Science Notes - Chapter 21
Section 1:
Energy Flow in Ecosystems
Energy Roles:
Each of the organisms in an ecosystem fills one of the energy roles of: producer, consumer, or decomposer.
Producers:
*Organism makes its own food
*Source of all food in ecosystem
*A few ecosystems originally obtain energy from a source other than sunlight-
this ecosystem is found in rocks deep in the earth, gets energy from hydrogen sulfide that is found in their environment
Consumers:
*organism that obtains energy by feeding on other organism
*classified by what they eat
-Herbivore – consumer that eats only plants
-Carnivore - consumer that eats only animals
– Some are scavengers that feed on the bodies of dead animals
-Omnivore – consumers that eat plants and animals
Decomposers:
*break down waste and dead organisms and return the raw materials to the ecosystem
*known as nature’s recyclers
*mushrooms and bacteria are decomposers
Food Chains and Food Webs:
*Energy enters the ecosystem as sunlight and is converted into food molecules by the producers
*Shows the movement of energy through an ecosystem. This can be shown in the diagrams called food chains and food webs.
Food Chain:
*a series of events in which one organism eats another and obtains energy
-First organism in food chain is the producer
-Second organism feeds on (or off of) the producer and is called the first level
consumer
-The Second level consumer eats the first level consumer
**Food chains show only one possible path, along which energy can move through the ecosystems.
Food Webs:
*consist of many overlapping food chains. Can show multiple ways in which consumers interact.
Energy Pyramids
*When an organism in an ecosystem eats, it obtains energy. (The energy comes from the food.)
*The energy pyramid shows the amount of energy that moves from one feeding level to the next.
*The most energy is available at the producer level of the pyramid. As you move up the pyramid each level has less energy available than the level below it!!!
*Only about 10% of the energy at one level of a food web is transferred to the next higher level. The other 90% of the energy is lost at each step (up on the pyramid) because of this there is not enough energy to support many feeding levels in an ecosystem.
*Organism at higher food levels don’t necessarily require less energy to live than lower levels. Since so much is lost, the amount of energy at producer level limits the # of consumers that it can support. This is why there are fewer animals at top of the pyramid.
Section 2:
Cycles of Matter
* Water cycle- the continuous process by which water moves from Earth’s surface to the atmosphere and back.
- Evaporation, condensation and precipitation make up the water cycle.
*Evaporation – the process by which molecules of liquid water absorb energy and change to a gas.
- Liquid evaporates from oceans, lakes and living things that give off water and forms a water vapor (a gas).
- Energy for evaporation comes from the heat of the sun.
*Condensation – the process by which a gas changes to a liquid.
- As the water vapor rises in the atmosphere, it cools down.
- Cool vapor turns back into tiny drops of liquid water. This is the process of condensation.
- This water vapor collects around particles of dust and forms clouds
* Precipitation – when water vapor condenses the drops of water in the cloud grow larger, eventually the heavy drops will fall from the cloud resulting in rain, sleet, hail or snow.
-Most precipitation falls back into the oceans or lakes.
The Carbon and Oxygen Cycles
- Producers, consumers and decomposers play roles in recycling carbon and oxygen.
- Producers take in carbon dioxide gas from the air during photosynthesis.
- They use the carbon to make food (sugars and starches)
- Consumers break down carbon (sugars) to obtain energy and release CO2.
- When producers and consumers die, decomposers break down their remains and return the carbon to the soil.
- Producers release oxygen as a result of photosynthesis
- Most organisms take in O2 from the air or water and use it to carry out life processes.
The Nitrogen Cycle
- Nitrogen moves from the air to the soil, into living things and back into the air.
- Our atmosphere is 78 % Nitrogen gas (free nitrogen-not combined with other kinds of atoms). Most organisms cannot use it in this form.
- Most organisms can use it when it is “fixed” or combined with other elements (nitrogen- containing compounds)
- Nitrogen fixation the process of changing free nitrogen into a usable form.
Returning Nitrogen to Environment
- Once nitrogen is fixed, consumers can use it to make proteins.
- Decomposers break down these complex compounds in animal wastes and dead organisms. Decomposition returns simple nitrogen compounds to the soil.
- Nitrogen can cycle from the soil to producers, then to consumers many times.
- Eventually, bacteria break down nitrogen compounds completely and release “free” nitrogen back into the air.