What is a producer, and what energy source does it usually use?
A producer makes its own organic nutrients, usually using sunlight for photosynthesis.
Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028) · 19.2
Revise Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028) specification point 19.2, Food chains and food webs, with free active-recall flashcards. Flip through the set or review every question and answer below.
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What is a producer, and what energy source does it usually use?
A producer makes its own organic nutrients, usually using sunlight for photosynthesis.
What is a consumer?
An organism that obtains energy by feeding on other organisms.
How do herbivores and carnivores differ in what they eat?
Herbivores eat plants; carnivores eat other animals.
How does a decomposer obtain energy?
From dead or waste organic material.
What do feeding roles describe, and do they specify an organism’s position in a particular food chain?
They describe the source of energy; by themselves, they do not specify a position in a particular food chain.
What does a food chain represent?
A sequence of energy transfers between organisms through feeding.
How are organisms arranged in a food chain?
A producer comes first, followed by consumers that feed on the preceding organisms.
What direction do arrows point in a food chain?
From the organism being eaten to the organism receiving energy.
What is a trophic level?
An organism’s feeding position in a food chain, food web or ecological pyramid.
What is the order of the first five trophic levels in a food chain?
Producer → primary consumer → secondary consumer → tertiary consumer → quaternary consumer.
What determines an organism’s trophic level in a food web?
The feeding route being considered.
How can overharvesting a food species affect its population and its consumers’ food supply?
It reduces the species’ population and can change the food available to its consumers.
How can overharvesting a food species affect its prey?
It can change the feeding pressure on its prey.
How can introducing a foreign species change feeding relationships in a habitat?
It can add new feeding relationships or alter existing ones.
Which organisms’ populations can change when a foreign species is introduced to a habitat?
Those it eats and those that use the same food sources.
How can food chains and food webs help trace the effects of a change to one species?
They show feeding relationships through which effects can reach connected organisms.
What determines the particular outcome of a disruption to a food web?
The feeding relationships involved.
How does a pyramid of numbers represent the number of organisms in a food chain?
Each bar represents a trophic level; its width shows the number of organisms at that level.
How are trophic levels arranged in a pyramid of numbers?
Producers are at the base, with successive consumer levels above them.
Why don't organism counts alone show how much living material is present at each trophic level?
Organisms can differ greatly in size.
Must a pyramid of numbers narrow steadily towards the top?
No; it need not narrow steadily towards the top.
What does a pyramid of biomass represent?
The total mass of living material at each trophic level in a food chain.
How are trophic levels arranged in a pyramid of biomass?
Producers form the base, with successive consumer levels above them.
What does the width of a bar in a pyramid of biomass represent?
The biomass at that trophic level.
Why does a pyramid of biomass indicate the amount of living material better than a pyramid of numbers?
It accounts for organisms’ mass, whereas a pyramid of numbers counts each organism as one regardless of size.
What does a pyramid of energy show?
The energy available at successive trophic levels in a food chain over a specified period.
How are trophic levels arranged in a pyramid of energy?
In feeding order, with producers at the base and consumer levels above them.
What does the width of a bar in a pyramid of energy represent?
The energy available at that trophic level.
Why do the bars in a pyramid of energy narrow towards the top?
Less energy is available at each successive trophic level.
What do pyramids of numbers and biomass measure, respectively?
What does a pyramid of energy show over a period that a pyramid of biomass does not?
How much energy passes through each trophic level.
How does uneaten biomass limit energy transfer to the next trophic level?
Not all organisms or parts of organisms are eaten, so their energy does not reach the next consumer.
How does egestion limit energy transfer to the next trophic level?
Some eaten material is not digested and is egested.
How does respiration limit energy transfer to the next consumer?
Organisms use energy in respiration, transferring energy to the surroundings as heat.
Where may energy in dead material and waste go instead of to the next level of a food chain?
To decomposers.
Why do food chains usually have fewer than five trophic levels?
Less energy is available at each successive level, eventually leaving too little to support another consumer level.
How does the energy pathway differ when humans eat crops directly versus eating livestock fed on those crops?
Directly: crop producer → human. Through livestock: crop producer → livestock → human, adding a trophic level.
How does livestock respiration affect the energy available to humans from livestock?
Livestock use some of the energy they obtain in respiration, so it is not passed to humans.
How does livestock biomass limit the energy humans obtain by eating livestock?
Not all livestock biomass is eaten or digested by humans.
Which is more energy efficient: eating crop plants directly or eating livestock fed on those crops?
Eating crops directly: more of the energy originally available in the crops reaches humans.