science education teaching booklet

Name:________ 1 Cycles Everywhere you look cycles in both nature and the mechanical world effect the way in which humans have advanced. However these cycles mostly go unnoticed by many people, can you think of 4 cycles around you? Natural Man made The Human Life cycle In the following activity you are going to be asked to form groups of 4 and in the space below construct a diagram that shows how the human life is a cycle. 2 To look at the human life cycle we must first look at where life starts. The female reproductive system Unlike the male's, a female's reproductive organs are located inside her body. The ovaries are the specialised organs, which produce the eggs or ova. The ova produced by a woman are present in an immature form at birth. Each ovary will contain around 200 000 eggs. The ovaries usually release only one ovum approximately every 28 days. This is called ovulation. Each ovary usually alternates production of ova so that only one is released at a time. Occasionally both ovaries will produce ova at the same time. If both are fertilised then non-identical twins may develop. The funnel of the oviduct catches the ovum and channels it down the tube to the uterus. If fertilisation has taken place during the journey, the embryo will implant in the uterus and develop and grow. If not fertilised, the ovum will be discharged through the cervix and vagina. The cervix is a ring of muscle separating the uterus and vagina. The vagina has three functions. It is: 1 the place where sperm are deposited by the male 2 the passageway for menstrual flow to leave the uterus 3 the passageway for the birth of a baby. Puberty At about the age of 10-14 years a girl's ovaries start to produce the female sex hormone oestrogen. At the same time her ovaries start to release ova. A number of other changes take place as well. A girl's breasts grow larger, her hips widen and hair grows in her armpits and pubic region. The uterus and the vagina also increase in size. Once puberty is reached females begin their menstrual cycle. The arrival of a girl's first period is known as menarche and indicates that her reproductive system has reached maturity. Chemical messengers called hormones control this cycle. Activities 1 Where are ova made? ______________________________________________________________________________ ______________________________________________________________________________ 2 How often are ova released? ______________________________________________________________________________ ______________________________________________________________________________ 3 Which are there more of, ova or sperm cells? ______________________________________________________________________________ ______________________________________________________________________________ 4 Describe how the female sex hormone oestrogen affects the body. ______________________________________________________________________________ ______________________________________________________________________________ 5 What happens to an ovum that is not fertilised? 3 ______________________________________________________________________________ ______________________________________________________________________________ 6 How does the uterus prepare for a fertilised ovum? ______________________________________________________________________________ ______________________________________________________________________________ Where do Ova and Sperm come from Meiosis is a special type of cell division used only for the production of gametes— sperm or egg cells. When gametes unite at the point of fertilisation their nuclei combine. If two human gametes each had 46 chromosomes and were to combine at fertilisation they would produce a single cell (or zygote) with 92 chromosomes. This cell would no longer be the cell of a human. Hence, it is important for the gametes to be produced with only a haploid number of chromosomes so that the zygote that is produced has the correct diploid number of chromosomes. Meiosis is similar to mitosis except that there are two divisions with four haploid cells being produced. The first division involves the separation of the pairs of chromosomes and the second division the separation of the chromatids. Fertilisation It is important to note that 28 days is the average length of this cycle. For some women it will be longer and for others it will be shorter. Timing for all other dates including ovulation and menstrual bleeding can vary, and even be missed altogether. If fertilisation takes place, days 15-28 will be vastly different. There are some important things to note about fertilisation in humans. The small amount of semen released at ejaculation (about 4 mL) contains millions of sperm. Many of these are killed by the acid in the female's vagina or simply are not strong enough or mobile enough to swim through the cervix. The ones that make it through the uterus swim into the oviduct in which the egg is travelling. Only one of these sperm, however, will fertilise the egg. Once the head of one sperm has broken through the egg's membrane, a barrier is set up stopping any other sperm from entering. How then are twins formed? Identical twins develop from a single ovum and sperm. Sometimes when the cell divides in two following fertilisation, it splits completely, and two embryos are implanted in the uterus lining. Because the two embryos have come from the one sperm and one ovum their chromosomes will be identical, giving them identical characteristics. Fraternal (non-identical) twins develop from the simultaneous release of two ova, which are fertilised by two different sperm. Different sperm and ovum means different chromosomes and therefore non-identical characteristics. 4 The growing embryo The dividing cells rapidly take on different forms, becoming nerve cells, blood cells, muscle cells, etc. These form tissues that in turn join with other tissues to become organs like the eye, heart and brain. By 6 weeks the embryo (about the size of a fingernail) has a pumping heart and a brain. A sac of fluid called the amniotic sac protects it. An umbilical cord joins the embryo to the placenta. The embryo's blood circulates through the placenta, picking up food and oxygen from the mother's blood and releasing carbon dioxide and other wastes into the mother's blood. Two months after fertilisation the embryo is now termed a foetus, and it has a face, limbs, fingers and toes. At 22-24 weeks the foetus' eyelids open and the hands begin to grip. At this stage the foetus looks very like a newborn baby, and begins to grow in length and put on weight. How to build a baby Once the embryo has formed it starts to grow through a process of cell division. Cells have the ability to replicate the DNA they contain. To do this the bases of the double helix separate from each other, in much the same way as a zip opens, leaving the bases exposed. Within each nucleus there are bases floating freely. These floating bases pair with the exposed bases and also attach themselves to the sugar and phosphate molecules of the adjacent base, causing two identical double helices to form. Mitosis Mitosis is the process that most cells use to divide. It is the process whereby a single cell divides to form two identical daughter cells. These daughter cells carry the same diploid number of chromosomes and exactly the same genetic information as the parent cell. The DNA within the nucleus has already duplicated itself when the cell starts to divide. The chromosomes shorten