ecology.pdf

Ecology Definitions **Need to Know all definitions** Ecology is the study of the interrelationship of plants and animals with each other and with their environment. An ecosystem refers to organisms and their interactions with their environment. Biosphere is...

Ecology Definitions **Need to Know all definitions** Ecology is the study of the interrelationship of plants and animals with each other and with their environment. An ecosystem refers to organisms and their interactions with their environment. Biosphere is all the parts of the earth where life exists. Habitat is the place where a species lives. Abiotic Factors are non-living features of the environment. Edaphic Factors are abiotic factors relating to soil. Biotic Factors are influences of living organisms on each other. Every species has its own set of conditions that it requires. These are called environmental factors. They include abiotic and biotic factors and vary greatly depending on whether the environment is terrestrial (land) or aquatic (water). Each species has adaptations to its environment, Adaptations are the features of an organism that allow it to have a better chance of survival in its habitat. Environmental factors affecting living organisms Biotic Factors - Feeding: If a species is used as food by another species, then its population will be reduced. If a species that is used as food is plentiful, then the consumer will become more numerous as it will be able to produce and feed more young. - Disease: Disease is generally caused by other living things. Disease usually reduces populations, sometimes very significantly. - Pollination: The transfer of pollen from an anther to a stigma. Carried out by insects such as bees. If bees are scarce, then pollination is not as successful and the number of seeds produced will dop, which will affect the plant population. - Nitrogen-fixing bacteria: Important in maintaining soil fertility. Found in the root nodules of leguminous plants and free-living soil. Replace nitrates used by the plants. - Decomposers: Break down the remains of dead plants and animals to the soil to be reused. Abiotic Factors - Climatic Factors: a. Light intensity has a major influence on the distribution of plants and some animals. Daisy’s only grow in areas where there is strong light exposure. Bluebells can photosynthesise in very little light and will grow only in areas with a lot of shade. b. Temperature is important in controlling the rate of chemical reactions. Temperatures vary very little in large bodies of water. Organisms living in water tend to be far less tolerant to heat changes. A 5oC change in temperature can kill a fish as it has no mechanisms to adapt to these changes. c. Exposure to the elements is another factor in coastal systems. Plants that live in the intertidal zone are exposed to large changes in their environment up to four times a day. They have many adaptations to survive the changes in its environment. - Edaphic Factors: a. pH is the measure of acidity or alkalinity of the soil. pH affects the availability of nutrients to the plants. Most plants like neutral to slightly alkaline soils. b. Mineral Content is determined by the underlying bedrock. Minerals are vital for plant growth. c. Water content is important because the minerals are obtained from the soil while they are in solution, if there is insufficient water, the soluble minerals will not be available. The plants will wilt, and photosynthesis will be reduced. Too much water can deprive the roots of oxygen and reduce growth. d. Humus is a dark organic substance made from decaying plant and animal material. It provides a good source of nutrients for plants and increases the ability of the soil to retain moisture. Abiotic Factors **Need to know examples from terrestrial and aquatic habitat of each factor** Factor Effect Example Altitude Higher altitudes are Trees cannot live at cooler, wetter, windier very high altitudes. than lower altitudes Aspect (i.e., direction a North-facing slopes are More plants grow on surface faces) cooler and darker than south-facing slopes. south-facing slopes.  Steepness Steep slopes lose Conifers can grow on water quickly and soils steep slopes (because are washed away. their leaves lose very little water). Climatic Factors Factor Effect Example Temperature Affects the rate of Higher temperatures reactions in living cause rapid plant things. growth in summer. Lower temperatures cause hibernation in hedgehogs and frogs in winter. Humidity (amount of High humidity reduces Woodlice are restricted water vapour in the air) evaporation. to the humid conditions within decaying leaves. Day length Affects plant flowering Many plants produce and germination along flowers due to the with migration, longer days in spring. hibernation, and Swallows migrate due reproduction in animals. to shorter autumn days. Light intensity Affects the rate of Trees grow tall to get