2009 IJSO BIOLOGY Cycles in Nature

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Notes to Teachers • Learning Objectives:

1. The meaning of the terms: species, population, community, habitat, ecosystem and biosphere (0.5 hr)

2. The concepts of food chain, food web, the pyramid of number, pyramid of biomass and pyramid of energy ­ the transfer of energy between different trophic levels and its relative efficiency; the importance of producers, consumers and decomposers in the cycling of nutrients (2.5 hrs)

3. The water, nitrogen and carbon cycles (1 hr) 4. The roles of decomposers and scavengers (0.5 hr)

1. Time Allocation: 4.5 hrs

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Learning Outcomes • Students should be able to:

1. define species, population, community, habitat, ecosystem and biosphere and describe their interrelationship;

2. draw food chain, food web, the pyramid of number, pyramid of biomass and pyramid of energy;

3. explain the flow of energy within an ecosystem; 4. assess the efficiency of energy transfer between trophic

levels; 5. relate the concept of energy flow between different

trophic levels to photosynthesis, respiration and chemosynthesis;

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Learning Outcomes • Students should be able to:

6. explain the roles of producers, consumers and decomposers in the cycling of nutrients;

7. state the major stages of the water, nitrogen and carbon cycles;

8. evaluate the importance of the nitrogen and carbon cycles;

9. develop an awareness of the effects of human interference on the nitrogen and carbon cycles; and

10. distinguish decomposers and scavengers.

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Cycles

­ Water cycle ­ Gases (O 2 and CO 2 ) cycle ­ Carbon cycle ­ Nitrogen cycle

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Ice / Water / water vapour

a b Ice

d c e

condensation / sublimation / freezing evaporation / melting

Water Water vapour

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Water Cycle

http://ga.water.usgs.gov/edu/watercycleprint.ht ml

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Evapotranspiration = Evaporation + transpiration

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Experiment to demonstrate transpiration

potted plant

bell jar

plastic bag

potted plant without stem and leaves

What can you observe?

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Gases cycle Carbon dioxide + water

Carbon compound e.g. starch + Oxygen

photosynthesis Respiration

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• Some terms: species / population / community / habitat / physical (abiotic factors) / biotic factors / ecosystem

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population

A

B

C

plant community

animal community

microorganism community

Ecosystem

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Artificial ecosystem – aquarium

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Natural ecosystem

tropical rain forest

coral reef

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Mode of nutrition Organism

Carbon source simple inorganic compound organic compound e.g. CO 2 , H 2 S e.g. carbohydrate (autotrophic nutrition) (heterotrophic nutrition)

Energy source light energy chemical energy chemical energy (photosynthesis) (chemosynthesis)

dead organic matter food living host • (need digestion) (need ingestion) (need not digestion) • & digestion • (saprophytic (holozoic nutrition) (parasitic • nutrition) 動物式營養 nutrition)

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Mode of nutrition?

• 1.human? • 2.tapeworm? (絛蟲) • 3.mushroom? (菇) • 4.pitcher plant?

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Pitcher plant – insectivorous plants

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Biotic components of an ecosystem 1.Producers e.g. green plants, grass, algae,

phytoplankton浮游植物

2.Consumers (primary/secondary/tertiary…/top)

3.Decomposers (saprophytic bacteria and fungi) ­ break down dead bodies, faeces and excretory wastes into inorganic minerals which can be released to soil and absorbed by the producers. They help the recycling of materials in the ecosystem.

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Decomposers­ saprophytic fungi)

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Saprophytic fungi – bread mold

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Decomposers ­ saprophytic fungi mushroom

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Food Chain • Transfer of materials and energy from plants to organisms

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Food Web

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Food Web in Grassland

http://teacherweb.com/NF/StPetersJuniorHigh/MrGWilliams/photo3.stm

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Trophic levels (食性層次) Write down one food chain which involves 5 organisms. Trophic level ( one specific food chain)

Organism

fifth trophic level / quarternary consumer ?

fourth trophic level / tertiary consumer ?

third trophic level / secondary consumer ?

second trophic level / primary consumer ?

first trophic level / producer ?