and thicken, becoming visible under a microscope. Each chromosome can now be seen to consist of two strands attached at only one point, the centromere. Each chromosome has made a copy of itself and now consists of two identical strands or chromatids. The process is precise. The 'double-stranded' chromosomes line up down the middle of the cell and split into their two chromatids. The chromatids move to opposite ends of the cell and when one of each chromatid reaches its destination, the cell divides into two identical cells, each with the same number of chromosomes as its parent. Questions 1 Why is it essential for the chromosomes to replicate before cell division occurs? _________________________________________________ _________________________________________________ _________________________________________________ Why is it important for the 'double-stranded' chromosomes to line up in single file down the centre of the cell prior to its splitting in two during mitosis? ________________________________________________ _________________________________________________ _________________________________________________ 3 If a cell started off with 28 chromosomes prior to going through mitosis how many chromosomes would it end with? 2 5 4 before cell division occurs? ______________________________________________________________________________ ______________________________________________________________________________ Why is it important for the cells that are produced to be identical to the parent cell in mitosis but not in meiosis? ______________________________________________________________________________ ______________________________________________________________________________ 5 Birth The normal position of the baby just before birth is upside down with its head resting just above the cervix. The cervix needs to open sufficiently to let the baby's head pass through into the vagina. At about this time the amniotic sac bursts and the amnion fluid escapes. This is commonly referred to as the 'waters breaking' and signifies the first stage of labour. The muscles in the uterus wall contract rhythmically throughout the birth. They press the baby's head through the cervix into the vagina, where the mother assists by pushing down with her abdominal muscles. The second stage of labour lasts from the time that the cervix is fully stretched until the baby is completely born. As soon as it is born the baby has its air passages cleaned of fluid and begins to breathe on its own. It is still attached to the placenta by the umbilical cord, which is clamped and then cut, releasing the baby from its mother. However, the placenta is still inside the mother's uterus. The expulsion of the placenta is called the afterbirth and is the third and final stage of labour. 1 Why is it not totally accurate to say that ovulation takes place on day 14 of the menstrual cycle? ______________________________________________________________________________ ______________________________________________________________________________ 2 What does this suggest about when fertilisation can occur? ______________________________________________________________________________ ______________________________________________________________________________ 3 Explain the difference between identical and non-identical twins. ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 4 When is the developing embryo termed a foetus? ______________________________________________________________________________ ______________________________________________________________________________ 5 Why can the umbilical cord be cut after birth? ______________________________________________________________________________ ______________________________________________________________________________ 6 Write each word in the box next to its meaning. cervix   ovum   foetus   sperm   embryo ova   vagina   ovaries   uterus   fertilisation ______________________________ The name for the baby soon after it has been fertilised. ______________________________ The name for the baby when it is bigger. ______________________________ The muscle that separates the uterus and the vagina. 6 ______________________________ The place where the fertilised egg attaches itself and where the baby grows. ______________________________ ______________________________ ______________________________ ______________________________ ______________________________ ______________________________ 7 The place where the baby comes out. What happens when an egg and a sperm meet? One female sex cell, or egg. More than one egg. Male sex cells. Places where the eggs are kept. Number the diagrams to represent the order in which they would occur. Write a brief description of the events taking place in each diagram. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Meiosis and Inheritance Gregor Mendel carried out experiments with pea plants to answer this question. He worked with pure-breeding red- and white-flowered pea plants. Pure breeding meant he could produce only red-flowered offspring from red-flowered parents and white-flowered offspring from whiteflowered parents. Mendel decided to use the pollen from red-flowered plants to cross-pollinate the white-flowered plants. All of the flowers that resulted from this cross were red. It seemed to Mendel that red somehow appeared stronger than white. He called red the dominant character and white the recessive character. Mendel then cross-pollinated these new red flowers. Each set of crosses that he performed produced both white and red flowers in roughly the proportions of 3/4 red flowers and 1/4 white flowers. It seems that genes work in pairs to determine which characteristic is shown or expressed. Geneticists would say that the gene with which Mendel was experimenting was pea flower colour and that the different forms of the gene (i.e. for red flowers and white flowers) are the alleles for that gene. The allele that produces a red flower is dominant so we can call it R. The allele for white flowers is recessive and we call it r. We use the capital and lowercase forms of the same letter, R and r, to show we are talking about the same gene. An RR combination of alleles will produce a red flower. Rr will also produce a red flower and only rr will produce a white flower. 7 The RR and rr combinations of alleles, where the offspring has identical alleles, are known as homozygous. The Rr combination of alleles is known as heterozygous. Genetic variations in people The chart shows some features that are dominant and recessive in people. 