AQA A-level Geography · 3.1.6

Biodiversity, ecosystems and succession

50 exam-style questions with answers for 3.1.6 Biodiversity, ecosystems and succession in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.1.6.1 · Biodiversity
Define the term biodiversity. [2 marks]
Answer:
The variety of life in an area or on Earth (1); including the variety of species, genes and ecosystems (1).
Question 2 · Spec 3.1.6.1 · Biodiversity
Distinguish between genetic diversity, species diversity and ecosystem diversity. [3 marks]
Answer:
Genetic diversity is the variation in genes within a species (1); species diversity is the variety and abundance of species in an area (1); ecosystem diversity is the variety of habitats and ecosystems in a region (1).
Question 3 · Spec 3.1.6.1 · Biodiversity
Describe the global pattern of biodiversity. [3 marks]
Answer:
Biodiversity is highest in the tropics and decreases towards the poles (1); tropical rainforests and coral reefs have the greatest number of species (1); biodiversity hotspots such as Madagascar and Indonesia have many species found nowhere else (1).
Question 4 · Spec 3.1.6.1 · Biodiversity
Explain why biodiversity is greater in the tropics than in cold environments. [3 marks]
Answer:
More solar energy and warmth give higher net primary productivity (1); a stable climate with little seasonal change supports year-round growth (1); species have had a long time to evolve without ice ages disrupting them (1).
Question 5 · Spec 3.1.6.1 · Trends
Describe the global trends in biodiversity. [3 marks]
Answer:
Monitored wildlife populations have fallen by around 70% on average since 1970 (1); up to a million species are threatened with extinction (1); current extinction rates are tens to hundreds of times higher than the long-term average (1).
Question 6 · Spec 3.1.6.1 · Trends
Describe local trends in biodiversity in the UK. [3 marks]
Answer:
Many farmland birds, hedgehogs and pollinating insects have declined (1); some species have recovered with protection, such as red kites and otters (1); loss of hedgerows, wetlands and meadows has reduced habitats (1).
Question 7 · Spec 3.1.6.1 · Trends
Explain what is meant by a mass extinction. [2 marks]
Answer:
A short period in which a very large proportion of the world's species die out (1); there have been five in Earth's history, and many scientists suggest a sixth is under way caused by human activity (1).
Question 8 · Spec 3.1.6.1 · Causes
Describe the main causes of declining biodiversity. [4 marks]
Answer:
Habitat loss and fragmentation from farming, urban growth and deforestation (1); overexploitation, such as overfishing and hunting (1); invasive non-native species (1); pollution and climate change (1).
Question 9 · Spec 3.1.6.1 · Causes
Explain how habitat fragmentation reduces biodiversity. [3 marks]
Answer:
Large habitats are split into small isolated patches (1); populations become too small to survive, and are cut off from other groups, reducing genetic diversity (1); edge effects expose species to different conditions and predators (1).
Question 10 · Spec 3.1.6.1 · Causes
Explain how invasive species can reduce biodiversity. [3 marks]
Answer:
They compete with native species for food and space (1); they may prey on native species or bring disease (1); native species without natural defences can be driven to extinction, for example on islands (1).
Question 11 · Spec 3.1.6.1 · Causes
Explain how pollution reduces biodiversity. [3 marks]
Answer:
Fertiliser runoff causes eutrophication, algal blooms and oxygen loss in water (1); pesticides kill insects and move up food chains (1); plastics, oil and chemicals poison wildlife and damage habitats (1).
Question 12 · Spec 3.1.6.1 · Causes
Explain how overexploitation reduces biodiversity. [3 marks]
Answer:
Species are harvested faster than they can reproduce, such as overfishing of cod (1); hunting and the illegal wildlife trade reduce populations, such as elephants and rhinos (1); the loss of top predators and key species disrupts the food web (1).
Question 13 · Spec 3.1.6.1 · Causes
A habitat had 80 species in 1990 and 62 species in 2020. Calculate the percentage change in species number. [2 marks]
