Energy and biomass in ecosystems

A producer is an organism that makes its own organic food from inorganic substances using an energy source, usually sunlight.

Herbivores eat producers, carnivores eat animals, and omnivores eat both producers and animals.

A food chain is a linear sequence showing how energy is transferred from one organism to another through feeding.

Decomposers break down dead organic matter and waste, releasing mineral nutrients back into the environment.

Sunlight captured by producers through photosynthesis.

Nutrients are reused when decomposers release them for producers, but energy is dissipated as heat at each transfer and cannot be recycled.

A consumer is an organism that gains energy and nutrients by feeding on other organisms.

A scavenger is a consumer that feeds on dead animals and helps begin nutrient recycling.

A trophic level is the feeding position an organism occupies in a food chain.

Biomass is the mass of living material in organisms (energy stored in organic matter).

Detritivores ingest dead material and digest it inside the body; saprotrophs digest outside the body using enzymes and then absorb nutrients.

Both break down dead organic matter; detritivores digest inside the body, while saprotrophs digest outside using enzymes and then absorb nutrients.

Mineral nutrients are inorganic nutrients such as nitrates and phosphates that plants can absorb to build biomass.

Trophic level 2 (primary consumer).

Photosynthesis converts light energy into chemical energy stored in glucose (biomass).

Scavenger.

From the food source to the consumer (direction of energy flow).

The arrows show the direction of energy flow, from the organism eaten to the organism that eats it.

Energy enters as sunlight, is transformed into biomass, and is lost as heat at each transfer, so it cannot be recycled back down the chain.

Energy flows one-way through food chains, and nutrients are recycled when decomposers release them back to soil or water for producers.

Consumers transfer energy through food chains and help control population sizes; many also recycle nutrients by feeding on dead matter and waste.

They prevent dead matter build-up and recycle nutrients so producers can grow and make new biomass.

They are the main entry point of energy into ecosystems and form the base of food chains and food webs.

Trophic level 2 is the primary consumer level (herbivores that feed on producers).

Producers (TL1) → primary consumers (TL2) → secondary consumers (TL3) → tertiary consumers/top predators (TL4+).

Productivity is the rate at which new biomass is produced in an ecosystem.

Productivity measures a rate: how quickly new biomass is produced.

Productivity is the rate at which new biomass is produced in an ecosystem, usually by producers through photosynthesis.

Primary productivity is the rate at which producers create biomass using photosynthesis.

Gross productivity is total energy captured; net productivity is what remains after respiration losses.

Gross productivity is the total biomass or energy gained by producers through photosynthesis before losses to respiration.

Heat stress and altered rainfall increase drought and reduce plant growth, so less biomass is produced.

Net productivity equals gross productivity minus respiration: NP = GP − R.

Net productivity is the biomass or energy remaining after respiration losses, available for growth, reproduction, and transfer to the next trophic level.

NP = GP − R.

Respiration represents energy used by organisms for metabolism and life processes, released mainly as heat.

Net productivity equals gross productivity minus respiration: NP = GP − R.

Energy is lost as heat through respiration at each transfer, so less energy remains to form new biomass at higher levels.

Net productivity is available to consumers because it is the biomass remaining after producers use energy for respiration.

Producers such as plants and algae are responsible for most productivity because they convert sunlight into chemical energy through photosynthesis.

Productivity measures how quickly new biomass is produced over time, not the total amount present.

Energy used in respiration is released as heat to the environment and cannot be passed to the next trophic level.

Net productivity is transferred because it represents biomass remaining after respiration.

Energy is lost at each trophic transfer, so progressively less energy is available to support higher trophic levels.

More energy is used for life processes and released as heat, leaving less energy available to form new biomass.

High light availability, suitable temperature, and sufficient nutrients can all increase productivity.

A food web is a network of interconnected food chains.

Energy transfer is inefficient; much energy is lost as heat and waste at each step, leaving too little to support many higher levels.

By adding pollutants and changing habitats, humans alter survival, reproduction, and energy transfer across trophic levels.

It removes producers and habitat, reducing energy entry into the food web and lowering the number of consumers the system can support.

A food web is a network of interconnected food chains showing multiple feeding relationships in an ecosystem.

Link the activity to the ecosystem change, then state the effect on biodiversity and/or energy flow in food webs.