photosynthesis. more light. Wind Causes physical Trees exposed to wind damage. grow better on the sheltered side and Increases evaporation. appear to lean away from the wind. Helps spread spores and some pollen and seeds. Edaphic Factors Factor Effect Example Soil pH Plants and animals are Acid soil (e.g., Bogs) adapted to specific pH have a pH less than 7, values. and support bog moss and heather. Neutral soils have pH values close to 7 and are preferred by most plants. Alkaline soils have pH values greater than 7, and are preferred by lime-loving plants e.g., birdsfoot trefoil and bee orchid. Soil type (determined by particle size) (a) sand (large Good drainage and air Few earthworms in particles) content. sand (no humus to eat). Low mineral and water content. (b) clay (small Impermeable to water Plants do not grow well, particles) and air. as the soil is too wet and difficult for roots to Easily waterlogged. penetrate. Organic matter (humus) Decaying organic Vital to plant life. matter (humus) Provides food for provides food, helps organisms such as bind soil particles, earthworms.  retains water and minerals Water content Absorbed by roots. Plants need to absorb water for transpiration, photosynthesis, and general metabolism. Minerals dissolve in water and are absorbed by roots. Air content Provides oxygen for Lack of oxygen in soil roots, microorganisms, prevents plant and and animals. animal growth. Mineral content Needed by plants. A lack of mineral causes stunted growth and yellowing of leaves – chlorosis. Aquatic habitats have special problems compared to terrestrial habitat. These problems include: - Light penetration: Plankton grow best in the upper layers of water due to higher light intensity. - Currents: move organisms, Plants & animals are washed away. Need for attachment (e.g., limpets and many seaweeds). - Wave action: moves and damages organisms - Salinity: Salt content means organisms adapt to freshwater or saltwater. Causes problems with water moving in or out of organisms and their cells. Limpets live in seawater, not freshwater. Organisms in seashore ponds must be able to withstand changes in salinity (due to rainfall and evaporation). - Oxygen: in lower concentration. - Tides: length of time organisms are exposed or submerged. Shore plants lose water when tide is out. Organisms on shores have shells or mucilage to retain water. Types of Organisms in an Ecosystem Definitions **Need to know all definitions** Producer (autotroph): An organism which makes its own food. Green plants make their own food by photosynthesis. Chemosynthetic organisms make their food using chemical energy. Consumer (heterotroph): an organism that takes in food from another organism. Herbivore: an animal which eats plants only e.g., rabbit, greenfly, honeybee. Carnivore: an animal which eats meat only e.g., fox, hawk, ladybird. Omnivore: an animal which eats both plant and animals e.g., sparrow, crow, blackbird, thrush, badger, field mouse, hedgehog. Decomposer: feeds on dead organic matter e.g., earthworm, many bacteria and fungi. Saprophyte: bacteria and fungi that feed on dead organic matter e.g., Rhizopus Primary consumer: an animal which feeds on producers e.g., herbivores or decomposers. Secondary consumer: an animal that feeds on primary consumers e.g., carnivores and scavengers (who feed on animals killed by other sources) Tertiary consumers: feed on secondary consumers. (1) Food Chain A Food Chain is a feeding relationship between plants, animals, and microorganisms. Energy flow: All organisms need energy to live. Sun is the primary source of energy. Energy flows from one organism to the next by means of a food chain. Food chains are normally only three to four steps long and are rarely more than five because only 10% of the energy is transferred from one link to the next. Grassland Food Chain (2) Aquatic Food Chain (3) Dependence and Interdependence: If a species relies on another species to survive, then it is said to be dependent. For example, the blackcurrant moth caterpillar needs currant bushes for food. However, the blackcurrant does not need the blackcurrant moth caterpillar to survive. If two species need each other to survive, they are said to be interdependent. For example, flowers need to pollinate them, and bees need flowers to supply their food in the form of nectar and pollen. Trophic level is the position of an organism in a food chain. First trophic level – Primary producers (green plants) Second trophic level – Herbivores that eat first trophic level species (primary consumers) Third trophic level – Carnivores that eat the herbivores in the second trophic level (secondary consumers) Fourth trophic level – Carnivores (tertiary consumers) that eat the carnivores in the third trophic level A food web is two or more interconnected food chains. (4) Pyramid of Numbers A pyramid of numbers is a chart showing the number of organisms at each trophic level. The numbers normally decrease as you move up the pyramid due to high energy loss (about 90% in respiration as heat, excretion, and decay) at each trophic level and the fact that organisms usually increase in size as you go up a pyramid and need to feed on a greater number. This limits the length of a food chain (4 or 5 steps). Pyramids of numbers are limited because the size of the organisms can change the standard shape, or it may not be possible to represent large numbers of organisms correctly.  (5) The size of organisms is not considered in a pyramid of numbers. e.g., one rose bush can support thousands of greenflies. When organism size is not considered very unusual pyramid shapes are likely to occur, this leads to an inverted food pyramid. (6) Niche **Know Definition and basic explanation** Niche is the functional role of an organism in its habitat. This includes a variety of factors including where it lives, what it eats and in turn, what eats it. Each species is adapted to its own niche. No two species can occupy the same niche for any length of time because competition will result in one species ousting the other, depending on which species is better adapted to the habitat. Nutrient Recycling Nutrient recycling is the way in which elements (e.g., carbon and nitrogen) are exchanged between the living and non-living components of an ecosystem. Carbon Cycle (7) -The Carbon Cycle starts with CO2 in the atmosphere where the concentration is about 0.03% and rising. - Plants remove carbon from the environment in photosynthesis and return it in respiration. - Animals obtain their carbon by eating plants; they release carbon in respiration. - Microorganisms (such as fungi and bacteria) return carbon to the environment when they decompose dead plants and animals. - Burning fossil fuels increases carbon dioxide in air and deforestation decrease uptake of carbon dioxide by plants. Nitrogen Cycle (8) Nitrogen Fixation - Nitrogen is needed by plants to make proteins, DNA, RNA, ATP, NAD+, NADP+, Chlorophyll etc. Nitrogen fixation is the conversion of nitrogen into nitrate, a form that can be used by plants. This is carried out by volcanic action, lightning, industrial processes and by some bacteria. Nitrogen-fixing bacteria can be found free in the soil or live in the root nodules of legumes (peas. beans, clover)The bacteria use the plant as a carbohydrate source of energy, protection & shelter (anaerobic conditions too) and the plant uses the nitrate produced by the bacterium (e.g., of mutualism). Assimilation- Nitrates are converted into plant and animal protein, DNA and RNA. Decomposition - Bacteria and fungi of decay convert the dead remains of plants or animals or their waste products to ammonia (NH 3). Nitrification - The ammonia is converted to nitrites and then to nitrates by nitrifying bacteria. Some of the nitrate formed in the soil is absorbed and assimilated by the plants. Denitrification - The conversion of nitrates to nitrogen gas. It is carried out by denitrifying bacteria in the soil. These bacteria are anaerobic and live in swampy soil or deep down in the soil (where water collects). Role of Organisms in The Nitrogen Cycle - Bacteria play a central role: a. Nitrogen-fixing bacteria, which convert atmospheric nitrogen to nitrates. b. Bacteria of decay, which convert decaying nitrogen waste to ammonia. c. Nitrifying bacteria, which convert ammonia to nitrates/nitrites. d. Denitrifying bacteria, which convert nitrates to nitrogen gas. - Fungi, like bacteria, help to convert dead plants and animals and their wastes into ammonia in the soil. - Plants absorb nitrates from the soil to make proteins. - Animals consume plants and use it to form animal protein. Human Impact on an Ecosystem Some of the issues that result from human activity include global warming, reduction in biodiversity, pollution, and the resistance of microorganisms to antibiotics. Biodiversity refers to a large variety of organisms in an ecosystem. When humans interfere, usually to farmland, biodiversity is lost. For example, when land is cleared only a small number of crops are grown. These few crops can only support a small number of organisms, which now have a superabundance of food. This can result in the populations of these species swelling to enormous numbers. There are no natural predators so humans will apply insecticides to control the organism. These insecticides kill not only the pest but also many other useful organisms. The effects of the insecticides often spread to adjoining areas, which continues to upset the balance of nature. Pollution is any harmful addition to the environment. Pollutants are the substances that cause the undesirable change. Most pollution arises from human activities such as dumping, sewage disposal, litter, radioactivity, and noise. Natural pollutants include volcanic emissions and smoke from forest fires. Pollution can affect air, freshwater, sea and soil or