Unit 18: Energy and Nutrient Transfer

Section 18.1 Food chains and food webs?

Section 18.2 Pyramids of numbers and biomass

Section 18.3 Energy Flow in Ecosystems

Section 18.4/18.5 Cycles of Matter

Numbers in a Food Web1) Number Pyramid:

• Shows the numbers of organisms in a trophic level for a specific food chain

Example:• 1 fox eats 25 birds• 25 birds eat 250 grasshoppers• 250 grasshoppers eat 3000

grass plants• Does not show the size of

the individuals2) Size Pyramid:

• Shows the relative size of each organism in the food chain

Example:• 1 tree supports 1500

caterpillars• 1500 caterpillars feed 100

birds• 100 birds feed 1 sparrowhawk

1

1500

100

1

Biomass in a Food Web3) Biomass Pyramid

• All living material in a trophic level is its biomass

• Average dried of weight of all organisms in an area• 35% of animals weight• 20% of plant weight• Remove H2O to see real

weight of organic molecules• biomass of the levels decreases

Why does the Energy Pyramid explain this?

• There is less energy to keep more complex organisms alive

The since every trophic level depends on the one under it, they are also limited by them• Land ecosystems rarely have more

than 4 trophic levels

Energy and the Future• Based on what we have talked about, what is the based diet for a growing poor nation?• Vegetarian

• Why?• It is more efficient. Eating producers cuts

out 90% of wasted energy in the ecosystem • If eating plants is more efficient, why do we need to eat so much?• Most of the energy is in cellulose, which

we can’t digest, so it is waste• Meat gives us more energy but costs more:• 0.5 kg or beef needs 2.5kg of plant

material• What would be a better alternative to meat?• Insects 80kgs for every person

State which type of pyramid each is

Energy Pyramid Number Pyramid Biomass Pyramid

Recycling Matter• Energy must be transferred through

trophic levels to power an ecosystem

• Stability comes from constant supply of new building materials• Members in the food chain need

to reproduce• Need elements (C, N, H, P, S) to

build organic molecules• 4 Biogeochemical Cycles1) Biological processes living things

breaking down material2) Geological processes geologic

activity breaking down rocks and minerals

3) Chemical/Physical processes clouds, lighting, rain, snow and other weather

4) Human Activity Human development; building and farming

Natural Cycles on Earth1)Water Cycle:Evaporation• Water absorbs energy from the

Sun and evaporates to water vapor; also transpiration

Condensation • Water vapor slowly collects over

time to form cloudsPrecipitation • Clouds grow heavy and rain,

snow, hail, etc… falls to the Earth

Accumulation • Water runs together on the

ground to form lakes, rivers, stream, and underground reservoirs

Repeat • Water eventually moves back to

the oceans or evaporates and the cycle starts again

Natural Cycles on Earth2) Carbon Cycle:• Animals, fire, and

geothermic activity send CO2 into the atmosphere

• Living things die and return carbon to the environment

• CO2 dissolves into rain

clouds and oceans• CO2 is pulled into

plants/algae and used in photosynthesis

• Other living things feed on carbon compounds like carbohydrates

• Carbon returns to the cycle

Natural Cycles on Earth3) Nitrogen Cycle:• All living things need Nitrogen but

most is in N2 gas which cant be used; need nitrates (nitrogen containing molecules)

• Nitrogen fixation changing N2 to NH3, NO2

-, and NO3-

• Sources1) Decomposers: release ammonia

(NH4+) as they break down material

2) Nitrifying bacteria: change ammonia (NH4

+) to nitrates3) Nitrogen-fixing bacteria: live in

the soil or root nodules of plants; change N2 into NH4

+ 4) Lightning: energy reacts N2 with O2

to form Nitrates; leach into soil through rainwater

• Denitrifying bacteria balance N2 in air by changing excess nitrates back into N2

Natural Cycles on Earth4) Phosphate Cycle:• All living things need

phosphates to build DNA and RNA

• Most phosphate is trapped in rocks and sediment layers in the Earth (Geological uplifting)

• Rivers and water sources breakdown rocks over time and leach phosphates into water sources

• Decaying organisms recycle phosphates into the ecosystem

Limits to GrowthWhy don’t we see a much larger biomass on Earth?• Every environment has a

limit keeping it in checkEnergy and nutrients can limit growth, however more often limited amounts of nitrogen or phosphorous stop excessive growth• Nitrogen is less common in

saltwater environments

• Phosphorous is the less common in freshwater environments