to the understanding of cell structure and function. They are dependent on the development of technologies. Some cellular structures and organelles require electronic microscopes referred to as ultrastructures.

MODELLING THE STRUCTURE & FUNCTION OF THE FLUID MOSAIC MODEL OF THE TYPES OF CELL MEMBRANE

The cell membrane is only 7-10 nm in width. This is too small for even electronic microscopes to give an accurate picture of this dynamic structure. The fluid mosaic model explains the characteristics as

o It is selectively permeable barrier rather than a closed wall or open gate. o It is made up of double phospholipid layer. The water loving phosphate heads face outwards

and inwards as they are attracted to the watery fluids inside and outside cells. o A combination of water loving cells and water repelling molecules results in a structure that

naturally forms spherical droplets in a watery medium. Lipids are the water-insoluble water repelling tails in the middle of the bilayer.

o Protein molecules are embedded in the double phospholipid layer. The proteins are varied and some may even combine with carbohydrates. When viewed from outside, they form a mosaic-like pattern dotted around the phospholipid layers and under certain circumstances, they can move around the layers.

CELL FUNCTION

INQUIRY QUESTION – How do cells coordinate activities within their internal environment and its external environment? Just like the city wall around medieval town, the cell membrane controls imports and exports; the entry of requirements and removal of wastes. this membrane maintains the integrity of the internal environment so that the cell can perform is functions and respond to changes in its external environment. MODELLING DIFFUSION AND OSMOSIS - Diffusion occurs in liquids when particles of a solute randomly move until they are

uniformly spread through a solvent to form a uniform solution. In living cells and organisms the solvent is water. Water, oxygen and carbon dioxide are small molecules that can diffuse through the cell membrane.

THE ROLE OF ACTIVE TRANSPORT, ENDOCYTOSIS AND EXOCYTOSIS - Sometimes materials leave and enter against the concentration gradient. Osmosis and

diffusion cannot account for this type of movement. Cells transport materials across the cell membrane against the concentration gradient whit the expenditure of energy in active transport.

- Active transport involves; o The expenditure of energy (from ATP molecules) o Carries materials from places of low concentration to places of high concentration. o Endocytosis and exocytosis as a means of bulk material movement through the

formation or release of vesicles

- Endocytosis is the process by which materials is engulfed and ingested into the cell. Incoming material binds to the plasma membrane and as a result the membrane invaginates and forms a vacuole or vesicle.

- Exocytosis is the process of cell secretion or excretion. Substances within the cell are enclosed within a vesicle and then ‘dock’ and ‘bind’ within the cell membrane.

CONCENTRATION GRADIENT

- A concentration gradient a transition between high levels of concentration particles to low concentration particles.

- Diffusion provide an example of a substance moving from a place where it was highly concentrated to a place with a lower concentration.

- Osmosis provide an example of a solvent moving from a highly concentrated area to a place where it was less concentrated. The movement of the solvent resulted in a lowering of the solvent concentration at the destination of the solvent.

- Is there is great disparity in the concentration across the cell membrane, the movement of materials through osmosis and diffusion will be faster if the gradient is only slight.

CHARACTERISTICS OF MATERIALS BEING EXCHANGE

- The following characteristics of the particles of matter influence their ability to move across the cell membrane.

o Lipid-soluble substances can dissolve in the lipid portion of the bilayer and diffuse through the membrane. Oxygen and carbon dioxide are lipid soluble.

o Large lipid-insoluble molecules and some ions enter through carrier proteins. These can be specific for some molecules. For example only some forms of glucose will be carried and there may be competition for the carries.

REMOVAL OF CELLURAL PRODUCTS AND WASTES IN EUKARYOTIC CELLS

- Cellular wastes products are formed as a by-product of metabolism. Carbon dioxide diffuses out through the cell membrane, while urea uses specific protein channels.

- Many eukaryotic cells produce chemicals as a part of their role and have to remove these products to fulfil their duties. These are some examples;

o The synapse is the junction between nerve cells. For the ‘nerve’ to jump across the gap the secreted substance is stored in a secretory vesicle that then docks and binds with the cell membrane, causing it to rupture at the point and release the contents into the extracellular fluid.

MODULE 2 – ORGANISATION OF LIVING THINGS

ORGANISATION OF CELLS

INQUIRY QUESTION - How are cells arranged in a multicellular organism? Comparing a unicellular organism with a multicellular organism is like comparing a self-sufficient farm with a nation. The increase in complexity means a need for specialisation and cooperation is vital.

