Ecosystems and Material Cycles

Question 1

Describe the different levels of organisation within an ecosystem.

Answer 1

• Population - all organisms of the same species in an area
• Community - all populations in an area
• Ecosystem - the interaction of living and non-living things in an area

Question 2

Describe how organisms can be affected by abiotic factors.

Answer 2

• Temperature (and day-night fluctuation due to cloud cover)
• Light - average intensity being lower can create competition
• Water - scarcity can create competition
• Pollutants - high levels of heavy metals, copper, iron, nickel etc can be toxic

Question 3

Name some biotic factors which can affect communities.

Answer 3

• Predation
• Competition
• Disease
• Symbiosis

Question 4

Roughly what percentage of energy is usually passed down to the next trophic level?

Answer 4

10%

Question 5

Define eutrophication.

Answer 5

Eutrophication is a type of water pollution caused by the addition of sewage or fertiliser. This leads to lots of algae growth, killing plants below that cannot get light, attracting decomposers, which use up all the oxygen so other life dies, reducing biodiversity.

Question 6

Describe advantages of biodiversity.

Answer 6

• Resistance to drastic changes
• More potential useful biochemicals
• Availability of species for pollination and pest control

Question 7

Describe how nitrogen is transferred between its three forms of storage.

Answer 7

Pure nitrogen is turned to nitrates through lightning, artificial fertilisers and nitrogen fixing bacteria. This is reversed by denitrifying bacteria.
Nitrates are turned to ammonium in decomposers. This is reversed by nitrifying bacteria.

Question 8

Explain crop rotation and its purpose.

Answer 8

Growing different crops each year in a cycle, replenishing nutrients that may have been depleted by the previous crop.

Question 9

Explain indicator species for water quality.

Answer 9

• Unpolluted water contains stonefly nymphs and mayfly nymphs.
• Slightly polluted water contains freshwater shrimps (Gammarus pulex).
• Very polluted water contains sludge worms and bloodworm midge larvae (Chironomus thummi).

Question 10

Explain indicators species for air quality.

Answer 10

• Blackspot fungus can be seen on roses in clean air.
• Lichens grow everywhere and are sensitive to sulphur dioxide.
• Crusty lichens are resistant to pollution, but leafy are not.

Question 11

Explain main factors for decay.

Answer 11

• Temperature - closeness to enzymes’ optimum temperatures
• Moisture - microorganisms grow faster
• Oxygen presence - most decomposers are aerobic