1 2 Carry out a survey in your class related to two characteristics. You could choose ability to roll the tongue, whether people have blue or non-blue eyes, whether people have free or attached earlobes, or any other suitable inherited characteristic. (a) Tabulate your results. (b) Which traits seem to be dominant and recessive in your class? Note: Tongue rolling may be learnt. Draw up a family tree for either yourself or a friend, showing the presence or absence of at least three features. Try to include at least four people in your tree. Birth control Eighty-five percent of women who use no contraceptives during vaginal intercourse become pregnant each year. The only guarantee against pregnancy is not having vaginal intercourse. Other contraceptive methods can greatly reduce the risk of pregnancy during vaginal intercourse. The Pill The Pill is taken daily in a monthly series. The Pill contains both synthetic oestrogen and progestin. They are like the hormones made by a woman’s ovaries. Usually, these hormones prevent the ovaries from releasing an egg (ovulation). They also thicken the cervical mucus, which would prevent sperm from joining with an egg. Rarely, they prevent a fertilized egg from 8 implanting in the uterus. Of every 100 women who use the Pill, eight will become pregnant during the first year of typical use. Fewer than one will become pregnant with perfect use. The Pill works best if taken at about the same time every day. Pregnancy can happen if • • • pills are started too late in the cycle two or more pills are missed in a row pills are taken in the wrong order Condoms Condoms collect semen before, during, and after ejaculation and can keep sperm from entering the vagina. Of 100 women whose partners use condoms, about 15 will become pregnant during the first year of typical use. Only two women will become pregnant with perfect use. More protection against pregnancy is possible if condoms are used with a spermicide foam, cream, jelly, suppository, or film. Latex condoms offer very good protection against HIV. They also reduce the risk of other sexually transmitted infections, including gonorrhea, syphilis, Chlamydia, chancroid, trichomoniasis, HPV, and herpes. Reproduction in Plants Angiosperms Plants reproduce in many different ways. Most of the plants you are familiar with are angiosperms or flowering plants. These range from mighty eucalypts to small herbs and grasses. Flowers are the reproductive organs for these plants. Some flowers contain only male gametes, sperm, which are contained in pollen on the stamens. Some flowers contain only female gametes, eggs, which are stored in the pistils. Many flowers, however, contain both types of gametes. Stamens are made up of two parts: the anther and the filament. The anther is a sac on the end of each filament that produces the pollen. Pistils are made up of three parts: the stigma, the style and the ovary. The ovary can be found at the base of the pistil and contains ovules in which the eggs are stored. The stigma is often feathery or sticky to enable it to capture pollen. The receptacle at the base of the flower supports all the reproductive parts. Pollination In order for a new plant to be formed the sperm must somehow meet the eggs. The transfer of pollen from the anther to the stigma is called pollination. Self-pollination is the transfer of pollen from the stamens to the pistils of the same plant. If the pollen is transferred from one plant to another then cross-pollination has occurred. Insects and other animals and the wind are responsible for taking the pollen from one plant to the next. Following pollination, a pollen tube grows down the style towards the egg cells in the ovary. The pollen tube contains the sperm and one of these fertilises the egg. Fertilisation occurs in the ovary. Fertilised eggs grow into plant embryos. Structures develop around each plant embryo, forming seeds. The ovary then enlarges to become a fruit. Fruit structures range from apples, oranges and grapes to structures such as gumnuts, Banksia follicles and even wheat grains. Most of the fruit we eat has been bred for increased fleshiness and flavour and fewer seeds. Activity 1 Shape, colour and scent are important for flowers that contain only male or only female gametes. Explain why this is so. 9 __________________________________________________________________________________ __________________________________________________________________________________ __ 2 Some flowers have stamens that extend far beyond their petals. Suggest how this could be both an advantage and a disadvantage to the plant. __________________________________________________________________________________ __________________________________________________________________________________ __ 3 Would you get much variety in plants if self-pollination took place most of the time? __________________________________________________________________________________ __________________________________________________________________________________ __ 4 A primary school student has brought you a flower and asked you to identify it as male or female. How will you respond? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ____ Water cycle Water can exist in solid, liquid or gaseous form and a balance must be maintained between all three parts of the Earth and between all three forms of water. Thus evolved the water cycle. Of course there are many factors that influence the cycle on a day-to-day basis. Evaporation from the oceans provides most of the water vapour. As a result, the air over the oceans becomes loaded with vapour. Winds move this air over the land until it reaches mountain barriers that cause it to rise. As the air rises, it cools and its density increases. This means that it can hold less water and reach saturation (or a temperature known as dew point). Further increases in altitude result in the water vapour condensing to form precipitation or rain. 10 Find the meaning of the following sections of the water cycle. Evaporation __________________________________________________________________________________ __________________________________________________________________________________ __ Transpiration __________________________________________________________________________________ __________________________________________________________________________________ __ Accumulation __________________________________________________________________________________ __________________________________________________________________________________ __ Condensation __________________________________________________________________________________ __________________________________________________________________________________ _ Subsurface Runoff __________________________________________________________________________________ __________________________________________________________________________________ __ What happens to the water after it has fallen as rain? Some of it makes it way back to the oceans via rivers. Humans in dams and reservoirs store some. A certain amount finds its way into ground water (e.g. the Sub-Artesian Basin) and may then rejoin the cycle at various points. Lastly, plants and animals use some. Water cycles through living things. Plants absorb it from the ground and lose much of this as vapour through their leaves in a process called transpiration. Animals drink it or obtain it in their food and lose it either by evaporation (e.g. sweating) or when they excrete. Water a Priceless Resource 11 Early European settlers in Australia faced the problem of finding reliable water supplies. In the 1880s an apparently limitless water source was found in inland areas. Farmers dug bores and tapped into underground water that was under pressure. They had discovered the water-bearing layers (aquifers) of the Great Artesian Basin that lies under one-fifth of the continent. At first, a lot of the water was allowed to run freely and was wasted, but now farmers are aware that the water supply is limited and must be conserved. Changes in soil Irrigation of areas like the Murray River and Murrumbidgee River valleys has been vital to Australia's agriculture. Production of many crops and irrigated pastures are important to our economy. However, irrigation has also contributed to a problem that already existed naturally in many soils—a high salt level (or salinity). Salt levels in soils rise because of low rainfall and high evaporation rates. Higher rainfalls can dissolve