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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 ecosystemAbiotic components - inorganic nutrients ,e.g water,carbon, gases and minerals - organic nutrients in leaves, fruit and meat
Biotic componentsA) 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 ecosystemsEcosystems 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 DecomposerSimple 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 decomposerThrough respiration, oxygen is taken out of the atmosphere or soil air and combined with the decomposing carbohydratesEnergy 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 photosynthesis The short wave energy is converted into chemical energy and stored in plant tissuesBy 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