land. Types of pollution - Domestic pollutions – household wastes - Agricultural pollution – use of sprays to control pests and weeds, overuse of fertilisers, and disposal of farm wastes such as slurry and silage effluent. - Industrial pollution - includes that may cause acid rain and wastes that may damage rivers. Ozone depletion – an example of air pollution **Know in detail** Ozone is a gas (O3) that forms a protective layer above the surface of the earth. It absorbs and shields the earth from incoming UV radiation. Ozone depletion is caused by CFCs e.g., in spray cans, refrigerators, insulating foam and industrial detergents. Some fire extinguishers (halons) and agricultural sprays (fumigants) also destroy ozone, as do emissions from high-flying jets. - Effects of ozone depletion Ozone absorbs harmful UV radiation from sun. Increased UV radiation can: a. damage DNA and cause skin cancer, eye cataracts (lens in the eye lose transparency) and weakened immunity. b. cause serious damage to crops and plant life, c. Plankton may be depleted thus affecting aquatic food chains and less oxygen to breathe. Control of ozone depletion - A reduction in use of CFCs will eventually allow the ozone to be replenished. Ozone is formed by the reaction of UV light with oxygen. - CFCs are now being replaced by HFCs which break down much faster and do not reach the upper atmosphere. - Do not use sprays or foam products that contain CFCs. - Fridges should not be dumped in landfill sites. They should be returned to organisations that will dispose of their CFCs in an environmentally friendly way. Conservation Conservation is the wise management of existing resources to maintain existing populations. Conservation practices in Fisheries **Know in detail** Problems are pollution, overfishing and use of small-mesh nets. -Pollution reduces number of fish in waters. It may take years to replenish. Solution - Reduce pollution which kills fish and prevents migratory fish e.g., salmon from reaching breeding grounds. -Overfishing Solution - Fish quotas are set to ensure that enough fish are left to replenish the stocks Net size Solution - Use large-mesh nets so that young fish can escape and breed. -Monitor the fisheries by: a. Taking and analysing water samples b. Checking fish catches and fishing equipment c. Sampling fish stocks to calculate their numbers. Waste Management Waste Management involves preventing pollution and conserving the environment. Waste Management Practices in Agri Industry **Know in Detail** Slurry – a liquefied waste material produced by animals- contains high levels of nitrogen and phosphorus which cause algal bloom. When these algae die, they are decomposed by bacteria which use up the oxygen in the water depleting it for other plants and animals. This addition of nutrients to fresh water is called eutrophication. By controlling the release of nutrients into rivers and lakes the water quality can be improved. Slurry can also be stored in leakproof pits. This slurry can then be spread out on dry land in the summer as nutrients for plants. Problems associated with Waste Disposal - Vermin: Waste attracts vermin such as rats and gulls. Rate carry disease and destroy food and property. Gull’s droppings carry disease and are a particular problem near airports, where bird strikes can cause damage to planes. - Odours: Dumps have passive odours which are unpleasant for those that live nearby. - Contamination: Waste can contaminate groundwater when unsuitable items are left at dumps. This can make groundwater unsafe to consume. Roles of Microorganisms in Waste Management - Sewage: Sewage is all biological waste produced by humans. It is treated on a local level using domestic septic tanks and on a larger scale by pumping the sewage to treatment plants. It is made safe by biological oxidation using microorganisms to break down organic waste and destroy pathogens. The remnants of these processes are then heat-treated to complete the process before being spread on the land as a fertiliser. - Bioremediation: Uses microorganisms to remove pollution and allow the area to revert to its unpolluted state. For example, breaking down oil spills. Importance of Waste Minimisation It is important to reduce waste to conserve resources. Reduce waste at source i.e., reduce packaging of goods (now a charge on plastic bags in Ireland). Buy loose vegetables and fruit Re-use – reuse carrier bags when shopping, reuse glass bottles, unwanted clothing charities. Recycle – sort household waste and use Bring Banks/Collection Scheme. Using a compost bin for vegetable peelings and garden waste. The compost can be added to soil to improve the growth of plants. Ecological Relationships and Factors that Control Populations These factors include competition, predation, parasitism, and symbiosis **Know definition and one example** Competition Competition is the struggle between organisms for the same resource