salt and carry it off in rivers to the ocean. High evaporation rates mean that traces of salt in groundwater are left as residue when the water evaporates. In addition, many rocks in Australia were laid down when seas covered areas of the continent and they already contain a lot more salt (sodium chloride) than rocks laid down in freshwater conditions. When they weather, they form a salty soil. Artesian water also contains a lot of dissolved salt so when it reaches the ground level and evaporates, it contributes to salt residues in soil. Wind can contribute to soil salinity by carrying salt onto the land in sea breezes. Human activities have increased soil salinity. Clearing of land has contributed for two reasons: top soil has been washed away, exposing subsoil layers which contain more salt, and water tables have risen, bringing dissolved salts closer to the surface. Irrigation also causes the water table to rise as extra water is absorbed into the groundwater. If the soils are very sandy and porous, water penetrates deeply. Murray-Darling River system The Murray-Darling river system is the largest river system in Australia. About 70% of its water is used for irrigation and less than 20% reaches the ocean. Australian wildlife has adapted to seasonal changes in river volume but the amount of water taken from the river for storage in dams or irrigation means that drought conditions along the river occur about six in every 10 years instead of about once every 20 years. Floods which flush out the river system now occur only once every 14 years compared with once every 3 years before waters were diverted for other purposes. In 1991 and 1992, the Darling River became the longest stretch of poisoned river ever found, with 1000 km of its length choked by poisonous blue-green algae. Pollution of the river by sewage runoff and fertilisers contributed to this algal growth. Stock losses occurred immediately but it is also believed the toxins produced by the algae will have long-term effects on surviving sheep and cattle. The 12 levels of blue-green algae only dropped when sufficient rainfall flushed out the river. Blue-green algal blooms continue to break out along the river system. Increasing salt levels, caused by run-off from soils with increased salinity, also pose a problem for the river's health even though salt is currently being pumped away at the rate of about 270 000 tonnes per year. The CSIRO has estimated that 12 billion trees need to be planted in the MurrayDarling Basin to keep salinity at a moderate level. In 1996, huge bank collapses occurred along a 2000 km stretch of the Darling River. This happened at a time when a record amount of water was being extracted from the river for agricultural purposes. 1 Activity What is the Great Artesian Basin? __________________________________________________________________________________ __________________________________________________________________________________ __ 2 Where does the water in the Great Artesian Basin originate? __________________________________________________________________________________ __________________________________________________________________________________ __ 3 What natural causes contribute to high salt levels in Australian soils? __________________________________________________________________________________ __________________________________________________________________________________ __ 4 Which human activities contribute to soil salinity? __________________________________________________________________________________ __________________________________________________________________________________ __ 5 What probably caused the blue-green algal bloom in the Darling River in 1991? __________________________________________________________________________________ __________________________________________________________________________________ __ Carbon & Nitrogen Cycles Carbon is a chemical element occurring in all living organisms. It is found in proteins, carbohydrates, lipids and many other organic compounds. The carbon dioxide in the atmosphere provides plants with their carbon through photosynthesis. The carbon is converted into a carbohydrate (glucose). As already discussed this glucose is used for many things within the plant —starch for storage, cellulose for cell walls and so on. Animals obtain their carbon through consumption of the plants or by eating other animals that eat the plants. The carbon is in the food chain but the atmosphere does not have an endless supply of carbon dioxide. Therefore the carbon must be put back—recycled. How does a plant or an animal return carbon to the atmosphere? 13 Remember that living organisms respire, that is, they use oxygen to release energy in their cells. Two by-products of this cellular respiration are water and carbon dioxide. Thus the carbon is returned to the atmosphere. Animals may also recycle carbon by excreting carbon in the soil. When an organism dies, decomposers release the carbon back into the soil and atmosphere by breaking down the organism's organic compounds. Other means of releasing carbon into the atmosphere come from the burning of fossil fuels. Coal, gas and petroleum are formed from the remains of plants and animals. As such they hold a store of carbon just waiting to be released into the atmosphere as carbon dioxide. The carbon cycle appears quite simple when compared to the second essential nutrient, nitrogen. Nitrogen is present in the proteins manufactured by all living organisms. Its cycle is dependent on the action of certain kinds of bacteria. Plants are not capable of absorbing nitrogen from the atmosphere as they can carbon. They must obtain their nitrogen from the soil— the habitat of the bacteria. When a plant or animal dies nitrogen is released into the soil as ammonia (a nitrogen compound, NH3). Bacteria in the soil use this ammonia as their source of energy. In using this energy they release nitrates. Plants take up both ammonia and nitrates through their roots, with nitrate being more easily absorbed. A second group of bacteria called nitrogen-fixing bacteria can absorb nitrogen as a gas from the air spaces in the soil. They then build this gas into ammonia, which is converted to nitrates by yet more bacteria. Rainwater can assist in the nitrogen cycle. Nitrates are very soluble, that is, they dissolve easily in water. As the rainwater passes through the soil it dissolves the nitrates, removing them or sending them deeper into the soil. And then there is another group of bacteria ... These bacteria obtain their energy by breaking down the nitrates into nitrogen gas which escapes from the soil into the atmosphere. 