Answer:
(62 − 80) ÷ 80 × 100 (1); = −22.5% (1).
Question 14 · Spec 3.1.6.1 · Impacts
Describe the potential impacts of declining biodiversity. [4 marks]
Answer:
Loss of ecosystem services such as pollination, clean water and soil fertility (1); less resilient ecosystems that are easier to damage (1); fewer genetic resources for food, crops and medicines (1); loss of tourism income and cultural value (1).
Question 15 · Spec 3.1.6.1 · Impacts
Explain why genetic diversity is important for the survival of a species. [2 marks]
Answer:
A wider gene pool makes it more likely that some individuals will survive disease or change (1); low genetic diversity makes populations vulnerable to extinction (1).
Question 16 · Spec 3.1.6.1 · Impacts
Describe the ecosystem services that ecosystems provide for people. [4 marks]
Answer:
Provisioning: food, water, timber and medicines (1); regulating: climate control, flood control and pollination (1); supporting: soil formation and nutrient cycling (1); cultural: recreation, tourism and spiritual value (1).
Question 17 · Spec 3.1.6.1 · Impacts
Explain how population growth and economic development put pressure on ecosystems. [4 marks]
Answer:
More people need more food, so land is cleared for farming (1); rising incomes increase demand for meat, timber, energy and goods (1); urban growth and industry destroy habitats and cause pollution (1); resource extraction and waste produce greenhouse gases that change climate (1).
Question 18 · Spec 3.1.6.1 · Impacts
Explain what is meant by sustainability of an ecosystem. [2 marks]
Answer:
Using ecosystem resources in a way that does not reduce their ability to function (1); so that they can continue to support people and wildlife in the future (1).
Question 19 · Spec 3.1.6.1 · Impacts
Explain how people can contribute to ecosystem development and sustainability. [3 marks]
Answer:
Protecting areas through national parks and reserves (1); restoring damaged habitats and rewilding (1); using sustainable farming, forestry and fishing methods such as agroforestry and quotas (1).
Question 20 · Spec 3.1.6.2 · Nature of ecosystems
Define the term ecosystem. [2 marks]
Answer:
A community of living things (plants and animals) interacting with each other (1); and with the non-living environment, such as soil, water and climate (1).
Question 21 · Spec 3.1.6.2 · Nature of ecosystems
Explain what is meant by a trophic level. [2 marks]
Answer:
A feeding level in a food chain (1); for example producers, primary consumers and secondary consumers (1).
Question 22 · Spec 3.1.6.2 · Nature of ecosystems
Distinguish between a food chain and a food web. [2 marks]
Answer:
A food chain shows a single line of feeding relationships (1); a food web shows the many interconnected food chains in an ecosystem (1).
Question 23 · Spec 3.1.6.2 · Nature of ecosystems
Describe the flow of energy through an ecosystem. [3 marks]
Answer:
Energy enters as sunlight, which producers convert to chemical energy by photosynthesis (1); energy passes to consumers when they eat producers and other consumers (1); at each level much energy is lost as heat, so only about 10% passes to the next (1).
Question 24 · Spec 3.1.6.2 · Nature of ecosystems
Explain why food chains are usually short. [2 marks]
Answer:
Only about 10% of energy passes between trophic levels (1); too little energy remains to support further levels (1).
Question 25 · Spec 3.1.6.2 · Nature of ecosystems
Explain the role of decomposers in an ecosystem. [2 marks]
Answer:
Bacteria and fungi break down dead organisms and waste (1); they release nutrients back into the soil for uptake by plants (1).
Question 26 · Spec 3.1.6.2 · Nature of ecosystems
Explain what is meant by a keystone species and give an example of its effect. [3 marks]
Answer:
A species with a disproportionately large effect on its ecosystem compared with its numbers (1); if it is removed, the ecosystem changes significantly (1); for example, sea otters eat urchins, which protects kelp forests from being overgrazed (1).
Question 27 · Spec 3.1.6.2 · Systems
Describe the inputs, stores, transfers and outputs in an ecosystem. [4 marks]
