Science - B7 - Ecology - Revision Cards in GCSE Biology

Communities

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An ecosystem is made up of living (biotic) and non-living (abiotic) parts. In an ecosystem, there are different levels of ecosystems. (Individuals (the smallest part), Populations (A group of individual organisms that make up a single species) and Communities (groups of different species).
Organisms need resources from both abiotic and biotic parts of an ecosystem to survive and reproduce. But resources are not infinite. Different species and different individuals compete for resources. Animals often compete for food, mates and territory. Whereas, plants often compete for water and mineral ions (minerals) from the soil, as well as for light and space.
There is interdependance between different species. This means that one species may rely on another species for different things, such as seed dispersal (the spreading of seeds), food, pollination and shelter.
A community is stable when all the species and environmental factors are balanced and population sizes stay more or less constant

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Food chains show the feeding relationshops within a community:
- Food Chains nearly always begin with a producer that makes it's own food. This is usually a green plant or algae that can photosynthesise.
- Producers are eaten by animals called primary consumers
- Primary consumers are eaten by secondary consumers.
- Secondary consumers are eaten by tertiary consumers.
- An apex predator is at the top of the food chain.
Predator-prey graphs show the cyclical nature of predator and prey populations in stable communities. A classic example is that of the Canada lynx and snowshoe hare:
- An increase in the hare numbers means more food is available for the lynx, so lynx numbers also increase
- The increase in lynx numbers means that the hares have more predators, so the hare numbers decrease
- The lynx then have less food available so their numbers decrease
- The decreasing lynx numbers allows the hare numbers to increase again, and the cycle repeats.

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The water cycle descirbes how water moves on, above or just below the surface of our planet between different locations, such as rivers, oceans and the atmosphere.
In order for this cycle to be completed, water has to change state.
The carbon cycle is present in all living organisms, when organisms die, the carbon is recycled so that it can be used by future generations.

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Biodiversity is the variety of all the different species in a given space. Sufficient biodiversity is important for the future of humans. However, we have had a histrocially difficult relationship with biodiversity.
For some time, and since the IR, humans have conducted many activities that have caused a severe decline in biodiversity.
The human population has rapidly expanded in recent decades. Resource use has increased accordingly. This has led to huge amounts of industrial waste and pollution, which is affecting:Sulfur dioxide can dissolve in moisture in the air (atmosphere) to make acid rain. Acid negatively impacts forest, freshwater and soil ecosystems as well as human health.
- Sewage and toxic chemicals, which are produced by industrial practices, as well as excess fertiliser from agriculture, all find their way into the Earth’s water sources.
- Smoke and gases are being added into the atmosphere constantly, particularly by power stations and cars.
- Toxic herbicides and pesticides used in farming, buried nuclear waste and household waste in landfill sites are all land pollutants.
The growth of the human race has meant that there is less space and fewer resources for other organisms on Earth. Building, dumping waste, farming and quarrying all take up space and deplete resources

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Carbon dioxide is a greenhouse gas. Therefore, it is important to keep its atmospheric concentration at suitable levels.
- Carbon dioxide is released into the atmosphere naturally as the waste product of respiration. However, many other unnatural processes, such as the burning of fossil fuels, also release carbon dioxide. Carbon dioxide is removed from the atmosphere naturally by green plants and algae during photosynthesis. Other natural stores of carbon include bodies of water and peat bogs.
The greenhouse effect describes how greenhouse gases (e.g. carbon dioxide and methane) act as a natural, insulating layer in the atmosphere, re-radiating most of the heat energy which has been reflected off the Earth’s surface back towards Earth.
The consensus among climate scientists is that the greenhouse effect is causing global warming.
As the atmospheric concentrations of greenhouse gases rise, there is a risk that the greenhouse effect could become too strong and the temperature could rise too high.

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The consequences of global warming include:
- Rising sea surface temperatures are causing bleaching of sensitive corals.
- The rate at which the climate is changing makes rapid adaptation key to avoiding extinction. This is particularly challenging for large-bodied animals that typically have longer generation times.
- Extreme meteorological events, such as floods, droughts, severe storms and wildfires are happening more often.
- Many migration patterns are likely to be altered by global warming.
- Melting ice causes sea levels to rise, which could flood coastal habitats forever, losing the land and associated biodiversity. Changes to the way sea ice changes through the year is affecting the survival of animals at both poles.
- Increased acidification (becoming more acidic) of the oceans is making it harder for corals to build their skeletons.
Programmes have been established by scientists and governments that attempt to mitigate (soften) the negative impact of humans on ecosystems and biodiversity, such as recycling waste, incentivising farmers, breeding programmes, government imposed targets, rare and threatened habitats.

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