14 Activity 1. List the role each of the three groups of bacteria plays in the nitrogen cycle? __________________________________________________________________________________ __________________________________________________________________________________ __ 2. Why is nitrogen important for plants and animals? __________________________________________________________________________________ __________________________________________________________________________________ __ 3. Matter is cycled through an ecosystem. Explain how the energy in an ecosystem is renewable. __________________________________________________________________________________ __________________________________________________________________________________ __ 4. In agriculture most of the crop is usually removed before it decomposes. How do farmers maintain the nitrogen in their soil? __________________________________________________________________________________ __________________________________________________________________________________ __ 5. List and describe the three different forms of the element carbon. __________________________________________________________________________________ __________________________________________________________________________________ __ 6. Where do plants get the carbon that they need to make sugar? __________________________________________________________________________________ __________________________________________________________________________________ __ 7. Describe three ways in which carbon can return to the atmosphere. __________________________________________________________________________________ __________________________________________________________________________________ __ __________________________________________________________________________________ __________________________________________________________________________________ __ 8. Where does respiration take place? 15 __________________________________________________________________________________ __________________________________________________________________________________ __ Food chains and webs Living things can be classified into three groups according to their role in the ecosystem. 1. Producers are organisms that produce their own food from their non-living environment. For example, during photosynthesis plants produce sugars and starches (carbohydrates) from carbon dioxide and water, using energy from sunlight. 2. Consumers are organisms that eat other organisms or their products. All animals are in this category. Those that eat plants are called herbivores; those that eat animals are called carnivores; those that eat both plants and animals are called omnivores. Consumers cannot make their own food, so they must eat other organisms to provide them with the energy and chemical building blocks to carry out their activities. 3. Decomposers are bacteria and fungi that break down plant and. animal remains into simple compounds and make them available again for use by plants and animals. For example, in a compost heap, bacteria and fungi break down food scraps and plant cuttings, which can then be used to enrich garden soils so that plants can grow better. The feeding relationships between producer and consumer organisms can be written down in a series of steps called a food chain. For example: Grass —> grasshopper —> magpie Each arrow indicates 'is eaten by': the grasshopper, which is eaten by the magpie, eats the grass. Here is another example: Grass —> grasshopper —> frog —> snake —> kookaburra The arrows also indicate the direction of the flow of energy from one organism to the next. In both of the food chains the grass is the producer and the animals are the consumers. The grasshopper is called the first-order consumer and the magpie and frog are second-order consumers. The snake and the kookaburra are third- and fourth-order consumers, respectively. The two food chains have some organisms in common, and there are other food chains that could be drawn which include the other animals. When many food chains interlock, a food web is created. 16 Energy and ecosystems Imagine that you are eating fish and chips for dinner. The fish most commonly sold is flake, which is shark meat. The food chain that links you and a shark is illustrated. The alga is the producer in this food chain. An animal that eats a producer is called a first-order consumer. The small fish is the first-order consumer. A consumer that eats a first-order consumer is called a second-order consumer. The large fish in the figure below is therefore a second-order consumer. The shark is a third-order consumer and the young people enjoying a meal of fish and chips are fourth-order consumers. Activity Jessica and Matthew made some observations over a period of a week about the feeding habits of a number of organisms in a small pond. Their results are listed below. • Snails eat water plants and algae. • Tadpoles eat algae. • Small fish eat snails, algae and water plants. • Larger fish eat snails, small fish and tadpoles. 1. Construct a food web using the above information. Start with the producers at the bottom and work upwards. Make sure your arrows face the right way. a. Which organisms are the producers? 17 __________________________________________________________________________________ __________________________________________________________________________________ __ b. Which organisms are first-order consumers? __________________________________________________________________________________ __________________________________________________________________________________ __ c. Which organisms are both second- and third-order consumers? __________________________________________________________________________________ __________________________________________________________________________________ __ d. Which organism is an omnivore? __________________________________________________________________________________ __________________________________________________________________________________ __ e. Which organisms are predators of the snail? __________________________________________________________________________________ __________________________________________________________________________________ __ f. Which organisms are competitors of the tadpoles? __________________________________________________________________________________ __________________________________________________________________________________ __ g. What would happen to the water plants and the larger fish if the snails increased in number? __________________________________________________________________________________ __________________________________________________________________________________ __ h. What would happen to the snails and the larger fish if the small fish disappeared? __________________________________________________________________________________ __________________________________________________________________________________ __ The biosphere of life 18 The biosphere is the place where all life as we know it exists. It comprises the Earth and its atmosphere. Beyond the atmosphere there is space. Our biosphere is isolated in space. So what enters or leaves our biosphere? In terms of matter, not much. Gravity prevents the atmosphere and substances from leaving, and meteorites represent the only arrival of matter. We say that the biosphere is a closed system, and all the matter contained within it is finite. Non-renewable resources can run out, and unwanted wastes can accumulate. What can enter (and leave) the biosphere is energy. Through nuclear fission the Sun provides us with a limitless supply of light and heat energy. Much of the energy is reflected back into space or absorbed by the atmosphere. The estimated 15% which reaches the Earth's surface can be trapped by plants. Green plants have the ability to trap light energy, and convert it into chemical energy in order to make a simple sugar, glucose. They do this in a process called photosynthesis: light energy carbon + water—> glucose + oxygen dioxide Fortunately for animals, this also removes carbon dioxide from the atmosphere and adds oxygen to it. The fate of the glucose is equally vital. Plants can convert it to other organic compounds such as more complex carbohydrates, lipids, proteins and vitamins. These then form the basis for all food on the planet, through many varied food chains. That is not the end of the story. When plants or animals die or produce wastes, these are recycled back through the biosphere. Remember, the supply of energy is limitless, not the matter to make up the chemical compounds. Gases are also recycled through the biosphere. Just think, you could have atoms as part of you that were once part of a dinosaur, a tree, a bacterium or even one of the gases of the atmosphere. ENVIRONMENTAL ISSUES Work in a small group and in the following space 1. List as many environmental issues as you can. 2. Classify each as a local' or 'global' problem. 