Document Sample
Ecosystem Powered By Docstoc
 F.6 geography
  The biosphere is made up of the living
  organisms of the earth , and their

- 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
    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

 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
 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

 Water : lost through evapotranspiration,
 runoff of drainage
 Animals: migrate away
 Plants and seeds : carried away by winds or
 removed by man through harvest or
 Gases and heat : escape back to the
Food chains and food web

 Autotrophs : make their own food

 Heterotrophs : get their energy from the
 autotrophs. They are the consumers and

 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
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
 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
 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

 -COHO- + O2 > H2O + chemical energy
               + CO2
The cycle of photosynthesis and respiration
  This involves both the primary producers and the
  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
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         – 2000gm/m²/year
 Mid- latitude grassland    – 500gm/m²/year
 desert                     - 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
 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
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

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
  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

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

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

Shared By: