IGCSE Biology 2017: 4.7: Understand the Concepts of Food Chains, Food Webs, Pyramids of Number, Pyramids of Biomass and Pyramids of Energy Transfer

FOOD CHAINS: Shows the feeding relationships between living organisms

FOOD CHAINS

Diagram showing an Example of a Food Chain

EXPLANATION:

The Flower is the Producer as it produces their own organic nutrients (Glucose) via Photosynthesis
As the Flowers (Producer) will be eaten by Snails, these are the Primary Consumers
As the Snails (Primary Consumer) will be eaten by Frogs, these are Secondary Consumers
As the Frogs (Secondary Consumer) will be eaten by Foxes, these are Tertiary Consumers at the top of the food chain

FOOD WEBS: Shows how food chains are linked together into more complex feeding relationships

FOOD WEBS

Diagram showing an Example of a Food Web

EXPLANATION:

Food web shows the numerous food chains joined together:

Food Webs show the Interdependence between organisms - change in
population of one organism will affect the population of another organism

If population of Earthworms decrease, population of Wood mouse may decrease as well as they will have less Earthworms to feed on, leading to starvation and death

If population of Shrews increase, population of Owl may increase as well as they will have more Shrews to feed on, increasing chances of survival

PYRAMIDS OF NUMBERS: Shows the population of each organism at each trophic level in a food chain

PYRAMIDS OF NUMBERS

Diagram showing an Example of Pyramid of Numbers

EXPLANATION:

In the diagram, the bars represent the population of the organism at each trophic level - the wider the bar, the larger the population
As energy is lost to the surroundings from one trophic level to the next, there are usually fewer organisms with each trophic level due to decreasing chances of survival
However, some diagrams may not resemble a pyramid as one large producer can feed many small consumers (e.g one Oaktree can feed many Insects)

PYRAMIDS OF BIOMASS: Shows the biomass (amount of living material) of organisms in each trophic level

PYRAMIDS OF BIOMASS

Diagram showing an Example of Pyramid of Biomass

EXPLANATION:

In the diagram, the bars represent the biomass of a population of organisms (calculated by multiplying individual biomass by population)
Pyramids of biomass will commonly be upright in shape, as the amount of food available (biomass) decreases with each trophic level as energy may be lost via respiration, incomplete digestion, or excretion/egestion

PYRAMIDS OF ENERGY TRANSFER: Shows the transfer of energy with each trophic level

PYRAMIDS OF ENERGY TRANSFER

Diagram showing an Example of Pyramid of Energy Transfer

EXPLANATION:

In the diagram, the bar shows the amount of energy available for the next trophic level
As energy is lost via respiration, incomplete digestion, or egestion/excretion, only 10% of energy is passed on from one trophic level to the next
As a result, this limits the trophic level in a food chain

UnknownJanuary 28, 2021 at 12:01 PM
When analyzing these diagrams, it would be helpful for students to review the meaning of producer and consumer. Students are often confused by the arrows, specifically the direction of the arrows. They often think the arrow is pointing to the organism that gets eaten, when it is just the opposite. Students need reminding that the arrow represents the flow of energy. For example, energy in the flower goes into the snail. Energy pyramids are always confusing. For this reason, I try to avoid numbers pyramids because they don't make sense anyway. It's about energy, not the number of individuals at each trophic level. I think the last pyramid is helpful because the sizes of each trophic level are representative of the amount of energy transferred and lost. Students would need to be reminded how energy is lost though (heat, metabolism, feces, bones, fur, shells, etc.)
Lucy BlakeMarch 21, 2021 at 1:03 AM
Thank you for these they are amazing!

IGCSE Biology 2017