With fewer producers, less energy is captured by photosynthesis and less biomass is created at the base of the food web.

Available energy decreases at each trophic transfer, so higher trophic levels have less energy and biomass.

Alternative feeding pathways allow organisms to switch prey if one species declines, helping maintain energy flow.

Most organisms feed on more than one species and have multiple predators, so energy can move through several pathways.

Removing producers reduces photosynthesis, so less energy becomes biomass at the base of the food web.

Pollution can reduce survival, growth, or reproduction of organisms, so less usable energy is passed to higher trophic levels.

By reducing producer biomass and habitat, less energy enters food webs and fewer consumers can be supported.

If one prey species declines, consumers may switch to alternative prey, allowing energy flow to continue.

Plastics persist and fragment into microplastics (<5 mm) that can be ingested at low trophic levels and passed upward.

Energy decreases at each trophic transfer due to inefficient transfer and heat loss, limiting the number of levels.

There is less energy and biomass available at higher trophic levels, so fewer large consumers can be supported and they often require large territories.

Built surfaces replace producers and fragment habitats, so less photosynthesis occurs and food webs weaken.

Pollutants can reduce growth, survival, or reproduction, so less biomass is passed to higher trophic levels.

The direction of energy flow from the organism eaten to the consumer.

Excess nitrogen/phosphorus can cause eutrophication, leading to oxygen depletion and loss of consumers in aquatic food webs.

Monocultures simplify food webs and reduce biodiversity, so the system is less able to recover from disturbance.

Removing key species can alter population sizes of other trophic levels and trigger trophic cascades, changing food web structure.

Human activities often reduce biodiversity and simplify food webs, which lowers resilience and makes ecosystems less able to recover from disturbances.

Energy transfers are inefficient with heat loss, and less energy/biomass is available at higher trophic levels to support additional levels.

Arrows represent the direction of energy flow from the organism eaten to the consumer.

Toxins can bioaccumulate in organisms and biomagnify up food chains, increasing exposure and health risk for humans as top consumers.

Food webs may not show population sizes, strength of interactions, or seasonal changes, so they simplify real ecosystems.

Habitat destruction, overexploitation, and pollution.

Global trade can introduce invasive species and spread pollutants rapidly, altering species interactions and energy flow in food webs.

Often 4 to 5 trophic levels from producers to top predators.

Biomass and numbers generally decrease at higher trophic levels because less energy is available to build new biomass.

When producers are removed, less energy enters food webs, biomass decreases, and ecosystem stability often falls.

Ecological pyramids are diagrams that represent trophic levels using numbers, biomass, or energy, with producers at the base.

A pyramid of numbers shows the number of individual organisms at each trophic level.

A pyramid of biomass shows the total dry mass of organisms at each trophic level.

A pyramid of energy shows energy flow per unit area per unit time at each trophic level.

One large producer, such as a tree, can support many consumers like insects, making the level above wider.

Water content varies widely and does not contain usable chemical energy, so drying allows fair comparison of stored energy between organisms and trophic levels.

Producers like phytoplankton have low standing biomass but reproduce rapidly, supporting larger consumer biomass.

Energy is lost as heat at every trophic transfer, so less energy is available at higher levels.

Producers capture incoming energy, usually sunlight, and convert it into biomass that supports all higher trophic levels.

They show that numbers, biomass, and available energy usually decrease at higher trophic levels.

Bioaccumulation is the buildup of toxins in a single organism over its lifetime because uptake is faster than removal.

Toxin builds up within one organism over time.

Pollution is the introduction of harmful substances or harmful energy into the environment.

Toxin concentration increases at higher trophic levels.

Biomagnification is the increasing concentration of toxins at higher trophic levels as predators consume contaminated prey.

They persist, build up in organisms, and can move through food chains for long periods.

Bioaccumulation happens within one organism over time. Biomagnification happens between trophic levels and increases up the food chain.

They eat many contaminated prey, so toxins stored in tissues reach the highest concentrations in top predators.

Pollutants reduce survival and reproduction, causing population declines and local extinctions.

Define biomagnification, describe a simple food chain, and state why top predators (and humans) get the highest concentration.

Mercury can move from plankton → small fish → larger fish → tuna, leading to highest concentrations in top consumers (including humans).