CELLS IN UNICELLURAR, COLONIAL AND MULITICELLULAR ORGANISIMS - Cells are the basic units of living things - Cells may live independently, in loosely aggraded groups or in highly organised complex

structures in organisms. In all cases, the cells’ requirements must be met and their waste removed.

- Organisms must reproduce for the survival of the species. These is a great variety in the organisms reproduce depending on the level of organisation, specialisation and complexity of their structures.

- Unicellular Organisms o In unicellular organisms a cell acts individually and independently. o Examples of unicellular organisms include bacteria and some cyanobacteria. o Unicellular organisms have generalised cells. They are mostly aquatic or live in damp

places. They are independent, divide by binary fission and may have some specialised features that enable movement and food capture.

o Small size means cell requirements and waste can move easily by diffusion, osmosis and active transport.

- Colonial Organisms o Colonial Organisms are organisms made up of slightly specialised cells that are

connected. o Examples of Colonial organisms are corals, sponges and some cyanobacteria that form

filaments, sheets or biofilms. o Colonial Organisms have cells in organised arranged structures. These structures work

together to meet the needs of other cells in the organism. o Cells in Colonial Organisms have become more specialised but some retain the ability to

develop into a number of different types, including sex cells. - Multicellular Organisms

o Multicellular organisms are made up of highly specialised and interdependent cells organised into tissues, organs and organ systems.

o Because so many cells are deep inside the organism, Multicellular organisms require cells, tissues and organs that are specialised for transporting cell requirements to and wastes away from the cell.

o Examples of Multicellular organisms are plants, animals and most fungi.

CELL SPECILISATION AND FUNCTION - Cell specialisation is needed to produce the structures that ensure all cells have met their

requirements. Cell specialisation is greatest in multicellular organisms. - The process of developing specialised structures and functions is called differentiation. - Cells become more specialised when they develop from stem cells into cells with features that

enable them to carry out a specific role.

THE STRUCTURE AND FUNCTION OF TISSUES

- A tissue is an organised group of similar cells that carry out specific functions in combination. - Differentiation of cells to form a specialised tissue is triggered by genes and the environmental

conditions of the cell. - Examples of tissues are epithelial tissue, which protects and controls water loss in animals and

epidermis tissue which in plants absorbs water and mineral irons, protects and controls gas exchange.

THE STRUCTURE AND FUNCTION OF ORGANS AND SYSTEMS

- An organ carries out a specific function and is usually made up of different tissues that work together in an organised way. For example the kidneys filter blood, removing wastes and achieving water and salt balance, and leaves carry out photosynthesis in plants.

- An organ system is the set of organs that work in a coordinated manner to meet a requirement of organisms and its cells, such as waste removal by excretory systems in animals, and anchoring and absorbing water and irons by the root systems in plants.

- There is usually a great variety of tissue types and organs within an organ system. Each organ within a system makes a different contribution to the overall functioning of the system.

- Organ systems do not work independently in animals. For example, there is overlap between the excretory system getting rid of wastes and the respiratory system also getting rid of waste carbon dioxide. No system can work without the circulatory system delivering food and oxygen via blood.

THE HIERARCHY

- The hierarchy has a chain of responsibility and interdependence. This interdependence is designed to meet the requirements of a cell regardless of how simple or complex the organism is. This requirement justifies the hierarchy organisation.

- The hierarchical relationship between organisms and their components can be demonstrated by the impact of certain diseases.

ORGANISATION OF CELLS

INQUIRY QUESTION - What is the difference in nutrient and gas requirements between autotrophs and heterotrophs? Some cells need light energy while others need chemical energy, autotrophs carry out photosynthesis whereas a heterotrophs cannot make their own food and must obtain nutrients from other organic substances. AUTOTROPHS

- Autotrophs are organisms that can make organic materials from water and carbon dioxide and small quantities of materials such as nitrates, sulfates and phosphates.

- Plants and algae are the dominate autotrophs on earth.

TRACING THE MOVEMENT OF PRODUCTS OF PHOTOSYNTHESIS - Oxygen released after photosynthesis moves through intercellular air spaces to the stomata,

where it enters the atmosphere. Some oxygen and glucose may be used in aerobic respiration in the mitochondria of plant cells. It is possible that water and carbon dioxide released from aerobic respiration is re-used in photosynthesis.

