The diet of a marsh bird changes during the year. In spring it feeds mainly on seeds of reeds. In summer it feeds on herbivorous insect larvae. In late summer it may also feed on small fish that have eaten the larvae.

Fallen leaves, dead insects and faeces accumulate on the floor of a woodland.

Iron-oxidizing bacteria are found in acidic drainage from abandoned mines where there is little light but a high concentration of iron(II) ions.

Students investigated a small stream ecosystem by defining a boundary around a 20 m section of stream. They recorded transfers of energy and matter across the boundary during 24 hours.

A food web was constructed from observations in a meadow community. Arrows show the direction of transfer of energy and biomass.

Energy available to each trophic level was estimated in a freshwater food chain.

Two organisms are found in the same lake. A green alga grows near the surface. A fish feeds on small crustaceans.

A student estimated the energy content of dry seeds by burning them beneath a tube containing water. A sample of seed with mass $0.80\ g$ heated $20.0\ g$ of water from $21.0^\circ\text{C}$ to $37.8^\circ\text{C}$. The specific heat capacity of water is $4.18\ J\ g^{-1}\ K^{-1}$.

The graph shows atmospheric carbon dioxide concentration measured at a remote monitoring station over several decades.

A terrestrial ecosystem contains producer biomass, consumer biomass, dead organic matter and atmospheric carbon dioxide.

Light intensity and net photosynthetic rate were measured at different depths in two lakes. Lake A is clear and Lake B is turbid due to suspended particles.

Researchers placed samples of leaf litter and animal faeces in mesh bags on a forest floor. Changes in dry mass and fungal hyphal length were recorded over several weeks.

Energy flow was estimated for four trophic levels in a temperate grassland food chain.

Iron-oxidizing bacteria were sampled from an acidic stream draining an old mine. The bacteria obtain energy by oxidizing iron(II) ions to iron(III) ions and use this energy to fix carbon dioxide.

Measurements were made in a young forest during two consecutive years. In the first year, carbon dioxide uptake by photosynthesis was greater than carbon dioxide release by respiration and decomposition. In the second year, a dry summer was followed by a fire that burned much of the above-ground biomass.

A sealed terrarium receives light through glass but no matter is added after it is closed. Plants, small animals, fungi, bacteria, soil, air and water are present inside.

Students estimated the energy content of dried seeds using simple combustion calorimetry. A known mass of dry seed was burned below a tube containing water. The temperature change of the water was recorded.

Researchers compared carbon production in a young mangrove forest over one year. Production values are expressed as $g\ C\ m^{-2}\ yr^{-1}$.

A simplified carbon cycle was prepared for a wetland ecosystem. Carbon pools are shown as boxes and carbon fluxes as arrows.

The graph compares estimated carbon dioxide emissions from combustion of different carbon stores in one region over 150 years.

A freshwater pond is studied as an ecosystem. Rainwater, dissolved mineral ions, sunlight, migrating insects and fallen leaves can cross the boundary drawn around the pond.

The figure shows feeding relationships recorded in a rocky shore community. Limpets graze on green algae. Small crabs feed on green algae and amphipods. Amphipods feed on detritus and green algae. Fish feed on amphipods and small crabs. Herons feed on fish and small crabs.

A fallen tree in a humid forest is colonized by fungi, bacteria, woodlice and insect larvae. After several months, the mass of visible dead wood decreases and mineral ions increase in the surrounding soil.

Atmospheric carbon dioxide concentration was measured at a remote monitoring station for several decades.

Scientists measured annual global fluxes of carbon dioxide and oxygen associated with photosynthesis and aerobic respiration. Values are shown as relative fluxes.

Researchers estimated energy available at successive trophic levels in a grassland food chain. The data are shown in an energy pyramid.

A wetland restoration project measured carbon fluxes before and after re-flooding. The measurements included gross primary production, respiration by organisms and accumulation of dead plant material.

The Keeling Curve records atmospheric carbon dioxide concentration at Mauna Loa Observatory. The graph shows annual fluctuations superimposed on a long-term trend.

Iron-rich acidic springs contain iron-oxidizing bacteria even in shaded channels where photosynthesis is very limited. The bacteria fix carbon dioxide and obtain energy by oxidizing iron(II) ions to iron(III) ions.

A teacher asks students to model carbon cycling in a small woodland that contains trees, herbivorous insects, birds, fungi and dead leaf litter.

A region contains natural forest, peatland and a coal-fired power station. During a drought, lightning starts a forest fire. In the same year, drained peat is burned for land clearance and coal continues to be burned for electricity.

Two sealed terraria are prepared with the same mass of plants and soil. One contains an active community of fungi and bacteria in the soil. The other soil has been sterilized before planting. Both terraria receive the same light for one year.

Ecologists compared two aquatic food chains. Chain A has phytoplankton, zooplankton, small fish and large predatory fish. Chain B has aquatic plants, insect larvae and predatory birds. Energy available at each trophic level was estimated.

A closed experimental chamber contains algae, aquatic snails and aerobic bacteria in pond water. Light intensity is varied over several days while dissolved oxygen and dissolved carbon dioxide are monitored.