19 What could be meant by the slogan 'Act locally, think globally'? __________________________________________________________________________________ __________________________________________________________________________________ __ __________________________________________________________________________________ __________________________________________________________________________________ __ 20 Biotic and abiotic The biosphere is made up of many ecosystems. In an ecosystem organisms interact with each other and their environment in a balanced way. Ecosystems can be further divided into habitats and environments. A habitat is the place where an organism lives. For example, a fish's habitat may be in a section of the harbour. An organism's environment includes both its physical (abiotic) and living (biotic) surroundings. The fish's abiotic environment includes coastal currents, tides, the temperature, water salinity, and chemicals added by human activities. Its biotic environment includes the organisms on which it feeds, or those that compete for the food and space (these may be its own or different species), and those, which may feed on it. All these environmental factors influence the survival of the fish. The broad area of science that deals with the study of organisms in their environments is called ecology. A better understanding of ecology is needed for humans to deal with many of the ecological issues that have arisen because of our impact on ecosystems. Activity 1 What is the difference between the biosphere, an ecosystem and a habitat? __________________________________________________________________________________ __________________________________________________________________________________ __ __________________________________________________________________________________ __________________________________________________________________________________ __ 2 Why is the biosphere regarded as a closed system? Explain how a carbon atom found in carbon dioxide in the atmosphere could become part of your body. __________________________________________________________________________________ __________________________________________________________________________________ __ 3 Explain why photosynthesis is essential to life. __________________________________________________________________________________ __________________________________________________________________________________ __ 4 List three biotic and three abiotic parts in the environment of a kangaroo. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ___ Cars, greenhouse and Kyoto Greenhouse effect Like the air in a greenhouse (or glasshouse) the Earth's atmosphere traps some solar radiation and warms the surface of our planet. About 10% of the energy reaching Earth as solar radiation is reflected by dust particles in the air or from the surface of clouds. 21 Much of the non-visible solar radiation that reaches Earth is absorbed by gases in the atmosphere, mainly carbon dioxide, ozone and water vapour. These are known as greenhouse gases. Ozone absorbs UV radiation, while carbon dioxide, water vapour and clouds absorb most of infrared radiation. The average temperature of the Earth remains relatively stable when the proportion of these gases in the atmosphere is balanced. Without the greenhouse effect of these gases the Earth's average temperature would be around -18°C rather than 15°C, affecting weather conditions, plant growth and animal growth. Atmosphere scientists fear the balance of these gases has been upset so that we have what they generally refer to as the enhanced greenhouse effect (often just called the greenhouse effect), an increase in the amount of heat being retained by the atmosphere. Other greenhouse gases, such as methane, nitrous oxide, chloroform, and chloro-fluorocarbons (CFCs), have also increased in concentration or have been introduced into the atmosphere as a result of the industrialisation of our society. Methane (CH4) is formed from the breakdown of organic matter. Cows and sheep produce methane from the bacterial digestion of cellulose. Rice paddies, garbage tips, coal mines and natural gas fields also release quantities of methane. Nitrous oxide is produced in car exhausts and through many industrial processes and the use of nitrogenous fertilisers and burning of forests. Chlorofluorocarbons were invented in the 1920s and were widely Did you Know used in refrigerators, as propellants in aerosol cans and to create the There is evidence from bubbles in plastic foam. Concern about their effect on the ozone ice core samples taken layer has led to international agreements to phase out their use. in the Antarctic that the CO2 concentrations in the atmosphere Kyoto Agreement have increased by The United Nations Framework Convention on Climate Change was 25% in the last 200 held in Kyoto Japan during December 1997. Here, many countries years. agreed to reduce their emissions of greenhouse gases. However, the Australian government would only agree to limiting the growth of emissions but not to reducing them. In 1994, Australia's total greenhouse gas emissions were calculated to be approximately 576 million tonnes. The main sources of these gases were motor vehicles, electricity production and land clearing. Activity 1 How does the Earth's atmosphere maintain relatively stable surface temperatures? __________________________________________________________________________________ __________________________________________________________________________________ __ 2 What factors affect how much solar radiation reaches the Earth's surface? 22 __________________________________________________________________________________ __________________________________________________________________________________ __ 3 Explain the difference between the terms 'greenhouse effect' and 'enhanced greenhouse effect'. __________________________________________________________________________________ __________________________________________________________________________________ __ 4 The amount of water vapour in the atmosphere is not likely to be altered directly by human activity. What factors would cause the concentration of water vapour to increase? __________________________________________________________________________________ __________________________________________________________________________________ __ 5 Why do you think the amount of methane in the atmosphere has increased so dramatically? __________________________________________________________________________________ __________________________________________________________________________________ __ 6 Deforestation is a major environmental issue not only in terms of the logging of native forests but because it contributes to the enhanced greenhouse effect. How would this practice cause changes in the concentration of greenhouse