Ecology II Review

1. How does energy flow through an ecosystem?


2. Describe how biogeochemical cycles such as water cycle, carbon cycle, nitrogen cycle, and phosphorus cycle work.
  • Water cycle:
    • A. EVAPORATION: from lakes, rivers, and oceans
    • B. TRANSPIRATION: from plants and trees
    • C. CONDENSATION: cloud formation
    • D. PRECIPITATION: rain, snow, sleet, hail
    • E. RUN OFF, or RETURNED back into the cycle
    • (source)
  • Carbon cycle:
    • Photosynthesis: During photosynthesis, plants and other autotrophs use CO2 along with water and solar energy, to build organic molecules (carbohydrates), thus storing the carbon for themselves and other organisms.
    • Cellular Respiration: Both autotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration. Consumers obtain energy-rich molecules that contain carbon by eating plants and animals.
    • Volcanic Eruptions and geothermal vents: Carbon from deep within the earth’s interior is brought back to the surface during eruptions of steam, gasses, and lava.
    • Decomposition: Carbon is returned to the environment through decomposers and cellular respiration (breathing releases CO2 back to the atmosphere).
    • Combustion: When wood or fossil fuels are burned, the chemical reaction releases carbon dioxide back into the atmosphere.
    • Deposition: Coal, petroleum, and calcium carbonate rock are deposited in sediment and underground. Calcium carbonate deposits are eroded by water to form carbon dioxide. Large amounts of carbon are tied up in wood, only returning to the atmosphere when wood is burned.
    • (source)
  • Nitrogen cycle:
    • NITROGEN FIXATION is the conversion of nitrogen gas to ammonia. Ammonia can be absorbed by plants from the soil, and used to make proteins, and enter the food web for consumers.
    • ASSIMILATION: Consumers obtain nitrogen from the plants and animals they eat by digesting the food’s proteins and using it to make their own proteins.
    • AMMONIFICATION:  Decomposers return the nitrogen from the remains of dead plants and animals back to the soil.  Nitrogen is also returned from animal and plant waste by decomposers (dung, urine, leaves, and bark).  Through ammonification, nitrogen that would be lost is recycled back into the ecosystem.
    • DENITRIFICATION:  Denitrification occurs when anaerobic bacteria (chemoautotrophs) break down nitrates and release nitrogen gas back into the atmosphere.
    • NITRIFICATION:  Bacteria convert ammonia into nitrogen compounds that plants can utilize more easily
    • (source)
  • Phosphorous cycle:
    • Phosphorous is released from rocks by weathering and enters the soil.
    • Phosphates enter plants via root systems, then into herbivores as the plants are eaten, then into carnivores as plants and/or herbivores are eaten.
    • Phosphates return to soil through excretion.
    • (source)
3. How are all organisms dependent upon each other? Use examples that include both energy and matter.

Organisms in an ecosystem depend on other organisms as sources of food and energy.

4. Describe and show the relationship among organisms, populations, communities, ecosystems, biomes, and the biosphere.

Groups of organisms form populations. Groups of populations form communities. All the communities in an area make up an ecosystem.  All the ecosystems in a specific geographic area make up a biome.  The biosphere would be the ecosystem of the entire earth and all the living organisms inhabiting it.

5. Give an example of an actual food chain and a food web. Explain how these are related.

Answers may vary. Here’s an example:

Food Chain:  Plants > Grasshopper > Mouse > Snake

Food Web:  Plants could be eaten by grasshoppers, mice, or rabbits; Grasshoppers could be eaten by mice or robins; Mice could be eaten by snakes or hawks; rabbits could be eaten by snakes or hawks; Robins could be eaten by hawks

Food chains are a simplified list of producers to consumers.  Food Webs show many relationships and food chains.

6. What happens to energy as it is passed from one trophic level to the next?

As energy is passed from one trophic level to the next, only about 10% is actually passed along.  Most energy is lost as heat.

7. How do the two types of succession affect a local ecosystem over a long period of time? What starts it?

Secondary Succession – the re-population of an area after its destruction due natural or man-made causes. Primary Succession – occurs where there has never before been an ecosystem. (source)  Succession is started by a major change in an ecosystem, either by natural or man-made conditions.

8. Assess the specific effects of human activities that result in such things as: climate change, population growth, pesticide use, and water consumption.
  • climate change – Since the beginning of the Industrial Revolution, human activities have contributed substantially to climate change by adding CO2 and other heat-trapping gases to the atmosphere. These greenhouse gas emissions have increased the greenhouse effect and caused Earth’s surface temperature to rise. The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from the burning of fossil fuels.
  • population growth – reduces the number of resources available
  • pesticide use – Runoff can carry pesticides into aquatic environments while wind can carry them to other fields, grazing areas, human settlements, and undeveloped areas, potentially affecting other species. Other problems emerge from poor production, transport and storage practices. Over time, repeated application increases pest resistance, while its effects on other species can facilitate the pest’s resurgence.
  • water consumption – Approx. 0.007% of all water on earth is accessible for direct human uses. This is the water found in lakes, rivers, reservoirs, and accessible underground sources. Only this water is regularly renewed by rain and snowfall, and is therefore available on a sustainable basis. The population is growing rapidly, putting more pressure on our water supply. (Demand is increasing.) The amount of water is effectively reduced by pollution and contamination. (Supply is decreasing.)
9. Describe how the various types of tropisms in plants increase their ability to survive in stressful environments.

Because stems are negatively gravitropic AND positively phototropic, they will always push to grow away from the ground and toward the best source of light, even if growing in limited light or small spaces.

10. Describe how specific adaptations (such as camouflage, structure, etc.) as well as behaviors or organisms affect their abilities to survive in certain habitats.

Specific colors (like white coats in areas that would have frequent snow) allow animals to better blend into surroundings.

11. Construct a graph that would illustrate the relationship of the population of rabbits to the population of foxes over a period 10 years.