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Leaving certificate biology

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  1. Ecology theory
    5 Topics
    |
    1 Quiz
  2. Unit 1
    Nutrient recycling
    4 Topics
    |
    1 Quiz
  3. Ecological relationships and population dynamics
    2 Topics
  4. Human impact on the ecosystem
    2 Topics
  5. Study of a grassland ecosystem
    3 Topics
  6. Responses in the Flowering Plant
    4 Topics
    |
    1 Quiz
  7. Unit 3
    Sexual reproduction in the flowering plant
    1 Topic
  8. The human reproductive system
    3 Topics
  9. The menstrual cycle
    2 Topics
  10. Pregnancy
    2 Topics
  11. The circulatory system
    4 Topics
  12. Blood
    5 Topics
  13. The heart
    5 Topics
Lesson 1, Topic 4
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Food chains

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What is a food chain ?

  • A food chain is a pathway along which food (energy) is passed from one species to another.
  • The arrows show the direction in which energy flows 
  • A grazing food chain is a pathway of energy flow that begins with a a plant

What is a trophic level ?

  • A trophic level is the feeding stage of a species in a food chain
  • Food chains rarely have more than 4 or 5 trophic levels because only a small proportion of energy is passed from one trophic level to the next

How is energy lost in a food chain ?

  • Heat: plants and animals loose energy in the form of heat to the environment which is not available to the the next trophic level
  • Undigested parts: some parts may not be digestable such as bones so this energy is lost to the next trophic level
  • Waste: Waste products such as feaces are produced which contain energy not available to the next trophic level

What is a food web?

  • A food web shows the interconnections between two or more food chains in an ecosystem 

Interpreting food webs

If  pesticide is spread which kills snails what will happen to the number other organisms in the above food web ?

  • Number of thrush will fall as there are fewer snails to eat
  • As the numbers of thrush fall hawks will have to rely on eating more blackbirds so the number of blackbirds will decrease
  • As there will be fewer blackbirds the number of earthworm will increase
  • With the larger numbers of earthworms badger numbers will increase as they will have more food available

Pyramids of numbers

  • A pyramid of numbers shows the number of organisms at each trophic level in a food chain

Limitations of pyramids of numbers

  • Do not take into account the size of the plants or animals
  • This will lead to an inverted pyramid as illustrated above

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