AQA Biology 4.7.4.2 · Triple only

Pyramids of biomass

A table of masses becomes a stack of bars, each drawn to scale. Producers at the bottom, and a ruler in your hand.

Triple Science · Higher tier

Calculates

Start here

One tree, many caterpillars.

An oak tree is covered in caterpillars eating its leaves.

If you had to guess, which weighs more in total: the one oak tree, or all the caterpillars on it?

What it shows

Total mass at each level.

Pyramids of biomass can be constructed to represent the relative amount of biomass in each level of a food chain. Trophic level 1 is at the bottom of the pyramid. The width of each bar is proportional to the biomass at that level, measured in g/m² or kg/m².

Information · made-up data for practice

Grassland, per square metre (made up): grass 400 g/m²; grasshoppers 80 g/m²; frogs 16 g/m².

Why is each bar narrower than the one below?

Pick one.

Drawing to scale · a taught step

Choose a scale that lets the widest bar fit the paper, then divide every value by it.

bar width = biomass ÷ scale value

Worked example, the grassland above, scale 1 cm = 40 g/m²:

grass: 400 ÷ 40 = 10 cm
grasshoppers: 80 ÷ 40 = 2 cm
frogs: 16 ÷ 40 = 0.4 cm

If a value is in kg/m², convert it to the scale’s unit first: 1 kg = 1000 g, so 0.8 kg/m² = 800 g/m². Draw each bar centred on the one below, label every level with its organism, and write the scale on the drawing.

Construct

Your turn: a woodland.

Information · made-up data for practice

Woodland, per square metre (made up): oak leaves 0.8 kg/m²; caterpillars 160 g/m²; blue tits 40 g/m². Scale: 1 cm = 80 g/m².

Pick the width of each bar.

Oak leaves · 0.8 kg/m²

bar width = biomass ÷ scale value

Caterpillars · 160 g/m²

bar width = biomass ÷ scale value

Blue tits · 40 g/m²

bar width = biomass ÷ scale value

Pick a width for each level and watch the pyramid draw.

Think again · top or bottom?

“Producers go at the top, because they come first.”

Your call

Choose

Where does trophic level 1 go in a pyramid of biomass?

Sort

True or false?

Place each statement.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Construct: An accurate pyramid of biomass from data, to a stated scale.
Calculate: Bar width = biomass ÷ scale value, after converting units.
Explain: Why biomass decreases at each level.

Key fact

A pyramid of biomass shows the total mass of living material at each trophic level, level 1 at the bottom. Bar width = biomass ÷ scale value; convert kg/m² to g/m² first and write the scale on the drawing.

Key note · AQA 4.7.4.2 (Biology only)

Pyramids of biomass

Pyramids of biomass can be constructed to represent the relative amount of biomass in each level of a food chain. Trophic level 1 is at the bottom of the pyramid.
Bar width is proportional to the total biomass at that level; units g/m² or kg/m².
Bar width = biomass ÷ scale value. Convert kg/m² to g/m² first. Write the scale on the drawing; centre each bar; label each level.
Biomass falls at each level because of the three losses: faeces; carbon dioxide and water in respiration; urea and water in urine (Transfer of biomass).

Photograph this card. Tomorrow, cover it and say each line first.

Previous and next

Connects to

Ask MrBadmus

Drawing the bars “a bit smaller” instead of to scale?

All biomass values are made up to fit one scale.