Energy and ecosystems Flashcards
How do ecosystems work?
The organisms found in any ecosystem rely on a source of energy to carry out all their activities.
The ultimate source for almost all organisms is sunlight, which is conserved as chemical energy by plants.
Most plants use sunlight in making organic compounds from carbon dioxide in the surrounding air or water.
These compounds include sugars, mostly used by the plants as respiratory substrates.
The rest are used to make other groups of biological molecules, which form the biomass of plants - how energy passes between other organisms.
What are producers?
Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide, and mineral ions.
What are consumers?
Organisms that obtain their energy by feeding on (consuming) other organisms rather than using the energy of sunlight directly. E.g. Animals.
Primary consumers directly eat producers (green plants) and are the first in the chain.
Secondary consumers eat primary consumers.
Tertiary consumers eat secondary consumers.
These two are usually predators but may be scavengers or parasites.
What are saprobionts?
Decomposers. A group of organisms that break down the complex materials in dead organisms into simple ones.
They release valuable minerals and elements in a form that can be absorbed by plants and so contribute to recycling.
They are mainly fungi and bacteria.
What is a food chain?
This describes the feeding relationship in which the producers are eaten by primary consumers, by secondary, then by tertiary, who may be eaten by quaternary consumers, in a long food chain.
Each stage in the chain is a trophic level.
The arrows on food chain diagrams represent the direction of energy flow.
What are food webs?
Most animals do not rely on a single food source and within a single habitat many food chains will be linked together to form a food web.
It is likely that all organisms within a habitat, even in an ecosystem, will be linked to others in the food web.
What is biomass?
The total mass of living material in a specific area at a given time.
The fresh mass is quite easy to assess, but the presence of varying amounts of water makes it unreliable.
Measuring the mass of carbon or dry mass overcomes this problem but, because the organism must be killed, it is only usually a small sample, so may not be representative.
How is biomass measured?
Using dry mass per given area, in a given time.
Grams per square metre (gm^-2) where an area is being sampled, for example, on grassland or seashore.
Where a volume is measured, e.g. in a pond or ocean, it is measured grams per cubic metre (gm^-3).
What is calorimetry?
This can be used to estimate the chemical energy store in dry mass.
In bomb calorimetry, a sample of dry material is weighed and is then burnt in pure oxygen within a sealed chamber, a bomb.
The bomb is surrounded by a water bath and the heat of combustion causes a small temperature rise in the water.
As we know the heat energy required to raise the temperature of 1g water by 1 degree, if we know the volume of water and the temperature rise we can calculate the energy released from the mass of burnt biomass in units such as kJkg^-1.
Why is energy lost in ecosystems?
The sun is the source of energy for ecosystems, however as little as 1% of this light energy may be captured by green plants and so made available to organisms in the food chain.
These organisms in turn pass on only a small fraction of the energy that they recieve to each successive stage in the chain.
Why is most of the sun’s energy not converted to organic matter by photosynthesis?
Plants normally only convert 1 - 3% of the sun’s energy available to them into organic matter:
Over 90% of the sun’s energy is reflected back into space by clouds or dust absorbed by the atmosphere.
Not all light wavelengths can be absorbed and used.
Light may not fall on a chlorophyll molecule.
Factors, e.g. low CO2 levels, may limit the rate of photosynthesis.
What is the gross primary production?
(GPP) - the total quantity of the chemical energy store in plant biomass, in a given area of volume, in a given time.
However, plants use 20-50% of this energy in respiration.
The energy store left is called net primary productivity.
NPP = GPP - respiratory losses (R).
What is the net primary productivity for?
It is available for plant growth and reproduction.
It is also available to other trophic levels in the ecosystem, consumers and decomposers.
Usually less than 10% of NPP in plants can be used by primary consumers for growth.
Secondary and tertiary consumers transfer up to about 20% of the energy available from their prey to their own bodies.
Why is low energy transferred at each stage?
Some of the organism is not consumed.
Some parts cannot be digested and so are lost in faeces.
Some of the energy is lost in excretory materials, such as urine.
Some losses occur as heat from respiration and to the environment. These are high in mammals and birds due to their high body temperature - much energy is needed to maintain temperature when heat is constantly lost to the environment.
What is the equation for net production of consumers?
N = I - (F + R)
N = net production.
I = the chemical energy store of ingested food.
F = the energy lost in faeces and urine.
R = the energy lost in respiration.
