Feeding Relationships (Edexcel GCSE Combined Science: Biology): Flashcards
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Trophic level
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Trophic level
A feeding level in a food chain, e.g. producer, primary consumer, secondary consumer or tertiary consumer.
Producer
An organism (e.g. a plant) that converts light energy into chemical energy, stored as biomass, forming the first trophic level.
What do the arrows in a food chain represent?
The transfer of energy from one trophic level of the food chain to the next.
What is the source of all energy in a food chain?
Light energy from the Sun.
Why is the Sun not included in food chains?
Because it is not a living organism.
Name the four steps of a food chain in order.
Producer → primary consumer → secondary consumer → tertiary consumer.
What is a primary consumer?
An organism (a herbivore or omnivore) that feeds on the producer.
How is energy lost between trophic levels?
Energy is used and lost at each stage, for example as heat energy transferred from organisms to their surroundings.
Why can a consumer be at different trophic levels within the same food web?
Because it may eat primary, secondary and/or tertiary consumers (e.g. an omnivore).
Food chains always begin with a , which converts light energy into chemical energy.
producer
The arrows in a food chain show the transfer of from one trophic level to the next.
energy
Food web
A network of interconnected food chains.
Consumer
An animal that gains energy by feeding on other organisms rather than producing its own food.
Why are food webs more realistic than single food chains?
Because animals rarely exist on just one type of food source, so a web shows the many connections between organisms.
What two key things do food webs show us?
The transfer of energy in an ecosystem, and the interdependence of organisms (how a change in one population can affect others).
In a food web, if the earthworm population decreased, what would happen to the grass plants?
The grass plant population would increase, as there are now fewer species feeding on them.
Why would the frog and mouse populations decrease significantly if earthworms decreased?
Because earthworms are their only food source.
Why would the sparrow population only decrease slightly if earthworms decreased?
Because sparrows eat earthworms but also have another food source (caterpillars) to rely on.
Can an animal be at more than one trophic level in a food web? Explain.
Yes; omnivores or predators can eat primary, secondary and/or tertiary consumers, placing them at more than one trophic level.
A food web is a network of interconnected .
food chains
Food webs show — how a change in one population can affect others.
interdependence
Pyramid of numbers
A diagram showing how many organisms are at each level of a food chain, where the width of each box shows the number of organisms at that trophic level.
Pyramid of biomass
A diagram showing the dry mass of the organisms at each trophic level; it is always pyramid-shaped.
Name the three types of food pyramid.
Pyramids of number, pyramids of biomass and pyramids of energy transfer.
Why is a pyramid of numbers not always pyramid-shaped?
Because the size of the organism matters; one large organism (e.g. an oak tree) contains enough energy to support many smaller organisms (e.g. insects).
Why are pyramids of biomass always pyramid-shaped?
Because the mass of organisms must decrease as you go up a food chain; a smaller mass cannot support a larger mass above it.
What is meant by 'biomass' in a pyramid of biomass?
The mass of the organisms at each level without the water they contain (their dry mass).
What does the area of each box in a pyramid of energy transfer represent?
The quantity of energy present in the biomass at that trophic level.
Roughly how much energy is passed on to the next trophic level?
Roughly only 10% of the energy is passed on; the rest is used and lost.
When drawing a pyramid of numbers, what rule must you follow about the order of organisms?
You cannot change the trophic level of the organisms; producers stay at the bottom, followed by primary, secondary and then tertiary consumers.
Pyramids of and pyramids of energy transfer are always pyramid-shaped.
biomass
Only about of the energy is passed on from one trophic level to the next.
10%
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