e.g., grass, dandelion, buttercup, and daisy compete for space, light, water, minerals; fox, thrush and hedgehog compete for earthworms. Competition reduces population numbers. Intra-specific competition takes place between members of the same species. Inter-specific competition involves different species e.g., blackbirds and thrushes competing for snails and insects. The two types of competition are: - Contest competition is an active physical confrontation between two organisms which allows one to win the resource e.g. competing stags (red deer) interlock anthers until one withdraws when competing for a mate. Robins – birdsong in spring is male robins warning off others from their territory. - Scramble competition each organism tries to acquire as much of the resource as possible e.g., chicks in nest depending on parent for food. Effects of competition - brings about evolution of a better-adapted species and elimination of the less well-adapted species. Adaptations to survive competition - A grass plant produces large quantities of pollen increasing its chance or reproduction. - Blackbird ‘song’ is to warn competitors to stay away. - Yellow petals of buttercups to attract insect pollinators. - Bacteria in soil secrete chemicals to inhibit their competitors. - The caterpillar of the cabbage white butterfly chews on cabbage leaves, while the adult butterfly drinks nectar from flowers. - Creeping buttercup uses fast-growing horizontal stems to colonise the habitat faster than dandelions. Predation Predation is the catching, killing, and eating of prey by its predator. Predator: an animal which kills other animals to use as a source of food. Prey: an animal that is caught and killed for food. Prey Predator Insects Spiders Fish/birds Humans Aphids Ladybird Predator adaptations **Know Three** - A fox has a. reddish fur used for camouflage to avoid detection by rabbits. b. Long canine teeth to kill prey and tear flesh. c. Great speed to outrun prey to capture it. Factors that improve the efficiency of predators: - Keen eyesight (e.g. hawk and other birds of prey), hearing, sense of smell and dentition - Catching whatever is easy, prevents wasting energy. - Being able to change diet as numbers of prey change e.g. foxes and spiders. - Living in packs can help locate food and make prey easier to catch. - Being able to migrate to areas where the prey is more plentiful - Camouflage - Catch large, rather than many small prey. - Ladybirds have strong mouthparts to enable them to chew aphids. Prey adaptations **Know Three** -Features that assist Rabbits to avoid being eaten: a. Rabbit digs narrow underground burrows – large predators are too big to enter. b. long ears – good hearing to detect predator. c. White tail – conspicuous warning signal to other rabbits. - Plant adaptations a. Some have thorns, spines, and stings e.g., holly and cacti. b. Some plants have a nasty taste to deter predators e.g., giant hogweed. - Animal adaptations a. Some can swim, fly and run faster than predator. b. Mimicking animals the predator would normally avoid e.g. hoverfly is a harmless insect but protects itself by mimicking the colouration of wasps. c. Staying in large groups e.g. in flocks and herds like deer. d. Camouflage enables them to blend with surroundings e.g. greenfly, stick insects, frogs. e. Warning colouration as seen in many butterflies and moths e.g. the spots on the wings of the peacock butterfly appear as eyes. f. Poisons e.g. caterpillar of large white butterfly, ladybirds contain large amounts of formic acid, which is unpalatable to predators. g. Mice flee and hide to avoid being eaten. Effects of predation in ecosystem: Predation maintains the prey species at a sustainable level. Predation is a major factor in evolution of the prey species. - Predation initially increases the numbers of predators and decrease the number of prey. - The numbers of predators and prey often show repeated cycles of rising and falling numbers. Predator-Prey Relationship **Need to Know** This is used in the biological control of pests. For example, ladybirds are used to control greenfly. Certain bacteria are used to control the larvae of butterflies to prevent them from destroying crops like cabbage. Parasitism Parasitism occurs when two organisms of different species live in close association and one organism (parasite) obtains its food from, and to the disadvantage of, the second organism (host). Parasite is an organism that feeds from and harms another organism. - Endoparasites: feed in a living host e.g., liver fluke, potato blight fungus, bacteria of disease in human body. - Ectoparasites: feed on the outside of the host e.g., fleas, athletes foot fungus, mosquitoes on human skin, greenfly on a rosebush, blood-sucking leeches on human skin, lice on hawks Parasites are often thought of as predators, but they differ by: a. Being smaller, often attacking from within b. being dependent on one particular