GAS EXCHANGE STRUCTURES IN ANIMALS AND PLANTS

- Each type of structure in gas exchange must provide: o A large surface area o A means of getting gas into the internal cells o Protection from damage o Maintenance of moisture

PHOTOTROPISM

- Phototropism occurs when the side of the plant just back from the tip and on the reverse side to the light sources grows at a faster rate. The stem then grows in a curved path towards the light.

- Darwin concluded that some influence was transmitted from the tip to further down the shoot, causing its growth to bend.

PHYSICAL AND CHEMICAL DIGETSTION

- Physical digestion occurs when food is made into smaller pieces by the action of teeth and muscular churning action of the stomach.

- Physical digestion greatly increases the surface area of foods so they are exposed for chemical digestion.

- The hydrochloric acid converts pepsinogen into an active form, pepsin, which breaks up proteins into peptides.

TRANSPORT

INQUIRY QUESTION - How does the composition of the transport medium change as it moves around an organism? Once requirements have entered the organism they need to reach cells. This problem has been solved in a variety of ways, but a common feature is a watery transport medium through the organism.

TRANSPORT SYSTEM IN ANIMALS - In animals, transport of materials within the internal environments is important because

materials must be exchanged with cells. This function is carried out by the circulatory system. TRANSPORT SYSTEM IN PLANTS

- The vascular system (also known as veins in plants) is made up of bundles pf separate tissues. These are known as xylem and phloem.

- Xylem carries water and some dissolved materials from the roots to the leaves. The water movement is called the transpiration stream. (moves in an upward direction only)

- Phloem carries the sugar products of photosynthesis to all parts of the plant in a process called translocation. The sugar solution in the plant is called the sap. (moves in both and upward and downward direction)

GAS EXCHANGE - Gaseous exchange involves gases oxygen and carbon dioxide, which are both small molecules

that diffuse through the lipid bilayer of cell membranes. Remember that diffusion occurs along the concentration gradient and the bigger gradient, the faster the diffusion.

- Plants both produce and use oxygen and carbon dioxide because they carry out both photosynthesis and aerobatic respiration. Most plants move only a small amount of and many trees have a high proportion of their tissues classified as non-living. These factors mean that the need for gaseous exchange is not as great as it is in animals.

DIFFERENT TRANSPORT SYSTEMS

PLANTS

ANIMALS

o Vascular system: vascular tissue in bundles

o Two separate tissues: xylem and phloem o Transport media: sap and transportation

stream o Materials carried in solution

o Circulatory system made of heart and blood vessels

o Transport media: blood or haemolymph o Heart pumps transport media around the

body o Special pigments may be uses that

improve the transport of gases

MODULE 3 – BIOLOGICAL DIVERSITY

EFFECTS OF THE ENVIROMENT ON ORGANISIMS

INQUIRY QUESTION- How do environmental pressures promote a change in species diversity and abundance? Species diversity is important to balance ecosystems on earth. This diversity can be affected slowly or quickly over time by natural selection pressures such as climate, spaces to live, diseases and competition for food. Human impacts and the pressures of human activity, such as pollution and land clearing, affects species diversity over a shorter period of time. Understanding how environmental pressures promote a change in species diversity and abundance helps ecologist to design strategies to reduce the effects of adverse change. SELECTION OF PRESSUERS ON ORGANISIMS IN ECOSYSTEMS A living thing does not live by itself. A living thing is part of its environment and is depends on this environment for its survival. All factors that affect living things, including their survival and reproduction, are called selection pressures. Environmental pressures or changes may act to ‘select’ those features of an organism that will enable it to survive and reproduce. All ecosystems are diverse, with their own unique biotic and abiotic factors. Therefore each ecosystem has their own selection pressures. When environmental factors change, species diversity and abundance also changes. Is this change happens slowly enough species may be able to adapt to the changes. However, is the changes happen to fast the species may be lost and biodiversity reduced. Living resources and the interactions with the living parts of the ecosystem referred to as biotic factors. The physical and chemical non-living resources and components are referred to as abiotic factors. Biotic Factors - Biotic factors are the living parts of the ecosystem. They include members of the same species as

well as members of other species. This includes any diseases that may impact on the organisms ability to survive.

- Biotic relationships are often liked to how organisms obtain their energy and include predator-prey relationships.

