Inheritance and ecology · GCSE Biology
Ecology
Competition, adaptations, food chains, quadrats and transects, the carbon cycle, biodiversity and human impact.
Ecology is who gets the resources, who eats whom, and how materials cycle. Sample properly, then explain the human effect on biodiversity.
The important bits
What you need to know
- 1
Organisms compete for resources. Plants compete for light, water, space and minerals. Animals compete for food, water, mates and territory. Abiotic factors are non-living (temperature, light, moisture, pH, minerals); biotic factors are living (prey, predators, pathogens, competitors).
- 2
Adaptations may be structural, behavioural or functional and make an organism better suited to its environment, increasing the chance of survival.
- 3
A food chain shows feeding relationships: producer → primary consumer → secondary consumer. Producers photosynthesise. On Higher tier, pyramids of biomass are drawn to scale and explain energy loss between trophic levels.
- 4
Quadrat sampling estimates population size in a uniform habitat: random coordinates, count, mean per quadrat, scale up to the field. A transect is used when there is a gradient, for example down a shore.
- 5
The carbon cycle: photosynthesis removes carbon dioxide; respiration, combustion and decomposition return it. Microorganisms decay dead material faster in warm, moist, aerobic conditions.
- 6
Biodiversity is the variety of species. It is reduced by deforestation, peat destruction, pollution and global warming. Maintaining biodiversity supports stability and resources for humans.
- 7
Water cycle processes include evaporation, transpiration, condensation and precipitation. Land use, sewage and fertiliser leaching affect water quality and aquatic life.
Go deeper
Sampling is a method mark factory
If the habitat looks even, use random sampling: number a grid, use a random number generator, place quadrats, count the organism, repeat, calculate a mean, then multiply by the number of quadrats that would fit the whole area. Do not “choose a typical patch”. That is bias. If the question shows a change from sea to land or from shade to light, stretch a transect line and sample at regular intervals, sometimes with a belt of quadrats. Write how you would make it valid: same quadrat size, same time of year, enough repeats. Percentage cover is used when individual plants cannot be counted easily, for example moss.
Go deeper
Cycles and human impact belong in the same answer
Carbon does not disappear. Photosynthesis locks it into glucose and then biomass. Respiration and decay return carbon dioxide. Combustion of fossil fuels and destruction of peat add extra carbon dioxide faster than it is removed, which links ecology to climate change. Deforestation for farming or palm oil cuts a carbon store and a habitat at once. A strong evaluation names a human activity, the mechanism (habitat loss, less photosynthesis, more methane from cattle, eutrophication from fertiliser), and a consequence for biodiversity. “Pollution is bad” earns nothing. Say which pollutant, which process, and which organisms decline.
See the idea in action
A field is 500 m². A 1 m² quadrat is placed 10 times at random and the mean nettle count is 4. Estimated population = 4 × 500 = 2000 nettles. If the student only sampled the shady hedge because “that is where they grow”, the estimate would be biased. For a rocky shore, a transect from low to high water with quadrats every 2 m would show zonation with abiotic factors such as drying time, not a single random field estimate.
Exam technique
Turn knowledge into marks
Match the sampling method to the habitat: random quadrats for uniform areas, transects for gradients. In carbon-cycle diagrams, arrows must show photosynthesis removing CO₂ and respiration, combustion and decay returning it. Always name a specific human activity and its mechanism.
Common mistakes
Do not give these marks away
- 01
Placing quadrats where the plants “look typical” instead of using random coordinates.
- 02
Drawing a food chain backwards, or putting the producer in the wrong place.
- 03
Saying carbon is used up, rather than cycled between atmosphere, organisms and fossil stores.
Which process removes carbon dioxide from the atmosphere in the carbon cycle?
ARespiration
BCombustion
CPhotosynthesis
DDecomposition
Show the answer
Photosynthesis. Producers absorb carbon dioxide to make glucose. Respiration, combustion and decomposition all return carbon dioxide to the air.
Quick questions
If this is the bit you searched
When should you use a transect instead of random quadrats?
When there is an environmental gradient, such as from a path into a wood or down a seashore. Random quadrats suit a uniform habitat.
What is biodiversity and why does it matter?
The variety of species in a habitat. High biodiversity makes ecosystems more stable and provides resources and services that humans depend on.