host c. only do a small amount of damage to host so that they do not harm their food source or home. Parasites sometimes reduce the numbers in a population e.g., potato blight or disease-causing bacteria, but often have little effect on host numbers. Symbiosis Symbiosis is a close relationship between two organisms of different species in which at least one of them benefits. Symbiosis increases the numbers of both species In one type of Symbiosis, mutualism, both organisms’ benefit. Examples of this are - Lichen: it consists of a fungus and an alga. The alga makes food for both, and the fungus absorbs minerals and water for both and give protection and support. - Nitrogen–fixing bacteria: in root nodules of legumes e.g., clover. Bacteria provide nitrates for plants to make protein and plants provides carbohydrates, shelter and anaerobic conditions for bacteria. - Bacteria: living in large intestine, supply us with vitamins B and K and protect us from pathogenic bacteria. We supply bacteria with food, water, and a protected site to live. Population Dynamics Population dynamics refers to the factors that cause changes in population numbers. Predator-prey numbers interact due to: a. availability of food: increases predator numbers when high but reduces them when low b. concealment: which means that some prey survive by hiding from the predators c. movement of predators: which means that predators move to new areas when prey numbers are low. (9) Human Population **Need to Know Examples** Human population continues to rise despite famine, disease, war, and contraception. The sudden increase in the twentieth century was due to fewer infant deaths and people living longer because of improved sanitation and medicines and disease eradication programmes. Numerous factors affect human population, including; - Famine: occurs when an acute shortage of food affects a population. Famine can lead to starvation, death, and mass emigration. Famine is often linked to war as war zones have reduced agriculture. -Disease: The ability to control and cure diseases (vaccines, antibiotics, improved sanitation, insecticides, safe anaesthetics, improved surgical methods and new drugs) have helped to reduce the death rate and increase human numbers. - Wars: War normally reduces population numbers temporarily due to death. Baby booms often follow wars. - Contraception: The use of contraceptives has reduced the birth rate.  Exam Questions 2015 – HL- Section A – Question 2 (a) What do ecologists mean by the term scramble competition? All of the individuals get some of the resources. (b) Give one example of a factor, other than light, which may be a source of competition among plants. Water/minerals/space/nutrients in the soil/pollinators (c) Give one example of a factor, other than food, which may be a source of competition among animals. Water/mates/shelter/territory/space (d) Caterpillars have mouth parts that are suitable for chewing on leaves, whereas the adult form, the butterfly, has long sucking mouth parts. Suggest how having different types of mouth parts reduces competition between the adults and the young of such species. They feed on different types of food/They feed on different parts of the plant (e) Answer the following questions in relation to a quantitative survey of a species of small herbaceous plant. (i) Name the method that you would employ. Frequency/Transect/Quadrat (ii) How would you ensure that your sampling was random? Throw a pen/pencil over your shoulder (iii) Name one edaphic factor that could affect the distribution of this plant in the ecosystem. Soil pH/Temperature/Moisture/Water content/Mineral content 2014 – HL - Section A – Question 1 From your knowledge of ecology explain any five of the following terms: (a) Biosphere. Part of the planet where life can exist (b) Niche. Functional role of an organism (c) Biotic factor. Living factor (d) Trophic level. Feeding stage an organism occupies in a food chain (e) Competition. Struggle between organisms for a resource in short supply (f) Symbiosis. Close association between two organisms of different species where at least one benefits Answer any two of (a), (b), (c). (30, 30) (a) Phytoplankton is the collective term covering the small photosynthetic organisms which are part of aquatic ecosystems. The solid line in the graph below shows the fluctuation in phytoplankton numbers in a lake over a twelve month period. The broken lines show the variations over that period in temperature, light and nutrient levels (i) What does the graph tell you about the phytoplankton population? The phytoplankton population decreases and is low in winter, Increases and is high in spring, Fluctuates during the summer, Increases at the beginning of the autumn and decreases at the end of autumn (ii) Why do you think that nutrient levels are high in winter and then drop sharply in spring? Nutrient levels are high in winter because plankton numbers