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.

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

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

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

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

Trophic level 2 (primary consumer).

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.

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

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

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

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.

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

Scavenger.

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+).

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Main input is sunlight; main output is heat.

Energy cannot be created or destroyed, only transformed.

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

Energy transfers are inefficient and some energy becomes heat.

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

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

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

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

An open system exchanges energy and matter with its surroundings.

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

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

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

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

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

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.

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

Cellular respiration.

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

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

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

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

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

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

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

Photosynthesis occurs in chloroplasts.

About 10% (order-of-magnitude).

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

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

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

Energy leaves mainly as heat released during respiration.

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

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

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

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

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

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

Biomass is the total dry mass of living organisms in a given area, representing stored chemical energy at a 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.

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

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

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.

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

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.

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

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

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

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

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

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

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

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.