Industry, agriculture, transport, and waste disposal can all introduce pollutants.

Energy cannot be created or destroyed; it can only be transformed from one form to another.

An open system exchanges both energy and matter with its surroundings.

Energy does not cycle; it flows through ecosystems and is lost as heat.

Every energy transfer is inefficient; some energy is dissipated as heat, so less usable energy remains.

Main input is sunlight; main output is heat.

Energy is used for respiration, movement and maintenance and much is lost as heat, so only a small proportion becomes new biomass.

Energy flows through ecosystems and is eventually lost as heat, so it cannot be recycled.

An open system exchanges energy and matter with its surroundings.

Use “energy is transformed” for the first law and “transfers are inefficient with heat loss” for the second law.

Sunlight is captured by producers, transferred by feeding through consumers, and leaves the system as heat at each step.

Energy is lost as heat at each transfer so less usable energy remains to build biomass at higher levels.

Heat loss at each transfer reduces usable energy at higher trophic levels, limiting the number of trophic levels supported.

Fewer energy transfers means less heat loss, so more of the original energy supports food production.

Ecosystems depend on energy input (photosynthesis) and recycling of matter (nutrients). Human actions can reduce productivity, remove biomass, and disrupt cycles.

Air pollutants damage plant tissues and climate change alters rainfall/temperature, reducing photosynthesis and productivity.

Pollutants can damage leaves or block stomata, reducing CO2 uptake and lowering photosynthesis.

Deforestation or urbanisation removes producers (plants) from ecosystems.

Trees store carbon. When forests are removed (often burned or decomposed), stored carbon is released as CO2 and less is absorbed.

Fewer trees means less transpiration and often less local rainfall, increasing drying and erosion risk.

Biomass is removed, so nutrients leave the ecosystem instead of being returned to soil by decomposition.

Human activities can alter nutrient cycles (nitrogen/phosphorus), the carbon cycle, and the water cycle.

Harvest removes biomass from the ecosystem, so energy and nutrients leave instead of being recycled by decomposition.

Harvest removes biomass, so fewer nutrients return to soil through decomposition, increasing reliance on fertilisers.

Deforestation reduces energy input (fewer producers) and reduces matter storage (less carbon in biomass/soil).

Harvest removes biomass → fewer nutrients return via decomposition → soil fertility declines unless fertiliser is added.

Humans reduce energy flow (lower productivity) and disrupt matter storage/transfer (alter cycles).

Energy is lost as heat from respiration and in waste/uneaten material (faeces, bones, plant fibre).

Cellular respiration is the process that releases energy from glucose in cells, usually using oxygen.

Energy efficiency is the percentage of energy transferred from one trophic level to the next.

Photosynthesis.

Photosynthesis is the conversion of light energy into chemical energy stored in glucose.

Cellular respiration.

Some energy is transferred to ATP for life processes and a significant amount is released as heat.

Inputs: carbon dioxide and water. Outputs: glucose and oxygen.

Incomplete consumption is when not all parts of an organism are eaten, so energy in those parts is not transferred.

On average, about 10% of energy at one trophic level becomes biomass available to the next level.

Heat loss from respiration and losses in waste/uneaten material.

Energy is used for respiration, movement and maintenance and is lost as heat and waste rather than becoming new biomass.

Yes. Plants respire continuously to release energy for life processes.

Inefficient digestion is when not all ingested food is absorbed; energy leaves the body as faeces.

Photosynthesis occurs in chloroplasts.

Low transfer efficiency leaves too little energy at higher trophic levels to support many levels, so chains are short.

Organisms use energy for metabolism and release much of it as heat, so less becomes new biomass available to the next level.

About 10% (order-of-magnitude).

It traps solar energy and stores it as chemical energy in biomass that can be transferred through food chains.

Energy leaves mainly as heat released during respiration.

Energy enters mainly as sunlight and is captured by producers via photosynthesis.

Less energy becomes new biomass at each transfer because most is lost as heat and waste, so biomass decreases at higher levels.

Fewer trophic transfers means less energy is lost as heat before reaching humans.

Because only a small proportion of energy becomes new biomass at each trophic transfer; most is lost as heat and waste.

Respiration releases heat, showing that energy transfers are inefficient and usable energy decreases.