Abiotic Factors - Abiotic factors are the non-living features of an environment which affect the survival of a species

of an environment which affect the survival of a species or population. - Abiotic factors include physical features such as temperature, rainfall, water, humidity, sunlight,

and soil. Chemical features include salinity, minerals, pH levels and oxygen ability. Aquatic Environments Abiotic factors in aquatic environments is outlined below - Rate of water flow - Salinity levels in water - Oxygen ability - Availability of light - Temperature ranges - Pressure

Terrestrial Environments Abiotic factors in terrestrial environments are outlined in the points below - Aspects of topography - Exposure to wind - Soil type - Temperature - Availability of water

ADAPTATIONS

INQUIRY QUESTION- How do adaptations increase the organisms ability to survive? As a result of biological diversity some organisms in a population have characteristics more suited to the environment than others of the same species. These characteristics increase the organisms’ ability to survive and reproduce in particular habitats. These characteristics are called adaptations. Changes in the environment select characteristics that enable these organisms to survive. Note that some organisms do not survive in their environment and become endangered and eventually extinct.

ADAPTATIONS OF ORGAINISIMS THAT INCREASE THEIR ABLITY TO SURIVIVE IN THEIR ENVIROMENT

All living things in natural environments exist in that environment because, once established, they have continued to compete, reproduce, obtain nutrients and defend themselves successfully, they have survived. Adaptations which increase an organisms’ ability to survive depends on the environment which the organism lives in. For example, adaptations that increase survival in soil with low nutrients levels is probably not going to increase an organisms ability to survive if the soils become rich in nutrients. Structural Adaptations - Structural adaptations refer to the shape or size of the body or details of physical features or

structures, such as the shape of a birds bill or spiky stems on a plant. - Hot dry habitats are the most extensive habitats in Australia. Many of Australian plants have

structural adaptations that minimise water loss and at the same time allow for gas exchange. Physical Adaptations - Physical adaptations refer to the function of the structural features. Saltbush grown in hot dry

environments. The salt glands reflect the heat, resulting in less heat absorption. Behavioural Adaptations - Behavioural Adaptations refer to the behaviour of the organism, this is an action done by the

organism. Examples include burrowing behaviours or courtship behaviours to attract a mate. - Some plants can orientate their leaves to follow the sun across the sky and therefore obtain

maximum sunlight for photosynthesis. Some plants also drop their leaves if the temperature becomes to cool.

Remember that Structural, Physical and Behavioural features are interrelated and often complex.

THE THEORY OF EVOLUTION BY NATURAL SELECTION

INQUIRY QUESTION- What is the relationship between evolution and biodiversity? Evolutionary theory states that all organisms have developed from pre-existing organisms. All organisms have a common origin. Over billions of years, changes in many directions have given rise to the extraordinary biological diversity of life on earth. The changes that have led to biodiversity have come about because of changes in the earths physical environments (abiotic factors such as climates), the earths chemical environment (abiotic factors such as changes to oceans and atmosphere) and biotic factors such as competition for resources. DIVERSIFICATION SINCE LIFE APEARED ON EARTH - Biological diversity is constantly changing. Diversity is increased by genetic changes and

evolutionary processes and reduced by processes such as habitat destruction and population decline and extinction.

- Fossils and geological evidence suggest that life on earth began in the oceans about 3800 million years ago. In this history many organisms have become extinct, some have remained virtually unchanged and some have remained virtually unchanged and some have changed and diversified.

- Overtime life forms have evolved adapted to a wide range of habitats. The table below summarises the appearance and diversification of life on earth, covering the major geological time periods and diversification in terms of theory of evolution.

HOW MACROEVOLUTIONARY CHANGES CAN DRIVE EVOLUTIONARY CHANGES AND SPECIATION - Evolutionary changes occurs on different scales, for example, an increase in the frequency of the

dark colouration in peppered moths from one generation to the next is ‘small’ scale change that occurred when industrial pollution resulted in shoot covering many surfaces. The change in selection pressure changes the survival rate of some organisms in the pollution.

- Microevolution is the term given to small scale changes that occur within a single population and across generations. Given enough time, microevolutionary change can produce major evolutionary changes.

- Macroevolution refers to changes on a much bigger scale over a long period of time. Examples include evolution of the horse, platypus and flowing plants.

- Evolution at both micro and macro levels relies on the same established mechanism of evolutionary change, including natural selection.