Answer:
Inputs: solar energy, rain and nutrients from weathering and the atmosphere (1); stores: biomass, litter and soil nutrients (1); transfers: feeding, decomposition and nutrient uptake (1); outputs: heat loss, respiration, run-off and harvested products (1).
Question 28 · Spec 3.1.6.2 · Systems
Explain the terms biomass and net primary production. [3 marks]
Answer:
Biomass is the total mass of living organisms in an area (1); gross primary production is the total energy fixed by plants in photosynthesis (1); net primary production is gross production minus the energy used in respiration (1).
Question 29 · Spec 3.1.6.2 · Systems
An ecosystem has a gross primary production of 20 units and plant respiration of 8 units. Calculate its net primary production. [2 marks]
Answer:
NPP = GPP − respiration (1); 20 − 8 = 12 units (1).
Question 30 · Spec 3.1.6.2 · Systems
Explain why net primary production is higher in tropical rainforests than in tundra. [3 marks]
Answer:
Rainforests receive more sunlight, heat and rainfall all year round (1); a long growing season allows continuous photosynthesis (1); tundra has a very short growing season and cold, frozen ground that limit plant growth (1).
Question 31 · Spec 3.1.6.2 · Systems
Explain why oceans generally have lower net primary production per unit area than tropical rainforests. [2 marks]
Answer:
Light does not penetrate far into water, limiting photosynthesis to the surface layer (1); nutrients are often scarce in open ocean (1).
Question 32 · Spec 3.1.6.2 · Nutrient cycling
Describe the Gersmehl model of mineral nutrient cycling. [4 marks]
Answer:
It shows three nutrient stores: biomass, litter and soil (1); the size of each circle shows the amount stored (1); arrows show flows between stores, with arrow width showing the size of the flow (1); nutrients are added by precipitation and weathering and lost by run-off and leaching (1).
Question 33 · Spec 3.1.6.2 · Nutrient cycling
Explain why most nutrients in a tropical rainforest are held in the biomass store. [3 marks]
Answer:
Heavy rainfall leaches nutrients out of the soil (1); the hot, wet climate decomposes litter very quickly, so the litter store is small (1); plants take up nutrients rapidly, so they are held in the biomass store (1).
Question 34 · Spec 3.1.6.2 · Nutrient cycling
Explain why the litter store is large in a coniferous forest (taiga). [3 marks]
Answer:
Needles are tough and slow to decompose (1); cold temperatures slow decomposers (1); so nutrients build up in the litter, while the soil store is small (1).
Question 35 · Spec 3.1.6.2 · Nutrient cycling
Explain how deforestation disrupts nutrient cycling. [3 marks]
Answer:
Removing trees removes the biomass store (1); with no canopy, heavy rain leaches nutrients from the soil and erodes it (1); litter input stops, so soil fertility falls (1).
Question 36 · Spec 3.1.6.2 · Succession
Define the term succession. [2 marks]
Answer:
The sequence of changes in the plant and animal community over time (1); in which species gradually replace each other until a stable community develops (1).
Question 37 · Spec 3.1.6.2 · Succession
Distinguish between primary and secondary succession. [2 marks]
Answer:
Primary succession occurs on newly formed or bare surfaces with no soil, such as lava or sand (1); secondary succession occurs where an existing community has been disturbed but soil remains (1).
Question 38 · Spec 3.1.6.2 · Succession
Explain the term seral stage. [2 marks]
Answer:
One of the stages in a succession, each with its own community of plants and animals (1); each stage modifies the environment, for example by adding humus, and makes it suitable for the next (1).
Question 39 · Spec 3.1.6.2 · Succession
Distinguish between climatic climax, sub-climax and plagioclimax. [3 marks]
Answer:
A climatic climax is the final stable community in balance with the climate (1); a sub-climax is a stage held short of the climatic climax by local factors such as soil or drainage (1); a plagioclimax is a community held in a stable stage by human activity such as grazing or burning (1).
Question 40 · Spec 3.1.6.2 · Succession
