Ecosystems and Communities


1. Biomes are composed of unique plant associations , each of which may be defined as an identifiable group of interacting plants and animals within a geographic area.

2. An ecosystem is defined as any community of interacting organisms, including their biotic and abiotic environment, described in terms of the flow of energy through that environment..

3. The ultimate source of energy for living things on earth is sunlight .

4. One tenth of a percent of light captured by plants in photosynthesis every year translates into 150 to 200 million tons of dry organic matter. Such matter is often referred to as biomass.

5. Autotrophs, such as plants, algae, cyanobacteria and certain chemotrophs are in ecological terms known as producers.

6. From these autotrophs energy passes to various consumers or heterotrophs that cannot utilize external energy and that must rely on other organisms for their required organic compounds.

7. In the energetics of ecosystems, the steps in energy transfers are called trophic levels

8. Label the Diagram below


9. Producers include the following three groups plants, algae in the kingdom protista and cyanobacteria from the kingdom monera

10. Light is captured and transformed into usable energy by the plant pigment chlorophyll found in membrane bound complexes called _______________________

11. Primary consumers are the herbivores which feed directly on the producers.

12. Secondary and tertiary (etc.) consumers are carnivores that feed on primary consumers.

13. The tadpoles of frogs feed exclusively on algae and other plants, whereas the adult frog is exclusively a carnivore. How can ecologists represent such complicated feeding patterns in species? Food webs

14. Why are organisms in tropic levels after quaternary consumers rare? If only 10% of the energy in a lower level is transfered to the level above

15. Organisms such as certain bacteria and fungi which help decompose dead tissue are known as saprobes or decomposers .

16. Why are decomposers vital to a healthy ecosystem? Without decomposers vital nutrients would remained locked up in dead material and waste products.

17. List 5 simple products freed by saprobes as they break down the organic matter in the remains and wastes of organisms. sugars, amino acids, water, carbon dioxide, and ___________________.

18. The base of all Eltonian or ecological pyramids is composed of producers

19. List three varieties of ecological pyramids. energy, biomass , and ______________________

20. Which type of ecological pyramid can be inverted or take on other markedly different forms? Pyramid of numbers Explain why. In a pyramid of numbers a forest with a few large trees can sustain hundreds or thousands of small herbivores such as insects.

21. In order to estimate numbers or biomass of species making up a trophic level elaborate tag and release (sampling) techniques have been developed.

22. Where is energy stored in living matter? In the covalent bonds found between the atoms of organic molecules

23. Pyramids of Energy have a typical stepped appearance which is predicted by the second law of thermodynamics which states, among other things, that energy transfers are never perfect - in other words some useful energy is always lost as heat.

24. Eventually, all of the energy entering the earth's ecosystems is released as heat, a low grade form of energy from which no useful work can be extracted.

25. Where humans live as secondary consumers, energy must first flow from a producer to a primary consumer, and the change entails a considerable loss in the energy level. For each 1000 calories stored by a beef-eating human, the producer will have stored nearly two million calories. (see figure below)



26. Humans are able to eat a wide range of foods both plant and animal. Therefore we are considered omnivores , capable of feeding at several trophic levels.

27. Human population could be sustained at a relatively high level if we became strict herbivores. But humans feeding at the herbivore level may face problems with nutritional quality. For example, many common plant foods cannot provide certain essential amino acids (such as tryptophan, methionine, and lysine.)

28. Infamous protein deficiency diseases such as kwashiorkor, can be avoided if a vegetarian diet includes legumes like soybeans and peas which in combination with grains have all the amino acids necessary for a balanced diet.

Kwashiorkor is a form of malnutrition common in developing countries among those living on a diet inadequate in calories and grossly deficient in PROTEIN. The signs of this nutritional disease are anemia, edema (swelling), liver damage, muscle wasting, loss of appetite, and general apathy. The disease occurs mainly in children, especially those already suffering from parasitic disease or infectious diarrhea. The principal cause, however, is a mainly carbohydrate diet that provides inadequate protein. (The name kwashiorkor is derived from the Ga language of West Africa and means "the disease of the displaced child.") Treatment consists of a well-balanced, protein-rich diet; the disorder is often fatal, however; those who survive may have physical stunting and mental retardation.

