Pearson Edexcel International A Level Biology: Productivity, Populations, Niche and Succession (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements 5.9 to 5.15 (productivity, populations, niche, Core Practical 11 and succession) of the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2. Topic 5 forms part of IA2, and no tiers apply. Revise from the study guide and revision notes before you start. Related pages: course hub, checklist and diagnostics.

Questions

1. A coastal wetland has a gross primary productivity of 2.40 kg dry mass m⁻² year⁻¹ and a net primary productivity of 1.50 kg dry mass m⁻² year⁻¹. (a) Calculate the mass of dry matter used in plant respiration. [1] (b) Express your answer to (a) as a percentage of the gross primary productivity. [1] (c) State what net primary productivity represents. [1]

2. The table shows the energy stored in each trophic level of a lake.

Trophic level	Producers	Primary consumers	Secondary consumers	Tertiary consumers
Energy (kJ m⁻² year⁻¹)	8 200	984	98.4	4.92

(a) Calculate the efficiency of transfer from producers to primary consumers. [1] (b) Calculate the efficiency of transfer from secondary to tertiary consumers. [1] (c) Explain two reasons why the efficiency of transfer is always less than 100%. [2]

3. A rock pool contains seaweeds, limpets, shore crabs, snails, bacteria, sea water and rock surfaces. Using the rock pool as an example, state what is meant by the terms population, community, habitat and ecosystem. [4]

4. Two species of ground beetle, A and B, live in the same woodland. The table shows when they are active and the percentage of each food type in their diet.

	Time of activity	Earthworms	Slugs	Insect larvae
Species A	Night	70	20	10
Species B	Day	10	25	65

(a) Use the data to explain how the two species can live in the same habitat. [3] (b) A third species, C, which hunts earthworms at night, is introduced. Predict what could happen to the population of A and explain your answer. [2]

5. Plan an investigation into whether the abundance of creeping buttercup changes with distance from a stream across a meadow. Include how you would measure an abiotic factor. [7]

6. A field of 1 500 m² was sampled with ten quadrats, each 0.25 m². The numbers of nettle plants in the quadrats were 7, 3, 9, 4, 0, 6, 5, 2, 8 and 4. (a) Calculate the mean number of plants per quadrat. [1] (b) Calculate the density of nettles per m². [1] (c) Estimate the number of nettles in the field. [1] (d) Calculate the frequency of nettles in the sample as a percentage. [1] (e) Suggest one way to make the estimate more reliable. [1]

7. Describe and explain the stages by which bare rock becomes a woodland climax community in a temperate climate. [6]

8. The table shows data from a bare quarry floor that was left to develop naturally.

Time since abandonment (years)	5	25	60	150
Plant species per 100 m²	4	11	19	23
Soil depth (cm)	0.5	3	9	18
Light reaching the ground (% of full sunlight)	95	85	40	8

(a) Calculate the percentage increase in species per 100 m² between 5 and 60 years. [2] (b) Calculate how many times greater the soil depth is at 150 years than at 5 years. [1] (c) Explain the change in light reaching the ground and suggest how it affects the species present. [2]

9. The herbivores in a meadow took in 620 kJ m⁻² year⁻¹ of energy in food. They lost 155 in faeces, 310 as heat from respiration and 31 in urine (same units). The rest was stored in new tissue. The meadow plants have a GPP of 14 500 kJ m⁻² year⁻¹ and use 5 800 kJ m⁻² year⁻¹ in respiration. (a) Calculate the energy stored in new tissue. [2] (b) Calculate the efficiency of conversion of energy taken in to new tissue. [1] (c) Calculate the percentage of the energy taken in that was absorbed. [1] (d) Calculate the NPP of the meadow plants. [1] (e) Calculate the percentage of the NPP represented by the 620 kJ eaten, giving your answer to 2 significant figures. [1] (f) Explain two reasons why herbivores do not use all the NPP. [2]

10. A transect was taken at 10 m intervals inland from the strandline of a sand dune system.

Distance (m)	0	10	20	30	40	50
Marram grass cover (%)	3	12	38	60	45	10
Plant species per m²	1	2	4	7	10	14
Humus in soil (%)	0.1	0.4	1.2	2.3	3.6	5.1
Soil moisture (%)	2	3	5	7	9	12

(a) Describe the change in the number of plant species with distance. [2] (b) Explain how the transect relates to succession and state which end of the transect is the oldest. [3] (c) Use the idea of niche to explain why marram grass cover falls beyond 30 m. [3] (d) Name one abiotic factor and one biotic factor that change along the transect and explain how each could affect where plants grow. [2]

Answers

1. (a) R = GPP − NPP = 2.40 − 1.50 = 0.90 kg dry mass m⁻² year⁻¹ [1]. (b) 0.90 ÷ 2.40 × 100 = 37.5% [1]. (c) The rate at which energy or biomass is stored in new plant tissue [1]. [3] Examiner insight: Keep the unit with the mass and the time period. A bare number such as 0.90 leaves the answer incomplete.

2. (a) 984 ÷ 8 200 × 100 = 12.0% [1]. (b) 4.92 ÷ 98.4 × 100 = 5.0% [1]. (c) Not all of the organism is eaten, or not all that is eaten is digested and absorbed, so some is egested [1]. Respiration releases heat, or energy is lost in excretion, so only the remainder becomes new tissue [1]. [4] Examiner insight: Two answers that both say “energy is lost” repeat one idea. Name where it is lost.

