Understanding ecology in GCSE Biology: exploring the web of life

From our mental health, to our ability to produce food, find new medicines and even breathe oxygen, we know that our lives are closely linked to the living organisms around us. We are part of a web of life, in which all living organisms are interconnected and dependent on each other for survival.

With climate change and biodiversity loss becoming all-too-common themes in our news, improving our understanding of the interactions between living things has never been more important, and this is where the study of ecology comes in! Helping students to develop their understanding of ecology is one of my favourite parts of teaching; in this article I aim to cover some of the main ecological concepts that come up at GCSE, and to inspire you with a few examples of ecology in action. 

Note that this article is intended to provide an outline only, and students should check individual specifications to find out exactly what is covered by each exam board.

Overview of ecology

Ecology is the study of the relationships between living organisms, and between living organisms and their physical environment.

At GCSE level ecology topics include:

• food chains and food webs

• the structure of ecosystems

• biotic and abiotic factors in ecosystems

• population growth

• predator-prey relationships

• biodiversity

• investigating abundance and distribution of organisms

• humans and the environment

• conservation

Levels of organisation

In the context of ecology the phrase ‘levels of organisation’ refers to the scale at which we study living organisms, for example at the smallest scale we can study individual organisms, and at the largest we can consider the biosphere, i.e. everywhere on Earth that supports life.

Three levels of organisation commonly covered at GCSE are:

• population: all of the individuals of a single species living in an area at one time

• community: all of the populations of living organisms living in an area at one time

• ecosystem: all of the organisms living in an area, their interactions with each other and their interactions with the non-living environment

The study of populations, communities and ecosystems can be used to answer many important questions about the natural world, for example:

Interactions in ecosystems

Living organisms do not exist in isolation, but interact with each other all the time. This means that any change that occurs in one species will impact other species within an ecosystem; this concept is known as interdependence. 

The interdependence between organisms in an ecosystem can take different forms, including:

• feeding relationships

• competition

• symbiosis

Feeding relationships

Animals eat plants (herbivory) or other animals (predation) to gain energy for survival. This means that consumer species are dependent on their food sources, and food species will be affected by feeding levels. 

Ideas connected to feeding relationships that are commonly addressed at GCSE include:

• Food chains: food chains show the flow of energy through ecosystems that occurs when organisms consume other organisms

• Food webs: multiple food chains can be joined together to show the web of feeding relationships within ecosystems

  • Food webs illustrate the importance of biodiversity within ecosystems; if a consumer species relies on a single food source and the food source is wiped out then the consumer species will also die out, but if a consumer has multiple food sources then the loss of one will be less significant

• Predator-prey relationships: predator and prey populations may be closely related in a predator-prey cycle as follows:

  • prey population size increases

  • more food is available for predators, so the predator population increases

  • more predators consume prey, so the prey population falls

  • less food is available, so the predator population decreases

  • repeat!

Competition

Organisms that require the same resources to survive may compete with each other for access to these resources.

• Intraspecific competition occurs when individuals of the same species compete for resources, e.g. when red deer males compete for mates

• Interspecific competition is competition for resources between members of different species, e.g. when lions and cheetahs compete for prey

Symbiosis

Symbiotic relationships are long-term interactions between individuals that live in close proximity to each other, e.g. 

• mutualism: a symbiotic relationship in which both members of the relationship benefit, for example clownfish live inside sea anemones, gaining protection from predators while also keeping the anemone free of parasites

• commensalism: a relationship that is beneficial to one member of the partnership and neutral to the other; an example of this is golden jackals following tigers in order to consume any food that is left after the tiger finishes eating

• parasitism: here one member of the relationship benefits while the other is harmed, for example Monotropa uniflora, known as the ghost plant, has no chlorophyll of its own, but instead takes sugars from fungi without giving anything in return

Jenny from Taipei, via Wikimedia Commons and Will Brown, via Wikimedia Commons

Biodiversity

Biodiversity is the variety of living organisms present in an area. Diversity can be measured at different levels, for example scientists might be interested in measuring:

• genetic diversity

• species diversity

• habitat diversity

• the biodiversity of all organisms on earth

As mentioned above, biodiversity is essential to the stability of ecosystems. The more diverse an ecosystem is, the more resilient it will be to change, and with the detrimental effects of climate change already becoming apparent, resilience in ecosystems is more important than ever.

Humans and biodiversity

Data suggests that biodiversity, in the UK and around the world, is in a state of crisis. The 2023 State of Nature Report shows huge declines in biodiversity in the UK since 1970, as well as indicating that nearly 1 in 6 British species is currently at risk of extinction.

It is clear that human activities are either directly or indirectly causing biodiversity losses. Some of the main factors include:

• habitat loss: human activities, such as farming and building, require land, leaving less and less space for wildlife

• exploitation of resources: hunting, fishing and logging are just some examples of resource use that can be detrimental to biodiversity if not carried out sustainably

• pollution: pollutants can be released into the environment by industry, agriculture or domestic dwellings; this can lead to problems at all levels of the food chain

• climate change: changing average temperatures and unpredictable weather patterns are affecting many aspects of organisms’ lives, from the timing of life-cycles, to sex-allocation (some species of reptile will either hatch into males or females depending on incubation temperature), to the spread of disease

Conservation

The extent of the biodiversity loss occurring around the world is alarming, and it is essential that action is taken to slow the rate of loss, and to help nature recover where possible. 

At GCSE level, several different conservation strategies are taught:

Conservation efforts often involve dealing with conflicts between the needs of wildlife and the needs of humans, so conservation scientists need to consider the effect that their work has on local human communities as well as on plant and animal species.

Ecology in exams

Many of the concepts covered in GCSE ecology are not especially complex, and students are often lulled into a false sense of security when they revise these topics. My experience as a teacher and examiner has shown me that exam questions relating to ecology can often be some of the most tricky, and students often lose marks in this topic even if they feel that they know it well. 

The reason for this is that ecology exam questions often present examples of species and habitats that are entirely new, and then ask students to interpret data or explain the ecology. This can be challenging for students who are not expecting it, and many may be nervous about drawing their own conclusions from data.

The example question below presents a dataset about crayfish and then asks a question about ecological sampling:

Unprepared students may see this question and panic that they don’t know anything about crayfish, or may be thrown by the Latin names or the seemingly complex dataset. The key thing to remember with questions like this is that students will never be expected to be experts on a species that is not covered by the specification, and there will therefore always be enough information provided to answer the question. 

My advice is to practise ecology data questions as much as possible; the same styles of question tend to come up year after year in exams, and familiarity is the best way to build confidence.

Boost your chances of biology success

Ecology is a huge topic, and the content covered at GCSE really just provides a glimpse into the kind of work that ecologists are doing all over the world. While all the key words, datasets and lists of conservation strategies can feel a little dry to study at a desk, remember that real organisms are out in their environments right now fighting for survival. The world needs passionate ecologists to stand up and contend for nature; maybe one day that could be you?!

Here at Save My Exams we have GCSE ecology resources for students studying AQA, Edexcel, WJEC and OCR gateway courses, so sign up today to access unlimited revision notes and all of our ecology topic questions.

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