AQA

Life Processes and Living Things

Living Things in their Environment

10.20 Adaptation and Competition	KS3	Physical factors which may affect organisms include: temperature; amount of light; availability of water; availability of oxygen and carbon dioxide. These factors vary according to the rime of day and the time of year. Organisms live, grow and reproduce in places where, and at times when, conditions are suitable. This helps to explain why the types of organisms vary from place to place and from time to time.
	FT and HT	Organisms have features which enable them to survive in the conditions in which they normally live. Candidates should be able, when provided with appropriate information, to: explain how animals are adapted for survival in arctic and desert environments in terms of: - body size and surface area - thickness of insulating coat - amount of body fat - camouflage; explain how plants are adapted to survive in arid conditions; suggest how other organisms are adapted to the conditions in which they live. Plants often compete with each other for space, and for water and nutrients from the soil. Animals often compete with each other for space, food and water. Candidates should be able, when provided with appropriate information, to suggest the factors for which organisms are competing in a given habitat. Animals which kill and eat other animals are called predators; the animals they eat are called prey. In a community: the number of animals of a particular species (its population) is usually limited by the amount of food available; if the population of prey increases, more food is available for its predators and their population may also increase; if the population of predators increases, more food is needed and the population of prey will decrease. The size of a population may be affected by: the total amount of food or nutrients available; competition for food or nutrients; competition for light; predation or grazing; disease.
10.21 Human Impact on The Environment	FT and HT	Humans reduce the amount of land available for other animals and plants by: building; quarrying; farming; dumping waste. Human activities may pollute: water — with sewage, fertiliser or toxic chemicals; air - with smoke and gases such as sulphur dioxide; land - with toxic chemicals, such as pesticides and herbicides, which may be washed from land into water. When fossil fuels are burned carbon dioxide is released into the atmosphere. Sulphur dioxide and nitrogen oxides may also be released. These gases dissolve in rain and make it more acid. Acid rain may damage trees directly. If the water in rivers and lakes becomes too acidic, plants and animals cannot survive. When the Earth's human population was much smaller, the effects of human activity were usually small and local. Rapid growth in the human population and an increase in the standard of living means that: raw materials, including non-renewable energy resources, are rapidly being used up; increasingly more waste is produced; unless waste is properly handled more pollution will be caused. Large scale deforestation in tropical areas, for timber and to provide land for agriculture, has: increased the release of carbon dioxide into the atmosphere (because of burning and the activities of microorganisms); reduced the rate at which carbon dioxide is removed from the atmosphere and 'locked up' for many years as wood. Increases in the numbers of cattle and rice fields have increased the amount of methane released into the atmosphere. The levels of carbon dioxide and methane in the atmosphere are slowly rising. Increasing levels of these gases may be enhancing the 'greenhouse effect'. An increase in the Earth's temperature of only a few degrees Celsius: may cause quite big changes in the Earth's climate; may cause a rise in sea level.
		Candidates should be able, when supplied with appropriate information, to use their scientific knowledge, weigh evidence and form balanced judgements about some of the major environmental issues facing society, including the importance of sustainable development.
	HT	Farmers add fertilisers to soil to replace the nutrients which crops remove. Excess fertilisers may be washed into lakes and rivers. Pollution of water by fertilisers may cause eutrophication. The stages in this process are: the rapid growth of water plants; death of some of these due to competition, e.g. for light; an increase in the number of microorganisms which feed on dead organisms; the increased use of oxygen from the water by these microorganisms for their respiration; the resultant death due to oxygen shortage of fishes and other aquatic animals. Untreated sewage provides food for microorganisms. This has the same effect (eutrophication) in water as dead vegetation. Carbon dioxide and methane in the atmosphere absorb much of the energy radiated by the Earth. Some of this energy is re-radiated back to the Earth and so keeps the Earth warmer than it would otherwise be.
10.22 Energy and Nutrient	KS3	Food chains show which organisms eat other organisms. Transfer In a food chain, A -> B -> C means that B eats A and C eats B. Food chains always begin with green plants (producers) which provide food for other organisms (consumers). Food chains are often interconnected to form food webs. Food chains and food webs show the transfer of energy and materials from one type of organism to another. The number of organisms at each stage of a food chain can be shown as a pyramid of numbers.
	FT and HT	Radiation from the Sun is the source of energy for all communities of living organisms. Green plants capture a small part of the solar energy which reaches them. This energy is stored in the substances which make up the cells of the plants. The mass of living material (biomass) at each stage in a food chain is less than it was at the previous stage. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass. Candidates should be able to interpret pyramids of biomass and construct them from appropriate information. At each stage in a food chain, less material and less energy are contained in the biomass of the organisms. This means that the efficiency of food production can be improved by reducing the number of stages in food chains.
	HT	The amount of material and energy in the biomass of organisms is reduced at each successive stage in a food chain because: some materials and energy are always lost in the organisms' waste materials; respiration supplies all the energy needs for living processes, including movement; much of this energy is eventually lost as heat to the surroundings; these losses are especially large in mammals and birds whose bodies must be kept at a constant temperature which is usually higher than that of their surroundings. The efficiency of food production can also be improved by: restricting energy loss from food animals by limiting their movement and by controlling the temperature of their surroundings: using hormones to regulate the ripening of fruits on the plant and during transport to consumers.
		Candidates should be able to evaluate the positive and negative effects of managing food production and distribution and be able to recognise that practical solutions to human needs may require compromise between competing priorities.
10.23 Nutrient Cycles	FT and HT	Living things remove materials from the environment for growth and other processes. These materials are returned to the environment either in waste materials or when living things die and decay. Materials decay because they are broken down (digested) by microorganisms. Microorganisms digest materials faster in warm, moist conditions. Many microorganisms are also more active when there is plenty of oxygen. Microorganisms are used: at sewage works to break down waste from humans; in compost heaps to break down waste plant materials. The decay process releases substances which plants need to grow. In a stable community, the processes which remove materials are balanced by processes which return materials. The materials are constantly cycled. The constant cycling of carbon is called the carbon cycle. In the carbon cycle: carbon dioxide is removed from the environment by green plants for photosynthesis; the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins which make up the body of plants; some carbon dioxide is returned to the atmosphere when green plants respire; when green plants are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins which make up their bodies; when animals respire some of this carbon becomes carbon dioxide and is released into the atmosphere; when plants and animals die, some animals and microorganisms feed on their bodies; carbon is released into the atmosphere as carbon dioxide when these organisms respire.
	HT	The constant cycling of nitrogen is called the nitrogen cycle. In the nitrogen cycle: green plants absorb nitrates from the soil; they use the nitrogen in these nitrates to make proteins; when green plants are eaten by animals and these animals are eaten by other animals, some of the nitrogen then becomes part of the proteins in their bodies; when putrefying (decay) bacteria and fungi break down the waste products of animals and the protein from dead animals and plants, ammonium compounds are produced; nitrifying bacteria convert ammonium compounds to nitrates. By the time microorganisms and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the material as plant nutrients, all the energy originally captured by green plants has been transferred.