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AQA GCSE · Question 07.2 · Ecology
Another farmer produced 4200 kg of maize seeds in a field. The farmer fed the maize to 1000 chickens. At full size, the mean mass of one chicken was 2.2 kg.
Complete the pyramid of biomass for the food chain from the maize seeds to the 1000 chickens. You should:
- label the x-axis
- use a suitable scale
- draw the two bars for the pyramid.
Another farmer produced 4200 kg of maize seeds in a field. The farmer fed the maize to 1000 chickens. At full size, the mean mass of one chicken was 2.2 kg.
Complete the pyramid of biomass for the food chain from the maize seeds to the 1000 chickens. You should:
- label the x-axis
- use a suitable scale
- draw the two bars for the pyramid.
How to approach this question
1. **Calculate Chicken Biomass:** First, calculate the total biomass of the 1000 chickens.
2. **Identify Producer and Consumer:** The maize is the producer (bottom of the pyramid), and the chickens are the primary consumers (level above).
3. **Label the x-axis:** This axis represents the amount of biomass. Label it "Biomass in kg".
4. **Choose a Scale:** Look at your two biomass values (maize and chickens). Your scale must be large enough to fit the larger value. A simple linear scale is best (e.g., 1 square = 200 kg or 1 big square = 1000 kg). The scale should be symmetrical around the central zero point.
5. **Draw the Bars:** Draw the bar for the producer (maize) on the bottom, centred on the y-axis. Its width should correspond to 4200 kg on your scale. Draw the bar for the consumer (chickens) on top of it, also centred. Its width should correspond to the total chicken biomass you calculated.
Full Answer
A completed pyramid of biomass showing:
1. **Producer Bar (Maize):** Biomass = 4200 kg.
2. **Primary Consumer Bar (Chickens):** Biomass = 1000 chickens × 2.2 kg/chicken = 2200 kg.
3. **X-axis label:** "Biomass in kg".
4. **Scale:** A suitable linear scale on the x-axis, centred at 0, that accommodates the largest bar (4200 kg). For example, each major grid line could represent 1000 kg, so the scale would go out to at least 5000 kg on each side of the centre.
5. **Drawing:** Two bars, centred on the y-axis. The bottom bar (maize) should be wider, corresponding to 4200 kg on the scale. The top bar (chickens) should be narrower, corresponding to 2200 kg on the scale.
A pyramid of biomass is a graphical representation of the biomass (total mass of organisms) present at each trophic level in an ecosystem.
1. **Calculate Biomass at Each Level:**
* **Producer (Maize):** The biomass is given as **4200 kg**.
* **Primary Consumer (Chickens):** There are 1000 chickens with a mean mass of 2.2 kg each.
Total chicken biomass = 1000 × 2.2 kg = **2200 kg**.
2. **Construct the Pyramid:**
* **Producers at the base:** The maize seeds are the producers, so their bar forms the base of the pyramid.
* **Consumers above:** The chickens are the primary consumers, so their bar goes on top of the maize bar.
* **Scale and Labels:** The horizontal axis (x-axis) is labelled "Biomass in kg". A linear scale is chosen that can accommodate the largest value (4200 kg). For example, each grid square could represent 400 kg. The pyramid is drawn symmetrically around a central vertical line (y-axis).
* **Bar widths:** The maize bar would have a total width corresponding to 4200 kg, and the chicken bar would have a total width corresponding to 2200 kg. As 4200 > 2200, the base is wider than the top layer, forming the characteristic pyramid shape. This shape illustrates that biomass decreases at successive trophic levels.
Common mistakes
✗ Incorrectly calculating the chicken biomass.
✗ Drawing the pyramid inverted (chickens at the bottom).
✗ Using a non-linear or poorly chosen scale.
✗ Not labelling the x-axis.
Practice the full AQA GCSE Biology Higher Tier Paper 2
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