Ecosystems (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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Why must materials be cycled through an ecosystem?
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Cards in this collection (78)
Why must materials be cycled through an ecosystem?
Materials are not endless. They must be recycled so new organisms can be built and grow.
Name three materials that cycle through an ecosystem.
Water, carbon and nitrogen.
Which components of an ecosystem do materials cycle between?
The biotic (living) and abiotic (non-living) components.
What is the role of microorganisms in the cycling of materials?
They cause decomposition — breaking down dead organisms and waste so the materials in them are released and re-used.
Define decomposition.
The breakdown of dead organisms and waste by microorganisms, releasing the materials they contain.
Which two groups of microorganism act as decomposers?
Bacteria and fungi.
What would happen to an ecosystem without decomposers?
Dead biomass would build up, and the materials locked inside it would never be released for new organisms to use.
Name the four main stages of the water cycle.
Evaporation, condensation, precipitation and the flow of fresh water through ecosystems.
Why is the water cycle important to living organisms?
It distributes fresh water across the globe, maintains habitats and refreshes the flow of nutrients.
Why can water move through all the stages of the water cycle?
Water can exist as a solid, liquid and gas at the temperatures found on Earth.
Why do plants need the water supplied by the water cycle?
Water is a raw material for photosynthesis, as well as being needed for transport and cell reactions.
Microorganisms release materials from dead organisms by the process of ＿＿＿＿＿＿＿＿.
Microorganisms release materials from dead organisms by the process of decomposition.
In the water cycle, water vapour cools and turns back into liquid by ＿＿＿＿＿＿＿＿.
In the water cycle, water vapour cools and turns back into liquid by condensation.
True or False?
Materials in an ecosystem are used once and then lost.
False.
They are cycled continuously between the living and non-living parts of the ecosystem.
True or False?
All microorganisms are harmful to other living things.
False.
Most are essential — without decomposers, materials would never be recycled through an ecosystem.
How is carbon taken out of the atmosphere?
By photosynthesis — plants take in carbon dioxide and use it to make glucose.
How does carbon pass from plants to animals?
By feeding — animals eat plants, or eat other animals that ate plants.
Which process returns carbon dioxide to the atmosphere from organisms?
Respiration, in plants, animals and microorganisms.
How do decomposers return carbon to the atmosphere?
They break down dead organisms and respire, releasing carbon dioxide.
How are fossil fuels formed in the carbon cycle?
Organisms die where decomposers are absent.
Over millions of years, heat and pressure turn the carbon in their bodies into fossil fuels.
Define combustion.
The burning of a fuel, which releases carbon dioxide into the atmosphere.
Why is burning fossil fuels raising atmospheric carbon dioxide?
It releases carbon that has been locked away for millions of years, faster than photosynthesis can remove it.
Give two ways deforestation raises atmospheric carbon dioxide.
Trees are often burnt, releasing carbon dioxide directly.
There are then fewer producers left to remove carbon dioxide by photosynthesis.
Why is the carbon cycle important to living organisms?
Carbon is part of all organic molecules, such as glucose, so life depends on it being recycled.
Name four reservoirs that carbon moves between.
The atmosphere, biomass, the oceans and the soil.
What can happen if the balance of carbon is disrupted?
Organisms suffer. Global warming is a large-scale example of the effect.
Carbon dioxide is removed from the atmosphere by plants during ＿＿＿＿＿＿＿＿.
Carbon dioxide is removed from the atmosphere by plants during photosynthesis.
Burning fossil fuels returns carbon to the atmosphere in a process called ＿＿＿＿＿＿＿＿.
Burning fossil fuels returns carbon to the atmosphere in a process called combustion.
True or False?
Only animals return carbon dioxide to the atmosphere.
False.
Plants and microorganisms respire too, and combustion also releases carbon dioxide.
True or False?
Photosynthesis and respiration have opposite effects on carbon.
True.
Photosynthesis removes carbon dioxide from the atmosphere; respiration returns it.
Define population.
All the organisms of the same species living in the same place at the same time.
Define community.
All the populations of different species living in the same area at the same time.
Define habitat.
The place where an organism lives.
Define ecosystem.
All the biotic and abiotic factors that interact within an area at one time.
List the levels of organisation from smallest to largest.
individual organism → population → community → ecosystem
What is the difference between a population and a community?
A population is one species only.
A community is all the populations of all the species in that area.
What is the difference between a habitat and an ecosystem?
A habitat is simply where an organism lives.
An ecosystem also includes all the living and non-living factors interacting there.