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Energy flow and energy loss

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Energy flow and energy loss ­ producers capture the light energy by photosynthesis and convert it into chemical energy stored in organic food. ­ lose energy in three ways: (i) their own respiration as heat (ii) being eaten by consumers (iii) being decomposed by decomposer when death.

­ chemical energy flows by feeding.

­ chemical energy stored in organic food released in cellular respiration in form of ATP

­ consumers at different trophic levels lose energy by the similar ways: respiration as heat / death / excretion.

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Pyramid of number/biomass/energy

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Pyramid of number (i) energy loss due to respiration as heat / death / excretion, less energy can only support a smaller number of organisms.

à the number of organisms decreases along the trophic level, pyramid of number is an upright triangle

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Inverted pyramid of number e.g. (i) the producer is very large but no. is small

(ii) consumers are parasites, small but many

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Different shapes of pyramid of number

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Pyramid of biomass . Biomass ­ amount of living materials in organisms at each trophic level per unit area at any one time.

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Inverted pyramid of biomass . Producers might be few or small, but reproduced at a massive rate to feed the larger number of grazing consumers.

e.g.: At grassland – the food chain in a fertile, productive field which is being constantly grazing by cows.

At ocean ­ phytoplankton reproduced at a massive rate to feed zooplankton.

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Inverted pyramid of biomass Fertile and productive field : sheep graze on grass

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Inverted pyramid of biomass

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Pyramid of energy

­ always in an upright position due to energy loss along food chain

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Material flow within an ecosystem

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Carbon Cycle

http://www.epa.gov/maia/html/nitrogen.html

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human activities that disturb carbon cycle

1. Over­consumption of fossil fuels

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human activities that disturb carbon cycle

2. Deforestation

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Greenhouse effect 溫室效應

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Nitrogen Cycle

5.absorption

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Nitrogen cycle • Plants absorbs N in form of nitrate (NO 3 ­ ) • N is important for protein synthesis • 1.lightning N 2 ­> NO 3 ­ 2.nitrogen fixation (固氮作用) by nitrogen­fixing bacteria N 2 ­> nitrogenous compound e.g amino acid 3. decomposition / industrial synthesis of fertilizers nitrification (硝化作用) by nitrifying bacteria NH 3 ­> NH 4 + ­> NO 2 ­ ­> NO 3 ­

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root nodules of leguminous plants (symbiotic / mutualistic nitrogen­fixing bacteria)

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pH change NH 3 NH 4 + NO 2 ­ NO 3 ­

+H ­H +O +O

Oxidation – H + release ­­­> pH reduces (acidic)

Conditions favourable for processes in nitrogen cycle

aerobic condition is favourable for nitrification.

anaerobic condition e.g. water­logging (水浸) is favourable for denitrification.

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Enhance crop productivity by (i) Adding chemical fertilizer (ii) Adding organic fertilizer (iii) Crop rotation (iv) Burning aerial portions of plants

and incorporating the ashes in soil (v) Deep ploughing

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Human activities that disturb N cycle

(i) Deforestation (ii) Overhunting (iii) Release of a large amount of nitrogen

oxides e.g. NO 2 into the atmosphere by vehicles

(iv) Excessive use of chemical fertilizer ­ Eutrophication(富養化作用) e.g. algal bloom (red tide)

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Scavengers Scavengers ­ animals that consume

already dead animals e.g. vultures, burying beetles, blowflies,

dung beetles and raccoons. The remains left by scavengers will be decomposed by the decomposers.

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Eutrophication(富養化作用) e.g. algal bloom 藻華 (red tide)

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Decomposers

­ saprophytic fungi and bacteria (not parasitic – disease causing)

­ break down dead bodies, faeces and excretory wastes

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Decomposers VS Scavengers

1.bacteria and fungi animals e.g. birds and insect

2.saprophytic nutrition _______ nutrition 3.no ingestion involved Ingestion of dead

bodies involved 4. _______ digestion Internal digestion

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The End

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