- Species evolve over time because the environment is constantly challenging organisms, selecting those characteristics that are best adapted to the environment. Only the ‘fittest’ survive. Living things most suited to their environment have the best chance of of surviving and reproducing therefore pass these characteristics onto their offspring.

- Speciation refers to the formation of new species due to Geological, Behavioural, Physical and Structural factors which prevent previously interbreeding populations from reproducing.

- Diversification of a species and branching into two or more species occurs as a groups adapt to different environments. If isolation occurs a species may form into distinct breeding populations.

Selection pressures are often not the same when the populations are in different environments’. Over time the populations genetically diverge enough so that they can no longer reproduce with each other, at this point they become a different species.

DIVERGENT EVOLUTION - Divergent evolution means evolving to be different; that is, evolution from an ancestor into

several different forms adapted to distinct ways of life. For example, marsupials and monotremes evolved from primitive mammals. When Australia became an isolated continent, marsupials spread widely, reducing competition for resources by occupying different niches and developing specialised diets. Adaptive radiation is an alternative term for divergent evolution.

- Variations among Galapagos species of mocking birds and finches are a classic examples of divergent evolution, with each species evolving from a common ancestor to exploit a specific type of food.

CONVERGENT EVOLUTION - Convergent evolution means evolving to be similar, it is the result of the independent evolution

of similar structures in different groups. - If unrelated organisms use the same resources, occupy similar niches in different habitat’s or are

subject to similar selection pressures over time they may end up with similar structures, physiology or behavioural through natural selection.

PUNCTUATED EQUILIBRIUM VS GRADUAL PROCESS OF NATURAL SELECTION PUNCTUATED EQUILIBRIUM GRADUAL PROCESS OF NATURAL SELECTION

o In the 1970’s the theory of punctuated

equilibrium was proposed. The theory does not discount Darwin’s theory, but it does propose that evolutionary change may be rapid as opposed to only gradual.

o The punctuated or rapid change periods are presumably the result of major environmental changes and selection pressures.

o The idea of punctuated equilibrium helps to explain why the fossil record is incomplete. If evolutionary change happens in a short amount of time span then the intermediate forms would not be around long enough to be apparent in the fossil record.

o Early in the 1900’s scientist refined Darwin’s theory to include the possibility of sudden evolutionary change as well as she slow gradual process suggested by Darwin.

o Evidence for gradualism includes fossil forms. Transitional fossils have been features that make them an intermediate form between major groups of organisms.

o It was generally believed that changes from generation to generation indicated that past species gradually evolved into other species over millions of years, this is referred to as gradualism.

THE EVOLUTION EVIDENCE

INQUIRY QUESTION-

What is the evidence that supports they theory of evolution by natural selection? A great deal of evidence exists to support the theory that present-day life forms have evolved over time through a process of natural selection and that all species share a common ancestor. The multiple lines of evidence come from studies of fossils, geology, living organisms, biochemistry, comparative anatomy, comparative embryology, biogeography. BIOCHEMICAL EVIDENCE - Biochemistry involves the study of the structure and function of the many chemicals that are

found in living organisms, such as proteins and nucleic acids.

- Example - Certain proteins are required to transport oxygen in organisms. Haemoglobin/myoglobin, haemocyanin and haemerythrin/myohaemrythrin are proteins that carry oxygen in different animals. The similarity of their biochemistry is evidence of the evolutionary relationships of these animals

- Biochemical differences – biochemical techniques are also used to compare proteins and nucleic acids in many microorganisms that may resemble some of the very early forms of life on earth. Common ancestry can be seen in the complex metabolic molecules that many different organisms share. Amino acids are a simple organic compound and a large proportion of our cells, muscles and tissues are made up of them. This means they carry out many important bodily functions such as giving cells their structure. Therefore they are the building of protein

COMPARATIVE ANATOMY - Comparative anatomy is the similar anatomy

across different species providing evidence of a common origin. This study of similarities provides evidence of a common ancestor which supports the theory of evolution by natural selection. For example, observations of the forelimbs of frogs, whales, lions, humans and bats show that they have a similar structure. They all have a humerus, radius and ulna bones with the length of these bones varying depending on the adaptations needed to survive in their different environments.

- Similar anatomy across different species is referred to as homologous structures. Vestigial organs (structures that have lost most or all of their ancestral function) also provide evidence of a common ancestor, therefore supporting the theory of evolution by natural selection.