3. Population: all the limpets, or all the shore crabs, in the pool [1]. Community: all the species together, such as seaweeds, limpets, crabs, snails and bacteria [1]. Habitat: the place where the organisms live, the rock pool with its water and rock surfaces [1]. Ecosystem: the community together with the abiotic factors such as water temperature, light, salinity and oxygen concentration [1]. [4] Examiner insight: Use the rock pool in each definition, so that the difference between the terms is clear.

4. (a) Their niches differ [1]. A is active at night and B by day, so they are not hunting at the same time [1]. A eats mostly earthworms (70%) while B eats mostly insect larvae (65%), so competition for food is reduced [1]. (b) C is a competitor for earthworms at night, so the food available to A falls [1]. A population of A could decline, or A could shift to eating more slugs or insect larvae [1]. [5] Examiner insight: A prediction needs its reason: say which resource is shared.

5. Choose a transect running at right angles to the stream across the meadow [1]. Place a quadrat at regular intervals along the line, for example every 2 m [1]. Record the abundance of creeping buttercup as number per quadrat or percentage cover [1]. Use the same size of quadrat each time and repeat with several transects so that results can be averaged [1]. Measure soil moisture at each quadrat by taking a soil sample, weighing it, drying it in an oven and reweighing [1]. Calculate the percentage of mass lost [1]. State a null hypothesis, such as there is no relationship between distance from the stream and the abundance of creeping buttercup [1]. [7] Examiner insight: Give figures such as the interval and the number of transects, and name what is measured at each point.

6. (a) Total = 48; 48 ÷ 10 = 4.8 per quadrat [1]. (b) 4.8 ÷ 0.25 = 19.2 per m² [1]. (c) 19.2 × 1 500 = 28 800 nettles [1]. (d) 9 of 10 quadrats contain nettles, so 90% [1]. (e) Use more quadrats, or place them using random coordinates to avoid bias [1]. [5] Examiner insight: Convert to 1 m² before scaling to the field. Scaling the quadrat mean directly gives an estimate four times too small.

7. Pioneer species such as lichens and mosses colonise the bare rock [1]. They are adapted to survive with little water and few nutrients [1]. Their weathering of the rock, together with their remains decaying, forms thin soil and humus [1]. Soil that is deeper and holds more water allows grasses and herbs to grow [1]. Taller plants such as shrubs shade out and outcompete the earlier species [1]. Eventually trees form a relatively stable climax community with high biodiversity, which is determined by the climate [1]. [6] Examiner insight: Link each stage to a change in the environment. A list of species does not explain why one replaces another.

8. (a) (19 − 4) ÷ 4 × 100 [1] = 375% [1]. (b) 18 ÷ 0.5 = 36 times [1]. (c) Taller plants and trees form a canopy that intercepts light [1], so only shade-tolerant species can grow near the ground, but more niches and deeper soil allow more species overall [1]. [5] Examiner insight: Show the subtraction in a percentage increase before dividing, so that your method can be followed.

9. (a) Stored = 620 − 155 − 310 − 31 [1] = 124 kJ m⁻² year⁻¹ [1]. (b) 124 ÷ 620 × 100 = 20.0% [1]. (c) (620 − 155) ÷ 620 × 100 = 75.0% [1]. (d) NPP = 14 500 − 5 800 = 8 700 kJ m⁻² year⁻¹ [1]. (e) 620 ÷ 8 700 × 100 = 7.1% [1]. (f) Some of the plant, such as roots, is not eaten, or other consumers and decomposers use some of it [1]. Some plant material is indigestible, such as cellulose, which is lost in faeces [1]. [8] Examiner insight: Check the denominator in each part: energy taken in, energy absorbed, or NPP.

10. (a) The number of species rises as distance increases [1], from 1 species per m² at 0 m to 14 at 50 m [1]. (b) Distance from the strandline reflects time since the sand was colonised, so the transect shows the stages of succession [1]. The 50 m end is oldest [1], because it has the most species and the most humus, so the soil has had longest to develop [1]. (c) Marram grass is a pioneer species adapted to dry, nutrient-poor sand [1]. Beyond 30 m, soil moisture and humus increase, so other species that are better competitors grow and shade it [1]. Marram’s niche is then reduced by interspecific competition, so its cover falls [1]. (d) Abiotic: soil moisture or humus increases, which makes it possible for plants that need more water or nutrients to survive [1]. Biotic: competition between plants for light and space, which excludes pioneers as taller species grow [1]. [10] Examiner insight: Link a change in an abiotic factor to a change in the community. “Because of succession” alone explains little.

Where marks are usually lost

• Calculating R or NPP without units.
• Using the wrong trophic level as the denominator in an efficiency calculation.
• Defining habitat and niche as if they were the same.
• Describing a trend without quoting figures from the table.
• Dividing by the final value rather than the starting value for a percentage increase.
• Listing species in succession without explaining the environmental change between stages.

Next steps

• Revision notes
• Study guide
• Edexcel A Level Biology hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, February 2021, Pearson Education Limited. Statements 5.9 to 5.15, Topic 5.