Quick answer: An ecological pyramid shows the number, biomass or energy at each trophic level, with producers at the base. Pyramids of numbers and biomass can be inverted (a single tree with parasites; phytoplankton in the sea). A pyramid of energy is always upright, because only about 10% of the energy at one level reaches the next and the rest is lost, mostly as heat.
Syllabus note: The rationalised NCERT Class 10 chapter Our Environment covers trophic levels, food chains and the 10% law, but it does not teach ecological pyramids by name. Pyramids are taught in detail in Class 12 (Ecosystem). Use this article to understand the 10% law better, and check your school's syllabus before learning the pyramid types for a Class 10 exam.
What is an ecological pyramid?
An ecological pyramid is a diagram of stacked bars. Each bar is one trophic level, and its width shows how much of something (individuals, biomass or energy) that level holds at a time. The idea was introduced by ecologist Charles Elton, so they are also called Eltonian pyramids.
- Base: first trophic level, the producers (green plants, phytoplankton).
- Next levels: herbivores (primary consumers), then carnivores (secondary and tertiary consumers).
- Apex: the top carnivores.
| Trophic level | Who is there | Example |
|---|---|---|
| First | Producers | Grass, phytoplankton |
| Second | Herbivores | Grasshopper, zooplankton |
| Third | Small carnivores | Frog, small fish |
| Fourth | Large carnivores | Snake, eagle, large fish |
There are three types: pyramids of numbers, biomass and energy.
Pyramid of numbers
A pyramid of numbers shows the number of individual organisms at each trophic level.
Upright: grassland or pond
In a grassland, a very large number of grass plants supports fewer grasshoppers, which support fewer frogs, which support only a few snakes. Numbers fall at each higher level, so the pyramid is upright.
Inverted: a single tree with parasites
One large tree (one producer) can feed many birds. Each bird can carry many parasites such as lice, and those parasites can have even more hyperparasites. Numbers increase going up, so the pyramid of numbers is inverted.
Why this happens: A pyramid of numbers ignores size. One huge tree counts as "1", the same as one blade of grass.
Pyramid of biomass
A pyramid of biomass shows the total dry mass of living organisms at each trophic level at one moment (the standing crop).
Upright: forest or grassland
The total mass of trees or grasses is much larger than the mass of the deer that eat them, which is larger than the mass of the tigers. The pyramid is upright.
Inverted: ponds, lakes and oceans
In many aquatic ecosystems the pyramid of biomass is inverted:
- The producers are phytoplankton, which are tiny and short-lived.
- They reproduce very fast, so a small standing mass is replaced again and again.
- Zooplankton and fish eat them quickly and live longer, so they build up more standing biomass.
- At any single moment, consumer biomass can be greater than producer biomass.
Key idea: The phytoplankton are not producing less food. They are producing it fast and being eaten fast, so the snapshot shows little of them.
Pyramid of energy: why it is always upright
A pyramid of energy shows the energy flowing through each trophic level over a period of time (for example, kJ per m² per year).
- Energy flows one way: sun → producers → herbivores → carnivores. It does not come back to the lower level.
- The 10% law: On average, only about 10% of the energy at one level is stored in the bodies of the next level. The remaining ~90% is used in life processes (respiration, movement, keeping warm) and lost as heat, or stays in undigested and dead matter.
Worked example, starting with 10,000 J in producers:
| Trophic level | Energy available |
|---|---|
| Producers | 10,000 J |
| Herbivores | 1,000 J |
| Small carnivores | 100 J |
| Large carnivores | 10 J |
Each step keeps about one-tenth of the energy, so each higher bar is narrower. The pyramid of energy is therefore always upright in every ecosystem.
Exam answer: "A pyramid of energy can never be inverted because energy flow is unidirectional and some energy is lost as heat at every trophic level. So each higher level always receives less energy than the level below it."
This is also why food chains usually have only 3–4 trophic levels: after a few steps there is too little energy left to support another level.
Summary table
| Pyramid | Grassland | Single tree with parasites | Pond / ocean |
|---|---|---|---|
| Numbers | Upright | Inverted | Upright |
| Biomass | Upright | Upright | Often inverted |
| Energy | Upright | Upright | Upright |
Exam tips
- Always place producers at the base of any pyramid you draw, and label each level.
- For "why is the energy pyramid always upright?", write two points: one-way flow of energy and loss of energy as heat at each level (10% law).
- For the inverted biomass pyramid, mention phytoplankton, their small standing mass and their fast turnover.
- Remember that the number pyramid is inverted on a tree, but the biomass pyramid on that tree is upright.
Common mistakes
- Saying the energy pyramid in the ocean is inverted. Only the biomass pyramid can be inverted there.
- Thinking 10% is an exact law of physics. It is an average; real transfer efficiency varies (roughly 5–20%).
- Saying energy is "destroyed" at each level. It is converted, mostly to heat, which living things cannot use again.
- Mixing up a pyramid of numbers with a pyramid of biomass in the single-tree example.
Frequently Asked Questions
Who introduced ecological pyramids?
The British ecologist Charles Elton introduced the idea in 1927, which is why they are also called Eltonian pyramids.
Can a pyramid of numbers be inverted?
Yes. In a single tree supporting many birds, and parasites on those birds, the number of organisms increases at each higher level, so the pyramid is inverted.
Why is the pyramid of biomass inverted in the sea?
Phytoplankton are tiny and reproduce very quickly, so their standing mass at any moment is small, while the zooplankton and fish that eat them live longer and build up more biomass.
Can a pyramid of energy ever be inverted?
No. Energy flows in one direction and part of it is lost as heat at every trophic level, so each higher level always has less energy than the one below.
What is the 10% law?
It states that, on average, only about 10% of the energy at one trophic level is passed on to the next level. The law is credited to Raymond Lindeman's 1942 work on energy flow.
Are ecological pyramids in the Class 10 CBSE syllabus?
The rationalised NCERT Class 10 book covers trophic levels and the 10% law but not the pyramid types by name. They are covered in Class 12 Biology.