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Edexcel Biology Unit 4 - Environment and Climate Change
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This document contains detailed notes and explanations for 'Environment and Climate Change', a section of Edexcel Unit 4 Biology.
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BIOLOGY A2 NOTESUNIT 4
Topic 5C: Environment and Climate Change
Term Definition
Food Chain A model showing the feeding relationships between a series of
organisms in an ecosystem
Trophic Level This describes the position of an organism in a food chain or web and
it’s feeding relationship with other organisms
Decomposers The final trophic level in any set of feeding relationships; these are
microorganisms such as bacteria and fungi that break down the
remains of animals and plants and return mineral nutrients to the soil.
Essential for recycling of nutrients.
Pyramid of Numbers A model of feeding relationships that represents the numbers of
organisms at each trophic level in a food chain.
Pyramid of Biomass A model of feeding relationships that represents the biomass of the
organisms at each trophic level.
Pyramid of Energy A model of feeding relationships that represents the total energy
store of the organisms at each trophic level in a food chain.
Secondary Production The process of making new animal biomass from plant material that
has been eaten
The main route by which energy enters an ecosystem is photosynthesis.
- During photosynthesis, plants convert light energy into a form that can be used by other organisms
- Energy is transferred through living organisms of an ecosystem when organisms eat other
organisms
- Each of these stages is known as a trophic level
- Energy locked up in the things that can be consumed by other organisms such as bones or faeces
gets recycled back into the ecosystem by decomposers.
Pyramids of energy – the amount of energy stored in the organisms decreases at each trophic level
along a food chain and at the same time, the energy store of the surroundings increases.
NOT ALL ENERGY GETS TRANSFERRED TO NEXT TROPHIC LEVEL:
- Only a small proportion of plant material becomes new animal material. The rest of it:
- The animal is unable to break down, so some energy is lost to the animal in undigested food and is
expelled an unused material in the faeces.
- Much of the material that is digested is used to drive respiration, a series of reactions that result in
ATP production. This is an exothermic process which heats the tissue of the animal and the
surrounding atmosphere.
- Some of the plant material is lost in metabolic waste products such as urea
A food chain can include up to 5 trophic levels
, The energy losses are too great to support any more trophic levels
% Efficiency of energy
transfers between trophic levels: (net productivity of a level/net productivity of the previous
level) x 100
NET PRIMARY PRODUCTIVITY
GPP (Gross Primary Productivity) – in plants, the rate at which light from the Sun catalyses the production
of new plant material.
NPP (Net primary productivity) – the material produced by photosynthesis and stored as new plant body
tissues. (NPP = GPP – R (where R is losses due to respiration))
- Measuring productivity involves finding the mass of representative samples of biomass and then
multiplying them to represent a whole ecosystem.
- Theoretical calculations can be used to convert biomass to energy rather than using empirical
measurements, so biomass is the better measure to use.
NPP of an ecosystem depends on all the abiotic factors and biotic factors that affect plant growth within
the ecosystem.
- Latitude is important because the light levels within a specific area are lower at latitudes nearer the
pole than closer to the equator.
- If you combine the NPP of each type of ecosystem with the area of the Earth’s surface if covers,
you can see how much each ecosystem type contributes to the overall NPP of the Earth.
Limitations of Energy Transfer Efficiency Calculations
- Very difficult to measure transfers for whole ecosystems as many assumptions need to be made
- You need to be certain that you have identified all the most abundant species in the ecosystem
- You also need to know how many are there, what an average body size is, how much energy that
body size represents
- How much of the biomass is transferred into decomposers at any stage of the life of the animal or
plant and so on.
Efficiency = energy output/energy input x 100
In Temperate Regions:
- There is like to be more biomass
- A bigger energy store in plant and animal bodies during summers
- In Winters, there is likely to be more decomposers
In Tropical Regions:
- There is substantial difference between the wet and dry seasons
- All of these factors affect estimates of energy at each trophic level.
Energy Transfer and Food Chain Length
- One of the main effects of inefficient transfers through food chains and webs is to limit the number
of trophic levels
- At higher trophic levels, the organisms usually need to move over larger distances, so it takes more
energy to find food and a mate needed for growth and reproduction.
- Food chains are generally longer in tropical regions than in polar regions because tropical regions
receive more light.
Mean length of food chain increases, there is a decrease in the number of organisms that are endothermic
(Aquatic environments)
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