COMPARATIVE EMBRYOLOGY - A branch of embryology that compares and

contrasts embryos of different species it is used to show how all animals are related.

- Comparative embryology provides evidence for evolution because the embryotic forms of divergent species are similar.

- Comparative embryology is the study of similarities in embryological development it provides evidence of a common ancestor between different species

- An example is both fish and human embryos have gill slits. In fish they develop into gills whereas in humans they disappear before birth. BIOGEOGRAPHY

- Biogeography is the study of the distribution of living things over the earth. Biogeographical distribution patterns provide evidence that species have originated from common ancestors and when isolated, they evolve into new species by natural selection. An example of this, is the break-up of the supercontinent pangaea, that contained species that have now been distributed worldwide. Therefore, the concept of biogeography supports the theory of evolution through natural selection as it explains how speciation has occurred over time. RELETIVE DATING

- Relative dating is when the age of the rock or fossil is compared to another rock or fossil For example, rock A is younger than rock B.

- This can provide evidence of the sequence of geological events but not the exact dates of an event.

- Techniques that determine the relative order of past events and the age of one rock layer relative to other rock layers

ABSOLUTE DATING TECHNIQUES - Absolute dating techniques provide evidence of the actual dates of geological events and the age

of fossils. They use radioactive isotopes which are radioactive elements that decay at a defined rate and the rate of decay is used to date the formation of igneous rocks, also called radioisotopes. For example, zircons are used to date items by comparing parent and daughter atoms.

- To determine the absolute age of a item, you can compare the parent isotopes to the daughter isotopes. For example, when half of the parent isotopes have decay and turned into daughter isotopes, that is called a half-life which means the item is approximately 2.2 billion years old.

MODULE 4 – ECOSYSTEM DYNAMICS

POPULATION DYNAMICS INQUIRY QUESTION - What effects can one species have on the other species in a community? All species interact with others in ecosystems, often in complex ways. Relationships between organisms, such as competition, commensalism, predation, symbiosis and disease, affect the abundance and distribution of species. Human activity in ecosystems also affects other species. Humans can change ecosystems enormously and quickly. Understanding the effects that one species can have on other species helps ecologist design strategies to reduce the effects of adverse changes. THE IMPACT OF ABIOTIC FACTORS IN AN ECOSYSTEM - Abiotic factors interact in complex ways. These interactions create many diverse habitats or

niches available to different species. Different species vary in their ability to live in different habitats.

- High levels of species diversity allow organisms to potentially use a wide variety of habitats. - Water is one of the most important abiotic factors influencing life on earth. Rainfall in Australia

is very unpredictable and varies with seasons. Differences in the availability of water is linked to other abiotic factors such as steepness of slopes, exposure to the sun, drying winds, the permeability of the soil.

THE IMPACT OF BIOTIC FACTORS IN AN ECOSYSTEM - Biotic factors interact with abiotic factors. These interactions can represented using the water

cycles, carbon and oxygen cycles, and nutrition cycles.

PAST ECOSYSTEMS INQUIRY QUESTION - How do selection pressures within an ecosystem influence evolutionary change? Ecosystems are limited in the total number or organisms that they can support. Ecosystems can change dramatically over time and can be impacted by selection pressures; that is abiotic and biotic factors including climatic events. When the environment changes, these selection pressures give a particular adaptive advantage to certain characteristics and therefore influences by evolutionary change. PALEONTOLOGICAL EVIDENCE - The study of fossils is called palaeontology and paleontological evidence is based on fossil

evidence. - Fossils are the remains or traces of living things that have been trapped in sediments, coal, tar,

amber or frozen in ice. The fossil record tells the story of past changes and the evolution of species over millions of years.

- The fossil record is incomplete. For fossils to form, the organism must die and be rapidly trapped in a substrate (e.g. sediment) so that decomposition or destruction does not occur.

- Transitional fossils have features that make them an intermediate form between major groups of organisms. They provide further evidence for evolutionary change.

- Examples of transitional fossil forms include seed ferns and the archaeopteryx. The archaeopteryx was a bird-like reptile with wings, reptilian teeth and a long-jointed tail.

- Palaeontologists calculate the age of a range of different fossils to determine when the organisms lived relative to each other. They also identify and classify fossils to create pictures of past ecosystem.

