Download
1 / 48
490 likes | 689 Vues
Food chains. What feeding relationships are shown here?. Feeding relationships. Energy transfer in the food chain. Why aren’t food chains very long?. This tiger is a top predator; the final level in a food chain. Most food chains only contain four or five species, why is this?.
E N D
Food chains What feeding relationships are shown here?
Why aren’t food chains very long? This tiger is a top predator; the final level in a food chain. Most food chains only contain four or five species, why is this? Energy is lost at all levels in food chains. Animals at the top of a long food chain would not get enough energy to survive.
Food chains and pyramids What can pyramids show about energy transfer?
What are pyramids of numbers? Pyramids of numbers are a quantitative way of representing food chains. They record the number of organisms at each trophic level in a specified area. What are the problems of representing food chains in pyramids of numbers? Pyramids of numbers only give an accurate impression of the flow of energy in a food chain if the organisms are of similar size. Measuring the biomass at each trophic level can give a more accurate picture.
Understanding pyramids of numbers In a pyramid of numbers, the length of each bar represents the number of organisms at each trophic level in a specified area. As a single tree can support many organisms, this food chain produces an unbalanced pyramid.
Understanding pyramids of biomass In a pyramid of biomass, the length of each bar represents the amount of organic matter – biomass – at each trophic level in a specified area. At each trophic level, the amount of biomass and energy available is reduced, giving a pyramid shape.
What are the benefits of eating plants? Your friend is at university and has phoned you to complain that all she can afford to eat is beans on toast. How could you make her feel better about her diet? What are the energy arguments for eating a plant-based diet?
A luxury item? How can the costs of these food items be compared fairly? A 400g steak costs £4.00. An 800g loaf of bread costs £0.80. This equals £1.00 per 100g. This equals £0.10 per 100g. Why is meat more expensive than bread?
How energy efficient is it to eat meat? Food chains can be used to understand why some foods cost more than others. Which of these chains is the most efficient? The first food chain is the most efficient because it contains fewest trophic levels, so less energy will be lost.
Is eating meat less energy efficient? Cattle and other livestock are fed grain and cereals. Would it be more energy efficient if humans ate the plant crops instead? If a one-acre field of corn is used to feed cows, it can support one person. If the same area is used to feed humans directly, it can support 10 people. Why is so much energy lost?
Why do some animals need more energy? Mammals and birds are able to regulate their body temperature. This has many advantages but it uses lots of energy. Other animals, such as snakes, lizards and fish, are unable to regulate their body temperature, so need less energy. Would it be more energy efficient to farm snakes for food than chickens?
energy used for growth (input) efficiency = energy supplied (output) How do you calculate efficiency? Energy efficiency can be calculated using the following equation: For example, if grass receives 1,000,000kJ of energy from the Sun and uses 20,000kJ of energy for growth, then: 20,000 kJ efficiency = 1,000,000 kJ = 0.02 = 2%
Why is maximizing yields important? Many farmers use intensive farming methods to maximize their yields. Why do they do this? • More food produced in the same amount of space. • Cheaper food for consumers. • Lower costs for farmers. • Increased energy efficiency. In what ways can farmers maximize their yields?
How do greenhouses increase yields? Greenhouse operators raise their yields and profits by maximizing photosynthesis and controlling other factors. Products can be grown earlier in the year and in conditions in which they would not normally grow. What factors would you need to control to get the maximum yields from photosynthesis? • light levels • carbon dioxide • temperature.
How can losses be reduced? Not all of a crop planted will be harvested. What happens to the rest? 13% lost to disease 58% harvested 13% lost to pests 16% lost to weeds What chemicals are used to cut competition? Herbicides are used to kill weeds, and pesticides are used to kill pests, such as insects and fungi.
What is hydroponics? Hydroponics is a technique used to grow plants without soil. The plants gain all their nutrients and minerals from specially-treated water circulating around their roots. Other conditions, such as the levels of light and carbon dioxide, are also closely controlled. Many salad crops, including tomatoes, lettuces and cucumbers, are grown in this way. In what conditions would hydroponics be useful?
Why use hydroponics? There are many advantages of using hydroponics. These include: • Lower risk of crops becoming diseased from soil-based pathogens and pests. • Fewer weeds. • A reduced need for pesticides and herbicides. • Crops can be grown in places with poor soil or little water for irrigation. However, hydroponics requires expensive equipment and technical knowledge and so will not be suitable for all situations.
Why are aquatic food chains efficient? The transfer of biomass and energy in aquatic food chains can be very efficient. Why is this? • The organisms do not thermoregulate, so they use less energy for respiration. • Very little phytoplankton escapes being eaten so decomposers take less of the energy. What could reduce the number of large fish caught?
Can fish be farmed? Most of the salmon and trout eaten in this country comes from fish farms. The fish are reared in giant tanks or cages. Put yourself in charge. What could you do to make sure you raised the biggest possible yield of fish?
How can livestock be farmed efficiently? Chickens and pigs lose energy through movement and thermoregulation. How could a farmer increase the yield of meat from livestock? The efficiency of meat production increases if animals are kept at a constant temperature and their movement is restricted. They can also be fed concentrates – food that leaves very little waste – and given antibiotics to combat infections. Is efficiency always the most important consideration?
What are the problems of livestock farming? If animals are kept in extremely cramped conditions, they may start to develop abnormal behaviour. For example, chickens may pluck out each other’s feathers. Animals are also more likely to catch diseases if they are living in a cramped, enclosed environment. To help prevent these problems, farmers must comply with EU regulations, but some people do not think these regulations are strict enough.
Intensive farming and the environment Intensive farming must be well managed to prevent environmental problems. These include problems include: • Pollution of water supplies by animal waste. • Accumulation of pesticides in food chains. • Eutrophication of rivers and lakes due to inappropriate use of artificial fertilizers. • Destruction of wildlife habitat for agricultural land. • Depletion of soil minerals.
How do we use biomass? Biomass supplies us with more than just food. How can biomass be used by humans?
What is biomass energy? Biomass energy is one of the oldest forms of energy. The biomass stored in wood can be burned for heating and cooking. Animal dung can also be burned for energy.
Biodiesel and bioethanol Could biomass fuels replace petrol?
How can biomass be used for fuel? Biomass can be used to make biodiesel and bioethanol. • Biodiesel is produced by chemically reacting vegetable oils or animal fats with alcohol and a catalyst. This bus runs on biodiesel made from soya beans. • Bioethanol is produced by fermenting the carbohydrates in sugar beet/cane or wheat crops.
More than our fair share? Biofuels have many advantages but using land to grow fuel reduces the area available for food crops. Humans take the biggest slice of the Earth’s resources, using about 40% of the biomass produced on land. How would growing biofuels affect this? Should humans leave more biomass for other organisms?
Glossary (1/2) • biomass – The organic material that makes up plants and animals. • carnivore –An organism that only eats other animals. • consumer –An organism that feeds on plants or animals. • fertilizer–A mixture of mineral salts needed to support plant growth. • food chain–A sequence that shows feeding relationships and the transfer of energy between organisms. • herbivore –A organism that only eats plants. • hydroponics – Growing plants without using soil.
Glossary (2/2) • omnivore – An organism that eats both plants and animals. • pyramid of biomass –A scale drawing that illustrates the biomass present at each stage of a food chain. • pyramid of numbers – A scale drawing that illustrates the number of organisms present at each stage of a food chain. • producer –A plant that makes food by photosynthesis. • respiration –A series of reactions that releases energy from organic molecules in both plants and animals. • trophic level – A feeding level in a food chain.
