Ch 19 Ecosystems

Question 1

Interactions among organisms in a community

Answer 1

Predation
Competition (interspecific / intraspecific)
Commensalism
Mutualism
Parasitism

Question 2

Interactions among organisms in a community

Answer 2

Predation ( + / - )
Competition (interspecific / intraspecific) ( - / - )
Commensalism ( + / 0 )
Mutualism ( + / + )
Parasitism ( + / - )

Question 3

Predator-prey cycle

Answer 3

1. The prey has plenty of food. It breeds and increases in number.
2. An increase in the prey population means that more food is available for the predator. The predator population increases
3. A large number of predator feed on a large number of prey. The prey population decreases.
4. The food supply becomes limited, the predator population decreases
5. The number of prey recovers and the cycle repeats

Question 4

Primary succession

Answer 4

• barren areas, soil is not present
• requires pioneer community of lichens

Question 5

Secondary succession

Answer 5

• pioneer community is not needed, soil is already present
• develops more quickly as seeds, roots and underground vegetative organs of plants still survive in soil

Question 6

Energy lost along trophic levels

Answer 6

1. Uneaten materials
2. Undigested and egested products
3. Excretory products
4. Heat during respiration

Question 7

Inverted pyramid of biomass

Answer 7

• phytoplankton -> zooplankton
• organisms at the lower trophic level have a much higher reproduction rate and shorter lifespan (higher turnover rate)

Question 8

Carbon cycle

Answer 8

• Carbon transfer between trophic levels and decomposers
  1. Carbon in producers, in the form of organic matter, is transferred to consumers at higher trophic levels by feeding
  2. Organic matter in dead bodies or waste material of organisms is used as food by decomposers
• Return of carbon dioxide to the atmosphere and oceans
  3. Carbon in organic matter is converted to carbon dioxide and released into the atmosphere and ocean during respiration of all organisms and decomposition of decomposers
  4. The dead bodies of organisms may become fossil fuels. During combustion of fossil fuels, the carbon inside the fuels is released as carbon dioxide
  5. The carbonate skeletons of marine organisms may deposit to the ocean bed and turn into limestone. When the carbonates in the limestone react with acids in water, or when they are heated under great pressure during volcanic eruption, carbon dioxide is released
• Removal or carbon dioxide from the atmosphere and oceans
  6. Carbon dioxide in the atmosphere and oceans is returned to the bodies of producers when the producers carry out photosynthesis.

Question 9

Nitrogen cycle

Answer 9

• Nitrogen transfer between trophic levels
  1. Nitrogen, in the form of organic matter, is transferred from producers to consumers at different trophic levels by feeding
• Addition of nitrogen to the soil
  2. Through decomposition, decomposers break down organic waste and the dead bodies of producers and consumers. The nitrogen in these materials is converted to ammonium compounds
  3. The ammonium compounds are turned into nitrites, which are then changed into nitrates by nitrifying bacteria in nitrification
  4. Lightning turns nitrogen in the atmosphere into nitrogen oxides, which is dissolved in rainwater to form nitrates in the soil
  5. Free-living nitrogen fixing bacteria in the soil convert nitrogen in the air to ammonium compounds, which are stored in their bodies in nitrogen fixation. When nitrogen fixing bacteria die they are decomposed by decomposers. The ammonium compounds in the bacteria are released into the soil and converted to nitrates by nitrification.
• Removal of nitrogen from the soil
  6. The nitrates formed are taken up by producers for the synthesis of proteins, nucleic acids and other nitrogen containing organic compounds
  7. In poorly aerated soil, denitrifying bacteria change nitrates in the soil into nitrogen gas by denitrification. Nitrogen gas diffuses into the atmosphere

Question 10

Studying distribution and abundance of organisms

Answer 10

• quadrant
• line transect
• belt transect

Question 11

Disadvantages of quadrant sampling

Answer 11

• No replicate is carried out and the results are not representative
• Not accurate for determining number of mobile animals
• Animals under the sediment surface will be missed if only animals on the surface are collected
• Sampling is not random, a biased sample may be taken

Question 12

Greater percentage decrease in energy content when the producer is tree and primary consumer is caterpillar

Answer 12

• Caterpillars mainly feed on leaves of trees, leaving most of the part of the biomass of trees unconsumed

Question 13

Why crop-growing provide more food for human consumption than cattle raising

Answer 13

• Crop-growing: humans obtain food through a shorter food chain / a smaller number of trophic levels
• Energy is lost along the food chain through respiration, death, excretory products and faeces
• More energy will be available to form organic matter for human consumption in crop-growing

Question 14

Human activities that pose threats to survival of dolphins

Answer 14

• Reclamation in coastal area / construction / dredging of seabeds in areas nearby causes deterioration of water quality of its natural habitats
• Disturbance caused by tourism drives the animal away from the habitat
• Fishing activity accidentally kill / injure the animal
• Heavy sea traffic drive away the animal