Energy flow - Biology SL Topic 4.2 role of photosynthesis, food chains, heat, food webs PDF

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Biology SL
Topic 4.2
role of photosynthesis, food chains, heat, food webs...

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Energy flow

Topic 4.2

Biology SL

The role of photosynthesis ➢ Photosynthetic organisms take simple inorganic carbon dioxide and convert it into energy-rich glucose ○

The addition of minerals allows the producers to synthesize complex molecules

➢ Chemical energy refers to the fact that organic compounds are rich in energy, thanks to the chemical bonds that exist between carbon and other atoms ○

Two ways to release the energy from organic compounds ■

Digest the food

■

Burn it

Food chains

➢ The flow of energy through a food chain is the process of passing energy from one organism to another through feeding ➢ A food chain is a sequence showing the feeding relationships and energy flow between species

➢ Trophic levels are used to indicate how many organisms the energy has flown through ○

1st trophic level => producers/autotrophs

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2nd trophic level => primary consumers

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3rd trophic level => secondary consumers

➢ Energy is lost in every trophic level so we can’t have more than 4-5 trophic levels

Heat ➢ Any heat produced by cellular respiration is lost to the environment ➢ If something is eaten, some of the chemical energy is passed onto the next organism ➢ If something dies, detritivores and decomposers will use its available energy ➢ During cell respiration not all energy is converted into ATP ○

Some of it is converted into heat energy ■

Once the heat energy leaves the body, it can’t be used as a biological energy resource ⇒ heat is lost from the ecosystem

➢ Unlike nutrients, energy can’t be recycled ○

Only chemical energy can be used from the next trophic level ■

Typically only 10-20% of the energy available is used from the previous step in a food chain 1

Energy flow

Topic 4.2

Biology SL

➢ This happens because ○

Not all of an organism is swallowed as a food source

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Not all of the food swallowed can be absorbed and used in the body

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Some organisms die without having being eaten by an organism from the next trophic level

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There’s considerable heat loss due to cell respiration at all trophic levels

Pyramid of energy ➢ A pyramid of energy is used to show how much and how fast energy flows from one trophic level to the next in a community ○

They take into account the rate of energy production, not just the quantity

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Unit: kilojoules per square meter per year (kJ/m /yr)

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➢ Energy is lost so each trophic level becomes smaller ➢ Pyramids of numbers show the population size of each trophic level, not the energy

Food webs ➢ The number of organisms in the chain and the quantity of light available will determine how long the chain is ➢ The biomass of a trophic level is an estimate of the mass of all the organisms within that level ➢ Some molecules along the food chain can’t participate in the accumulating biomass, because they’re lost in various forms ○

carbon dioxide, water, urea, feaces

➢ Sometimes it’s necessary to describe a food web rather than a food chain, because many animals have complex dietary preferences

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