Ecosystem revision

Closed loop systems

• In a perfect closed loop system no materials enter or leave the system. Waste products from one organism or process are used by another organism or process. It can be said, therefore, that the output from one part of the system becomes the input to another part.

• No ecosystem can be a perfect closed loop system because some output is always lost, eg some organisms migrate, some nutrients are transported away by the wind or by rain and rivers.

Recycling waste products• Within a natural ecosystem, most waste materials are not lost.

They can be used as food or reactants for animals, plants and microorganisms.

• Oxygen is a waste product from photosynthesis. It is used in respiration.

• Carbon dioxide is a waste product from respiration. It is used in photosynthesis.

• Dead organic matter (eg fallen leaves, fruits, flowers, faeces, remains of bodies) is used directly as food or processed into useful nutrients by microorganisms. These microorganisms use digestive enzymes to break down complex molecules into simpler nutrients.

Closed loop system

• There is only a certain amount of carbon on Earth. This carbon is cycled through a number of stages where it exists in different forms. For example:

• Carbon exists in the atmosphere as carbon dioxide. This can be taken out of the atmosphere by the process of photosynthesis - the carbon then becoming part of glucose molecules.

• These glucose molecules are then broken down during respiration. The process of respiration releases carbon back into the atmosphere as carbon dioxide.

• Carbon dioxide could also be released into the atmosphere by combustion of wood and fossil fuels.

• Microorganisms and some animals feed on dead organic matter. The carbon then becomes part of these microorganisms. This process is known as decomposition, the carbon has become part of new organisms in the system

Reproductive strategies

• Different organisms have very different approaches to achieving successful reproduction.

• For example, mammals produce a very small number of eggs but millions of sperm. This makes sense because the fertilised egg develops inside the female, so there is a greater chance of it surviving.

• On the other hand, fish and amphibians produce large numbers of eggs because fertilisation takes place outside the body and the fertilised eggs are rarely cared for by the adults.

• When organisms produce large numbers of reproductive cells (such as pollen, sperm and eggs) or reproductive structures (such as flowers and fruit), these ensure that reproduction is likely to be successful.

• The unsuccessful cells and structures are recycled into the ecosystem. They are usually used as nutrients for animals or microorganisms.

Ecosystem services

• air, water, soil, minerals, pollination, fish, game, decomposers.

The importance of vegetation• Vegetation is an essential part of many ecosystems. There are a number of

reasons for this. • One of the key reasons involves the process of photosynthesis – that is,

when plants use the energy from sunlight to convert water and carbon dioxide into glucose and oxygen. Both glucose and oxygen are essential for animals

• Other reasons why vegetation is so important in many ecosystems include the facts that:

• Roots help to stabilise the soil – preventing it from being eroded by heavy rain (especially in rainforests). Vegetation also reduces soil erosion since foliage protects the soil from direct rainfall.

• Trees provide shade from the sun and help to insulate the forest floor at night – therefore stabilising the temperature.

• Transpiration from trees helps to promote cloud formation.

How do humans affect ecosystems?

• Humans rely on natural ecosystems to provide many ‘ecosystem services’- such as pollination of crops, and cleaning air and water. Humans also rely on ecosystems to provide them with fertile soil, mineral nutrients, fish and game.

• However, human activities often affect ecosystems in negative ways because human systems are not closed loop systems.

• Human waste enters other natural ecosystems, where it can cause them to become unbalanced. Sometimes this waste can build up to harmful levels

• Examples of human waste that can affect ecosystems are:• household waste• industrial waste• agricultural waste• gases produced when fossil fuels are burned• Humans sometimes harvest plants and animals from natural

ecosystems and this can also unbalance them.• For example, harvesting timber can lead to soil erosion and

loss of habitat, while harvesting fish from the oceans can cause species to become threatened and unbalance food webs.

• In some parts of the world, natural vegetation has been removed and replaced with crops for food or the production of fuels (called ‘biofuels’), or by grazing animals.

• As well as destroying the natural habitat and reducing biodiversity, soil erosion can cause rivers to become silted up (clogged up with silt), plus the lack of shade and the lack of moisture in the soil can cause desertification (when fertile land turns into relatively lifeless desert).

Sustainability and ecosystems• When humans remove substances or organisms from an ecosystem, this is

only sustainable if the rate at which we remove them is less than or equal to the rate at which they can be replaced by natural processes, such as reproduction.

• For example, the way in which crude oil is used is not sustainable because it takes millions of years to form from the decay of dead organisms.

• We are removing crude oil from underground reservoirs in the crust very quickly. When it is burned, the energy that is released was captured by photosynthesis millions of years ago when the organisms were alive.

• Energy that was trapped in this way can be called ‘fossil sunlight energy’.• In a perfect closed loop system, the inputs and outputs of the organisms are

balanced - but the system that formed the crude oil no longer actually exists, so the input when crude oil is burned unbalances the present system (it is an ‘extra’ input).

• Sustainable development is more likely to be possible if sunlight is used as a primary energy source, for example by using biofuels. A biofuel is a fuel produced from renewable resources - such as plant biomass - where the carbon dioxide emitted by burning them is balanced by the carbon dioxide absorbed by the plants as they grow.

• Fish populations can be preserved if quotas are observed, which means that each country has an entitlement to catch only a certain number of each type of fish. Some animal populations can be restocked.

Hidden uses of oil

How is oil used in farming (indirectly or directly).

1) Making pesticides/herbicides/ fertilisers2) Processing food. 3) Ploughing and planting crops.4) Distributing products.

Task : Describe what is would be like farming without oil. What is the problem with this?

• Forests can be preserved if the trees are replanted. Sustainable cropping of forests–which involves cutting down selected trees in an area (rather than felling every tree) - can also be adopted to maintain the forest ecosystem.

• Sometimes, there are tensions between conservation efforts and the needs of local communities. For example, even though the process of mining for gold in the Brazilian rainforest damages the natural ecosystem, the people employed as miners still need to earn money to support their families.

Timber/fish

• How can the cutting down of trees and the fishing of fish be sustainable?

• Replace felled trees with new• Only fish to certain quotas

Bioaccumulation• Bioaccumulation is when toxins build up in a food chain. The

animals at the top of the food chain are affected most severely.• This is what happens:• Small amounts of toxic substances - often from human activity - are

taken up by plants.• These plants are eaten by primary consumers.• The primary consumers are eaten by secondary consumers, and

the secondary consumers are eaten by higher level consumers.• At each stage (trophic level) of the food chain, harmless substances

are excreted but the toxins remain in the tissues of the organisms - so the concentration of toxin becomes most concentrated in the body tissues of the animals at the top of the food chain.

DDT

• An example of bioaccumulation is the use of DDT as an insecticide in the 1950s and 1960s. Birds of prey were badly affected because it made the shells of their eggs very thin, causing them to break easily when the birds tried to incubate them.

Eutrophication

• When fertilisers are added to farmland in large quantities, plants and animals in nearby rivers and lakes can sometimes be killed, but not by poisoning. The steps in eutrophication are quite complicated.

Eutrophication

Eutrophication video

• http://www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_21c/further_biology/ecosystems/revision/6/