population interaction worksheet · web viewk) fish on a coral reef stake out their territory and...

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1. A biogeochemical cycle “recycles” elements throughout the ecosystem because they need to keep getting re-used and are important because they make essential matter continuously available and connect all ecosystems together.

2. Photosynthesis – takes in carbon dioxide and converts it to oxygen and water.

3. Three roles plants have in the water cycle: roots take up water from the ground, transpiration (evaporation of water from leaves), prevent/reduce run off,

4. Nitrogen fixing bacteria and lightning are both able to break down molecular nitrogen (N2) into usable forms. Fun fact: Even though most of our air (78%) is N2 , plants cannot use N2 directly so it needs to be converted into different forms and nitrogen compounds the plants can use.

5. Carbon is critical to the biosphere because it is part of photosynthesis and cellular respiration, produces carbon dioxide and many carbon based compounds.

6. After it is released to the atmosphere, most of the biosphere’s carbon dioxide is taken in by plants and trees and stored in their leaves, stems and roots.

7. Photosynthesis and cellular respiration are called the biotic phases of the carbon cycle because they are done by living things (plants and animals).

p. 31 #8-11

8. Eutrophication – process where nutrient levels in aquatic ecosystems increase, leading to an increase in the population of primary producers (algae)

9. The nutrient that was the main cause of the eutrophication in northwestern Ontario lakes was phosphorous.

10. One possible source of excess phosphorous in aquatic ecosystems is that it comes from excess fertilizers that are used on farmlands – the extra phosphorous that isn’t used by the crops enter the ground and end up in the water.

11. Some of the fertilizer that was meant for your nice pretty lawn actually ended up in the fish pond – the excess phosphorous from the fertilizer caused an algal bloom in the fish pond killing the fish and turning the water green.

p. 36 #12,13

12. Greenhouse effect – radiation comes from the sun to the earth – some of this radiation gets trapped by greenhouse gases and instead of leaving, get trapped in the Earth’s atmosphere.

13. Three ways to reduce carbon dioxide in the atmosphere: plant trees, recycle, use less energy, use clean energy, drive less, bike/walk more

p. 39 #10, 12, 13 (just list)

10. a) How human activities affect the phosphorous cycle: Overuse of fertilizers or using fertilizers high in phosphorous can upset the natural balance of the cycle.

b) Ways to avoid eutrophication? Reduce the amount of fertilizers, or use environmentally friendly fertilizers

12. Positive actions to take to reduce nutrient pollution of aquatic systems:

a) Farmers – do not overuse fertilizers and/or apply them properly

b) Fertilizer companies – create environmentally friendly fertilizers

c) Governments – monitor levels in aquatic system, legislate the chemicals allowed

d) Consumers – buy what you need, buy environmentally friendly products

13. Three human activities that can result the balance of carbon dioxide in the biosphere: recycle, plant trees, don’t cut down trees, walk/bike/carpool, drive less


1.What is the initial source of energy in this community? sun

2.What is the producer in this community? grass

3.Which are the first order consumers? Grasshopper, rabbit that eat the grass

4.Which are the second order consumers? Frog that ate the grasshopper

5.If a snake was added to the diagram,

a) when would the snake be a third order consumer?

Grass → grasshopper →frog→ snake

b) when would the hawk be a fourth order consumer?

Grass → grasshopper →frog→ snake → hawk

6.What link in the food chain, which acts on all other links, is missing from the diagram?


7.Would you expect more toads or more hawks in the community? Explain.

Toads, lower down in the food chain

8.If the number of grasshoppers in this community decreased, what three things might happen initially? – more grass- less frogs- less hawks

9.Complete a food chain with five links (using the diagram above) by writing the names of the organisms that feed on one another.

Grass → grasshopper →frog→ snake → hawk


p. 36 #14,15

14. Trophic level – feeding level , how the organism gets its energy

Trophic efficiency – how much of the energy in organisms in one trophic level is transferred to the next higher trophic level

15. Biomagnification – increase in the concentration of a toxin at is moves from one trophic level to the next

Bioaccumulation – process where toxins are ingested by an organism at a rate greater than they are consumed

p. 40 #17, 18

17. Energy decreases from one trophic level to the next because the organisms use most of the energy from the biomass they consume for their own functions. Some energy is lost at heat from the bodies of the organisms.

18. How bioaccumulation affects the sustainability of an ecosystem:

DDT – agricultural insecticide, entered the environment through run off from land, absorbed by algae – eaten by microscopic animals – eaten by small fish – eaten by birds. DDT levels increased at each trophic level - affected the bird reproduction.

PCBS – used in industry. Entered air, water and soil while used and disposed of.

Affected the higher trophic levels - Peregrine Falcon.


1. Explain the difference between density dependent and density independent limiting factors.

Density dependent – affect a crowded population differently

Density independent – affect a population regardless of their density

2. Each of the statements below involves a situation that will affect the growth of a population. Classify each of the statements as DD (density dependent) or DI (density independent) and give a reason for your choice.

a) A lion and a cheetah attempt to occupy the same niche. The more aggressive lion survives, the cheetah does not.

Density independent – aggression has nothing to do with the density

b) Coyotes cross the winter pack ice and enter Newfoundland. The moose population starts to decline.

Density dependent – coyotes eat moose so the more coyotes that enter Newfoundland, the more moose will be eaten

c) A severe frost wipes out 50% of the coffee crop in Brazil.

Density independent – frost will kill crops regardless of how many there are

d) A forest fire destroys much of the wildlife in an area of northern Manitoba.

Density independent – fire will burn anything in its path, regardless of how much is there

e) Due to severe overcrowding in a small village, many children do not survive to reach adulthood.

Density dependent – not enough food and supplies when there are more children

f) Since lynx prey on hares, an increase in the hare population causes an increase in the lynx population.

Density dependent – predator/prey – more hare means more food for the lynx that prey on them

g) A severe flood in the Red River Valley causes a decline in the deer population.

Density independent – flood destroys whatever is in its path regardless of density

h) Due to stress, large numbers of female lemmings miscarry their young and fail to reproduce.

Density independent – depends on what is causing the stress, but if that stress affects them then it doesn’t matter how many there are not to be affected by it

i) Many fish die due to change in the winds and appearance of the El Nino ocean current off the coast of Peru and Chile.

Density independent – the change in conditions affects whatever is in its path regardless of its density

j) Because rabbits in Australia have no natural enemies, their population increases rapidly.

Density dependent – predator/prey – nothing to feed on it so it will thrive

k) Fish on a coral reef stake out their territory and chase away any younger fish that try to live there.

Density dependent – the more fish on the coral reef, the more younger fish get chased away

l) An extensive drought on the Serengeti Plain threatens wildebeest, giraffe, zebra, and springbok populations.

Density independent – drought affects whatever is in its path regardless of its density