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Food Chains, Food Webs & Energy Flow . IB Topic 5.1 . Recap … Some common problems . In food chains & food webs, arrows ( ) are used to show which organism eats which For example: Grass grasshopper toad The grasshopper eats the grass NOT the grass eats the grasshopper. Food webs.
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Food Chains, Food Webs & Energy Flow IB Topic 5.1
Recap … Some common problems • In food chains & food webs, arrows () are used to show which organism eats which • For example: • Grass grasshopper toad • The grasshopper eats the grass • NOT the grass eats the grasshopper
Food webs • Food webs are interconnected food chains • Why? • Since one organism often eats more than just one type of food • A food chain does not tell the whole story • Can be very complex …
There is no set number • Some food chains have six trophic levels, but most have four • The number of levels is limited to how much energy enters the ecosystem • A lot of energy is lost at each level • Determining trophic levels in a food web can be difficult … why?
Difficulties … • Some organisms occupy more than one trophic level or take their food from multiple trophic levels • Many ecosystems are not fully understood • Ditto for feeding preferences • Food webs do not show change over time as a population changes • Seasons • Disturbances
Energy! That’s why organisms eat, right? • Producers are the most important organisms … why? • Sunlight is the initial source of energy for all vegetation • Some food chains can start without sunlight (deep sea hydrothermal vents rely on chemicals instead of light) • Think about the food you like to eat – can you trace it back to the sun?
Energy Flow • Light is absorbed by producers (photosynthesis) • Energy is transferred from one organism to another as carbohydrates, lipids, and proteins are digested
Energy Transfer • Only chemical energy can be used by the next trophic level (remember ATP?) • Only a small amount of energy which an organism absorbs is converted into chemical energy • No organism can utilize 100% of energy present in the organic molecules of the food it eats • Only 10-20% of the energy is used
Why only 10%? • Where does the energy go? • Not all of the organism is swallowed as a food source • Not all swallowed food can be absorbed/used (bones, hair, seeds) • Lost as fecal matter; spit up • Some organisms die before being eaten • Considerable heat loss due to cellular respiration • Moving, running,
Pyramid of Energy • Used to show how much and how fast energy flows from one trophic level to the next in a community • Units are: • Energy per unit area per unit time • Kilojoules per square meter per year • kJ m-2 yr-1
Why the shape? • Take a look at figure 5.3 page 130 • Because energy is lost, each level is always SMALLER than the one before it • Organisms cannot create energy, they can only transfer it • Each level is smaller by ~10%
Energy vs. Nutrients • Energy: • Enters in the form of light chemical energy most is lost as heat • Not recycled (you can’t give energy back to the burger you ate for lunch) • Nutrients: • Recycled • There is not enough in the biosphere to meet all the needs • So, elements like carbon and nitrogen are recycled • Locked up in cells of organisms until they die • Only available by eating and decomposition
Lets hear it for the decomposers • How do we get those precious nutrients stored in the cells of plants and animals? • Decay • Detritivores & saprotrophs • Break down the body parts of dead organisms • Important for soil (nitrogen – key element for plants)
Review • Which diagram shows the flow of energy through a community with three trophic levels?
Review Which is the best prediction about biomass? A. The biomass of X is more than the biomass of W. B. The biomass of X is less than the biomass of Y. C. The biomass of V + X + Z is equal to the biomass of W. D. The biomass of Y is less than the biomass of Z.
Review Which of the species feed both as secondary consumers and as tertiary consumers? A. I, II and IV only B. I, III and V only C. I, IV and V only D. III, IV and V only