Carbon and water cycles in ecosystems

Ecology • Organisation of an ecosystem

Flashcards

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Explain how photosynthesis links the carbon and food cycles.

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Photosynthesis converts inorganic carbon into organic compounds that form plant biomass, which becomes food for consumers, transferring carbon through the food chain.

Key concepts

What you'll likely be quizzed about

Carbon cycle: main processes and diagram interpretation

Photosynthesis removes carbon dioxide from the atmosphere and converts it into glucose in plant biomass; arrows on diagrams point from atmospheric CO2 to plant biomass to show this uptake. Respiration by plants, animals and decomposers converts organic carbon back to carbon dioxide; arrows point from biomass to the atmosphere to show CO2 release. Combustion of fossil fuels and plant material converts stored organic carbon into carbon dioxide; arrows show an extra input to atmospheric CO2. Decay or decomposition breaks dead organisms into simpler compounds and returns carbon to the atmosphere or soil as part of microbial respiration. Diagrams often label sinks (long-term stores) such as fossil fuels, soils and biomass and flows such as photosynthesis, respiration, combustion and decay, allowing direct interpretation of cause → effect relationships .

Water cycle: main processes and diagram interpretation

Evaporation transfers liquid water from oceans, lakes or soil into the atmosphere as water vapour; energy from the Sun causes the change of state. Transpiration releases water vapour from plants after root uptake and internal transport; diagrams show plant uptake and transpiration as connected arrows between soil, plant and atmosphere. Condensation converts water vapour into liquid droplets forming clouds; precipitation follows as rain, snow, hail or sleet and returns water to the surface. Infiltration moves surface water into the ground to form groundwater; subsurface flow and springs return groundwater to rivers and oceans. Surface runoff transports water across land into rivers, lakes and seas. Diagrams use arrows to show state changes and movement between stores such as atmosphere, surface water and groundwater .

Importance of the cycles to living organisms

The carbon cycle supplies carbon atoms for building organic molecules such as carbohydrates, proteins and lipids; photosynthesis provides the carbon that supports food chains, so reduced photosynthesis or lost carbon sinks reduce food availability. The water cycle supplies fresh water required for cellular reactions, transport of solutes and temperature regulation; precipitation and groundwater are primary freshwater sources for terrestrial organisms. Stable cycling maintains nutrient supply and waste removal; interruption (for example by deforestation or excessive combustion) increases atmospheric CO2 and reduces sinks, altering climate and harming species distributions and ecosystem services .

Materials cycling through abiotic and biotic components

Ecosystem cycling involves movement between abiotic stores (atmosphere, soil, water, fossil fuels) and biotic stores (producers, consumers, decomposers). Producers fix inorganic carbon and take up water and mineral ions from abiotic pools; consumers transfer these materials through feeding. Decomposers break down dead organic matter, releasing carbon dioxide and mineral ions back to soil and atmosphere so that producers can reuse them. Limiting factors change the rate of cycling: temperature, oxygen level and moisture strongly affect decomposition rates; light intensity and CO2 concentration limit photosynthesis; precipitation and evaporation rates affect water availability and groundwater recharge .

Key notes

Important points to keep in mind

Photosynthesis fixes atmospheric carbon into plant biomass; respiration and combustion return carbon to the atmosphere.

Evaporation and transpiration move water into the atmosphere; condensation and precipitation return it to the surface.

Decomposers recycle carbon and mineral ions from dead organisms back to abiotic pools.

Temperature, moisture and oxygen commonly limit decomposition rates.

Aquifers are underground permeable rock layers that store groundwater (long-term water sinks) .

Diagrams show sinks (stores) and flows (processes); read arrows as cause → effect to interpret cycles .

Deforestation reduces carbon sinks and transpiration, increasing atmospheric CO2 and altering local water balance .

The water cycle involves physical state changes; the carbon cycle involves chemical conversions between carbon compounds.