gases? __________________________________________________________________________________ __________________________________________________________________________________ __ __________________________________________________________________________________ __________________________________________________________________________________ __ 7 Do you think there are advantages to an enhanced greenhouse effect? __________________________________________________________________________________ __________________________________________________________________________________ __ Conservation and the environment So what if a species becomes extinct, or a rainforest disappears to make way for farmland or developments? Is saving them just too difficult in a world with an expanding population and all its needs? Early you made a list of the environmental problems we face. This could have been very long and maybe even a little depressing. By understanding the cause of some of these problems, we 23 humans should be able to find solutions. We cannot 'give up' on the planet. It is the only one we have! Conservation Conservation is the protection and careful management of our natural resources. Conservation or national parks are one means of protecting some of the great variety of living organisms (referred to as the biodiversity) in Australia. One only has to look at a list of threatened or endangered species to realise that urgent action is required to save many of our native animals and plants. What has caused this loss of biodiversity? In Australia there are two main causes: • loss of habitat—this may result from farming, mining, building cities or climatic changes • introduced species—these may compete with native species for food (e.g. rabbits), or directly kill wildlife (e.g. cats, foxes). Introduced plants can also overrun natural vegetation. In other parts of the world hunting and poaching of some animals (e.g. rhinoceros and tigers) has been an additional problem. In Australia the yellow-footed rock wallaby was shot to near extinction as sport. The clearing of forests for wood and developments is also a controversial issue. Each year Australia exports about 5 million tonnes of woodchips to make paper and disposable products. In addition we use about 1 million tonnes of paper per year. Ecologists now talk of sustainable development. This was defined by The World Commission on Environment and Development in 1987 as 'development which meets the needs of the present without compromising the ability of future generations to meet their own needs'. From such definitions come the ideas of the 3Rs—'reduce, recycle, reuse'. Consider your own lifestyle. How well does it fit in with the definition? Does extinction really matter? Does it really matter if a few species that we have never really heard much about become extinct? The answer should be 'yes' for a number of reasons. Each organism has a role in an ecosystem, for example a link in a food chain. If it is lost then that role may not be performed and many other species may be affected. Many organisms are of great value to humans, such as a source of medicines or food, or to keep another organism's numbers in check. We have yet to catalogue the vast variety of life on the planet and its potential uses. Who knows what useful compounds as yet remain undiscovered. The final reason is an ethical one. Do we have the right to cause the elimination of another species? How would future generations view us if we allowed this to happen? How can you make a difference Individuals can have an effect in many ways: by deciding what they will and won't buy, by applying the rules of the 3Rs, by becoming aware and using their vote wisely. Of course there are many issues involved in conservation. These often involve jobs and other economic aspects. For example, the wood chipping industry employs many people and the economies of some towns rely on the money generated from it. Mining companies are always looking for new resources. They also employ many people and contribute money to the economy by way of taxes and royalties. Our challenge is to balance these aspects and to leave the planet no worse off for future generations. Activity 1 What is meant by 'biodiversity'? __________________________________________________________________________________ __________________________________________________________________________________ __ 2 What human activities have caused animals and plants to become endangered? 24 __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ____ 3 List the reasons why it is important to conserve endangered species. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ____ 4 In your own words explain what is meant by 'sustainable development'. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ____ What about human population It took more than 3.5 million years for the human population to reach 2.5 billion. To add another 2.5 billion people has taken just 30 years. At the moment the world's population increases every year by about 95 million people. That is more than five times Australia's population every year. The areas of most rapid population growth are Asia, Africa and South America. As the population continues to increase, the effects of human activities such as clearing of natural habitats, production and release of pollutants, industrialisation and urbanisation will also increase. If the population continues to grow at its current rate the impact on the environment could be disastrous, with the worst possible outcome being our own extinction. Huge increases in the population of a species are not uncommon in nature but usually they are eventually controlled by factors such as food supply, space shelter, predators, competitors and disease. Will the human population stabilise under these controls or will we control it before disaster occurs? Some limits to growth Improved technology has brought about a 'Green Revolution' in recent decades. Developments in plant and animal breeding and the use of fertilisers and irrigation have helped to increase food production for a growing world population. However, there is a price to pay for these advances. Water and soil are two essential resources for human survival and they are both finite. Only 3.5% of water on Earth occurs as fresh water and most of this is in the form of ice in polar regions. The demand for fresh water is increasing twice as fast as human population growth. At the same time water supplies are becoming polluted with fertilisers, sewage and pesticides. Finding reliable water supplies has always been a problem in Australia because it is such a dry continent, and water pollution adds to this problem. 