Revision Notes: Pyramids of Biomass and Number

Producers

• Plants are producers, creating their own food through photosynthesis.

• Photosynthesis uses sunlight, water, carbon dioxide, and nutrients to chemically produce food.

• Producers are also known as autotrophs.

Consumers

• Animals obtain energy either directly by eating plants or indirectly by eating animals that have consumed plants.

• Organisms that cannot produce their own food are called consumers, or heterotrophs.

Pyramids in Food Chains

• Pyramids represent each trophic level in a food chain with horizontal bars.

• The width of each bar signifies the number of organisms or the amount of biomass at that level.

• The base of the pyramid represents the producers, followed by primary consumers, and so on.

• Energy availability decreases as you go up the trophic levels, leading to fewer organisms at each level.

• This energy loss limits the length of food chains, typically to no more than five trophic levels due to insufficient energy to support additional levels.

Pyramid of Biomass

• The pyramid of biomass illustrates the total mass of organisms at each stage of a food chain.

• Producers generally have a higher biomass than primary consumers, resulting in a pyramid shape. This is a general rule and will always be produced as a pyramid shape.

Pyramid of Numbers

• The pyramid of numbers shows the relative number of organisms at each stage of a food chain.

• The shape of the pyramid may vary, and it is not always pyramid-shaped. The shape depends on the number of organisms at each level.

  • For example, one tree can support numerous caterpillars, altering the typical pyramid shape.

  • However, food chains starting with grass will typically show a pyramid shape.

Examples of Pyramid Shapes

• Not Pyramid Shaped (Pyramid of Numbers): Example: 1 Oak Tree → 2000 Insects → 90 Sparrows → 1 Hawk

• Pyramid Shaped (Pyramid of Numbers): Grass-based food chains typically follow a pyramid shape.

Additional Examples

• Example 1:

  • Bush: 500 (Biomass)

  • Gazelle: 100 (Numbers)

  • Cheetah: 10

  • Sparrowhawk: 1

• Example 2:

  • Oak Tree (Pyramid of Numbers)

  • Caterpillar

  • Blue tit

  • Sparrowhawk

• Example 3:

  • Oak Tree (Pyramid of Biomass)

  • Caterpillar

  • Blue tit

  • Sparrowhawk