Give an example of a small and a large ecosystem.
A small one: a garden pond.
A large one: the whole of Antarctica.
Give an example of a population.
All the oak trees in one woodland, or all the badgers living there.
Name two biotic components of an ecosystem.
Plants and animals — any living part of the ecosystem.
Name two abiotic components of an ecosystem.
Light intensity and water availability.
Temperature and mineral ions are other examples.
A group of organisms of the same species living in the same place is a ＿＿＿＿＿＿＿＿.
A group of organisms of the same species living in the same place is a population.
An ecosystem is made up of biotic and ＿＿＿＿＿＿＿＿ factors interacting together.
An ecosystem is made up of biotic and abiotic factors interacting together.
True or False?
A community includes the non-living parts of an ecosystem.
False.
A community is only the living populations. Adding the abiotic factors makes it an ecosystem.
True or False?
Removing one species can affect a whole community.
True.
Species depend on each other for food, shelter and pollination — this is interdependence.
Define abiotic factor.
A non-living factor in an environment, such as temperature or light intensity.
Define biotic factor.
A living factor in an environment, such as predators, food supply or disease.
Name four abiotic factors that can affect a community.
Temperature, light intensity, moisture level and soil pH.
Name two biotic factors that can affect a community.
Predators and the availability of food.
In what two ways can a factor affect a population?
It can change the size of the population.
It can change the distribution of the population — where the organisms live.
How can light intensity affect a community?
Low light slows photosynthesis, so fewer plants grow, and the animals that depend on them are affected too.
How can soil pH affect the distribution of a plant?
A plant grows only within a suitable pH range. Wild azaleas, for example, need a soil pH of about 4.5 to 6.5.
How can moisture level affect a community?
Too little water limits plant growth and the survival of animals that need it, changing which species can live there.
How can predators affect a population?
More predators reduce the prey population; fewer predators allow it to increase.
How can the availability of food affect a population?
When food is scarce, competition increases and the population falls. Plentiful food lets it grow.
Why does the same change affect different species differently?
Each species has its own requirements and tolerances, so a change that suits one may harm another.
Temperature and light intensity are examples of ＿＿＿＿＿＿＿＿ factors.
Temperature and light intensity are examples of abiotic factors.
Predators and food availability are examples of ＿＿＿＿＿＿＿＿ factors.
Predators and food availability are examples of biotic factors.
True or False?
Populations are usually affected by one factor at a time.
False.
Most populations are shaped by a combination of abiotic and biotic factors acting together.
True or False?
Disease is a biotic factor.
True.
It is caused by living organisms, so it counts as a living factor in the environment.
Define interdependence.
The way all organisms in a community depend on one another, so a change to one species affects the others.
Define predation.
A relationship in which one organism, the predator, hunts and eats another, the prey.
Define mutualism.
A relationship in which both species benefit.
Define parasitism.
A relationship in which the parasite benefits and the host is harmed.
Give an example of mutualism.
Bees and flowering plants — the bee gets nectar and the plant is pollinated.
Give an example of parasitism.
A tapeworm in an animal's intestines, feeding on the host's food and depriving it of nutrients.
Why does a parasite usually keep its host alive?
A dead host is no longer useful — the parasite would lose its supply of food and shelter.
What keeps population sizes in a community fairly constant?
All the species and environmental factors being in balance.
This is why a change to one species affects the others.
What happens to a predator population if its prey declines?
The predator population also decreases, because there is less food available.
Why is a species with only one food source more vulnerable?
If that food source declines, its population falls sharply, with no alternative to switch to.
Define competition.
When organisms need the same limited resource, so they compete for it in order to survive and reproduce.
Name three resources that plants compete for.
Light, water and mineral ions from the soil.
They also compete for space.
Name three resources that animals compete for.
Food, water and territory.
They also compete for mates.
What is the difference between the two types of competition?
Intraspecific competition is between members of the same species.
Interspecific competition is between members of different species.
In ＿＿＿＿＿＿＿＿, both organisms in the relationship benefit.
In mutualism, both organisms in the relationship benefit.
A parasite lives on or in a ＿＿＿＿＿＿＿＿, taking what it needs and giving nothing in return.
A parasite lives on or in a host, taking what it needs and giving nothing in return.
True or False?
Competition only happens between different species.
False.
Members of the same species often compete most fiercely, as they need exactly the same resources.
True or False?
Removing one species affects only the species that ate it.
False.
Because of interdependence, the effects spread through the whole community.
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