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Food chains & Food webs


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Doc Scientia curriculum Grade 8

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Food chains & Food webs

  2. 2. Introduction ECOLOGY: The study of living organisms and the places where they live..Living organisms that live together in an environment are interdependent.But the environmental conditions, e.g. soil, water and climate also play an importantrole. Ecosystems vary in size. Examples are the Kruger National Park, Kalagadi, theBotanical gardens and the Gariep dam.
  3. 3. ECOSYSTEM: An area where living (biotic) and non-living (abiotic) things live and interact with each other. BIODIVERSITY: The diverse spectrum of life found in one habitat.ECOSYSTEMS are grouped into biomes, namely:• SAVANNA• MIDLATITUDE GRASSLANDS• BOREAL FOREST• TROPICAL RAIN FOREST• SCRUBLAND• OPEN WOODLAND• DESERT• TUNDRA HABITAT: The area in which plants and animals live.There are various habitats in an ecosystem. .Examples:A cheetah’s habitat is SAVANNA GRASSLANDS.
  4. 4. Various plants and animals can be found in each habitat.The plants and animals in a habitat depend on each other for food and protectionand they form a community. COMMUNITY: All the living things in one habitat.Communities consist of a variety of populations, such as herds of kudu, flocks of sparrows andschools of fish. POPULATION: One kind of living organism that is found in one habitat.
  5. 5. Food chainsExample of a food chain :
  6. 6. . Sun provides energy. Snake is then eaten by the Plants (producers) falcon. use this energy to produce their own food. Frog is eaten by the snake (tertiary consumer). Grasshopper (primary consumer) Frog eats the grass. (secondary consumer) eats the grasshopper.
  7. 7. After the falcon dies, its body is broken down by detritivores and decomposers and energy is released into the soil, atmosphere and water.Energy is transferred from one organism to the other in this manner. FOOD CHAIN: It is the relationship where energy (in food) flows between living organisms.
  8. 8. CIRCULATION OF NUTRIENTS : Consumers: • primary • secondary • tertiary Die and are Eaten by decomposed by Die and are Detritivores and Producers decomposed by Decomposers Consumed by NutrientsUsed in photosynthesis
  9. 9. Exercise 101 Give one word for the following descriptions : 1.1 The relationship where energy (in food) flows between FOOD CHAIN living organisms. 1.2 One kind of living organism that is found in a habitat. POPULATION 1.3 The variety of life found in an ecosystem. BIODIVERSITY 1.4 All the living organisms of a specific kind that live POPULATION together in an ecosystem. 1.5 The diversity of life in a habitat. COMMUNITY 1.6 An area where living (biotic) and non-living (abiotic) ECOSYSTEM things live and interact with each other, e.g. a jungle.
  10. 10. 2 Study the sketch below and answer the questions that follow:2.1 What does this sketch represent? An ecosystem2.2 Use the sketch as reference and give an example of:2.2.1 a predator: Lion/cheetah/eagle2.2.2 an omnivore: Ostrich2.2.3 a herbivore: Giraffe/zebra/springbok/blue wildebeest2.3 Write down two different food chains that are found in this sketch. grass → springbok → cheetah tree → giraffe → lion
  11. 11. 2.4 Explain why there are so many more herbivores in the habitat than carnivores. There is more food for the herbivores to eat than for the carnivores. If there were more carnivores in this habitat, the herbivores would not have been a sufficient amount of food for the carnivores.2.5 Explain why giraffes and zebras do not compete for food. Giraffes eat leaves from trees, while zebras feed on grass. Therefore these two animals eat different types of food and thus they do not compete for food.2.6 Explain why lions and cheetahs compete against each other in this habitat. Lions and cheetahs are both carnivores. Both these animals may hunt the same animals and therefore they are each other’s competitors.
  12. 12. 3 Study the diagram below and answer the questions that follow C B D A plants soil surface decomposers food excretion decomposition respiration
  13. 13. 3.1 What does this diagram represent? A food chain3.2 What does the arrow at D represent? Radiation from the sun3.3 What is another name that can be given to plants? Give a reason for your answer. Producers, because plants have the ability to produce their own food.3.4 What does B represent? Give an example. Secondary consumers for example snakes3.5 Can C be a herbivore? Motivate your answer. No, because herbivores only feed on plants (producers) and they are the primary consumers. C is a tertiary consumer.3.6 Complete A, B and C with your own examples so that the diagrams follow logically. A: mouse B: snake C: eagle3.7 What do plants, A, B and C release into the atmosphere during respiration? Carbon dioxide (CO 2)3.8 What does “excretion” mean? Excretion is waste products that are excreted by humans and animals.3.9 Give an example of decomposers. Bacteria/Fungi
  14. 14. Food websFOOD WEB: A variety of interlinked food chains.
  15. 15. Various food chains and how they are linked:• Worms, grasshoppers, mice, guinea fowls and antelope eat grass and plants.• Herbivores are a source of food for various predators, carnivores and omnivores.  The grasshopper is eaten by the frog and the bird.  The snake catches the mouse.  The genet catches the mouse, frog, guinea fowl, bird and snake.  The antelope is eaten by the leopard.  The genet, guinea fowl and bird are eaten by the eagle.• Because the food chains overlap, a food web exists.• Decomposers are always at the top of the food chain or food web.• Decomposers recycle the nutrients in dead plants and animals and plough it back• into the soil.• These nutrients will make the soil fertile and make it possible for plants to grow.
