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 Web 1)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 individuals 2) 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

Biomass in a Food Web 3) 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 H 2 O 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 PyramidNumber PyramidBiomass 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 Cycles 1)Biological processes  living things breaking down material 2)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 Earth 1)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 clouds Precipitation  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 Earth 2) Carbon Cycle: Animals, fire, and geothermic activity send CO 2 into the atmosphere Living things die and return carbon to the environment CO 2 dissolves into rain clouds and oceans CO 2 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 Earth 3) Nitrogen Cycle: All living things need Nitrogen but most is in N 2 gas which cant be used; need nitrates (nitrogen containing molecules) Nitrogen fixation  changing N 2 to NH 3, NO 2 -, and NO 3 - Sources  1)Decomposers: release ammonia (NH 4 + ) as they break down material 2)Nitrifying bacteria: change ammonia (NH 4 + ) to nitrates 3)Nitrogen-fixing bacteria: live in the soil or root nodules of plants; change N 2 into NH 4 + 4)Lightning: energy reacts N 2 with O 2 to form Nitrates; leach into soil through rainwater Denitrifying bacteria  balance N 2 in air by changing excess nitrates back into N 2

Natural Cycles on Earth 4) 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 Growth Why don’t we see a much larger biomass on Earth? Every environment has a limit keeping it in check Energy 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