Ecosystem
F.6 geography
Biosphere
The biosphere is made up of the living
organisms of the earth , and their
environments
Ecology
- Ecology is the study of the relationship
between organisms and their environment
The Ecosystem and the food chain
An ecosystem is a system describing the
interactions between living organisms
1. Components of an ecosystem
Abiotic components
- inorganic nutrients ,e.g water,carbon,
gases and minerals
- organic nutrients in leaves, fruit and meat
Biotic components
A) Producers are green plants which
convert simple inorganic matter such as
CO2 , water and minerals into organic
compounds
B) Consumers are the different types of
animals that eat producers
-
primary consumers: herbivores that feed on plants
Secondary consumers: carnivores
Tertiary and quarternary consumers
Omnivores
Detritivores
C) decomposer
- like bacteria and fungi
- They recycle nutrients by breaking down
dead organisms into inorganic compounds
again for absorption by green plants
Inputs and outputs of ecosystems
Ecosystems have inputs of matter and energy used
to build the biological structures ,to reproduce,
and to maintain necessary internal energy levels.
Matter and energy are also exported from an
ecosystem
The inputs to, and outputs from , any ecosystem
represent a link with other parts of the
environment. Some of the outputs from one area
become inputs into adjacent areas
Inputs
Solar radiation : supplies energy to the ecosystem
Water : supplied by rainfall, irrigation,etc
Nutrients : supplied by rock weathering or by
man’s use of fertilizers
Animals : animals migrate into the areas
Plants and seeds : wind and streams may carry
seed which germinate into plants, and man also
introduce seeds or seedlings
Outputs
Water : lost through evapotranspiration,
runoff of drainage
Animals: migrate away
Plants and seeds : carried away by winds or
removed by man through harvest or
lumbering
Gases and heat : escape back to the
atmosphere
Food chains and food web
Autotrophs : make their own food
Heterotrophs : get their energy from the
autotrophs. They are the consumers and
decomposers
The food chain is a specific pathway of food
transfer in which one kind, or one level of
organisms feed upon another in a sequence of
levels
The trophic levels( 營養層次）
The primary producers- plants and algae
which use light energy to converts CO2 and
H2O to carbohydrates which support life
through the process of photosynthesis
Primary consumers
Secondary consumers
Tertiary consumers
Decomposer
Simple food chain rarely occur. Instead
there are many interconnections of linear
food chains into food webs
Photosynthesis and respiration
Photosynthesis is the production of
carbohydrates, consisting of the elements
carbon, hydrogen and oxygen. It is the
process by which the autotrophs convert
solar energy ,in the form of sunlight, to
chemical energy
Water + carbon dioxide + sunlight energy > carbohydrates + oxygen
H2O +
CO2
+ sunlight energy > CHOH
+ O2
The energy is released through the process
of respiration
Respiration
The process of respiration is actually an
oxidation process in which the carbohydrate
breaks down to simpler molecules, carbon
dioxide and water, releasing energy in the
process
-COHO- + O2 > H2O + chemical energy
+ CO2
The cycle of photosynthesis and respiration
This involves both the primary producers and the
decomposers
Water is drawn up into the body of a living plan
In the green leaves of the plants, photosynthesis
takes place
Light energy is absorbed by the leaf cell
Carbon dioxide is brought in from the atmosphere
Oxygen is liberated and begins its atmospheric
cycle
The plants tissue dies and falls to the ground
It is acted on by the decomposer
Through respiration, oxygen is taken out of the
atmosphere or soil air and combined with the
decomposing carbohydrates
Energy is now liberated
Both carbon dioxide and water enter the
atmosphere as gases
The materials components- hydrogen, oxygen and
carbon – are recycled within the system
Plant nutrients are recycle in the same way
The earth does not lose or gain matter and the
materials never leave the system, they are just
stored in other ways.
