4. ECOLOGY

Question 1

Explain the processes by which energy enters and flows through ecosystems.

Answer 1

a. light energy is the initial energy source for (all) organisms
b. producers change light energy into chemical energy by photosynthesis
c. producing carbohydrates and other organic compounds
d. organic compounds used for energy/growth
e. energy passed in the form of food/carbon compounds along food chains
f. cellular respiration releases energy as ATP from food
- ATP needed for active transport, anabolic processes
g. energy is lost as heat (during cellular respiration)
h. only approximately 10% of energy is passed to the next trophic level
i. energy lost in bones/hair which are not fully eaten by the next trophic level
j. energy lost in feces, some parts cannot be digested)
k. decomposers/saprotrophs remove energy from wastes/dead bodies
l. energy is not recycled

Question 2

Producers extract phosphates and nitrates from soil. Outline how these ions are used in the synthesis of organic molecules. [3]

Answer 2

• absorbed by roots and transported in xylem
• they are joined to carbon compounds
• phosphates used to synthesize nucleic acids and phospholipids
• nitrates are used to synthesize nucleic acids and proteins

Question 3

Distinguish between sustainability of natural ecosystems and agricultural areas.

Answer 3

• sustainability of an ecosystem allows for continued survival of organisms
• natural ecosystems can be sustainable for a long period of time (unlike agricultural areas) as it has a high biodiversity
• nutrient cycling is better than in agricultural areas where nutrients are removed with the collection of crops
• soil is degraded in agricultural sites

Question 4

Explain how increased CO2 levels lead to the greenhouse effect.

Answer 4

• short wave radiation from the sun passes though the atmosphere (it is not absorbed by CO2
• the surface of the Earth emits long wave radiation which is absorbed by CO2 in the atmosphere
• it results in the increase in temperature on Earth, global warming

Question 5

Outline the features of ecosystems that make them sustainable.

Answer 5

a. recycling of nutrients such as nitrogen

c. decomposers break down organic matter/release «inorganic» nutrients ✔

d. energy supplied by the sun

e. energy flow along food chains

f. autotrophs supply the food that supports primary consumers ✔

g. oxygen «for aerobic respiration» released by autotrophs

h. carbon dioxide «for photosynthesis» released by respiration ✔

i. populations limited by food supply/predator-prey/interactions/competition
OR
populations regulated by negative feedback
OR
fewer/less of each successive trophic level «along the food chain»/OWTTE ✔

j. supplies of water from rainfall/precipitation/rivers/water cycle ✔