Explain the role of pioneer species. [2 marks]
Answer:
They are the first to colonise bare or disturbed ground (1); they are tolerant of harsh conditions and start to build soil by adding organic matter (1).
Question 41 · Spec 3.1.6.2 · Terrestrial ecosystems
Explain the inter-connections between climate, vegetation, soil and topography. [4 marks]
Answer:
Climate controls temperature and rainfall, which determine what vegetation can grow and how soils form (1); vegetation adds organic matter and protects soil, and soil supplies water and nutrients to plants (1); topography affects drainage, temperature and exposure, creating different soils on a slope (1); a change in one component affects all the others (1).
Question 42 · Spec 3.1.6.2 · Terrestrial ecosystems
Explain how an ecosystem might respond to a reduction in rainfall. [3 marks]
Answer:
Plant growth falls and drought-tolerant species replace those that need more water (1); less food and cover reduce animal numbers or cause migration (1); soil dries and may erode, so productivity and biodiversity fall (1).
Question 43 · Spec 3.1.6.2 · Terrestrial ecosystems
Explain what is meant by ecosystem resilience and a tipping point. [4 marks]
Answer:
Resilience is the ability of an ecosystem to recover after a disturbance (1); a resilient ecosystem returns to its previous state, for example after a small fire (1); a tipping point is a threshold beyond which change becomes rapid and hard to reverse (1); the ecosystem then moves to a different state, such as rainforest becoming savanna (1).
Question 44 · Spec 3.1.6.2 · Terrestrial ecosystems
Explain how climate change is changing ecosystems. [3 marks]
Answer:
Species are moving towards the poles and up mountains as temperatures rise (1); the timing of events, such as flowering and migration, is changing, which can disrupt food webs (1); extreme events such as drought, fire and coral bleaching damage ecosystems (1).
Question 45 · Spec 3.1.6.2 · Terrestrial ecosystems
Describe how human exploitation changes ecosystems. [4 marks]
Answer:
Deforestation removes habitats and changes local climate (1); farming replaces diverse ecosystems with monocultures (1); overfishing and hunting alter food webs (1); pollution and introduced species change the conditions and the species present (1).
Question 46 · Spec 3.1.6.1 · Biodiversity
Explain what is meant by a biodiversity hotspot. [2 marks]
Answer:
A region with a very high number of species found nowhere else (1); that is under serious threat from habitat loss, such as Madagascar, the Philippines and the tropical Andes (1).
Question 47 · Spec 3.1.6.2 · Nature of ecosystems
Distinguish between a pyramid of numbers and a pyramid of biomass. [2 marks]
Answer:
A pyramid of numbers shows the number of organisms at each trophic level (1); a pyramid of biomass shows the dry mass of living material at each level, and usually narrows steadily upwards (1).
Question 48 · Spec 3.1.6.2 · Nature of ecosystems
Explain how the removal of top predators affects an ecosystem. [3 marks]
Answer:
Numbers of herbivores and smaller predators increase (1); overgrazing reduces vegetation and the food available to other species (1); biodiversity falls and the structure of the ecosystem changes (1).
Question 49 · Spec 3.1.6.2 · Succession
Explain how soil develops during primary succession. [3 marks]
Answer:
Lichens and mosses break down rock and add organic matter when they die (1); the soil deepens and holds more water and nutrients (1); this allows larger plants such as grasses, shrubs and trees to colonise (1).
Question 50 · Spec 3.1.6.2 · Succession
Explain why species diversity and biomass tend to increase during a succession. [3 marks]
Answer:
As soil develops, more species can survive, so diversity increases (1); larger plants such as trees add to biomass (1); complex food webs develop until the climax community is reached (1).

← 3.1.5 Fires in nature and hazard case studies 3.1.6 Biomes: tropical rainforest and savanna →

Biodiversity, ecosystems and succession

All 50 questions and answers

More AQA A-level Geography topics

Cookies on Knowledge Noodles

Cookie settings