Net Primary Production
1. Biomass
The net production by photosynthesis is
measured in terms of biomass per unit
surface area
Biomass is the dry weight of the organic
matter and of all ecosystem
Net Primary production
This is the number of grams of dry organic matter
produced annually from a square metre of surface
Equatorial forest
Mid- latitude grassland
desert
– 2000gm/m²/year
– 500gm/m²/year
- 3 gm/m²/year
Net primary production and climate
Climatic factors such as light intensity,
temperature and availability of water
control the net production
The highest production is in TRF
There is low production in desert climates
and at high latitudes
The Arctic has no production, because of
the combination of short growing season
and low temperature
The flow of energy in the biosphere
1. The energy flow system of a green plant
Solar short wave energy falling on a green leaf is
partly reflected and partly absorbed through
photosynthesis
The short wave energy is converted into chemical
energy and stored in plant tissues
By respiration,chemical energy is converted to
sensible heat
The stored sensible heat is evaporated away
leaving the plant as latent heat,or lost to the
atmosphere through longwave radiation or direct
conduction
Energy flow along the food chain
Solar energy is absorbed, reflected and scattered in
various way in the atmosphere
Less than half is received by plants and a small
proportion is processed into organic compounds
through photosynthesis
Respiration also reduces the gross primary
production leaving the net primary production
which is a small proportion of the energy absorbed
by the green plants
The net primary production becomes an
input for the next trophic level though not
all energy from net primary production is
usuable
Some is toxic or indigestible parts may not
be consumed at all
Some is consumed and then excreted as
faeces, and some are discharged as
metabolic wastes such as urine
A small proportion of net primary
production is held in the biomass ,after
respiration – net secondary production
The same processes of energy transfer
operate at the higher trophic levels, with
energy being lost during each step
About 10-50% of the energy stored in
organic matter at one level can be passed up
the chain to the next level
The normal limit is four levels of consumers
The biomass also decreases with each
upward step in the chain – the number of
individuals of the consuming species is
lower at each higher level
Implications of the decrease of energy up the food
chain
As we go up the food chain, less and less
energy is available in a unit area
Organism feeding at highest levels must
find food over a wide area, to find enough
to sustain themselves
A larger population can be supported by
feeding at a lower level
For example: far more energy could be make
available if the food chain was shortened
( human eat more plants rather than cattle )
Man’s impact on energy flow in
the ecosystem
Many man’s activities change the energy
flow to maximize net primary productivity
The fossil fuel which run tractors, and farm
machinery use energy inputs similar to light
and chemical energy
The use of pesticides alters the energy flows
in agricultural ecosystems by reducing the
number of primary consumers
Bringing food to animals in feedlots save
them from expending stored energy in
looking for food, thus allowing them to
rapidly gain weight
The Flow of matter/ materials in
the Biosphere
The three principal components of
carbohydrates (-CHOH-): hydrogen (H),
carbon (C ), and oxygen (O) ,are called
macronutrient
Six other macronutrients are : nitrogen (N) ,
Calcium (Ca), Potassium (K), magnesium
(Mg), sulphur (S), and phosphorus (P)
The macronutrients are all required in
substantial quantities for organic life to
thrive
Matter in cycle includes water and a wide
range of mineral substance
They are referred to as nutrients, and their
transfers from one part of the ecosystem to
another make up the nutrient or
biogeochemical cycle
The Carbon cycle
All life is composed of carbon compounds
It exist in two forms : carbon dioxide and
organic carbon ( carbohydrates , fat ,
protein )
Carbon dioxide is a minor constituents of
the atmosphere
A larger amounts of CO2 is dissolved in the
water in the ocean
The greatest amount lies in storage as
carbonate sediments
The process
Plants use solar energy,CO2 from the
atmosphere,and water and minerals from
the soil to change inorganic nutrients into
organic compounds such as carbohydrates,
proteins and fats
The fixation of carbon means carbon is
fixed into solid carbohydrate
Through respiration, organic carbons is
oxidized to become CO2, yielding energy.
Thus changes in state are form gas to solid
and back to gas
Green plants not only provide food, but also
give out oxygen, vital to the lives of animals
and men