PART 6: Food Chains, Food Webs, Energy Transfer in Trophic levels, Pyramids of Numbers, Biomass and Energy

How are all organisms in an ecosystem related to one another

Via feeding relationships (food chains and food webs)

Explain the difference between food chains and food webs

Food chains: Shows one simple chain/path of energy slow and is less realistic (since animals usually eat more than 1 thing)

Food webs: Shows the total number of interacting food chains in a community of organisms. They are better representations of biotic interactions than food webs (shows variety in diet)

What is the first step in a food chain

1. Producers

• the first organism in a food chain is always a producer: usually a photosynthetic organism like a plant

• They convert light energy into chemical energy providing a source of energy for

  • themselves

  • all the other organisms in the ecosystem

What is the second step in a food chain

2. Consumers

• The rest (excluding step 3) of the organisms in a food chain are consumers

• They obtain food (and therefore the energy) by eating other organisms

  • Consumers which feed on plants = herbivores (eg rabbits and cows)

  • Consumers which feed on plants and animals = omnivores (eg beats and crows)

  • Consumers which only eat animals = carnivores

What is the first, second, third and forth consumer called

• 1st - Primary consumer

• 2nd - Secondary consumers

• 3rd - Tertiary consumers

• 4th - Quaternary consumer

What is the 3rd and final step in a food chains which isnt always shown in food chains but is always in reality really there

3. Decomposers

• Decomposers are microscopic organisms that feed on dead decaying organic matter and recycle nutrients in ecosystems

• Examples: aphids, ticks, bacteria, funghi, woodlice, earthworms

What are the more scientific words for

• Producers

• Consumers

• Decomposers

• Producers = Autotrophs

• Consumers = Heterotrophs

• Decomposers = Saprotrophs (scavengers and detritivores)

What is each level/step in a food chain known as

A tropic level

What do the arrows between tropic levels show

Energy flow

How much energy is transferred from one trophic level to the next

Only 10%, 90% is ‘lost’

Why is 90% of the energy ‘lost’

1. The organisms use some of the energy from themselves to carry out the 7 vital functions

2. Respiration (one of the 7 vital functions) is not 100% effective and some energy is lost as heat

3. Not all the organisms can be digested - some energy is lost during egestion (shitting of undigested food)

Explain using the fact that only 10% of energy is passed along why there are usually not more than 5 trophic levels in a food chain

Because less energy is transferred at each trophic level until there is not enough to sustain another trophic level

Explain the by the number of organisms tend to decrease from one trophic level to the next (exceptions like parasites and saprotrophs)

There is less energy to support them

Explain what pyramids of numbers, biomass and energy represent

• Pyramids of numbers: compare the number of organisms at each trophic level until

• Pyramid of biomass: compare the mass of biological material at each trophic level

• Pyramid of energy: compare the amount of energy passing through each trophic level

In terms of shape and structure which pyramid always look the same

Pyramids of energy