Energy and ecosystems
Food chains and energy transfer
An ecosystem includes all the organisms living in a particular area known as the community
as well as all the non-living elements of that particular environment. The distribution and
abundance of organisms in a habitat is controlled by both biotic factor (living) e.g.
predators, disease and abiotic factors (non-living) such as light levels and temperature. Each
species has a particular role in its habitat called its niche which consists of its biotic and
abiotic interactions with the environment.
Groups or organisms:
- Producers- photosynthetic organisms that manufacture organic substances e.g.
sugars, using light energy, water, CO2, and mineral ions. Plants.
- Consumers- organisms that obtain their energy by feeding on other organisms rather
than using the energy of sunlight directly. Primary consumers directly eat producers.
Secondary consumers eat primary consumers and so on with tertiary consumers.
Secondary and tertiary consumers are usually predators but may also be parasites.
Animals.
- Saprobionts (decomposers)- organisms that break down the complex materials in
dead organisms into simple ones. This releases valuable minerals and elements that
can be absorbed by plants and so contribute to recycling. Fungi and bacteria.
Food chain- the relationship in which the producers are eaten by primary consumers,
primary consumers are eaten by secondary consumers and so on. Each stage in this chain is
referred to as a trophic level. The arrows on food chain diagrams represent the direction of
energy flow.
, Biomass- the total mass of living materials in a specific area at a given time. It is measured
using dry mass per given area in a given time , grams per square metre (g m -2). Where a
volume is being sampled, e.g. in the ocean, g m-3 is used.
The biomass can be measured in terms of mass of carbon or dry mass of tissue per given
area per given time. The dry mass is used as the wet mass can vary too much. The chemical
energy stored in dry biomass can be estimated using calorimetry. This is carried out in a
bomb calorimeter in which a sample of known mass is burnt in pure oxygen. The bomb
calorimeter is submerged in water and therefore the change in water temperature can be
used to calculate the energy in the sample.
Energy transfer and productivity
- Net primary productivity (NPP) – the chemical energy store that is left in plant
biomass after respiratory losses to the environment have been taken into account.
- Gross primary productivity (GPP) – the total chemical energy store in plant biomass,
in a given area or volume, in a given time. however plants use some of this energy
for respiration which is why there is NPP.
- Therefore, NPP = GPP – R
- R = respiratory loss
- The net primary production is available for plant growth and reproduction as well as
to other trophic levels in the ecosystem such as decomposers and consumers.
- The net production of consumers (N) such as animals can be calculated by:
- N= I – (F+R)
- where I represents the chemical energy store in ingested food, F represents the
chemical energy lost to the environment in faeces and urine and R represents the
respiratory losses to the environment.
The Sun is the source of all energy in ecosystems with photosynthetic organisms using this
to produce their own food. These can be termed autotrophs and are producers. Those
organisms that cannot synthesise their own food are called heterotrophs with all animals
being these. Only around 10% of chemical food energy is passed on between organisms in
the food chain. The other 90% is lost to the surroundings as:
- uneaten parts e.g. the bones.
- decay of dead material e.g. bacteria may decay some material.
- excretion e.g. energy is lost in faeces
- exothermic reactions e.g. heat lost in respiration.
Food chains and energy transfer
An ecosystem includes all the organisms living in a particular area known as the community
as well as all the non-living elements of that particular environment. The distribution and
abundance of organisms in a habitat is controlled by both biotic factor (living) e.g.
predators, disease and abiotic factors (non-living) such as light levels and temperature. Each
species has a particular role in its habitat called its niche which consists of its biotic and
abiotic interactions with the environment.
Groups or organisms:
- Producers- photosynthetic organisms that manufacture organic substances e.g.
sugars, using light energy, water, CO2, and mineral ions. Plants.
- Consumers- organisms that obtain their energy by feeding on other organisms rather
than using the energy of sunlight directly. Primary consumers directly eat producers.
Secondary consumers eat primary consumers and so on with tertiary consumers.
Secondary and tertiary consumers are usually predators but may also be parasites.
Animals.
- Saprobionts (decomposers)- organisms that break down the complex materials in
dead organisms into simple ones. This releases valuable minerals and elements that
can be absorbed by plants and so contribute to recycling. Fungi and bacteria.
Food chain- the relationship in which the producers are eaten by primary consumers,
primary consumers are eaten by secondary consumers and so on. Each stage in this chain is
referred to as a trophic level. The arrows on food chain diagrams represent the direction of
energy flow.
, Biomass- the total mass of living materials in a specific area at a given time. It is measured
using dry mass per given area in a given time , grams per square metre (g m -2). Where a
volume is being sampled, e.g. in the ocean, g m-3 is used.
The biomass can be measured in terms of mass of carbon or dry mass of tissue per given
area per given time. The dry mass is used as the wet mass can vary too much. The chemical
energy stored in dry biomass can be estimated using calorimetry. This is carried out in a
bomb calorimeter in which a sample of known mass is burnt in pure oxygen. The bomb
calorimeter is submerged in water and therefore the change in water temperature can be
used to calculate the energy in the sample.
Energy transfer and productivity
- Net primary productivity (NPP) – the chemical energy store that is left in plant
biomass after respiratory losses to the environment have been taken into account.
- Gross primary productivity (GPP) – the total chemical energy store in plant biomass,
in a given area or volume, in a given time. however plants use some of this energy
for respiration which is why there is NPP.
- Therefore, NPP = GPP – R
- R = respiratory loss
- The net primary production is available for plant growth and reproduction as well as
to other trophic levels in the ecosystem such as decomposers and consumers.
- The net production of consumers (N) such as animals can be calculated by:
- N= I – (F+R)
- where I represents the chemical energy store in ingested food, F represents the
chemical energy lost to the environment in faeces and urine and R represents the
respiratory losses to the environment.
The Sun is the source of all energy in ecosystems with photosynthetic organisms using this
to produce their own food. These can be termed autotrophs and are producers. Those
organisms that cannot synthesise their own food are called heterotrophs with all animals
being these. Only around 10% of chemical food energy is passed on between organisms in
the food chain. The other 90% is lost to the surroundings as:
- uneaten parts e.g. the bones.
- decay of dead material e.g. bacteria may decay some material.
- excretion e.g. energy is lost in faeces
- exothermic reactions e.g. heat lost in respiration.