- Different plants and animals have different habitat needs so their fossils provide clues to the environment of past ecosystems, For example: o Limestone is a sedimentary rock composed of fragments of marine organisms (e.g. molluscs

and corals), which live in warm, shallow seas. The presence of limestone is evidence that the area was once covered by warm, shallow bodies of water.

GEOLOGICAL EVIDENCE - Geological evidence for past changes in ecosystems can be found in rock structure and

formation (e.g. sediments). - The characteristics of sediments depend on the environment in which they formed. For

example, some sands and gravels are dropped by glaciers and become glacial deposits, indicating that the climate must have been cold.

- Mountains in Tasmania and NSW have glacial deposits and features of glacial erosion even though no glaciers exist there today.

ABORIGINAL ROCK PAINTINGS - Aboriginal rock art includes rock engravings (petroglyphs) and rock paintings (pictographs). This

art, along with songs, stories and customs, are an important part of Aboriginal culture, connecting people with their land and spiritual heritage.

- Archaeological evidence suggests modern humans reached Southeast Asia 70 000 years ago, spreading to Australia by at least 65 000 years ago.

- Red ochre paintings discovered at the centre of the Arnhem Land plateau depict two emu-like birds.

- The birds have been identified by some palaeontologists as the megafauna species Genyornis newtoni two-metre tall, flightless birds that are now extinct.

- The different styles of art have been studied and arranged into a chronological sequence. Some rock art is estimated to date from 8000-50 000 years ago, during the last ice age when the Earth was much cooler.

ICE CORE DRILLING - Ice core drilling provides evidence of past climates going back at least 800 000 years. Ice cores

are drilled in mountain glaciers and in polar ice caps, such as Antarctica and Greenland - Analysis of ice cores help scientists reconstruct past climates by using data about air

temperatures. - Analysis of the gas bubbles stored in ice cores provides data about past changes in

concentration of atmospheric gases OTHER EVIDENCE FOR THE PAST CHANGES IN ECOSYSTEMS - Sediment and dead organisms accumulate in layers on the ocean floor over millions of years.

Oceanographic vessels drill core sediment samples from ocean floors. - Sequences of sediments might reveal polar, sub-tropical or temperate species of plankton. - Corals build their hard skeletons from calcium carbonate. This contains isotopes of oxygen as

well as trace metals that can determine the temperature of the water in which the coral grew.

RADIOMETRIC DATING - Radiometric dating is a

technique, based on the decay of certain radioactive elements such as uranium, rubidium, potassium, carbon and argon, used to accurately date igneous rock.

- When molten magma crystallises to form igneous rocks, the minerals in the rock contain a certain proportion of radioisotopes in relation to stable elements.

- By determining the relative amount of the parent material to the daughter material a determination of the age of the rock can be made.

- Radiocarbon dating is used to date sediments and fossils up to about 50 000 years old.

GAS ANALYSIS - Gas analysis is used to interpret past climates by analysing gases trapped in ice cores. - Gas analysis is the study of gases trapped in ice core bubbles, ocean sediments, corals and the

shells of marine plants and animals. - Gases in ice cores provide a highly reliable record of the Earth's atmospheric composition at the

time the ice was formed. - Because most gases reside in the atmosphere long enough to be well mixed globally, ice cores

around the world record the same atmospheric composition in bubbles trapped at the same time.

- The exact oxygen ratios can tell scientists how much ice covered the Earth. Through analysis of gases in ice cores scientists can also learn how changing levels of atmospheric carbon dioxide (CO2), methane and other greenhouses gases occur over time

EVIDENCE OF PRESENT-DAY ORGANISIMS EVOLVING FROM PAST ORGANISIMS - Even though scientists agree that present-day organisms have evolved from organisms in the

past they are continually trying to find new evidence about the relationships between them and how evolution occurs.

- As more fossils are discovered and as technologies for analysing and dating them improve, more pieces of evidence are put together.

- The study of genetics and DNA sequencing, combined with fossil evidence, provides an even fuller picture.

THE EVOLUTION OF SMALL MAMMALS - Fossil evidence shows that the huge diversity of present-day mammals evolved from mammal-

like reptiles called synapsid. - Using fossil evidence (and now DNA analysis) scientists claim that all mammals are related. - The earliest known mammals were tiny, shrew-sized creatures that laid eggs but fed their young

milk. Primitive mammals existed at the same time as the dinosaurs.