  16. 16. Activity 13Investigate your area. See how many different food chains you can identify andwrite them down. Food chains in my environment:Seed → pigeon/mouse → cat/owlFlowers → butterfly/moth → spider/gecko → crowFlowers → plant louse → ladybug → spider → crowCrops → snale → corn cricket → woodpeckerCrops → mouse → cat/owlLeaves → worms → hoopoe → catDetermine how many of these food chains are connected, and then draw your ownfood web. Seed Flowers Crops Leaves Pigeon Mouse Butterfly Moth Plant-louse Snail Worms Spider Ladybug Corn cricket Hoopoe Gecko Wood pecker Cat Crow WWW.DOCSCIENTIA.CO.ZA
  17. 17. 3.4 Fossil fuelsThere are some circumstances where animals and plants die and it isimpossible for them to decompose and so their remains becomeearthbound.Over a long period of time the remains of these animals and plants areCONVERTED BY HEAT AND PRESSURE INTO FOSSIL FUELS, e.g. coal and oilEnergy is released when these fuels are burned.People all over the world are dependent on this energy for electricity, heating,petrol, etc.NON-RENEWABLE RESOURCES: cannot be replenished (made again) in a short space of time..Fossil fuels are non-renewable resources.
  18. 18. The mining and burning of fossil fuels lead to pollution.Harmful greenhouse gasses are released into the atmosphere – ACID RAIN is formed. GREENHOUSE GASES: Gases whose molecules can absorb harmful infrared radiation from the sun and release them within our atmosphere. INTERDEPENDENCE IN ECOSYSTEMSOrganisms depend on other biotic (living) organisms and abiotic (non-living)aspects of their habitat.These dependencies result in certain relationships better known as SYMBIOSIS.There are three different symbioses (interdependencies): SYMBIOSIS Mutualism Parasitism Commensalism
  19. 19. MUTUALISM:Both parties benefit from the relationship that was createdExamples:Animal-animal  crocodile and Egyptian ploverA crocodile lies with its mouth open so that the Egyptian plover is able to get rid ofsmall pieces of meat that got stuck between the crocodile’s teeth.The plover feeds on the small pieces of meat that were stuck betweenthe teeth. Animal-plant  bees and flowers Bees depend on the flower’s nectar for nutrients. On the other hand flowers depend on bees to spread their pollen and thus ensure pollination.Plant-plant  lichensLichens actually consist of two plants – fungi and algae.The fungi absorbs water and nitrogenous substances and provide them to thealgae. The algae produce carbohydrates through photosynthesis and provide them to the fungi .
  20. 20. COMMENSALISM:In this relationship one party will benefit, while the other will not benefit nor will itbe disadvantaged.Examples:Animal-animal  white egret and cattleWhile cattle are grazing, insects are driven into the air and are eaten bywhite egret. The white egret is benefitting, but there is no benefit ordisadvantage to the cattle. Animal-plant  finches and trees Finches build their nests in tall trees. The tree provides protection against predators and floods, so the finch is benefitting. The tree is not at a disadvantage due to the nest, but it also does not benefit by this relationship.Plant-plant  orchids and treesOrchids are not fed by the trees. They need the trees so that they maygrow higher and thus get more sunlight necessary for photosynthesis.Since orchids do not feed on the trees, the tree is not disadvantaged but italso does not benefit from this relationship.
  21. 21. PARASITISM:In this instance one party will be disadvantaged while the other benefits.Examples: Animal-animal  ticks and dogsThe tick is benefitting from this relationship since it feeds on the dog.On the other hand the dog is disadvantaged and may even become infectedwith an illness like biliary. Plant-plant  dodder on other plants Dodder obtains all its water, nutrients and carbohydrates from its host and all of this is to the host’s disadvantage. The abiotic aspects in a habitat play just as important role in the survival of biotic organisms. Abiotic factors: Water, soil, oxygen and carbon dioxide.
  22. 22. Exercise 111 Consider the diagram below and answer the questions that follow . Seed Birds Mouse Snake Eagle1.1 What does this diagram represent? A food web1.2 If there was an increase in snakes, which animal will also increase? Give a reason for your answer. Eagles, because the more snakes there are, the more food there is for the eagles. The circumstances are favourable for the eagles to increase. WWW.DOCSCIENTIA.CO.ZA
  23. 23. 1.3 If there was an increase in snakes, which animal would decrease? Give a reason for your answer. Birds and mice, because they serve as a food source for the snakes. If there are more snakes to feed on them, the amount of birds and mice will decrease .1.4 What animals are the ... in this case: primary consumer: bird; mouse secondary consumer: snake; eagle predator: snake; eagle herbivore: bird; mouse2 Give one word/term for the following: 2.1 Fuels like oil, natural gasses and petrol FOSSIL FUELS 2.2 Interdependence in ecosystems SYMBIOSIS 2.3 One party benefits, while the other does not benefit nor is it COMMENSALISM disadvantaged. 2.4 These remains of animals and plants have been converted FOSSIL FUELS over millions of years. 2.5 A variety of food chains that are linked. FOOD WEB
  24. 24. 3. Match column A to column B. Write down the correct letter next to the description. E A. Parasitism The relationship between ants and plant lice. A variety of food chains that overlap. C B. Ecology The area where plants and animals live. G C. Food web The relationship between a clown fish D. Fossil fuels and an anemone. F A herd of springbok on the grasslands. E. Mutualism H It is produced from the remains of plants and animals under extreme F. Commensalism heat and pressure. D The study of living organisms and the places where they live. G. Habitat B The relationship between humans and H. Population tapeworms. A