25 Land degradation is a major global problem. Arid regions such as Australia are especially fragile. Human activities such as clearing of land, irrigation and increasing frequency of fires have contributed to loss of top soil and increasing soil salinity. It has been estimated that the survival of 250 million people around the world is currently threatened by land degradation. More of the Australian continent is being turned into desert each year as a result of both natural and human activities. Some possible solutions Large-scale clearing of land for agriculture can reduce rainfall in that area. Large-scale planting of native trees may help to modify rainfall patterns as well as helping to prevent soil erosion and reduce soil salinity. Farmers should not overstock their lands and they need to review their use of irrigation. Mulching of ground can be a helpful step in regenerating degraded land. Conservation is the protection and careful use of natural resources. There are many ways that we can contribute to conservation. Examples include planting trees, re-using and recycling materials such as glass and paper, composting food wastes, and buying products that are less harmful to the environment. Activity 1 List the factors that can control population numbers in natural populations. __________________________________________________________________________________ __________________________________________________________________________________ __ 2 What two natural resources are under particular threat? __________________________________________________________________________________ __________________________________________________________________________________ __ 3 Why is Australia not capable of supporting the large populations found in other parts of the world? __________________________________________________________________________________ __________________________________________________________________________________ __ 4 Design a poster entitled 'Threat to survival'. __________________________________________________________________________________ __________________________________________________________________________________ __ Find each of the following words. 26 REPLICA GREENHOUSE OXYGEN NITROGEN SALINITY E D E R E G N A D N E E P I G I N S I O E P A D A Q U I F E R P V M N O I T A S I L I T R E F I INHERITANCE ENVIRONMENT DOMINANT CYCLICAL EXTINCTION I R D A E N L R T I T E T I R Y R E P X C A M T S E E N C Y E U O P O R Y I I E I T A O N N P Y N S L E C L L R E N I E I I R N M O L C L S A P I R S E Y T O O E I U E I D E M E U I T D R D T N G T S C I O O O R I E T O U E T N I S A D E H E S R E U G C U REPRODUCTION ENDANGERED POLLUTION CARBON ANGIOSPERMS D A O I L I N N R A E R U E T S E U N V E E C E C U T R C N I O X C O E E Y V S D L C O O T O I T S I R C I C N F A E X S C N C I I G L D L I I R R Y A C E S B N I E O T R T B E G A E C E T I C U I T I I O N E E N F Y A R N T B A G R N N N I R C E G S O C BIODIVERSITY FERTILISATION AQUIFER RECESSIVE CYCLE I E C N A T I R E H N I N V T C O H O H E I A S A L I N I T Y S N N N E I R E E N L G E P A I R E I Q S S F U V E V I V N I A I 27 Review Accumulation - the process in which water pools in large bodies (like oceans, seas and lakes). Condensation - the process in which water vapour (a gas) in the air turns into liquid water. Condensing water forms clouds in the sky. Water drops that form on the outside of a glass of icy water are condensed water. (This term appears twice in the diagram.) Evaporation - the process in which liquid water becomes water vapour (a gas). Water vaporizes from the surfaces of oceans and lakes, from the surface of the land, and from melts in snowfields. Precipitation - the process in which water (in the form of rain, snow, sleet, or hail) falls from clouds in the sky. Subsurface Runoff - rain, snowmelt, or other water that flows in underground streams, drains, or sewers. Surface Runoff - rain, snowmelt, or other water that flows in surface streams, rivers, or canals. Transpiration - the process in which some water within plants evaporates into the atmosphere. Water is first absorbed by the plant's roots, and then later exits by evaporating through pores in the plant. 28 Human impact on the water cycle Humans, like all living organisms, need water, not only for drinking, but also for a range of other activities including irrigation, washing, industry, and even flushing toilets. Our demands are great, but they need to be balanced with the supply. We must also ensure that we do not harm our water supplies. Not just for our own sake but for that of all living things. Firstly let us examine the balance. The overuse of water for irrigation especially along the MurrayDarling Basin causes changes in salinity, resulting in land loss by dry-land salinity, and river salting. Scientists are working to 'intercept' the salt as it flows along the river. Planting more trees along the river has also been shown to reduce the problem. Factories often use water for cooling. This means that the water returned to the waterway can often be warmer than is desirable for the organisms that live in it. Another obvious problem for waterways is pollution. This not only occurs in rivers and dams, but also in the oceans. What things pollute the water? • Nutrients, such as fertilisers—an excessive amount of these in the water can cause excessive growth of algae, called blooms. This can upset the oxygen balance in the water and some also produce toxins. The process of excess nutrient build-up is called eutrophication. • Toxins—these can include pesticides (see section 10.4), heavy metals and industrial wastes. Many aquatic creatures can bio-accumulate toxins to alarming levels. • Oil—a particularly unpleasant pollutant, which is not only toxic, but also coats animals and threatens their lives. • Detergents—can affect the life cycles of some animals, and contribute to eutrophication. • Physical pollutants—such as litter, especially plastics that can entangle animals. 1 Which part of the water cycle represents water in its liquid form? In its gaseous form? __________________________________________________________________________________ __________________________________________________________________________________ __ 2 How does water, which has fallen as rain, make its way back to the oceans? What things could be added to the water as this happens? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ ____ 3 How might the following affect the water cycle? a. using more water for agriculture __________________________________________________________________________________ __________________________________________________________________________________ __ b. building factories next to rivers __________________________________________________________________________________ __________________________________________________________________________________ __ c. washing cars in the street so that the water goes down the storm water drain 29 __________________________________________________________________________________ __________________________________________________________________________________ __ d. using too much fertiliser on crops __________________________________________________________________________________ __________________________________________________________________________________ __ Graphing Activity The following table gives an estimate of the world's population from 1650 to 1990. Graph this on graph provided notice there is room for figures up to the year 3000. Year Population in billions 1650 500 1700 575 1750 675 1800 825 1850 1050 1900 1525 1950 2500 1990 5500 1 2 3 4 5 6 7 Why are these said to be estimated rather than actual world population figures? By how much did the population increase from 1650 to 1950? By how much did it grow from 1950 to 1990? Use your graph to estimate the world's population in the year: a 2050 b 3000 What do you think life will be like in the year 3000? What problems might the people of this time face? What solutions might be available? Some countries such as China have laws restricting the number of children permitted to a couple. Is this fair? Should all countries do this? (People in rich countries have more impact on the environment.) Should religious beliefs interfere? What else do you think could be done to cope with the world's increasing population? Discuss your ideas with others in the class. 30