Energy Flow in Ecosystems

Question 1

Primary source of energy

Answer 1

○ Sun
○ Provides energy to the earth in the form of heat and light
○ Major source of energy that drives the ecosystems on earth

Question 2

Role of photosynthesis

Answer 2

○ Auto(self)trophic(feeding) producers use photosynthesis
○ Use the energy from the sun (photosynthesis) and simple inorganic substances to manufacture organic matter (food)
○ Energy is stored in the chemical bonds and is released when the chemical bonds are broken

Question 3

Role of cellular respiration

Answer 3

○ Metabolic process of the chemical breakdown of organic matter to release energy
○ The process consumers use to extract energy from organic matter
○ Herbivores consume large amounts of plants material
○ Extract the energy stored in the chemical bonds by cellular respiration
○ Producers also perform cellular respiration

Question 4

Energy flow

Answer 4

• Energy transfer from plant to consumer is not completely efficient - only 10% of the energy is transferred from producer to consumer
  □ Not all plant material is eaten and/or absorbed by the gut
  □ Energy is lost through movement and respiration

Question 5

Food chains/webs

Answer 5

○ Food chains and food webs are qualitative models that allow ecologists to measure the sustainability of feeding relationships in an ecosystem
○ Each position of an organism has in a chain is referred to as a ‘trophic (feeding) level’
○ Each organism feeds and obtains its energy and matter from the preceding one
○ Energy and matter are transferred progressively from one trophic level to the next

Question 6

Primary consumer

Answer 6

• Herbivore
• Feed directly on producers
• E.g. wombats, sheep

Question 7

Secondary consumer

Answer 7

• Carnivore
• Feed on primary consumers
• E.g. dingoes, platypuses

Question 8

Top consumer

Answer 8

• Apex predator
• Feed on secondary consumers
• E.g. wedgetail eagle, sharks

Question 9

Omnivore

Answer 9

• Feed on both plants and animals
• E.g. foxes, bandicoots

Question 10

Scavenger

Answer 10

• Feed on dead remains of other organisms
• E.g. foxes, ravens

Question 11

Detritivore

Answer 11

• Feed on dead or decaying organic remains and wastes
• Help speed up decay by breaking down larger pieces of detritus into smaller pieces (largen surface area for decomposers to work more efficiently)
• E.g. dung beetles, maggots, earthworms

Question 12

Decomposer

Answer 12

• Decompose/break down complex organic molecules into simpler inorganic forms and return nutrients to the soil or water
• E.g. fungi, some bacteria

Question 13

Distinguish between food chains and food web

Answer 13

○ A food web is a group of food chains that are linked together showing the interactions between food chains in a community
○ Distinguishing feature is that an organism can occupy different trophic levels in different food chains
○ Members of populations can move in and out of food chains/food webs at different times
- E.g. birds feeding off seeds in different ecosystems (depending on the seed)

Question 14

Ecological pyramid

Answer 14

• Diagrams that show the relative levels of one of three different factors present in an ecosystem at each trophic level
• Three types: numbers, biomass, energy

Question 15

Number

Answer 15

• Number of organisms at each trophic level
• Usually food chains have a drop in number of organisms as the trophic level rises
• Inverted pyramid of number
  ◊ When more organisms occupy the trophic level above the preceding level
  ◊ E.g. producer - eucalyptus tree, primary consumer - wattlebirds, secondary consumer - parasites (on the bird)

Question 16

Biomass

Answer 16

• The biomass (amount of organic matter in terms of mass) present
• Expressed as dry weight per unit (g/m2)
  ◊ Living biological matter contains water which is inorganic and cannot be used as an energy source
  Can be calculated
  ◊ At a given time
  ◊ Rates (e.g. measuring biomass in a given area the duration of a year (g/m2/year))
• At each successive trophic level, the biomass decreases
  ◊ Consumers must eat considerable amounts of food to fulfill energy needs
• Inverted pyramid of biomass
  ◊ Occurs when the producer has a short life cycle and can reproduce at a fast rate, counteracting their biomass

Question 17

Energy

Answer 17

• The amount of energy transferred from one trophic level to the next
• Expressed in units of energy per area in a given time
  ◊ E.g. kilojoules per square metre per year (kJ/m-2/y-1)
• The rate at which energy is transferred from one trophic level to another in a community
• Ecologists can make predictions about whether a community can be sustained and what the impact changes in rates of energy transfer will have on the community
• Only some of the energy stored in a trophic level goes to the next level (10% on average)
• Can never be inverted
• Drawing pyramids of energy
  ◊ Producer at the bottom
  ◊ Each level labelled (producer, primary consumer, secondary consumer, tertiary consumer)
  ◊ Draw to scale
  ◊ Use data is provided
  ◊ If no data, measure one tenth of preceding trophic level (average energy transfer efficiency rule of 10%)
  ◊ Labelled arrows to indicate energy leaving each trophic level in the form of heat