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