A related disease, nutritional MARASMUS, results from an extremely low intake of all nutrients, including protein, and calories. The symptoms are similar to those of kwashiorkor, but edema is not present. The child with marasmus is underweight, wasted, and often emaciated, whereas the so-called sugar baby case of kwashiorkor shows little weight loss because energy stores are preserved. Michael C. Latham, Grolier Multimedia Encyclopedia.

29. Why is the gross primary productivity by producers in an ecosystem greater than the net primary productivity? Because producer metabolism is not subtracted out of the gross primary productivity figure.

30. Net primary productivity (NP) can be thought of as new growth, seed production, and simple storage of energy rich compounds such as lipids and carbohydrates.

31. What is net community productivity? ____________________________________________________

32. Which marine biome has the largest gross primary productivity. Open ocean (pelagic photic zone)

33. The pathways of elements and minerals as they are taken up and released into the physical environment are called biogeochemical cycles.

34. The biogeochemical cycles have three major places where elements are accumulated including:

a) integrated in the bodies of living organisms

b) readily available water soluble exchange pools in soil

c) or locked away in reservoirs as in shells or atmospheric nitrogen

35. Nearly all biogeochemical cycles would be incomplete without the help of the ever-waiting decomposer.

36. Nitrogen is found in a number of vital organic molecules including protein, DNA , RNA, and ________________

37. Plants and nearly all other producers must have their nitrogen primarily in the form of _____________ in order to incorporate it into amino acids.

38. Describe what conditions are necessary for a deep lake to experience fall or spring thermal overturn.


39. Describe the biochemical cycles of carbon and nitrogen. Trace these elements from the point of their releases from a decaying animal to their incorporation into a living animal. (AP exam question.)


When an animal dies various decomposers begin the slow process of recycling its elements including nitrogen. Certain soil bacteria can put nitrogen gas back into the atmosphere through a process called denitrification . In this step, the certain bacteria release nitrogen from urea, uric acid, and other nitrogen compounds produced by decaying organic matter. Not all the nitrogen is converted to N2 gas, some remains as soluble nitrate or ammonium ions as part of the __________________ pools in the soil. These soluble ions are quickly absorbed by plants.

In a process called nitrogen fixation, various microorganisms such as Rhizobium, the bacteria in the root nodules of legumes, can combine hydrogen with nitrogen gas to form ammonia . Other microorganisms are able to convert the ammonia by a process called nitrification into nitrates which are readily used by higher plants to construct amino acids and finally proteins. Animals then ingest these plants and break down their proteins and use the amino acids to make their own proteins.

40. Fill in the Nitrogen Cycle diagram below:



41. Although ammonium ions (NH4+) are chemically easier for plants to incorporate into amino acids that nitrate, and may be found in soil, why are these ions far less available than nitrates? ______________________________________________

42. Why do farmers rotate crops between grains one year and beans or peas the year after? By rotating crops so that some years legumes like beans and peas are grown insures that nitrogen is available for crops like wheat or corn.

43. Explain cultural eutrophicaton. Cultural eutrophication results from human activities which pollute waterways with excess nutrients such as nitrates and phosphates

44. Phosphorus enters the roots of plants as the soluble phosphate ion ____________.

45. What are the main organic molecules which contain phosphorus? all 5 nucleotides A, T, C, G, and U, DNA, RNA, and the ____________________ of photosynthesis and respiration.

46. Calcium is critical to the proper functioning of ______________________ and many enzymatic reactions. List three situations where calcium plays a role in membrane related metabolism.

a) Calcium's release from Smooth ER activates muscle contraction

b) Necessary for neural transmission at a synapse

c) ________________________________________________

47. What mineral in the soil, or shells acts as a reservoir for calcium? Carbonates.

48. The main reservoir of carbon for photosynthesis is carbon dioxide. Write a simple balanced equation for photosynthesis

light energy + 6 H2O + 6 CO2 ---> C6H12O6 + ___________

49. In the oceans and other waters plants and algae use the bicarbonate ion (HCO3-) from dissolved carbon dioxide and carbonate rock as their principle carbon source.

50. Photosynthesis fixes carbon dioxide into sugar whereas animal and plant respiration releases CO2 back to the atmosphere. Write a simple balanced equation for respiration.

C6H12O6 + ___________ ---> 6 H2O + 6 CO2 + _______________

51. Why is carbon dioxide considered a "greenhouse" gas? Carbon dioxide is considered a greenhouse gas because it allows visible light through but absorbs heat radiation which could gradually increase the temperature of the atmosphere.