Food chains, Food webs and Pyramids

Section 1 of 9Feeding terms

Producer

• Producer an organism that makes its own organic nutrients, usually using sunlight.

Consumer

• Consumer an organism that gets energy by feeding on other organisms, classed as primary, secondary, tertiary or quaternary.

Herbivore

• Herbivore an animal that eats plants.

Carnivore

• Carnivore an animal that eats other animals.

Omnivore

• Omnivore an animal that eats plants and animals.

Decomposer

• Decomposer an organism that gets energy from dead or waste organic material.

Section 2 of 9Food chains

Food chain

Food chain shows the transfer of energy from one organism to the next, beginning with a producer.

Source

• Source the Sun is the source of all energy in a food chain.

Arrows

• Arrows show the direction of energy transfer, from the organism eaten to the one that eats it.

Method

• Method energy passes by ingestion, or eating.

Position	Organism	Explanation
Producer	Grass	Makes food by photosynthesis
Primary consumer	Mouse	Eats the producer
Secondary consumer	Barn owl	Eats the primary consumer

Section 3 of 9Roles in a chain

Role	Gets energy from	Trophic level
Producer	Sunlight	1
Primary consumer	Producers	2
Secondary consumer	Primary consumers	3
Tertiary consumer	Secondary consumers	4
Decomposer	Dead organisms	All levels

Section 4 of 9Food webs

Food web

Food web a network of interconnected food chains.

Realistic

• Realistic animals rarely feed on only one food source.

Interdependence

• Interdependence a change in one population affects others.

Information

• Information webs show more about energy transfer than single chains.

Section 5 of 9Predicting changes in a web

Predicting changes in a web

Fewer of an organism

• Fewer of an organism its food source increases because fewer feed on it.

Single-food predators

• Single-food predators decrease significantly if their only food falls.

Predators with other food

• Predators with other food decrease only slightly.

Wording

• Wording use increase or decrease, not die out.

Reason

• Reason always give the reason for an increase or decrease.

Section 6 of 9Human impact on webs

Overharvesting

• Overharvesting removing too many of a food species reduces populations throughout the web.

Introduced species

• Introduced species foreign species added to a habitat can have long-lasting knock-on effects.

Section 7 of 9More from the specification

Ecological Pyramids of Biomass

• Pyramids of biomass represent the total dry mass of living biological matter at each successive trophic level, almost universally presenting an upright pyramid shape due to non-recoverable respiratory energy losses.

Pyramids of Numbers and Inverted Structures

• A pyramid of numbers quantifies individual organism counts;

  • it can become inverted when a single massive producer supports thousands of primary consumers,
  • or when consumers host numerous parasites.
  • (such as an oak tree)

Ecological Resilience in Food Webs

• Complex interconnected food webs provide alternative feeding pathways for consumers, stabilizing community dynamics against environmental perturbations far more effectively than isolated linear food chains.

Microorganism

• A living organism so small that it can only be seen clearly with a microscope.

Bacteria

• Single-celled microorganisms, much smaller than plant or animal cells.

Carbon cycle

• The movement of carbon between air, living things, soil and fossil fuels.

Fossil fuel

• Fuel formed from long-dead organisms.

Nitrogen

• Element in amino acids and nitrogenous bases.

Carbon

• Element with four valence electrons that forms the backbone of organic molecules.

Biomass

• The dry mass of living matter in an organism or trophic level.

Growth

• A permanent increase in size and dry mass.

Ecosystem

• Community plus environment.

Section 8 of 9Key terms

Term	Meaning
Producer	Organism that makes its own food.
Consumer	Organism that eats other organisms.
Herbivore	Animal that eats plants.
Carnivore	Animal that eats animals.
Food web	A network of interconnected food chains.
Interdependence	Populations affecting each other.

Section 9 of 9Exam technique

1

Drawing arrows from the eater to the eaten — arrows point from the eaten to the eater.

2

Saying a species would die out — say its population would decrease.

3

Starting a chain with an animal — every chain starts with a producer.

4

Saying removing a consumer affects only one organism — populations are interdependent.