DIVERSIFICATION OF MAMMALS - For 145 million years during the Jurassic period dinosaurs dominated the Earth. Scientists

believe that the dominance of dinosaurs meant that mammals remained small, were confined to a limited number of niches and only slowly increased in species diversity. Fossil assemblages from this time period are rich in evidence of dinosaurs but contain few mammal fossils.

- A catastrophic event occurred on Earth 65 Mya. Over a period of 10 million years, dinosaurs, including Pterosaurs (flying reptiles), and other groups of organisms became extinct.

- Only one lineage of dinosaurs survived-the ancestors of modern birds. The extinction left huge niche vacancies in habitats. Those mammals that survived the extinction exploited these niches, evolving to inhabit many environments.

THE EVOLUTION OF MEGAFAUNA - Long after the mass extinction of dinosaurs at the end of the Cretaceous there was a trend

towards an increased body size, as seen in the evolution of megafauna. - This evolution coincided with a period in the Earth's geological history, starting about 2.58 Mya,

that was punctuated by a series of global glacial phases. - All continents saw the rise of very large animals. Some scientists claim that the increase in body

size was a response to the glacial conditions. - Australia was home to the largest ever marsupial mammal, diprotodont, which was three- to

four-metres long, about two-metres tall, weighed up to 3.6 tonnes and looked like a giant wombat.

THE EXTINCTION OF MEGAFAUNA - The end of the last ice age (about 10 000-15 000 years ago) saw the rapid demise of many large

animals around the world. This is sometimes called the mass Quaternary extinction. - The climate in Australia changed from cold-dry to warm-dry. As a result, surface water became

scarce and most inland lakes became completely dry. Most large, predominantly browsing megafauna lost their habitat.

- This led to a large number of niche vacancies. As Australia became more arid, marsupial fauna diversified into a variety of habitats. Australia has a few remaining land dwelling megafauna, such as the red kangaroo, but most marsupial mammals are much smaller than the megafauna

THE EVOLUTION OF SCLEROPHYLL PLANTS - Sclerophyll plants are tough-leaved, woody plants common to many parts of Australia. Although

they are extremely diverse, sclerophyll plants are most suited to dry conditions, poor soils and frequent fires.

- Sclerophyll plants include eucalypts, tea-trees, grevilleas, hakeas, acacias and banksias. Scientists claim that Australia's generally weathered and infertile soils have allowed the widespread growth of sclerophyll vegetation.

- Fossils provide evidence of the evolution of sclerophyll plants. Until about 50 Mya the continents that made up Gondwana shared common plant types. The climate at the time was temperate and moist, as shown by fossils of plants with soft leaves. Australia was dominated by forests of Antarctic beech and ferns

- As Australia separated from Antarctica and drifted north, conditions became drier. The beech forests contracted and were replaced by sclerophyll plants.

- Sclerophyll plants diversified across Australia to occupy many different niches. For example, Eucalyptus pseudoglobulus grows up to 40 metres tall inland and yet it can adapt to exposed coastal cliffs by growing as a small Mallee form.

FUTURE ECOSYSTEMS

INQUIRY QUESTION - How can human activity impact on an ecosystem?

Human activities, such as over-exploitation, habitat destruction, monocultures and pollution can reduce biodiversity and impact on the magnitude, duration and speed of ecosystem change. Increasing evidence shows that human-introduced changes have already triggered changes in the diversity, abundance and distribution of many species and played a key role in the recent extinction of others. Human activities, such as conservation management, monitoring of biodiversity and restoration practices can have positive impacts on an ecosystem. THE ROLE OF HUMAN-INDUCED SELECTION PRESSURES - Extinctions have occurred naturally throughout the history of life on earth. A recent but extremely

important factor affecting rates of extinction is people and human induced selection pressures. - Human induced selection pressures include land clearance and deforestation resulting in soil loss,

erosion and habitat loss. Pollution that comes from the production, use and disposal poisonous and non-biodegradable substances such as plastics. Most of these human induced selection pressures have come from the impact of our rapidly growing human population.

MODELS THAT PREDICT THE FUTURE HUMAN IMPACTS ON BIODIVERSITY - Models are used by sciences to increase the accuracy and reliability of predictions. For example,

models of ecosystem interactions, such as food webs and succession models, can be used to predict the impact of change.

- The accuracy and reliability of the modelling relies on a number of variables, including the representativeness of the sampling, the quality of the data input and the quality of often complex equations.