5.1 Communities and Ecosystems

Assessment Statements
• Define species, habitat, population, community, ecosystem, and ecology
• Distinguish between autotroph and heterotroph
• Ditinguish between consumer, detritivores and saprotrophs
• Describe what is meant by a food chain, giving three examples, each with at least 3 linkages (4 organisms)
• Describe what is meant by food web
• Define trophic level
• Deduce the trophic level or organisms in a food chain and a food web
• Construct a food web containing up to 10 organisms, using appropriate information
• State that light is the initial energy source for almost all communities
• Explain the energy flow in a food chain
• State that energy transformations are never100% efficient
• Explain reasons for the shape of pyramids of energy
• Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
• State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.

Create a food chain with at least 5 organisms
1. Ocean
2. Freshwater Lake
3. Desert
4. Temperate Forrest
5. Rain Forrest
6. Antarctic Ocean
7. Tundra
8. Savanna
9. Temperate Grassland
10.Coral Reef
Label Autotrophs/ Producers, and Heterotrophs/Consumers
Show energy flow of food chain with arrows
Label the Trophic Levels
Include decomposers at the end of the chain
What are detritivores and saprotrophs?

Species: a group of organism that can interbreed and produce fertile offspring

Population: a group of organisms of the same species who live in the same area

Community: a group of populations living and interacting with each other

Ecology: the study of relationships between living organisms and between organisms and their environment

Ecosystem: a community and its abiotic (nonliving; temperature, humidity, wind, rainfall etc.) environment

Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances
Heterotroph: an organism that obtains organic molecules from other organisms

Consumers, Detritivores, Saprotrophs

an organism that ingests other organic matter that is living or recently killed.
an organism that ingests non-living organic matter.
an organism that lives on or in nonliving organic matter, secreting digestive enzymes into it and absorbing the products of digestion, examples; bacteria and fungi

Define the terms species, population and community.
Species: Population:. Community: [3]

Producer
→
Primary consumer
→
Secondary consumer
→
Tertiary consumer
Oak tree
Quercus
→
Caterpillar
Archips
Sea lettuce
Ulva
→
Saguaro cactus
Carnegiea
→
Finger limpet
Collisella
Jackrabbit
Lepus
→
→
→
Spotted towhee
Pipilo
→
Rock crab
Cancer
Rattlesnake
Crotalus
→
→
Cooper’s
Hawk
Accipitor
Giant
Octopus
Octopus
Red-tailed
Hawk
Beauteo

Trophic level is the position of an organism in a food chain
5 th trophic level
4 th trophic level
3 rd trophic level
2 nd trophic level
1 st trophic level

Describe what is meant by a food chain using an example with four named organisms. [4] food chains describe the feeding relationships between species; arrows show (one) path of energy flow in an ecosystem / energy flow described; food chain with arrows pointing in the correct direction; producer first step in chain; three other named organisms making a realistic food chain; [4 max]
Accept explicit common names exact enough to identify the food source e.g. Oak not tree, sparrow not bird, rye grass not just grass, etc.

Few consumers feed on only one source of food. A food web shows a much more realistic picture of the feeding relationships of the organisms in a habitat.

Organisms can change trophic levels depending on what they are eating at any particular time.

Describe what is meant by a food chain and a food web. [6]

The diagram below shows a simplified food web for a lake
State the initial energy source for the above food web. [1]
Define the term trophic level. [1]
Deduce the trophic level of the immature game fish.[1]
In the food web shown, identify one heterotroph and one autotroph. [1]

Explain, using an example of a food chain, how trophic levels can be deduced. [4]

Energy and Food Chains
State that light is the initial energy source for almost all communities.

Energy and Food Chains
Arrows in a food chain show the direction of flow of both the energy and nutrients that keep organisms alive.
Energy flow through an ecosystem can be quantified and analyzed.
At each step in the food chain, energy is lost from the chain in various ways.
Some is not consumed, some leave the food chain as waste or when an animal dies, and some is used by living organisms as they respire.
The lost energy cannot be passed to the next trophic level.

STATE: Energy transformations are never 100% efficient

An area of the African savannah where grass, antelopes and cheetahs form a simple food chain
Energy loss 1 –not consumed. The grass stores energy from photosynthesis but antelopes only eat some parts of the grass, so they don’t consume all the energy stored.
Energy loss 2- not assimilated. The grass that is eaten passes through the digestive system of the antelope but not all of it is digested and absorbed, some passes out in the feces.
Energy loss 3- cell respiration. The antelope uses energy to move and keep its body temperature constant. As a result, some energy is lost to the environment as heat.
The energy remaining after respiration goes into building the antelope’s body, and this energy becomes available to the cheetah when it eats the antelope.

Transfer of energy between trophic levels is represented by energy pyramids.

The width of each of the levels in the pyramid is proportional to the amount of energy it represents

Energy losses occur at every step in a food chain.
Every link in the chain results in losses, so that eventually there will be insufficient energy to support any further trophic levels.
That’s why most food chains contain between 3 and 5 organisms.
Energy enters an ecosystem is light, converted to stored chemical energy and finally is lost as heat.

The diagram below represents an energy pyramid and four trophic levels.
Identify the trophic level of the organisms indicated below.
I: IV
[2]
(ii) Calculate the approximate amount of energy in kilojoules transferred in m–2 yr–1 from trophic level I to trophic level II.
______________________kJ

Explain the reason for the shape of a pyramid of energy. [3]

Energy Flow and Nutrient Recycling
All organic matter from organisms, including everything from living or dead material or waste, is eventually consumed by other organisms.
All these organisms respire and release energy as heat.
All the energy that enters an ecosystem as light energy is trapped by photosynthesis, will eventually be converted to heat and become unavailable to be used again by living things.

Nutrients are continually recycled.
A nitrogen atom may be absorbed as nitrate by a plant root, and used to make an amino acid.
The amino acid may pass into an
Animal when the plant is eaten,
And then pass out of the animal’s
Body during excretion.
Soil bacteria may convert urea
In the excreted material back
Into nitrate and the cycle begins.

STATE: Saprotrophic bacteria and fungi (decomposers) recycle nutrients