5 Energy and Ecosystems Flashcards
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.
what is the source of all energy in an ecosystem?
the sun
with photosynthetic organisms using this to produce their own food.
what 3 groups can organisms be divided into according to how they obtain their energy and nutrients?
producers
consumes
saprobionts
producers
photosynthetic organisms that manufacture organic substances using light energy, water, CO2 and mineral ions
consumers
organisms that obtain their energy by feeding on other organisms
primary consumers
those that directly eat producers
secondary consumers
those eating primary consumers
usually predators
tertiary consumers
those eating secondary consumers
usually predators
saprobionts
decomposers
a group of organisms that break down the complex materials in dead organisms into simple ones
in doing so, they release valuable materials and elements in a form that can be absorbed by plants and so contribute to recycling
the majority of this work is carried out by fungi and bacteria
food chain
describes a feeding relationship in which the producers are eaten by primary consumers
these in turn are eaten by secondary consumers, which are then eaten by tertiary consumers
each stage in this chain is referred to as a trophic level
the arrows on a food chain diagram represents the direction of energy flow
food web
within a single habitat many food chains linked together to form a web
most animals don’t rely on a single food source
biomass
the total mass of living material in a specific area at a given time
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.
what is biomass measured in?
grams per square metre
gm-2
gross primary production
the chemical energy store in plant biomass, in a given area or volume
net primary production
the chemical energy store in plant biomass after respiratory losses to the environment have been taken
into account
NPP = GPP – R
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 herbivores.
why is a low percentage of energy transferred at each stage?
- some of the organisms is not consumed
- some parts are consumed but cannot be digested and are therefore lost in the faeces
- some of the energy is lost in excretory materials, such as urine
- some energy losses occur as heat from respiration and lost to the environment. these losses are high in mammals and birds because of their high body temp. much energy is needed to maintain their body temp when heat is constantly being lost to the environment.
net production of consumers equation
N= I - (F+R) N is net production I is chemical energy store of ingested food F is energy lost in faeces and urine R is energy lost in respiration
the inefficiency of energy transfer between trophic levels means…
- most food chains only have 4 or 5 trophic levels because insufficient energy is available to support a large enough breeding population at TLs higher than these
- the total mass of organisms in a particular place (biomass) is less at higher TL
- the total amount of energy available is less at each TL as one moves up a food chain
nutrient cycles
Nutrients are recycled within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle.
what vital roles in recycling chemical elements such
as phosphorus and nitrogen do Microorganisms play?
• The role of saprobionts in decomposition.
• The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants.
• The role of bacteria in the nitrogen cycle:
Nitrogen-fixing bacteria in the soil and within the root nodules of some plants convert nitrogen gas in the atmosphere to ammonia. Nitrifying bacteria convert ammonia to nitrites or nitrates. Denitrifying bacteria converts nitrates back to nitrogen gas.
what sequence do all nutrient cycles have?
- the nutrient is taken up by producers (plants) as simple, inorganic molecules
- the producer incorporates the nutrient into complex organic molecules
- when the producer is eaten, the nutrient passes into consumers (animals)
- it then passes along the food chain when these animals are eaten by other consumers
- when the producers and consumers die, their complex molecules are broken down by saprobiontic MOs (decomposers) that release the nutrient in its original simple form. the cycle is then complete. the role of these saprobionts in nutrient cycles is important. without them, nutrients would remain locked up as part of complex molecules that cannot be taken up and used again by plants
nitrogen cycle
Nitrogen is an element used in many biological molecules of which there is a finite amount on earth. Due to this it must be recycled from dead organisms and waste products. Most of this is carried out by bacteria in the soil.
although 78% of the atmosphere is nitrogen, very few organisms can use nitrogen gas directly. plants take up most of the N they require in the form of nitrate ions (NO3-), from the soil. these ions are absorbed using active transport by the roots.
4 stages of nitrogen cycle
ammonification
nitrification
nitrogen fixation
denitrification
ammonification
When an organism dies or produces waste (e.g. faeces), it is decomposed by saprobionts.
This releases the nutrients contained inside.
Saprobionts decompose the organisms’ biomass by extracellular digestion and inorganic ammonium ions are released into the soil.
Ammonification is a by-product of saprobiont nutrition.