are low. Nutrient levels drop sharply in spring because plankton numbers are high. Plankton are absorbing and using the nutrients in spring (iii) Give an example of an inorganic nutrient, necessary for phytoplankton growth, that you would expect to find in lake water. Nitrates (iv) Zooplankton is the collective term for the small animals present in the lake. Copy the graph for phytoplankton into your answer book and then, on the same axes and using a dashed (---) line, show how the numbers of zooplankton would vary over the twelve month period. Briefly explain the graph that you have drawn. Zooplankton population is lower than phytoplankton population. Zooplankton population curve matches the phytoplankton population curve. Zooplankton spring population peak shifted to the right. Zooplankton autumn population peak shifted to the right. Explanation of the curve drawn Zooplankton prey on and consume phytoplankton. Predator population numbers are always smaller than prey population numbers. There is a time lag required for predator population numbers to increase after prey population numbers have increased (v) Other than the effect of the zooplankton, suggest why the phytoplankton population drops in late autumn. Low temperature or low light intensity (b). Read the passage below and answer the questions that follow. European rabbits were introduced by settlers into Australia in 1859. Within 70 years the rabbit population grew enormously across most of the continent. The rapid spread of the rabbit led to the destruction of large areas of vegetation, leading to the extinction of many plant species. Loss of vegetation leads to soil erosion as the exposed soil is washed or blown away, removing valuable soil nutrients required for new plants to develop. This soil is typically deposited in waterways, causing siltation and destroying aquatic ecosystems. Farmers battled the problem, fencing their properties with special netting, using poisons, digging out warrens and finally introducing the Myxoma virus as a form of biological control. This virus, a benign parasite of the Brazilian forest rabbit, was lethal for European rabbits. It quickly reduced Australia’s rabbits to a mere 5% of former numbers. However, this solution was not long-lasting and rabbit numbers recovered. (i) Describe a procedure for estimating rabbit numbers in an ecosystem. - Rabbits were captured using mammal traps and the number captured noted - Rabbits were tagged using a metal band attached to their legs - Tagging is inconspicuous and does not hinder the movement of the rabbits - Rabbits were released into the same habitat in which they were caught - A week later, mammal traps were reset and rabbits were recaptured - The number of rabbits recaptured and the total number caught was noted - The following formula was used to calculate the number of rabbits living in the habitat Number caught on Day 1 x Number caught on Day 2Number caught on Day 2 that were tagged x 100 (ii) Suggest one reason for the initial rapid increase of the rabbit population. No predators (iii) Give two possible effects on an ecosystem of the extinction of a plant species. Soil erosion and Fewer nutrients present (iv) Suggest one advantage and one disadvantage of biological control of a pest organism. Advantage: No harmful chemicals are used. Disadvantage: Balance of nature is upset. (v) Suggest one reason why the rabbit numbers recovered. Rabbits developed immunity (c) (i) Name three factors can that affect human population. War/Famine/Disease Contraception/Birth/death rates/Natural disasters (ii) Suggest two reasons why the human population increased so rapidly from the mid-1800s. Better nutrition/New technologies/Improved hygiene. (iii) Suggest what could happen to biological diversity as the human population continues to increase. It could decrease (iv) The vast amount of waste generated is one of the consequences of this huge increase. Mention the three main ways in which waste can be minimised. Reduce, Reuse and Recycle (v) What is pollution? Any harmful addition to the environment (vi) What is the role of microorganisms in pollution control? Decomposition (vii) Describe the role of 1. Plants 2. Animals in the Nitrogen Cycle and in the Carbon Cycle. Plants: - Absorb nitrates from soil - Synthesise proteins - Absorbs carbon dioxide - Synthesises carbohydrates through photosynthesis - Excrete carbon dioxide via respiration - Die, releasing carbon and nitrogen-containing nutrients into the soil Animals: - Consume plants - Assimilate amino acids received from plants into animal protein - Assimilate carbohydrates received from plants - Produce nitrogenous waste such as urea - Excrete carbon dioxide via respiration - Die, releasing carbon and nitrogen-containing nutrients into the soil References 1.Sopinterest.blogspot.com 2. study.com 3. study.com 4. AZolifesciences.com 5. Noon Academy.com 6. Noon Academy.com 7. BYJUs.com 8. study.com